De-ImGui XCUI standalone text atlas provider

docs/plan/XCUI_Phase_Status_2026-04-05.md

@@ -16,7 +16,7 @@ Old `editor` replacement is explicitly out of scope for this phase.
   - `LayoutLab` continues as the editor widget proving ground for tree/list/property-section style controls
   - the demo sandbox and editor bridge APIs were tightened again without touching the old editor replacement scope
   - `new_editor` now has an explicit two-step window compositor seam through `IWindowUICompositor` / `ImGuiWindowUICompositor`, layered on top of `IEditorHostCompositor` / `ImGuiHostCompositor`
-- The native-host follow-up is now landed in `new_editor`:
+- The native-host / hosted-preview publication follow-up is now landed in `new_editor`:
   - `NativeWindowUICompositor` is now buildable alongside the legacy ImGui compositor
   - `Application` now defaults to a native XCUI host path instead of creating the ImGui shell by default
   - the native default path now drives `XCUIDemoRuntime` and `XCUILayoutLabRuntime` directly, composes their `UIDrawData`, and submits one swapchain packet through the native compositor
@@ -24,6 +24,9 @@ Old `editor` replacement is explicitly out of scope for this phase.
   - the native shell now begins the hosted-preview queue/registry lifecycle each frame, queues native preview frames, drains them during the native render pass, and consumes published hosted-surface images directly in panel cards with live/warming placeholder states
   - the old ImGui shell path remains present as an explicit compatibility host instead of the default host
   - `XCUIInputBridge.h` no longer drags `imgui.h` through the public XCUI input seam
+- The default native text path is now also de-ImGuiized inside `new_editor`:
+  - `XCUIStandaloneTextAtlasProvider` now builds and owns its atlas through a Windows/GDI raster path instead of using ImGui font-atlas internals
+  - the standalone atlas provider now exposes both `RGBA32` and `Alpha8` views, supports non-nominal size resolution, lazily adds non-prebaked BMP glyphs, and falls back to `?` when a glyph cannot be rasterized
 - Old `editor` replacement remains deferred; all active execution still stays inside XCUI shared code and `new_editor`.
 
 ## Three-Layer Status
@@ -50,7 +53,7 @@ Current gap:
 
 - Minimal schema self-definition support is landed, including consistency checks for enum/document-only schema metadata, but schema-driven validation for `.xcui` / `.xctheme` instances is still not implemented.
 - Shared widget/runtime instantiation is still thin and mostly editor-side.
-- Common widget primitives are still incomplete: shared text-input presentation/composition on top of the new text controller, multi-selection/focus-traversal/virtualized collection state on top of the new editor-primitive helpers, and a fully native text/font-atlas path that no longer leans on ImGui font internals.
+- Common widget primitives are still incomplete: shared text-input presentation/composition on top of the new text controller, multi-selection/focus-traversal/virtualized collection state on top of the new editor-primitive helpers, shared scroll/navigation-scope/caret-layout helpers, and promotion of the current native text-atlas path into a shared/cross-platform text subsystem.
 
 ### 2. Runtime/Game Layer
 
@@ -118,9 +121,10 @@ Current gap:
 Current gap:
 
 - The default shell host is now native, but the legacy ImGui shell and panel path still exists as a compatibility host and is still compiled into `new_editor`.
+- The default native shell path is still compiled through an `Application` translation unit that directly includes legacy ImGui host/presenter/compositor code, and `new_editor/CMakeLists.txt` still treats those legacy ImGui sources and include paths as target-global defaults.
 - The native shell currently proves direct runtime composition, but its shell chrome is still a bespoke `Application`-side layout rather than a fully shared XCUI-authored editor shell document.
 - Editor-specialized widgets are still incomplete at the shared-module level: the authored prototypes exist, but virtualization, multi-selection/focus traversal, toolbar/menu chrome, menu interaction widgets, and icon-atlas widgets are not yet extracted into reusable XCUI modules.
-- The default native path still depends on ImGui font-atlas internals through `XCUIStandaloneTextAtlasProvider`, so text rendering is not yet cleanly de-ImGuiized even though the shell/panel composition path is native by default.
+- The default native text path now uses a standalone Windows/GDI atlas through `XCUIStandaloneTextAtlasProvider`, but that provider still lives inside `new_editor` and is not yet promoted into a shared/cross-platform text subsystem.
 
 ## Validated This Phase
 
@@ -131,17 +135,19 @@ Current gap:
 - `new_editor_xcui_layout_lab_runtime_tests`: `12/12`
 - `new_editor_xcui_rhi_command_compiler_tests`: `7/7`
 - `new_editor_xcui_rhi_render_backend_tests`: `5/5`
+- `new_editor_xcui_standalone_text_atlas_provider_tests`: `6/6`
 - `new_editor_xcui_hosted_preview_presenter_tests`: `20/20`
 - `new_editor_imgui_window_ui_compositor_tests`: `7/7`
 - `new_editor_native_window_ui_compositor_tests`: `8/8`
 - `new_editor_xcui_editor_command_router_tests`: `5/5`
-- `new_editor_application_shell_command_bindings_tests`: `8/8`
+- `new_editor_application_shell_command_bindings_tests`: `11/11`
 - `new_editor_xcui_shell_chrome_state_tests`: `11/11`
 - `new_editor_xcui_panel_canvas_host_tests`: `4/4`
 - `new_editor_imgui_xcui_panel_canvas_host_tests`: `1/1`
 - `new_editor_native_xcui_panel_canvas_host_tests`: `4/4`
 - `new_editor_xcui_layout_lab_panel_tests`: `3/3`
 - `XCNewEditor` Debug target builds successfully
+- `XCNewEditor.exe` native-default smoke run stayed alive for `5s`
 - `core_ui_tests`: `52 total` (`50` passed, `2` skipped because `KeyCode::Delete` currently aliases `Backspace`)
 - `scene_tests`: `68/68`
 - `core_ui_style_tests`: `5/5`
@@ -253,7 +259,7 @@ Current gap:
   - generic preview frame submission no longer carries an ImGui draw-list pointer
   - the ImGui presenter now resolves inline draw targets through an explicit ImGui-only binding seam
   - panel/runtime callers still preserve the same legacy and native-preview behavior
-- Native hosted-preview publication is now wired through the default shell path:
+- Native hosted-preview publication milestone is now wired through the default shell path:
   - `NativeWindowUICompositor` publishes hosted preview textures as SRV-backed XCUI registrations and frees them through the compositor seam
   - `Application::BeginHostedPreviewFrameLifecycle(...)` now resets queue/registry state for both legacy and native frame paths
   - hosted-preview surface readiness now keys on published texture availability instead of ImGui-style descriptor validity
@@ -266,19 +272,38 @@ Current gap:
 - XCUI asset document loading changed to prefer direct source compilation before `ResourceManager` fallback for the sandbox path, fixing the LayoutLab crash.
 - `UIDocumentCompiler.cpp` repaired enough to restore full local builds after the duplicated schema-helper regression.
 - MSVC debug build hardening was tightened again so large parallel `engine` rebuilds stop tripping over compile-PDB contention.
+- `XCUIStandaloneTextAtlasProvider` no longer uses ImGui font-atlas/internal baking helpers:
+  - atlas ownership now stays inside a standalone provider implementation built on Windows/GDI glyph rasterization
+  - default editor atlas prewarms the current supported nominal sizes, exposes both `RGBA32` and `Alpha8` atlas views, lazily inserts non-prebaked BMP glyphs, and falls back to `?` for unrasterizable codepoints
+  - standalone atlas coverage now includes reset/rebuild, non-nominal size resolution, lazy glyph insertion/fallback behavior, and smoke use without any ImGui context
 
 ## Phase Risks Still Open
 
 - Schema instance validation is still open beyond `.xcschema` self-definition and artifact round-trip coverage.
 - `ScrollView` is still authored/static; no wheel-driven scrolling or virtualization yet.
-- The default native text path still builds its font atlas on top of ImGui font types/internal baking helpers.
+- The default native shell path still compiles through an `Application.cpp` unit that directly pulls in ImGui compatibility host code, so the native default path is not yet isolated at the translation-unit boundary.
+- `new_editor/CMakeLists.txt` still builds the legacy ImGui host/compositor/backend sources and include directories as target-global defaults instead of a compatibility-only slice.
+- The default native text path now owns its atlas without ImGui, but the provider is still Windows-only and remains trapped inside `new_editor` instead of a shared/cross-platform text layer.
 - Hosted-preview compatibility presentation still depends on an ImGui-only inline presenter path when not using the queued native surface path.
 - Editor widget coverage is still prototype-driven inside `LayoutLab`; it has not yet been promoted into a full reusable shared widget/runtime layer with command routing, virtualization, and property-edit transactions.
 
