Add procedural skybox scene coverage

engine/assets/builtin/shaders/skybox/skybox.frag.glsl

@@ -0,0 +1,35 @@
+// XC_BUILTIN_SKYBOX_OPENGL_PS
+#version 430
+
+layout(std140, binding = 0) uniform EnvironmentConstants {
+    vec4 gSkyboxTopColor;
+    vec4 gSkyboxHorizonColor;
+    vec4 gSkyboxBottomColor;
+    vec4 gCameraRightAndTanHalfFov;
+    vec4 gCameraUpAndAspect;
+    vec4 gCameraForwardAndUnused;
+};
+
+in vec2 vNdc;
+
+layout(location = 0) out vec4 fragColor;
+
+void main() {
+    float tanHalfFov = gCameraRightAndTanHalfFov.w;
+    float aspect = gCameraUpAndAspect.w;
+
+    vec3 viewRay = normalize(
+        gCameraForwardAndUnused.xyz +
+        vNdc.x * aspect * tanHalfFov * gCameraRightAndTanHalfFov.xyz +
+        vNdc.y * tanHalfFov * gCameraUpAndAspect.xyz);
+
+    float vertical = clamp(viewRay.y, -1.0, 1.0);
+    vec3 color = gSkyboxHorizonColor.rgb;
+    if (vertical >= 0.0) {
+        color = mix(gSkyboxHorizonColor.rgb, gSkyboxTopColor.rgb, pow(clamp(vertical, 0.0, 1.0), 0.65));
+    } else {
+        color = mix(gSkyboxHorizonColor.rgb, gSkyboxBottomColor.rgb, pow(clamp(-vertical, 0.0, 1.0), 0.55));
+    }
+
+    fragColor = vec4(color, 1.0);
+}

engine/assets/builtin/shaders/skybox/skybox.frag.vk.glsl

@@ -0,0 +1,35 @@
+// XC_BUILTIN_SKYBOX_VULKAN_PS
+#version 450
+
+layout(set = 0, binding = 0, std140) uniform EnvironmentConstants {
+    vec4 gSkyboxTopColor;
+    vec4 gSkyboxHorizonColor;
+    vec4 gSkyboxBottomColor;
+    vec4 gCameraRightAndTanHalfFov;
+    vec4 gCameraUpAndAspect;
+    vec4 gCameraForwardAndUnused;
+};
+
+layout(location = 0) in vec2 vNdc;
+
+layout(location = 0) out vec4 fragColor;
+
+void main() {
+    float tanHalfFov = gCameraRightAndTanHalfFov.w;
+    float aspect = gCameraUpAndAspect.w;
+
+    vec3 viewRay = normalize(
+        gCameraForwardAndUnused.xyz +
+        vNdc.x * aspect * tanHalfFov * gCameraRightAndTanHalfFov.xyz +
+        vNdc.y * tanHalfFov * gCameraUpAndAspect.xyz);
+
+    float vertical = clamp(viewRay.y, -1.0, 1.0);
+    vec3 color = gSkyboxHorizonColor.rgb;
+    if (vertical >= 0.0) {
+        color = mix(gSkyboxHorizonColor.rgb, gSkyboxTopColor.rgb, pow(clamp(vertical, 0.0, 1.0), 0.65));
+    } else {
+        color = mix(gSkyboxHorizonColor.rgb, gSkyboxBottomColor.rgb, pow(clamp(-vertical, 0.0, 1.0), 0.55));
+    }
+
+    fragColor = vec4(color, 1.0);
+}

