refactor: extract viewport object id picker

editor/src/Viewport/ViewportObjectIdPicker.h

@@ -0,0 +1,95 @@
+#pragma once
+
+#include "ViewportHostSurfaceUtils.h"
+
+#include <XCEngine/RHI/RHICommandQueue.h>
+#include <XCEngine/RHI/RHIEnums.h>
+#include <XCEngine/RHI/RHITexture.h>
+#include <XCEngine/Rendering/ObjectIdEncoding.h>
+
+#include <array>
+#include <cstdint>
+
+namespace XCEngine {
+namespace Editor {
+
+struct ViewportObjectIdPickContext {
+    RHI::RHICommandQueue* commandQueue = nullptr;
+    RHI::RHITexture* texture = nullptr;
+    RHI::ResourceStates textureState = RHI::ResourceStates::Common;
+    uint32_t textureWidth = 0;
+    uint32_t textureHeight = 0;
+    bool hasValidFrame = false;
+    ImVec2 viewportSize = ImVec2(0.0f, 0.0f);
+    ImVec2 viewportMousePosition = ImVec2(0.0f, 0.0f);
+};
+
+struct ViewportObjectIdReadbackRequest {
+    RHI::RHICommandQueue* commandQueue = nullptr;
+    RHI::RHITexture* texture = nullptr;
+    RHI::ResourceStates textureState = RHI::ResourceStates::Common;
+    uint32_t pixelX = 0;
+    uint32_t pixelY = 0;
+};
+
+inline bool CanPickViewportObjectId(const ViewportObjectIdPickContext& context) {
+    return context.commandQueue != nullptr &&
+        context.texture != nullptr &&
+        context.textureWidth > 0 &&
+        context.textureHeight > 0 &&
+        context.hasValidFrame &&
+        context.viewportSize.x > 1.0f &&
+        context.viewportSize.y > 1.0f &&
+        context.viewportMousePosition.x >= 0.0f &&
+        context.viewportMousePosition.y >= 0.0f &&
+        context.viewportMousePosition.x <= context.viewportSize.x &&
+        context.viewportMousePosition.y <= context.viewportSize.y;
+}
+
+inline bool BuildViewportObjectIdReadbackRequest(
+    const ViewportObjectIdPickContext& context,
+    ViewportObjectIdReadbackRequest& outRequest) {
+    outRequest = {};
+    if (!CanPickViewportObjectId(context)) {
+        return false;
+    }
+
+    outRequest.commandQueue = context.commandQueue;
+    outRequest.texture = context.texture;
+    outRequest.textureState = context.textureState;
+    outRequest.pixelX = ClampViewportPixelCoordinate(
+        context.viewportMousePosition.x,
+        context.textureWidth);
+    outRequest.pixelY = ClampViewportPixelCoordinate(
+        context.viewportMousePosition.y,
+        context.textureHeight);
+    return true;
+}
+
+template <typename ReadPixelFn>
+bool TryPickViewportObjectIdEntity(
+    const ViewportObjectIdPickContext& context,
+    ReadPixelFn&& readPixel,
+    uint64_t& outEntityId) {
+    outEntityId = 0;
+
+    ViewportObjectIdReadbackRequest request = {};
+    if (!BuildViewportObjectIdReadbackRequest(context, request)) {
+        return false;
+    }
+
+    std::array<uint8_t, 4> rgba = {};
+    if (!readPixel(request, rgba)) {
+        return false;
+    }
+
+    outEntityId = static_cast<uint64_t>(Rendering::DecodeObjectIdFromColor(
+        rgba[0],
+        rgba[1],
+        rgba[2],
+        rgba[3]));
+    return true;
+}
+
+} // namespace Editor
+} // namespace XCEngine