+## Execution-Plan Alignment
+
+- Against `XCUI完整架构设计与执行计划.md`, current `new_editor` progress should be treated as an early `Phase 8` foothold rather than full `Milestone E` completion:
+  - landed: `NativeWindowUICompositor`, native shell packet composition, native hosted-preview publication, XCUI-owned texture registrations, native panel surface-image presentation, standalone native text-atlas ownership inside `new_editor`
+  - not yet landed: default-path translation-unit isolation from legacy ImGui host code, promotion of the native text-atlas path into a shared/cross-platform text subsystem, shared XCUI-authored editor shell chrome
+- That means the next de-ImGui push should not keep centering on hosted-preview publication; that milestone is now effectively closed for the default native shell path.
+- The real remaining default-path blockers are:
+  - isolate legacy ImGui shell/compositor/presenter wiring from the default `Application` build path
+  - stop treating ImGui include paths and backend sources as the default `new_editor` compilation surface
+  - harden and promote `XCUIStandaloneTextAtlasProvider` / editor font bootstrap into a shared native text subsystem
+  - move native shell chrome out of bespoke `Application` layout code and into a shared XCUI shell model or authored shell document
+
 ## Next Phase
 
 1. Expand runtime/game-layer ownership from the current `SceneRuntime` UI context into scene-declared HUD/menu bootstrapping, draw submission, and higher-level runtime UI policies.
 2. Promote the current editor-facing widget prototypes out of authored `LayoutLab` content and into reusable XCUI widget/runtime modules, then continue with toolbar/menu chrome, shell-state adoption, virtualization, and broader focus/multi-selection behavior.
-3. Strip the remaining default-path ImGui seams down to compatibility-only code, starting with the standalone text/font-atlas path and then the remaining hosted-preview fallback layers.
-4. Promote the native shell chrome and card layout out of bespoke `Application` code into a shared XCUI/editor-layer shell model or authored shell document.
-5. Continue phased validation, commit, push, and plan refresh after each stable batch.
+3. Isolate legacy ImGui shell/compositor/presenter wiring from the default native path first, starting with `Application` translation-unit separation and a `new_editor` build split that stops treating ImGui include paths and sources as the default compilation surface.
+4. Promote the current standalone native text/font path out of `new_editor`, harden its atlas invalidation/caching contract, and remove the remaining default-path ImGui text/bootstrap ownership around compatibility-only code.
+5. Promote the native shell chrome and card layout out of bespoke `Application` code into a shared XCUI/editor-layer shell model or authored shell document.
+6. Continue phased validation, commit, push, and plan refresh after each stable batch.

new_editor/src/XCUIBackend/XCUIStandaloneTextAtlasProvider.cpp

@@ -1,6 +1,21 @@
 #include "XCUIBackend/XCUIStandaloneTextAtlasProvider.h"
 
-#include <imgui_internal.h>
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <windows.h>
+#include <wingdi.h>
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <limits>
+#include <memory>
+#include <unordered_map>
+#include <utility>
+#include <vector>
 
 namespace XCEngine {
 namespace Editor {
@@ -8,65 +23,688 @@ namespace XCUIBackend {
 
 namespace {
 
-IXCUITextAtlasProvider::FontHandle MakeFontHandle(const ImFont* font) {
+constexpr float kDefaultNominalFontSize = 18.0f;
+constexpr int kAtlasPadding = 1;
+constexpr int kMaxAtlasDimension = 4096;
+constexpr std::size_t kInvalidFontIndex = (std::numeric_limits<std::size_t>::max)();
+constexpr wchar_t kPrimaryFontFace[] = L"Segoe UI";
+constexpr wchar_t kFallbackFontFace[] = L"Microsoft YaHei";
+constexpr std::array<int, 5> kSupportedFontSizes = { 13, 14, 16, 18, 20 };
+constexpr std::array<std::pair<std::uint32_t, std::uint32_t>, 2> kPrebakedCodepointRanges = {{
+    { 0x0020u, 0x007Eu },
+    { 0x00A0u, 0x00FFu },
+}};
+
+struct CachedPixelBuffer {
+    std::vector<unsigned char> bytes = {};
+    int width = 0;
+    int height = 0;
+    int bytesPerPixel = 0;
+
+    void Clear() {
+        bytes.clear();
+        width = 0;
+        height = 0;
+        bytesPerPixel = 0;
+    }
+
+    bool IsValid() const {
+        return !bytes.empty() && width > 0 && height > 0 && bytesPerPixel > 0;
+    }
+};
+
+struct GlyphRecord {
+    int sizeKey = 0;
+    std::uint32_t codepoint = 0u;
+    bool visible = false;
+    bool colored = false;
+    float advanceX = 0.0f;
+    float x0 = 0.0f;
+    float y0 = 0.0f;
+    float x1 = 0.0f;
+    float y1 = 0.0f;
+    int bitmapWidth = 0;
+    int bitmapHeight = 0;
+    int atlasX = 0;
+    int atlasY = 0;
+    std::vector<unsigned char> alpha = {};
+};
+
+struct BakedFontRecord {
+    int sizeKey = 0;
+    IXCUITextAtlasProvider::BakedFontInfo metrics = {};
+    std::unordered_map<std::uint32_t, IXCUITextAtlasProvider::GlyphInfo> glyphs = {};
+};
+
+IXCUITextAtlasProvider::FontHandle MakeDefaultFontHandle() {
     IXCUITextAtlasProvider::FontHandle handle = {};
-    handle.value = reinterpret_cast<std::uintptr_t>(font);
+    handle.value = 1u;
     return handle;
 }
 
-ImFont* ResolveFontHandle(IXCUITextAtlasProvider::FontHandle handle) {
-    return reinterpret_cast<ImFont*>(handle.value);
+bool IsDefaultFontHandle(IXCUITextAtlasProvider::FontHandle handle) {
+    return handle.value == MakeDefaultFontHandle().value;
 }
 
-float ResolveNominalFontSize(const ImFont& font) {
-    return font.LegacySize > 0.0f ? font.LegacySize : 16.0f;
+std::size_t ResolveFontIndex(IXCUITextAtlasProvider::FontHandle handle) {
+    return IsDefaultFontHandle(handle) ? 0u : kInvalidFontIndex;
 }
 
-float ResolveRequestedFontSize(const ImFont& font, float requestedFontSize) {
-    return requestedFontSize > 0.0f ? requestedFontSize : ResolveNominalFontSize(font);
+std::uint64_t MakeGlyphKey(int sizeKey, std::uint32_t codepoint) {
+    return (static_cast<std::uint64_t>(static_cast<std::uint32_t>(sizeKey)) << 32u) |
+        static_cast<std::uint64_t>(codepoint);
 }
 
-bool IsFontOwnedByAtlas(const ImFont* font, const ImFontAtlas* atlas) {
-    return font != nullptr && atlas != nullptr && font->OwnerAtlas == atlas;
+void AppendCodepointRange(
+    std::vector<std::uint32_t>& outCodepoints,
+    std::uint32_t first,
+    std::uint32_t last) {
+    if (first > last) {
+        return;
     }
 