engine/assets/builtin/shaders/skybox/skybox.ps.hlsl

@@ -0,0 +1,34 @@
+// XC_BUILTIN_SKYBOX_D3D12_PS
+cbuffer EnvironmentConstants : register(b0) {
+    float4 gSkyboxTopColor;
+    float4 gSkyboxHorizonColor;
+    float4 gSkyboxBottomColor;
+    float4 gCameraRightAndTanHalfFov;
+    float4 gCameraUpAndAspect;
+    float4 gCameraForwardAndUnused;
+}
+
+struct PSInput {
+    float4 position : SV_POSITION;
+    float2 ndc : TEXCOORD0;
+};
+
+float4 MainPS(PSInput input) : SV_Target {
+    const float tanHalfFov = gCameraRightAndTanHalfFov.w;
+    const float aspect = gCameraUpAndAspect.w;
+
+    float3 viewRay = normalize(
+        gCameraForwardAndUnused.xyz +
+        input.ndc.x * aspect * tanHalfFov * gCameraRightAndTanHalfFov.xyz +
+        input.ndc.y * tanHalfFov * gCameraUpAndAspect.xyz);
+
+    const float vertical = clamp(viewRay.y, -1.0f, 1.0f);
+    float3 color = gSkyboxHorizonColor.rgb;
+    if (vertical >= 0.0f) {
+        color = lerp(gSkyboxHorizonColor.rgb, gSkyboxTopColor.rgb, pow(saturate(vertical), 0.65f));
+    } else {
+        color = lerp(gSkyboxHorizonColor.rgb, gSkyboxBottomColor.rgb, pow(saturate(-vertical), 0.55f));
+    }
+
+    return float4(color, 1.0f);
+}

engine/assets/builtin/shaders/skybox/skybox.shader

@@ -0,0 +1,22 @@
+Shader "Builtin Skybox"
+{
+    SubShader
+    {
+        Pass
+        {
+            Name "Skybox"
+            Tags { "LightMode" = "Skybox" }
+            Resources
+            {
+                EnvironmentConstants (ConstantBuffer, 0, 0) [Semantic(Environment)]
+            }
+            HLSLPROGRAM
+            #pragma vertex MainVS
+            #pragma fragment MainPS
+            #pragma backend D3D12 HLSL "skybox.vs.hlsl" "skybox.ps.hlsl" vs_5_0 ps_5_0
+            #pragma backend OpenGL GLSL "skybox.vert.glsl" "skybox.frag.glsl"
+            #pragma backend Vulkan GLSL "skybox.vert.vk.glsl" "skybox.frag.vk.glsl"
+            ENDHLSL
+        }
+    }
+}

engine/assets/builtin/shaders/skybox/skybox.vert.glsl

@@ -0,0 +1,16 @@
+// XC_BUILTIN_SKYBOX_OPENGL_VS
+#version 430
+
+out vec2 vNdc;
+
+void main() {
+    const vec2 positions[3] = vec2[3](
+        vec2(-1.0, -1.0),
+        vec2(-1.0,  3.0),
+        vec2( 3.0, -1.0)
+    );
+
+    vec2 position = positions[gl_VertexID];
+    gl_Position = vec4(position, 1.0, 1.0);
+    vNdc = position;
+}

engine/assets/builtin/shaders/skybox/skybox.vert.vk.glsl

@@ -0,0 +1,16 @@
+// XC_BUILTIN_SKYBOX_VULKAN_VS
+#version 450
+
+layout(location = 0) out vec2 vNdc;
+
+void main() {
+    const vec2 positions[3] = vec2[3](
+        vec2(-1.0, -1.0),
+        vec2(-1.0,  3.0),
+        vec2( 3.0, -1.0)
+    );
+
+    vec2 position = positions[gl_VertexIndex];
+    gl_Position = vec4(position, 1.0, 1.0);
+    vNdc = position;
+}

engine/assets/builtin/shaders/skybox/skybox.vs.hlsl

@@ -0,0 +1,18 @@
+// XC_BUILTIN_SKYBOX_D3D12_VS
+struct VSOutput {
+    float4 position : SV_POSITION;
+    float2 ndc : TEXCOORD0;
+};
+
+VSOutput MainVS(uint vertexId : SV_VertexID) {
+    const float2 positions[3] = {
+        float2(-1.0f, -1.0f),
+        float2(-1.0f,  3.0f),
+        float2( 3.0f, -1.0f)
+    };
+
+    VSOutput output;
+    output.position = float4(positions[vertexId], 1.0f, 1.0f);
+    output.ndc = positions[vertexId];
+    return output;
+}

engine/include/XCEngine/Components/CameraComponent.h

@@ -64,6 +64,18 @@ public:
     const Math::Color& GetClearColor() const { return m_clearColor; }
     void SetClearColor(const Math::Color& value) { m_clearColor = value; }
 