-ImFontBaked* ResolveBakedFont(
-    IXCUITextAtlasProvider::FontHandle fontHandle,
-    ImFontAtlas* atlas,
-    float requestedFontSize) {
-    ImFont* font = ResolveFontHandle(fontHandle);
-    if (!IsFontOwnedByAtlas(font, atlas)) {
+    outCodepoints.reserve(outCodepoints.size() + static_cast<std::size_t>(last - first + 1u));
+    for (std::uint32_t codepoint = first; codepoint <= last; ++codepoint) {
+        outCodepoints.push_back(codepoint);
+    }
+}
+
+std::vector<std::uint32_t> BuildPrebakedCodepointSet() {
+    std::vector<std::uint32_t> codepoints = {};
+    codepoints.reserve(768u);
+    for (const auto& range : kPrebakedCodepointRanges) {
+        AppendCodepointRange(codepoints, range.first, range.second);
+    }
+    codepoints.push_back(0xFFFDu);
+    std::sort(codepoints.begin(), codepoints.end());
+    codepoints.erase(std::unique(codepoints.begin(), codepoints.end()), codepoints.end());
+    return codepoints;
+}
+
+HFONT CreateEditorFont(int pixelHeight, const wchar_t* faceName) {
+    return ::CreateFontW(
+        -pixelHeight,
+        0,
+        0,
+        0,
+        FW_NORMAL,
+        FALSE,
+        FALSE,
+        FALSE,
+        DEFAULT_CHARSET,
+        OUT_TT_PRECIS,
+        CLIP_DEFAULT_PRECIS,
+        ANTIALIASED_QUALITY,
+        DEFAULT_PITCH | FF_DONTCARE,
+        faceName);
+}
+
+bool QueryTextMetrics(HDC dc, HFONT font, TEXTMETRICW& outMetrics) {
+    outMetrics = {};
+    if (dc == nullptr || font == nullptr) {
+        return false;
+    }
+
+    HGDIOBJ previous = ::SelectObject(dc, font);
+    const BOOL result = ::GetTextMetricsW(dc, &outMetrics);
+    ::SelectObject(dc, previous);
+    return result != FALSE;
+}
+
+bool FontHasGlyph(HDC dc, HFONT font, std::uint32_t codepoint) {
+    if (dc == nullptr || font == nullptr || codepoint > 0xFFFFu) {
+        return false;
+    }
+
+    WORD glyphIndex = 0xFFFFu;
+    WCHAR wideCodepoint = static_cast<WCHAR>(codepoint);
+    HGDIOBJ previous = ::SelectObject(dc, font);
+    const DWORD result = ::GetGlyphIndicesW(
+        dc,
+        &wideCodepoint,
+        1u,
+        &glyphIndex,
+        GGI_MARK_NONEXISTING_GLYPHS);
+    ::SelectObject(dc, previous);
+    return result != GDI_ERROR && glyphIndex != 0xFFFFu;
+}
+
+bool IsAdvanceOnlyWhitespace(std::uint32_t codepoint) {
+    return codepoint == 0x0020u ||
+        codepoint == 0x00A0u ||
+        (codepoint >= 0x2000u && codepoint <= 0x200Au) ||
+        codepoint == 0x202Fu ||
+        codepoint == 0x205Fu ||
+        codepoint == 0x3000u;
+}
+
+TEXTMETRICW MergeTextMetrics(
+    const TEXTMETRICW& primaryMetrics,
+    bool hasPrimaryMetrics,
+    const TEXTMETRICW& fallbackMetrics,
+    bool hasFallbackMetrics) {
+    TEXTMETRICW merged = {};
+    if (hasPrimaryMetrics) {
+        merged = primaryMetrics;
+    }
+    if (!hasFallbackMetrics) {
+        return merged;
+    }
+    if (!hasPrimaryMetrics) {
+        return fallbackMetrics;
+    }
+
+    merged.tmHeight = (std::max)(primaryMetrics.tmHeight, fallbackMetrics.tmHeight);
+    merged.tmAscent = (std::max)(primaryMetrics.tmAscent, fallbackMetrics.tmAscent);
+    merged.tmDescent = (std::max)(primaryMetrics.tmDescent, fallbackMetrics.tmDescent);
+    merged.tmExternalLeading = (std::max)(primaryMetrics.tmExternalLeading, fallbackMetrics.tmExternalLeading);
+    merged.tmAveCharWidth = (std::max)(primaryMetrics.tmAveCharWidth, fallbackMetrics.tmAveCharWidth);
+    merged.tmMaxCharWidth = (std::max)(primaryMetrics.tmMaxCharWidth, fallbackMetrics.tmMaxCharWidth);
+    return merged;
+}
+
+class GdiFontContext {
+public:
+    explicit GdiFontContext(int sizeKey)
+        : m_sizeKey(sizeKey) {
+        m_dc = ::CreateCompatibleDC(nullptr);
+        if (m_dc == nullptr) {
+            return;
+        }
+
+        m_primaryFont = CreateEditorFont(sizeKey, kPrimaryFontFace);
+        m_fallbackFont = CreateEditorFont(sizeKey, kFallbackFontFace);
+        m_hasPrimaryMetrics = QueryTextMetrics(m_dc, m_primaryFont, m_primaryMetrics);
+        m_hasFallbackMetrics = QueryTextMetrics(m_dc, m_fallbackFont, m_fallbackMetrics);
+        m_lineMetrics = MergeTextMetrics(
+            m_primaryMetrics,
+            m_hasPrimaryMetrics,
+            m_fallbackMetrics,
+            m_hasFallbackMetrics);
+    }
+
+    ~GdiFontContext() {
+        if (m_primaryFont != nullptr) {
+            ::DeleteObject(m_primaryFont);
+            m_primaryFont = nullptr;
+        }
+        if (m_fallbackFont != nullptr) {
+            ::DeleteObject(m_fallbackFont);
+            m_fallbackFont = nullptr;
+        }
+        if (m_dc != nullptr) {
+            ::DeleteDC(m_dc);
+            m_dc = nullptr;
+        }
+    }
+
+    bool IsValid() const {
+        return m_dc != nullptr && (m_hasPrimaryMetrics || m_hasFallbackMetrics);
+    }
+
+    IXCUITextAtlasProvider::BakedFontInfo BuildBakedFontInfo() const {
+        IXCUITextAtlasProvider::BakedFontInfo info = {};
+        info.lineHeight = static_cast<float>(m_lineMetrics.tmHeight);
+        info.ascent = static_cast<float>(m_lineMetrics.tmAscent);
+        info.descent = static_cast<float>(m_lineMetrics.tmDescent);
+        info.rasterizerDensity = 1.0f;
+        return info;
+    }
+
+    bool RasterizeGlyph(std::uint32_t codepoint, GlyphRecord& outRecord) const {
+        outRecord = {};
+        outRecord.sizeKey = m_sizeKey;
+        outRecord.codepoint = codepoint;
+        outRecord.colored = false;
+
+        if (!IsValid()) {
+            return false;
+        }
+
+        HFONT resolvedFont = ResolveFontForCodepoint(codepoint);
+        if (resolvedFont == nullptr) {
+            return false;
+        }
+
+        if (IsAdvanceOnlyWhitespace(codepoint)) {
+            HGDIOBJ previous = ::SelectObject(m_dc, resolvedFont);
+            SIZE textExtent = {};
+            WCHAR wideCodepoint = static_cast<WCHAR>(codepoint);
+            const BOOL extentResult = ::GetTextExtentPoint32W(m_dc, &wideCodepoint, 1, &textExtent);
+            ::SelectObject(m_dc, previous);
+            outRecord.visible = false;
+            outRecord.advanceX = extentResult != FALSE
+                ? static_cast<float>(textExtent.cx)
+                : static_cast<float>(m_lineMetrics.tmAveCharWidth);
+            return true;
+        }
+
+        HGDIOBJ previous = ::SelectObject(m_dc, resolvedFont);
+        MAT2 transform = {};
+        transform.eM11.value = 1;
+        transform.eM22.value = 1;
+
+        GLYPHMETRICS glyphMetrics = {};
+        const DWORD bufferSize = ::GetGlyphOutlineW(
+            m_dc,
+            static_cast<UINT>(codepoint),
+            GGO_GRAY8_BITMAP,
+            &glyphMetrics,
+            0u,
+            nullptr,
+            &transform);
+        ::SelectObject(m_dc, previous);
+
+        if (bufferSize == GDI_ERROR) {
+            return false;
+        }
+
+        outRecord.visible = glyphMetrics.gmBlackBoxX > 0u && glyphMetrics.gmBlackBoxY > 0u;
+        outRecord.advanceX = static_cast<float>(glyphMetrics.gmCellIncX);
+        outRecord.bitmapWidth = static_cast<int>(glyphMetrics.gmBlackBoxX);
+        outRecord.bitmapHeight = static_cast<int>(glyphMetrics.gmBlackBoxY);
+        outRecord.x0 = static_cast<float>(glyphMetrics.gmptGlyphOrigin.x);
+        outRecord.y0 = static_cast<float>(m_lineMetrics.tmAscent - glyphMetrics.gmptGlyphOrigin.y);
+        outRecord.x1 = outRecord.x0 + static_cast<float>(glyphMetrics.gmBlackBoxX);
+        outRecord.y1 = outRecord.y0 + static_cast<float>(glyphMetrics.gmBlackBoxY);
+
+        if (!outRecord.visible) {
+            return true;
+        }
+
+        std::vector<unsigned char> bitmapBuffer(bufferSize);
+        previous = ::SelectObject(m_dc, resolvedFont);
+        const DWORD writeResult = ::GetGlyphOutlineW(
+            m_dc,
+            static_cast<UINT>(codepoint),
+            GGO_GRAY8_BITMAP,
+            &glyphMetrics,
+            bufferSize,
+            bitmapBuffer.data(),
+            &transform);
+        ::SelectObject(m_dc, previous);
+        if (writeResult == GDI_ERROR) {
+            return false;
+        }
+
+        const int sourceStride = (static_cast<int>(glyphMetrics.gmBlackBoxX) + 3) & ~3;
+        const std::size_t requiredBytes =
+            static_cast<std::size_t>(sourceStride) *
+            static_cast<std::size_t>((std::max)(0, outRecord.bitmapHeight));
+        if (bitmapBuffer.size() < requiredBytes) {
+            return false;
+        }
+        outRecord.alpha.resize(
+            static_cast<std::size_t>(outRecord.bitmapWidth) *
+            static_cast<std::size_t>(outRecord.bitmapHeight));
+        for (int y = 0; y < outRecord.bitmapHeight; ++y) {
+            const unsigned char* sourceRow = bitmapBuffer.data() + static_cast<std::size_t>(y * sourceStride);
+            unsigned char* destRow = outRecord.alpha.data() +
+                static_cast<std::size_t>(y * outRecord.bitmapWidth);
+            for (int x = 0; x < outRecord.bitmapWidth; ++x) {
+                const unsigned int value = static_cast<unsigned int>(sourceRow[x]);
+                destRow[x] = static_cast<unsigned char>((value * 255u + 32u) / 64u);
+            }
+        }
+
+        return true;
+    }
+
+private:
+    HFONT ResolveFontForCodepoint(std::uint32_t codepoint) const {
+        if (FontHasGlyph(m_dc, m_primaryFont, codepoint)) {
+            return m_primaryFont;
+        }
+        if (FontHasGlyph(m_dc, m_fallbackFont, codepoint)) {
+            return m_fallbackFont;
+        }
         return nullptr;
     }
 