+    bool IsSkyboxEnabled() const { return m_skyboxEnabled; }
+    void SetSkyboxEnabled(bool value) { m_skyboxEnabled = value; }
+
+    const Math::Color& GetSkyboxTopColor() const { return m_skyboxTopColor; }
+    void SetSkyboxTopColor(const Math::Color& value) { m_skyboxTopColor = value; }
+
+    const Math::Color& GetSkyboxHorizonColor() const { return m_skyboxHorizonColor; }
+    void SetSkyboxHorizonColor(const Math::Color& value) { m_skyboxHorizonColor = value; }
+
+    const Math::Color& GetSkyboxBottomColor() const { return m_skyboxBottomColor; }
+    void SetSkyboxBottomColor(const Math::Color& value) { m_skyboxBottomColor = value; }
+
     void Serialize(std::ostream& os) const override;
     void Deserialize(std::istream& is) override;
 
@@ -80,6 +92,10 @@ private:
     uint32_t m_cullingMask = 0xFFFFFFFFu;
     Math::Rect m_viewportRect = Math::Rect(0.0f, 0.0f, 1.0f, 1.0f);
     Math::Color m_clearColor = Math::Color(0.192f, 0.302f, 0.475f, 1.0f);
+    bool m_skyboxEnabled = false;
+    Math::Color m_skyboxTopColor = Math::Color(0.18f, 0.36f, 0.74f, 1.0f);
+    Math::Color m_skyboxHorizonColor = Math::Color(0.78f, 0.84f, 0.92f, 1.0f);
+    Math::Color m_skyboxBottomColor = Math::Color(0.92f, 0.93f, 0.95f, 1.0f);
 };
 
 } // namespace Components

engine/include/XCEngine/Rendering/FrameData/RenderCameraData.h

@@ -35,8 +35,17 @@ struct RenderCameraData {
     Math::Matrix4x4 projection = Math::Matrix4x4::Identity();
     Math::Matrix4x4 viewProjection = Math::Matrix4x4::Identity();
     Math::Vector3 worldPosition = Math::Vector3::Zero();
+    Math::Vector3 worldRight = Math::Vector3::Right();
+    Math::Vector3 worldUp = Math::Vector3::Up();
+    Math::Vector3 worldForward = Math::Vector3::Forward();
     Math::Color clearColor = Math::Color::Black();
     RenderClearFlags clearFlags = RenderClearFlags::All;
+    bool perspectiveProjection = true;
+    float verticalFovRadians = 60.0f * Math::DEG_TO_RAD;
+    float orthographicSize = 5.0f;
+    float aspectRatio = 1.0f;
+    float nearClipPlane = 0.1f;
+    float farClipPlane = 1000.0f;
     uint32_t viewportWidth = 0;
     uint32_t viewportHeight = 0;
 };

engine/include/XCEngine/Rendering/FrameData/RenderEnvironmentData.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <XCEngine/Core/Math/Color.h>
+
+#include <cstdint>
+
+namespace XCEngine {
+namespace Rendering {
+
+enum class RenderEnvironmentMode : uint32_t {
+    None = 0,
+    ProceduralSkybox
+};
+
+struct ProceduralSkyboxData {
+    Math::Color topColor = Math::Color(0.18f, 0.36f, 0.74f, 1.0f);
+    Math::Color horizonColor = Math::Color(0.78f, 0.84f, 0.92f, 1.0f);
+    Math::Color bottomColor = Math::Color(0.92f, 0.93f, 0.95f, 1.0f);
+};
+
+struct RenderEnvironmentData {
+    RenderEnvironmentMode mode = RenderEnvironmentMode::None;
+    ProceduralSkyboxData skybox = {};
+
+    bool HasProceduralSkybox() const {
+        return mode == RenderEnvironmentMode::ProceduralSkybox;
+    }
+};
+
+} // namespace Rendering
+} // namespace XCEngine

engine/include/XCEngine/Rendering/FrameData/RenderSceneData.h

@@ -3,6 +3,7 @@
 #include <XCEngine/Core/Math/Vector3.h>
 #include <XCEngine/Core/Math/Vector4.h>
 #include <XCEngine/Rendering/FrameData/RenderCameraData.h>
+#include <XCEngine/Rendering/FrameData/RenderEnvironmentData.h>
 #include <XCEngine/Rendering/FrameData/VisibleRenderItem.h>
 
 #include <array>
@@ -81,6 +82,7 @@ struct RenderLightingData {
 struct RenderSceneData {
     Components::CameraComponent* camera = nullptr;
     RenderCameraData cameraData;
+    RenderEnvironmentData environment;
     RenderLightingData lighting;
     std::vector<VisibleRenderItem> visibleItems;
 

engine/include/XCEngine/Rendering/Pipelines/BuiltinForwardPipeline.h

@@ -38,6 +38,7 @@ class RenderSurface;
 namespace Pipelines {
 namespace Detail {
 class BuiltinForwardOpaquePass;
+class BuiltinForwardSkyboxPass;
 class BuiltinForwardTransparentPass;
 } // namespace Detail
 
@@ -57,6 +58,7 @@ public:
 
 private:
     friend class Detail::BuiltinForwardOpaquePass;
+    friend class Detail::BuiltinForwardSkyboxPass;
     friend class Detail::BuiltinForwardTransparentPass;
 
     struct OwnedDescriptorSet {
@@ -98,6 +100,15 @@ private:
         Math::Vector4 baseColorFactor = Math::Vector4::One();
     };
 
+    struct SkyboxConstants {
+        Math::Vector4 topColor = Math::Vector4::Zero();
+        Math::Vector4 horizonColor = Math::Vector4::Zero();
+        Math::Vector4 bottomColor = Math::Vector4::Zero();
+        Math::Vector4 cameraRightAndTanHalfFov = Math::Vector4::Zero();
+        Math::Vector4 cameraUpAndAspect = Math::Vector4::Zero();
+        Math::Vector4 cameraForwardAndUnused = Math::Vector4::Zero();
+    };
+
     struct PassLayoutKey {
         const Resources::Shader* shader = nullptr;
         Containers::String passName;
@@ -235,9 +246,11 @@ private:
     RHI::RHIResourceView* ResolveTextureView(const VisibleRenderItem& visibleItem);
     static LightingConstants BuildLightingConstants(const RenderLightingData& lightingData);
     static AdditionalLightConstants BuildAdditionalLightConstants(const RenderAdditionalLightData& lightData);
+    bool HasProceduralSkybox(const RenderSceneData& sceneData) const;
     bool BeginForwardScenePass(const RenderPassContext& context);
     void EndForwardScenePass(const RenderPassContext& context);
     bool ExecuteForwardOpaquePass(const RenderPassContext& context);
+    bool ExecuteForwardSkyboxPass(const RenderPassContext& context);
     bool ExecuteForwardTransparentPass(const RenderPassContext& context);
     bool DrawVisibleItems(
         const RenderContext& context,
@@ -247,12 +260,16 @@ private:
         const RenderContext& context,
         const RenderSceneData& sceneData,
         const VisibleRenderItem& visibleItem);
+    bool EnsureSkyboxResources(const RenderContext& context);
+    bool CreateSkyboxResources(const RenderContext& context);
+    void DestroySkyboxResources();
 
     RHI::RHIDevice* m_device = nullptr;
     RHI::RHIType m_backendType = RHI::RHIType::D3D12;
     bool m_initialized = false;
     Resources::ResourceHandle<Resources::Shader> m_builtinForwardShader;
     Resources::ResourceHandle<Resources::Shader> m_builtinUnlitShader;
+    Resources::ResourceHandle<Resources::Shader> m_builtinSkyboxShader;
 
     RenderResourceCache m_resourceCache;
 
@@ -263,6 +280,10 @@ private:
     RHI::RHISampler* m_shadowSampler = nullptr;
     RHI::RHITexture* m_fallbackTexture = nullptr;
     RHI::RHIResourceView* m_fallbackTextureView = nullptr;
+    RHI::RHIPipelineLayout* m_skyboxPipelineLayout = nullptr;
+    RHI::RHIPipelineState* m_skyboxPipelineState = nullptr;
+    RHI::RHIDescriptorPool* m_skyboxConstantPool = nullptr;
+    RHI::RHIDescriptorSet* m_skyboxConstantSet = nullptr;
     RenderPassSequence m_passSequence;
 };
 

engine/include/XCEngine/Resources/BuiltinResources.h

@@ -28,6 +28,7 @@ Containers::String GetBuiltinUnlitShaderPath();
 Containers::String GetBuiltinDepthOnlyShaderPath();
 Containers::String GetBuiltinShadowCasterShaderPath();
 Containers::String GetBuiltinObjectIdShaderPath();
+Containers::String GetBuiltinSkyboxShaderPath();
 Containers::String GetBuiltinDefaultPrimitiveTexturePath();
 