-    const float resolvedFontSize = ResolveRequestedFontSize(*font, requestedFontSize);
-    if (resolvedFontSize <= 0.0f) {
-        return nullptr;
+    int m_sizeKey = 0;
+    HDC m_dc = nullptr;
+    HFONT m_primaryFont = nullptr;
+    HFONT m_fallbackFont = nullptr;
+    TEXTMETRICW m_primaryMetrics = {};
+    TEXTMETRICW m_fallbackMetrics = {};
+    TEXTMETRICW m_lineMetrics = {};
+    bool m_hasPrimaryMetrics = false;
+    bool m_hasFallbackMetrics = false;
+};
+
+std::uintptr_t MakePixelDataKey(const CachedPixelBuffer& pixels, std::uint64_t generation) {
+    return reinterpret_cast<std::uintptr_t>(pixels.bytes.data()) ^
+        static_cast<std::uintptr_t>(generation * 1315423911ull);
 }
 
-    return font->GetFontBaked(resolvedFontSize);
+int ResolveSupportedSizeKey(float requestedSize, float nominalSize) {
+    const float targetSize = requestedSize > 0.0f ? requestedSize : nominalSize;
+    auto bestIt = std::min_element(
+        kSupportedFontSizes.begin(),
+        kSupportedFontSizes.end(),
+        [targetSize](int lhs, int rhs) {
+            const float lhsDistance = std::fabs(targetSize - static_cast<float>(lhs));
+            const float rhsDistance = std::fabs(targetSize - static_cast<float>(rhs));
+            return lhsDistance < rhsDistance;
+        });
+    return bestIt != kSupportedFontSizes.end() ? *bestIt : static_cast<int>(std::lround(targetSize));
+}
+
+bool PopulateGlyphInfo(
+    const GlyphRecord& glyph,
+    int atlasWidth,
+    int atlasHeight,
+    IXCUITextAtlasProvider::GlyphInfo& outInfo) {
+    outInfo = {};
+    outInfo.requestedCodepoint = glyph.codepoint;
+    outInfo.resolvedCodepoint = glyph.codepoint;
+    outInfo.visible = glyph.visible;
+    outInfo.colored = glyph.colored;
+    outInfo.advanceX = glyph.advanceX;
+    outInfo.x0 = glyph.x0;
+    outInfo.y0 = glyph.y0;
+    outInfo.x1 = glyph.x1;
+    outInfo.y1 = glyph.y1;
+    if (!glyph.visible) {
+        return true;
+    }
+    if (atlasWidth <= 0 || atlasHeight <= 0) {
+        return false;
+    }
+
+    outInfo.u0 = static_cast<float>(glyph.atlasX) / static_cast<float>(atlasWidth);
+    outInfo.v0 = static_cast<float>(glyph.atlasY) / static_cast<float>(atlasHeight);
+    outInfo.u1 = static_cast<float>(glyph.atlasX + glyph.bitmapWidth) / static_cast<float>(atlasWidth);
+    outInfo.v1 = static_cast<float>(glyph.atlasY + glyph.bitmapHeight) / static_cast<float>(atlasHeight);
+    return true;
+}
+
+std::vector<std::size_t> BuildVisiblePackOrder(const std::vector<GlyphRecord>& glyphs) {
+    std::vector<std::size_t> order = {};
+    order.reserve(glyphs.size());
+    for (std::size_t index = 0; index < glyphs.size(); ++index) {
+        if (glyphs[index].visible) {
+            order.push_back(index);
+        }
+    }
+
+    std::sort(
+        order.begin(),
+        order.end(),
+        [&glyphs](std::size_t lhs, std::size_t rhs) {
+            const GlyphRecord& left = glyphs[lhs];
+            const GlyphRecord& right = glyphs[rhs];
+            if (left.bitmapHeight != right.bitmapHeight) {
+                return left.bitmapHeight > right.bitmapHeight;
+            }
+            if (left.bitmapWidth != right.bitmapWidth) {
+                return left.bitmapWidth > right.bitmapWidth;
+            }
+            if (left.sizeKey != right.sizeKey) {
+                return left.sizeKey < right.sizeKey;
+            }
+            return left.codepoint < right.codepoint;
+        });
+    return order;
+}
+
+bool TryPackVisibleGlyphs(
+    std::vector<GlyphRecord>& glyphs,
+    int atlasWidth,
+    int& outAtlasHeight) {
+    outAtlasHeight = 1;
+    if (atlasWidth <= 0) {
+        return false;
+    }
+
+    for (GlyphRecord& glyph : glyphs) {
+        glyph.atlasX = 0;
+        glyph.atlasY = 0;
+    }
+
+    const std::vector<std::size_t> packOrder = BuildVisiblePackOrder(glyphs);
+    int cursorX = kAtlasPadding;
+    int cursorY = kAtlasPadding;
+    int rowHeight = 0;
+
+    for (std::size_t index : packOrder) {
+        GlyphRecord& glyph = glyphs[index];
+        const int requiredWidth = glyph.bitmapWidth + kAtlasPadding * 2;
+        const int requiredHeight = glyph.bitmapHeight + kAtlasPadding * 2;
+        if (requiredWidth > atlasWidth) {
+            return false;
+        }
+
+        if (cursorX + requiredWidth > atlasWidth) {
+            cursorX = kAtlasPadding;
+            cursorY += rowHeight;
+            rowHeight = 0;
+        }
+
+        glyph.atlasX = cursorX + kAtlasPadding;
+        glyph.atlasY = cursorY + kAtlasPadding;
+        cursorX += requiredWidth;
+        rowHeight = (std::max)(rowHeight, requiredHeight);
+        outAtlasHeight = (std::max)(outAtlasHeight, cursorY + rowHeight + kAtlasPadding);
+        if (outAtlasHeight > kMaxAtlasDimension) {
+            return false;
+        }
+    }
+
+    return true;
 }
 
 } // namespace
 
-XCUIStandaloneTextAtlasProvider::XCUIStandaloneTextAtlasProvider() {
+struct XCUIStandaloneTextAtlasProvider::Impl {
+    bool ready = false;
+    float nominalSize = kDefaultNominalFontSize;
+    CachedPixelBuffer alpha8Pixels = {};
+    CachedPixelBuffer rgba32Pixels = {};
+    std::uint64_t pixelGeneration = 0u;
+    std::unordered_map<int, BakedFontRecord> bakedFonts = {};
+    std::vector<GlyphRecord> glyphRecords = {};
+    std::unordered_map<std::uint64_t, std::size_t> glyphIndices = {};
+};
+
+namespace {
+
+void ResetImpl(XCUIStandaloneTextAtlasProvider::Impl& impl) {
+    impl.ready = false;
+    impl.nominalSize = kDefaultNominalFontSize;
+    impl.alpha8Pixels.Clear();
+    impl.rgba32Pixels.Clear();
+    impl.bakedFonts.clear();
+    impl.glyphRecords.clear();
+    impl.glyphIndices.clear();
+    ++impl.pixelGeneration;
+}
+
+bool RebuildAtlasPixels(XCUIStandaloneTextAtlasProvider::Impl& impl) {
+    int chosenAtlasWidth = 0;
+    int chosenAtlasHeight = 1;
+    for (const int candidateWidth : { 1024, 2048, 4096 }) {
+        int packedHeight = 1;
+        if (TryPackVisibleGlyphs(impl.glyphRecords, candidateWidth, packedHeight)) {
+            chosenAtlasWidth = candidateWidth;
+            chosenAtlasHeight = packedHeight;
+            break;
+        }
+    }
+
+    if (chosenAtlasWidth == 0 || chosenAtlasHeight <= 0) {
+        return false;
+    }
+
+    impl.alpha8Pixels.width = chosenAtlasWidth;
+    impl.alpha8Pixels.height = chosenAtlasHeight;
+    impl.alpha8Pixels.bytesPerPixel = 1;
+    impl.alpha8Pixels.bytes.assign(
+        static_cast<std::size_t>(chosenAtlasWidth) * static_cast<std::size_t>(chosenAtlasHeight),
+        0u);
+
+    for (const GlyphRecord& glyph : impl.glyphRecords) {
+        if (!glyph.visible || glyph.bitmapWidth <= 0 || glyph.bitmapHeight <= 0) {
+            continue;
+        }
+
+        for (int y = 0; y < glyph.bitmapHeight; ++y) {
+            const unsigned char* sourceRow = glyph.alpha.data() +
+                static_cast<std::size_t>(y * glyph.bitmapWidth);
+            unsigned char* destRow = impl.alpha8Pixels.bytes.data() +
+                static_cast<std::size_t>((glyph.atlasY + y) * impl.alpha8Pixels.width + glyph.atlasX);
+            std::copy(sourceRow, sourceRow + glyph.bitmapWidth, destRow);
+        }
+    }
+
+    impl.rgba32Pixels.width = chosenAtlasWidth;
+    impl.rgba32Pixels.height = chosenAtlasHeight;
+    impl.rgba32Pixels.bytesPerPixel = 4;
+    impl.rgba32Pixels.bytes.assign(
+        static_cast<std::size_t>(chosenAtlasWidth) *
+            static_cast<std::size_t>(chosenAtlasHeight) *
+            4u,
+        0u);
+    for (std::size_t pixelIndex = 0; pixelIndex < impl.alpha8Pixels.bytes.size(); ++pixelIndex) {
+        const unsigned char alpha = impl.alpha8Pixels.bytes[pixelIndex];
+        unsigned char* rgba = impl.rgba32Pixels.bytes.data() + pixelIndex * 4u;
+        rgba[0] = 255u;
+        rgba[1] = 255u;
+        rgba[2] = 255u;
+        rgba[3] = alpha;
+    }
+
+    for (auto& [sizeKey, bakedFont] : impl.bakedFonts) {
+        (void)sizeKey;
+        bakedFont.glyphs.clear();
+    }
+
+    for (const GlyphRecord& glyph : impl.glyphRecords) {
+        IXCUITextAtlasProvider::GlyphInfo glyphInfo = {};
+        if (!PopulateGlyphInfo(
+                glyph,
+                impl.alpha8Pixels.width,
+                impl.alpha8Pixels.height,
+                glyphInfo)) {
+            return false;
+        }
+        impl.bakedFonts[glyph.sizeKey].glyphs.insert_or_assign(glyph.codepoint, glyphInfo);
+    }
+
+    ++impl.pixelGeneration;
+    return true;
+}
+
+bool AddGlyphRecord(
+    XCUIStandaloneTextAtlasProvider::Impl& impl,
+    int sizeKey,
+    std::uint32_t codepoint) {
+    const std::uint64_t glyphKey = MakeGlyphKey(sizeKey, codepoint);
+    if (impl.glyphIndices.find(glyphKey) != impl.glyphIndices.end()) {
+        return true;
+    }
+
+    GdiFontContext context(sizeKey);
+    if (!context.IsValid()) {
+        return false;
+    }
+
+    if (impl.bakedFonts.find(sizeKey) == impl.bakedFonts.end()) {
+        BakedFontRecord bakedFont = {};
+        bakedFont.sizeKey = sizeKey;
+        bakedFont.metrics = context.BuildBakedFontInfo();
+        impl.bakedFonts.insert_or_assign(sizeKey, std::move(bakedFont));
+    }
+
+    GlyphRecord glyph = {};
+    if (!context.RasterizeGlyph(codepoint, glyph)) {
+        return false;
+    }
+
+    const std::size_t previousGlyphCount = impl.glyphRecords.size();
+    impl.glyphRecords.push_back(std::move(glyph));
+    impl.glyphIndices.insert_or_assign(glyphKey, previousGlyphCount);
+    if (!RebuildAtlasPixels(impl)) {
+        impl.glyphIndices.erase(glyphKey);
+        impl.glyphRecords.pop_back();
+        RebuildAtlasPixels(impl);
+        return false;
+    }
+
+    return true;
+}
+
+const BakedFontRecord* FindBakedFont(
+    const XCUIStandaloneTextAtlasProvider::Impl& impl,
+    int sizeKey) {
+    const auto it = impl.bakedFonts.find(sizeKey);
+    return it != impl.bakedFonts.end() ? &it->second : nullptr;
+}
+
+} // namespace
+
+XCUIStandaloneTextAtlasProvider::XCUIStandaloneTextAtlasProvider()
+    : m_impl(std::make_unique<Impl>()) {
     RebuildDefaultEditorAtlas();
 }
 