 bool TryParseBuiltinPrimitiveType(const Containers::String& path, BuiltinPrimitiveType& outPrimitiveType);

engine/src/Components/CameraComponent.cpp

@@ -48,6 +48,10 @@ void CameraComponent::Serialize(std::ostream& os) const {
     os << "cullingMask=" << m_cullingMask << ";";
     os << "viewportRect=" << m_viewportRect.x << "," << m_viewportRect.y << "," << m_viewportRect.width << "," << m_viewportRect.height << ";";
     os << "clearColor=" << m_clearColor.r << "," << m_clearColor.g << "," << m_clearColor.b << "," << m_clearColor.a << ";";
+    os << "skyboxEnabled=" << (m_skyboxEnabled ? 1 : 0) << ";";
+    os << "skyboxTopColor=" << m_skyboxTopColor.r << "," << m_skyboxTopColor.g << "," << m_skyboxTopColor.b << "," << m_skyboxTopColor.a << ";";
+    os << "skyboxHorizonColor=" << m_skyboxHorizonColor.r << "," << m_skyboxHorizonColor.g << "," << m_skyboxHorizonColor.b << "," << m_skyboxHorizonColor.a << ";";
+    os << "skyboxBottomColor=" << m_skyboxBottomColor.r << "," << m_skyboxBottomColor.g << "," << m_skyboxBottomColor.b << "," << m_skyboxBottomColor.a << ";";
 }
 
 void CameraComponent::Deserialize(std::istream& is) {
@@ -95,6 +99,20 @@ void CameraComponent::Deserialize(std::istream& is) {
             std::replace(value.begin(), value.end(), ',', ' ');
             std::istringstream ss(value);
             ss >> m_clearColor.r >> m_clearColor.g >> m_clearColor.b >> m_clearColor.a;
+        } else if (key == "skyboxEnabled") {
+            m_skyboxEnabled = (std::stoi(value) != 0);
+        } else if (key == "skyboxTopColor") {
+            std::replace(value.begin(), value.end(), ',', ' ');
+            std::istringstream ss(value);
+            ss >> m_skyboxTopColor.r >> m_skyboxTopColor.g >> m_skyboxTopColor.b >> m_skyboxTopColor.a;
+        } else if (key == "skyboxHorizonColor") {
+            std::replace(value.begin(), value.end(), ',', ' ');
+            std::istringstream ss(value);
+            ss >> m_skyboxHorizonColor.r >> m_skyboxHorizonColor.g >> m_skyboxHorizonColor.b >> m_skyboxHorizonColor.a;
+        } else if (key == "skyboxBottomColor") {
+            std::replace(value.begin(), value.end(), ',', ' ');
+            std::istringstream ss(value);
+            ss >> m_skyboxBottomColor.r >> m_skyboxBottomColor.g >> m_skyboxBottomColor.b >> m_skyboxBottomColor.a;
         }
     }
 }

engine/src/RHI/Vulkan/VulkanPipelineState.cpp

@@ -4,9 +4,11 @@
 #include "XCEngine/RHI/Vulkan/VulkanPipelineLayout.h"
 #include "XCEngine/RHI/Vulkan/VulkanShader.h"
 #include "XCEngine/RHI/Vulkan/VulkanShaderCompiler.h"
+#include "XCEngine/Debug/Logger.h"
 
 #include <algorithm>
 #include <map>
+#include <sstream>
 #include <vector>
 
 namespace XCEngine {
@@ -110,10 +112,21 @@ bool VulkanPipelineState::EnsurePipelineLayout(const GraphicsPipelineDesc& desc)
 bool VulkanPipelineState::CreateGraphicsPipeline(const GraphicsPipelineDesc& desc) {
     VulkanCompiledShader vertexShader = {};
     VulkanCompiledShader fragmentShader = {};
-    if (!CompileVulkanShader(desc.vertexShader, vertexShader, nullptr) ||
-        !CompileVulkanShader(desc.fragmentShader, fragmentShader, nullptr) ||
+    std::string vertexError;
+    std::string fragmentError;
+    if (!CompileVulkanShader(desc.vertexShader, vertexShader, &vertexError) ||
+        !CompileVulkanShader(desc.fragmentShader, fragmentShader, &fragmentError) ||
         vertexShader.type != ShaderType::Vertex ||
         fragmentShader.type != ShaderType::Fragment) {
+        std::ostringstream message;
+        message << "VulkanPipelineState failed to compile graphics shaders.";
+        if (!vertexError.empty()) {
+            message << " Vertex: " << vertexError;
+        }
+        if (!fragmentError.empty()) {
+            message << " Fragment: " << fragmentError;
+        }
+        Debug::Logger::Get().Error(Debug::LogCategory::Rendering, message.str().c_str());
         return false;
     }
 
@@ -316,18 +329,23 @@ bool VulkanPipelineState::CreateGraphicsPipeline(const GraphicsPipelineDesc& des
     pipelineInfo.renderPass = m_renderPass;
     pipelineInfo.subpass = 0;
 
-    const bool success = vkCreateGraphicsPipelines(
+    const VkResult pipelineCreateResult = vkCreateGraphicsPipelines(
         m_device,
         VK_NULL_HANDLE,
         1,
         &pipelineInfo,
         nullptr,
-        &m_pipeline) == VK_SUCCESS;
+        &m_pipeline);
+    const bool success = pipelineCreateResult == VK_SUCCESS;
 
     vkDestroyShaderModule(m_device, fragmentModule, nullptr);
     vkDestroyShaderModule(m_device, vertexModule, nullptr);
 
     if (!success) {
+        std::ostringstream message;
+        message << "VulkanPipelineState vkCreateGraphicsPipelines failed with VkResult="
+                << static_cast<int>(pipelineCreateResult);
+        Debug::Logger::Get().Error(Debug::LogCategory::Rendering, message.str().c_str());
         return false;
     }
 

engine/src/Rendering/Execution/CameraRenderer.cpp

@@ -1,5 +1,6 @@
 #include "Rendering/Execution/CameraRenderer.h"
 
+#include "Components/CameraComponent.h"
 #include "Rendering/Caches/DirectionalShadowSurfaceCache.h"
 #include "Rendering/Passes/BuiltinDepthOnlyPass.h"
 #include "Rendering/Passes/BuiltinObjectIdPass.h"
@@ -241,6 +242,23 @@ RenderDirectionalShadowData BuildDirectionalShadowData(
     return shadowData;
 }
 
+RenderEnvironmentData BuildEnvironmentData(const CameraRenderRequest& request) {
+    RenderEnvironmentData environment = {};
+    if (request.camera == nullptr ||
+        request.surface.GetDepthAttachment() == nullptr ||
+        !HasRenderClearFlag(request.clearFlags, RenderClearFlags::Color) ||
+        !request.camera->IsSkyboxEnabled() ||
+        request.camera->GetProjectionType() != Components::CameraProjectionType::Perspective) {
+        return environment;
+    }
+
+    environment.mode = RenderEnvironmentMode::ProceduralSkybox;
+    environment.skybox.topColor = request.camera->GetSkyboxTopColor();
+    environment.skybox.horizonColor = request.camera->GetSkyboxHorizonColor();
+    environment.skybox.bottomColor = request.camera->GetSkyboxBottomColor();
+    return environment;
+}
+
 } // namespace
 
 CameraRenderer::CameraRenderer()
@@ -407,6 +425,7 @@ bool CameraRenderer::BuildSceneDataForRequest(
     }
 
     outSceneData.cameraData.clearFlags = request.clearFlags;
+    outSceneData.environment = BuildEnvironmentData(request);
     if (request.hasClearColorOverride) {
         outSceneData.cameraData.clearColor = request.clearColorOverride;
     }

engine/src/Rendering/Extraction/RenderSceneUtility.cpp

@@ -22,12 +22,22 @@ RenderCameraData BuildRenderCameraData(
     cameraData.viewportWidth = viewportWidth;
     cameraData.viewportHeight = viewportHeight;
     cameraData.worldPosition = camera.transform().GetPosition();
+    cameraData.worldRight = camera.transform().GetRight();
+    cameraData.worldUp = camera.transform().GetUp();
+    cameraData.worldForward = camera.transform().GetForward();
     cameraData.clearColor = camera.GetClearColor();
+    cameraData.perspectiveProjection =
+        camera.GetProjectionType() == Components::CameraProjectionType::Perspective;
+    cameraData.verticalFovRadians = camera.GetFieldOfView() * Math::DEG_TO_RAD;
+    cameraData.orthographicSize = camera.GetOrthographicSize();
+    cameraData.nearClipPlane = camera.GetNearClipPlane();
+    cameraData.farClipPlane = camera.GetFarClipPlane();
 
     const Math::Matrix4x4 view = camera.transform().GetWorldToLocalMatrix();
     const float aspect = viewportHeight > 0
         ? static_cast<float>(viewportWidth) / static_cast<float>(viewportHeight)
         : 1.0f;
+    cameraData.aspectRatio = aspect;
 