+XCUIStandaloneTextAtlasProvider::~XCUIStandaloneTextAtlasProvider() = default;
+
 void XCUIStandaloneTextAtlasProvider::Reset() {
-    m_atlas.Clear();
-    m_defaultFont = nullptr;
-    m_ready = false;
+    if (m_impl == nullptr) {
+        m_impl = std::make_unique<Impl>();
+        return;
+    }
+
+    ResetImpl(*m_impl);
 }
 
 bool XCUIStandaloneTextAtlasProvider::RebuildDefaultEditorAtlas() {
     Reset();
-    m_ready = BuildDefaultXCUIEditorFontAtlas(m_atlas, m_defaultFont);
-    return m_ready;
+
+    if (m_impl == nullptr) {
+        return false;
+    }
+
+    const std::vector<std::uint32_t> prebakedCodepoints = BuildPrebakedCodepointSet();
+    for (const int sizeKey : kSupportedFontSizes) {
+        GdiFontContext context(sizeKey);
+        if (!context.IsValid()) {
+            ResetImpl(*m_impl);
+            return false;
+        }
+
+        BakedFontRecord bakedFont = {};
+        bakedFont.sizeKey = sizeKey;
+        bakedFont.metrics = context.BuildBakedFontInfo();
+        m_impl->bakedFonts.insert_or_assign(sizeKey, std::move(bakedFont));
+
+        for (std::uint32_t codepoint : prebakedCodepoints) {
+            GlyphRecord glyph = {};
+            if (!context.RasterizeGlyph(codepoint, glyph)) {
+                continue;
+            }
+
+            const std::uint64_t glyphKey = MakeGlyphKey(sizeKey, codepoint);
+            m_impl->glyphIndices.insert_or_assign(glyphKey, m_impl->glyphRecords.size());
+            m_impl->glyphRecords.push_back(std::move(glyph));
+        }
+    }
+
+    if (m_impl->bakedFonts.empty() || !RebuildAtlasPixels(*m_impl)) {
+        ResetImpl(*m_impl);
+        return false;
+    }
+
+    m_impl->ready = true;
+    return true;
 }
 
 bool XCUIStandaloneTextAtlasProvider::IsReady() const {
-    return m_ready && ResolveDefaultFont() != nullptr;
+    return m_impl != nullptr &&
+        m_impl->ready &&
+        !m_impl->bakedFonts.empty() &&
+        m_impl->rgba32Pixels.IsValid();
 }
 
 bool XCUIStandaloneTextAtlasProvider::GetAtlasTextureView(
@@ -74,74 +712,59 @@ bool XCUIStandaloneTextAtlasProvider::GetAtlasTextureView(
     AtlasTextureView& outView) const {
     outView = {};
 
-    ImFontAtlas* atlas = ResolveAtlas();
-    if (atlas == nullptr) {
+    if (!IsReady() || m_impl == nullptr) {
         return false;
     }
 
-    unsigned char* pixels = nullptr;
-    int width = 0;
-    int height = 0;
-    int bytesPerPixel = 0;
-    PixelFormat resolvedFormat = preferredFormat;
-
-    switch (preferredFormat) {
-    case PixelFormat::Alpha8:
-        atlas->GetTexDataAsAlpha8(&pixels, &width, &height, &bytesPerPixel);
+    const CachedPixelBuffer* resolvedPixels = nullptr;
+    PixelFormat resolvedFormat = PixelFormat::Unknown;
+    if (preferredFormat == PixelFormat::Alpha8 && m_impl->alpha8Pixels.IsValid()) {
+        resolvedPixels = &m_impl->alpha8Pixels;
         resolvedFormat = PixelFormat::Alpha8;
-        break;
-    case PixelFormat::RGBA32:
-    case PixelFormat::Unknown:
-    default:
-        atlas->GetTexDataAsRGBA32(&pixels, &width, &height, &bytesPerPixel);
+    } else if (m_impl->rgba32Pixels.IsValid()) {
+        resolvedPixels = &m_impl->rgba32Pixels;
         resolvedFormat = PixelFormat::RGBA32;
-        break;
+    } else if (m_impl->alpha8Pixels.IsValid()) {
+        resolvedPixels = &m_impl->alpha8Pixels;
+        resolvedFormat = PixelFormat::Alpha8;
     }
 
-    if (pixels == nullptr || width <= 0 || height <= 0 || bytesPerPixel <= 0) {
+    if (resolvedPixels == nullptr || !resolvedPixels->IsValid()) {
         return false;
     }
 
-    outView.pixels = pixels;
-    outView.width = width;
-    outView.height = height;
-    outView.stride = width * bytesPerPixel;
-    outView.bytesPerPixel = bytesPerPixel;
+    outView.pixels = resolvedPixels->bytes.data();
+    outView.width = resolvedPixels->width;
+    outView.height = resolvedPixels->height;
+    outView.stride = resolvedPixels->width * resolvedPixels->bytesPerPixel;
+    outView.bytesPerPixel = resolvedPixels->bytesPerPixel;
     outView.format = resolvedFormat;
-    outView.atlasStorageKey = reinterpret_cast<std::uintptr_t>(atlas);
-    outView.pixelDataKey = reinterpret_cast<std::uintptr_t>(pixels);
+    outView.atlasStorageKey = reinterpret_cast<std::uintptr_t>(m_impl.get());
+    outView.pixelDataKey = MakePixelDataKey(*resolvedPixels, m_impl->pixelGeneration);
     return true;
 }
 
 std::size_t XCUIStandaloneTextAtlasProvider::GetFontCount() const {
-    const ImFontAtlas* atlas = ResolveAtlas();
-    return atlas != nullptr ? static_cast<std::size_t>(atlas->Fonts.Size) : 0u;
+    return IsReady() ? 1u : 0u;
 }
 
 IXCUITextAtlasProvider::FontHandle XCUIStandaloneTextAtlasProvider::GetFont(std::size_t index) const {
-    const ImFontAtlas* atlas = ResolveAtlas();
-    if (atlas == nullptr || index >= static_cast<std::size_t>(atlas->Fonts.Size)) {
-        return {};
-    }
-
-    return MakeFontHandle(atlas->Fonts[static_cast<int>(index)]);
+    return IsReady() && index == 0u ? MakeDefaultFontHandle() : FontHandle{};
 }
 
 IXCUITextAtlasProvider::FontHandle XCUIStandaloneTextAtlasProvider::GetDefaultFont() const {
-    return MakeFontHandle(ResolveDefaultFont());
+    return IsReady() ? MakeDefaultFontHandle() : FontHandle{};
 }
 
 bool XCUIStandaloneTextAtlasProvider::GetFontInfo(FontHandle fontHandle, FontInfo& outInfo) const {
     outInfo = {};
 
-    ImFontAtlas* atlas = ResolveAtlas();
-    ImFont* font = ResolveFontHandle(fontHandle);
-    if (!IsFontOwnedByAtlas(font, atlas)) {
+    if (!IsReady() || ResolveFontIndex(fontHandle) == kInvalidFontIndex || m_impl == nullptr) {
         return false;
     }
 
     outInfo.handle = fontHandle;
-    outInfo.nominalSize = ResolveNominalFontSize(*font);
+    outInfo.nominalSize = m_impl->nominalSize;
     return true;
 }
 
@@ -151,15 +774,17 @@ bool XCUIStandaloneTextAtlasProvider::GetBakedFontInfo(
     BakedFontInfo& outInfo) const {
     outInfo = {};
 
-    ImFontBaked* bakedFont = ResolveBakedFont(fontHandle, ResolveAtlas(), fontSize);
+    if (!IsReady() || ResolveFontIndex(fontHandle) == kInvalidFontIndex || m_impl == nullptr) {
+        return false;
+    }
+
+    const int sizeKey = ResolveSupportedSizeKey(fontSize, m_impl->nominalSize);
+    const BakedFontRecord* bakedFont = FindBakedFont(*m_impl, sizeKey);
     if (bakedFont == nullptr) {
         return false;
     }
 
-    outInfo.lineHeight = bakedFont->Size;
-    outInfo.ascent = bakedFont->Ascent;
-    outInfo.descent = bakedFont->Descent;
-    outInfo.rasterizerDensity = bakedFont->RasterizerDensity;
+    outInfo = bakedFont->metrics;
     return true;
 }
 
@@ -170,51 +795,46 @@ bool XCUIStandaloneTextAtlasProvider::FindGlyph(
     GlyphInfo& outInfo) const {
     outInfo = {};
 
-    if (codepoint > IM_UNICODE_CODEPOINT_MAX) {
+    if (!IsReady() || ResolveFontIndex(fontHandle) == kInvalidFontIndex || m_impl == nullptr) {
         return false;
     }
 
-    ImFontBaked* bakedFont = ResolveBakedFont(fontHandle, ResolveAtlas(), fontSize);
+    const int sizeKey = ResolveSupportedSizeKey(fontSize, m_impl->nominalSize);
+    const BakedFontRecord* bakedFont = FindBakedFont(*m_impl, sizeKey);
     if (bakedFont == nullptr) {
         return false;
     }
 
-    ImFontGlyph* glyph = bakedFont->FindGlyph(static_cast<ImWchar>(codepoint));
-    if (glyph == nullptr) {
-        return false;
-    }
-
-    outInfo.requestedCodepoint = codepoint;
-    outInfo.resolvedCodepoint = glyph->Codepoint;
-    outInfo.visible = glyph->Visible != 0;
-    outInfo.colored = glyph->Colored != 0;
-    outInfo.advanceX = glyph->AdvanceX;
-    outInfo.x0 = glyph->X0;
-    outInfo.y0 = glyph->Y0;
-    outInfo.x1 = glyph->X1;
-    outInfo.y1 = glyph->Y1;
-    outInfo.u0 = glyph->U0;
-    outInfo.v0 = glyph->V0;
-    outInfo.u1 = glyph->U1;
-    outInfo.v1 = glyph->V1;
+    const auto glyphIt = bakedFont->glyphs.find(codepoint);
+    if (glyphIt != bakedFont->glyphs.end()) {
+        outInfo = glyphIt->second;
         return true;
     }
 
-::ImFontAtlas* XCUIStandaloneTextAtlasProvider::ResolveAtlas() const {
-    return m_ready ? &m_atlas : nullptr;
+    if (codepoint <= 0xFFFFu && AddGlyphRecord(*m_impl, sizeKey, codepoint)) {
+        const BakedFontRecord* refreshedBakedFont = FindBakedFont(*m_impl, sizeKey);
+        if (refreshedBakedFont != nullptr) {
+            const auto refreshedGlyphIt = refreshedBakedFont->glyphs.find(codepoint);
+            if (refreshedGlyphIt != refreshedBakedFont->glyphs.end()) {
+                outInfo = refreshedGlyphIt->second;
+                return true;
+            }
+        }
     }
 
-::ImFont* XCUIStandaloneTextAtlasProvider::ResolveDefaultFont() const {
-    ImFontAtlas* atlas = ResolveAtlas();
-    if (atlas == nullptr) {
-        return nullptr;
+    const BakedFontRecord* fallbackBakedFont = FindBakedFont(*m_impl, sizeKey);
+    if (fallbackBakedFont == nullptr) {
+        return false;
     }
 
-    if (IsFontOwnedByAtlas(m_defaultFont, atlas)) {
-        return m_defaultFont;
+    const auto fallbackGlyphIt = fallbackBakedFont->glyphs.find(static_cast<std::uint32_t>('?'));
+    if (fallbackGlyphIt == fallbackBakedFont->glyphs.end()) {
+        return false;
     }
 
-    return atlas->Fonts.empty() ? nullptr : atlas->Fonts[0];
+    outInfo = fallbackGlyphIt->second;
+    outInfo.requestedCodepoint = codepoint;
+    return true;
 }
 
 } // namespace XCUIBackend

new_editor/src/XCUIBackend/XCUIStandaloneTextAtlasProvider.h

@@ -3,7 +3,7 @@
 #include "IXCUITextAtlasProvider.h"
 #include "XCUIEditorFontSetup.h"
 
-#include <imgui.h>
+#include <memory>
 
 namespace XCEngine {
 namespace Editor {
@@ -12,6 +12,7 @@ namespace XCUIBackend {
 class XCUIStandaloneTextAtlasProvider final : public IXCUITextAtlasProvider {
 public:
     XCUIStandaloneTextAtlasProvider();
+    ~XCUIStandaloneTextAtlasProvider();
 
     XCUIStandaloneTextAtlasProvider(const XCUIStandaloneTextAtlasProvider&) = delete;
     XCUIStandaloneTextAtlasProvider& operator=(const XCUIStandaloneTextAtlasProvider&) = delete;
@@ -28,13 +29,10 @@ public:
     bool GetBakedFontInfo(FontHandle font, float fontSize, BakedFontInfo& outInfo) const override;
     bool FindGlyph(FontHandle font, float fontSize, std::uint32_t codepoint, GlyphInfo& outInfo) const override;
 
-private:
-    ::ImFontAtlas* ResolveAtlas() const;
-    ::ImFont* ResolveDefaultFont() const;
+    struct Impl;
 
-    mutable ::ImFontAtlas m_atlas = {};
-    ::ImFont* m_defaultFont = nullptr;
-    bool m_ready = false;
+private:
+    std::unique_ptr<Impl> m_impl;
 };
 
 } // namespace XCUIBackend

tests/NewEditor/CMakeLists.txt

@@ -745,18 +745,10 @@ else()
 endif()
 
 if(EXISTS "${NEW_EDITOR_STANDALONE_TEXT_ATLAS_PROVIDER_HEADER}" AND
-   EXISTS "${NEW_EDITOR_STANDALONE_TEXT_ATLAS_PROVIDER_SOURCE}" AND
-   EXISTS "${NEW_EDITOR_FONT_SETUP_HEADER}" AND
-   EXISTS "${NEW_EDITOR_FONT_SETUP_SOURCE}" AND
-   EXISTS "${CMAKE_BINARY_DIR}/_deps/imgui-src/imgui.cpp")
+   EXISTS "${NEW_EDITOR_STANDALONE_TEXT_ATLAS_PROVIDER_SOURCE}")
     add_executable(new_editor_xcui_standalone_text_atlas_provider_tests
         test_xcui_standalone_text_atlas_provider.cpp
-        ${NEW_EDITOR_FONT_SETUP_SOURCE}
         ${NEW_EDITOR_STANDALONE_TEXT_ATLAS_PROVIDER_SOURCE}
-        ${CMAKE_BINARY_DIR}/_deps/imgui-src/imgui.cpp
-        ${CMAKE_BINARY_DIR}/_deps/imgui-src/imgui_draw.cpp
-        ${CMAKE_BINARY_DIR}/_deps/imgui-src/imgui_tables.cpp
-        ${CMAKE_BINARY_DIR}/_deps/imgui-src/imgui_widgets.cpp
     )
 
     xcengine_configure_new_editor_test_target(new_editor_xcui_standalone_text_atlas_provider_tests)
@@ -767,19 +759,18 @@ if(EXISTS "${NEW_EDITOR_STANDALONE_TEXT_ATLAS_PROVIDER_HEADER}" AND
         GTest::gtest
         GTest::gtest_main
         user32
+        gdi32
         comdlg32
     )
 
     target_include_directories(new_editor_xcui_standalone_text_atlas_provider_tests PRIVATE
         ${CMAKE_SOURCE_DIR}/engine/include
         ${CMAKE_SOURCE_DIR}/new_editor/src
-        ${CMAKE_BINARY_DIR}/_deps/imgui-src
-        ${CMAKE_BINARY_DIR}/_deps/imgui-src/backends
     )
 
     xcengine_discover_new_editor_gtests(new_editor_xcui_standalone_text_atlas_provider_tests)
 else()
-    message(STATUS "Skipping new_editor_xcui_standalone_text_atlas_provider_tests because standalone atlas provider, font setup, or ImGui sources are missing.")
+    message(STATUS "Skipping new_editor_xcui_standalone_text_atlas_provider_tests because standalone atlas provider files are missing.")
 endif()
 
 if(EXISTS "${NEW_EDITOR_RHI_COMMAND_COMPILER_HEADER}" AND

tests/NewEditor/test_xcui_standalone_text_atlas_provider.cpp

@@ -11,12 +11,15 @@ using XCEngine::Editor::XCUIBackend::XCUIStandaloneTextAtlasProvider;
 
 TEST(XCUIStandaloneTextAtlasProviderTest, BuildsDefaultEditorAtlasWithoutImGuiContext) {
     XCUIStandaloneTextAtlasProvider provider = {};
-
     IXCUITextAtlasProvider::AtlasTextureView atlasView = {};
+    IXCUITextAtlasProvider::AtlasTextureView alphaView = {};
     ASSERT_TRUE(provider.IsReady());
     ASSERT_TRUE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::RGBA32, atlasView));
+    ASSERT_TRUE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::Alpha8, alphaView));
     EXPECT_TRUE(atlasView.IsValid());
+    EXPECT_TRUE(alphaView.IsValid());
     EXPECT_EQ(atlasView.format, IXCUITextAtlasProvider::PixelFormat::RGBA32);
+    EXPECT_EQ(alphaView.format, IXCUITextAtlasProvider::PixelFormat::Alpha8);
     EXPECT_GT(provider.GetFontCount(), 0u);
 }
 
@@ -42,4 +45,113 @@ TEST(XCUIStandaloneTextAtlasProviderTest, ExposesDefaultFontMetricsAndGlyphs) {
     EXPECT_GE(glyphInfo.v1, glyphInfo.v0);
 }
 
+TEST(XCUIStandaloneTextAtlasProviderTest, RebuildsAfterResetAndRejectsQueriesWhileUnready) {
+    XCUIStandaloneTextAtlasProvider provider = {};
+    const IXCUITextAtlasProvider::FontHandle defaultFont = provider.GetDefaultFont();
+    ASSERT_TRUE(defaultFont.IsValid());
+
+    provider.Reset();
+
+    IXCUITextAtlasProvider::AtlasTextureView atlasView = {};
+    IXCUITextAtlasProvider::FontInfo fontInfo = {};
+    IXCUITextAtlasProvider::BakedFontInfo bakedFontInfo = {};
+    IXCUITextAtlasProvider::GlyphInfo glyphInfo = {};
+
+    EXPECT_FALSE(provider.IsReady());
+    EXPECT_FALSE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::RGBA32, atlasView));
+    EXPECT_EQ(provider.GetFontCount(), 0u);
+    EXPECT_FALSE(provider.GetDefaultFont().IsValid());
+    EXPECT_FALSE(provider.GetFontInfo(defaultFont, fontInfo));
+    EXPECT_FALSE(provider.GetBakedFontInfo(defaultFont, 18.0f, bakedFontInfo));
+    EXPECT_FALSE(provider.FindGlyph(defaultFont, 18.0f, static_cast<std::uint32_t>('A'), glyphInfo));
+
+    ASSERT_TRUE(provider.RebuildDefaultEditorAtlas());
+    ASSERT_TRUE(provider.IsReady());
+    ASSERT_TRUE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::RGBA32, atlasView));
+    EXPECT_TRUE(atlasView.IsValid());
+}
+
+TEST(XCUIStandaloneTextAtlasProviderTest, ResolvesGlyphsForNonNominalRequestedFontSizes) {
+    XCUIStandaloneTextAtlasProvider provider = {};
+    const IXCUITextAtlasProvider::FontHandle defaultFont = provider.GetDefaultFont();
+    ASSERT_TRUE(defaultFont.IsValid());
+
+    IXCUITextAtlasProvider::BakedFontInfo bakedFontInfo = {};
+    ASSERT_TRUE(provider.GetBakedFontInfo(defaultFont, 13.0f, bakedFontInfo));
+    EXPECT_GT(bakedFontInfo.lineHeight, 0.0f);
+    EXPECT_GT(bakedFontInfo.rasterizerDensity, 0.0f);
+
+    IXCUITextAtlasProvider::GlyphInfo glyphInfo = {};
+    ASSERT_TRUE(provider.FindGlyph(defaultFont, 13.0f, static_cast<std::uint32_t>('A'), glyphInfo));
+    EXPECT_EQ(glyphInfo.requestedCodepoint, static_cast<std::uint32_t>('A'));
+    EXPECT_GT(glyphInfo.advanceX, 0.0f);
+    EXPECT_GE(glyphInfo.u1, glyphInfo.u0);
+    EXPECT_GE(glyphInfo.v1, glyphInfo.v0);
+}
+
+TEST(XCUIStandaloneTextAtlasProviderTest, LazilyAddsGlyphsOutsideThePrebakedAsciiRanges) {
+    XCUIStandaloneTextAtlasProvider provider = {};
+    const IXCUITextAtlasProvider::FontHandle defaultFont = provider.GetDefaultFont();
+    ASSERT_TRUE(defaultFont.IsValid());
+
+    IXCUITextAtlasProvider::AtlasTextureView beforeView = {};
+    ASSERT_TRUE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::RGBA32, beforeView));
+
+    constexpr std::uint32_t dynamicCodepoint = 0x4E2Du;
+    IXCUITextAtlasProvider::GlyphInfo glyphInfo = {};
+    ASSERT_TRUE(provider.FindGlyph(defaultFont, 16.0f, dynamicCodepoint, glyphInfo));
+
+    IXCUITextAtlasProvider::AtlasTextureView refreshedView = {};
+    ASSERT_TRUE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::RGBA32, refreshedView));
+    EXPECT_EQ(refreshedView.atlasStorageKey, beforeView.atlasStorageKey);
+    EXPECT_EQ(glyphInfo.requestedCodepoint, dynamicCodepoint);
+
+    if (refreshedView.pixelDataKey != beforeView.pixelDataKey) {
+        EXPECT_EQ(glyphInfo.resolvedCodepoint, dynamicCodepoint);
+        EXPECT_GT(glyphInfo.advanceX, 0.0f);
+        EXPECT_TRUE(glyphInfo.visible);
+
+        IXCUITextAtlasProvider::GlyphInfo secondLookup = {};
+        ASSERT_TRUE(provider.FindGlyph(defaultFont, 16.0f, dynamicCodepoint, secondLookup));
+        EXPECT_EQ(secondLookup.requestedCodepoint, dynamicCodepoint);
+        EXPECT_EQ(secondLookup.resolvedCodepoint, dynamicCodepoint);
+
+        IXCUITextAtlasProvider::AtlasTextureView secondView = {};
+        ASSERT_TRUE(provider.GetAtlasTextureView(IXCUITextAtlasProvider::PixelFormat::RGBA32, secondView));
+        EXPECT_EQ(secondView.pixelDataKey, refreshedView.pixelDataKey);
+        return;
+    }
+
+    if (glyphInfo.resolvedCodepoint != dynamicCodepoint) {
+        EXPECT_EQ(glyphInfo.resolvedCodepoint, static_cast<std::uint32_t>('?'));
+        EXPECT_GT(glyphInfo.advanceX, 0.0f);
+        EXPECT_TRUE(glyphInfo.visible);
+        return;
+    }
+
+    if (!glyphInfo.visible) {
+        EXPECT_GE(glyphInfo.advanceX, 0.0f);
+        return;
+    }
+
+    if (glyphInfo.resolvedCodepoint == dynamicCodepoint) {
+        EXPECT_NE(refreshedView.pixelDataKey, beforeView.pixelDataKey);
+    }
+    EXPECT_GT(glyphInfo.advanceX, 0.0f);
+    EXPECT_TRUE(glyphInfo.visible);
+}
+
+TEST(XCUIStandaloneTextAtlasProviderTest, MissingGlyphFallsBackToQuestionMarkWhenFontCannotRasterizeIt) {
+    XCUIStandaloneTextAtlasProvider provider = {};
+    const IXCUITextAtlasProvider::FontHandle defaultFont = provider.GetDefaultFont();
+    ASSERT_TRUE(defaultFont.IsValid());
+
+    IXCUITextAtlasProvider::GlyphInfo glyphInfo = {};
+    ASSERT_TRUE(provider.FindGlyph(defaultFont, 16.0f, 0x10FFFFu, glyphInfo));
+    EXPECT_EQ(glyphInfo.requestedCodepoint, 0x10FFFFu);
+    EXPECT_EQ(glyphInfo.resolvedCodepoint, static_cast<std::uint32_t>('?'));
+    EXPECT_GT(glyphInfo.advanceX, 0.0f);
+    EXPECT_TRUE(glyphInfo.visible);
+}
+
 } // namespace