     Math::Matrix4x4 projection = Math::Matrix4x4::Identity();
     if (camera.GetProjectionType() == Components::CameraProjectionType::Perspective) {

engine/src/Rendering/Pipelines/BuiltinForwardPipeline.cpp

@@ -3,11 +3,13 @@
 #include "Debug/Logger.h"
 #include "Core/Asset/ResourceManager.h"
 #include "RHI/RHICommandList.h"
+#include "Rendering/Detail/ShaderVariantUtils.h"
 #include "Rendering/Materials/RenderMaterialResolve.h"
 #include "Rendering/RenderSurface.h"
 #include "Resources/BuiltinResources.h"
 
 #include <cstddef>
+#include <cmath>
 
 namespace XCEngine {
 namespace Rendering {
@@ -40,6 +42,32 @@ private:
     BuiltinForwardPipeline& m_pipeline;
 };
 
+class BuiltinForwardSkyboxPass final : public RenderPass {
+public:
+    explicit BuiltinForwardSkyboxPass(BuiltinForwardPipeline& pipeline)
+        : m_pipeline(pipeline) {
+    }
+
+    const char* GetName() const override {
+        return "BuiltinForwardSkyboxPass";
+    }
+
+    bool Initialize(const RenderContext& context) override {
+        return m_pipeline.EnsureInitialized(context);
+    }
+
+    void Shutdown() override {
+        m_pipeline.DestroyPipelineResources();
+    }
+
+    bool Execute(const RenderPassContext& context) override {
+        return m_pipeline.ExecuteForwardSkyboxPass(context);
+    }
+
+private:
+    BuiltinForwardPipeline& m_pipeline;
+};
+
 class BuiltinForwardTransparentPass final : public RenderPass {
 public:
     explicit BuiltinForwardTransparentPass(BuiltinForwardPipeline& pipeline)
@@ -75,10 +103,66 @@ bool IsDepthFormat(RHI::Format format) {
            format == RHI::Format::D32_Float;
 }
 
+const Resources::ShaderPass* FindCompatibleSkyboxPass(
+    const Resources::Shader& shader,
+    Resources::ShaderBackend backend) {
+    const Resources::ShaderPass* skyboxPass = shader.FindPass("Skybox");
+    if (skyboxPass != nullptr &&
+        ::XCEngine::Rendering::Detail::ShaderPassHasGraphicsVariants(shader, skyboxPass->name, backend)) {
+        return skyboxPass;
+    }
+
+    if (shader.GetPassCount() > 0 &&
+        ::XCEngine::Rendering::Detail::ShaderPassHasGraphicsVariants(shader, shader.GetPasses()[0].name, backend)) {
+        return &shader.GetPasses()[0];
+    }
+
+    return nullptr;
+}
+
+RHI::GraphicsPipelineDesc CreateSkyboxPipelineDesc(
+    RHI::RHIType backendType,
+    RHI::RHIPipelineLayout* pipelineLayout,
+    const Resources::Shader& shader,
+    const Containers::String& passName) {
+    RHI::GraphicsPipelineDesc pipelineDesc = {};
+    pipelineDesc.pipelineLayout = pipelineLayout;
+    pipelineDesc.topologyType = static_cast<uint32_t>(RHI::PrimitiveTopologyType::Triangle);
+    pipelineDesc.renderTargetCount = 1;
+    pipelineDesc.renderTargetFormats[0] = static_cast<uint32_t>(RHI::Format::R8G8B8A8_UNorm);
+    pipelineDesc.depthStencilFormat = static_cast<uint32_t>(RHI::Format::D24_UNorm_S8_UInt);
+    pipelineDesc.sampleCount = 1;
+
+    pipelineDesc.rasterizerState.fillMode = static_cast<uint32_t>(RHI::FillMode::Solid);
+    pipelineDesc.rasterizerState.cullMode = static_cast<uint32_t>(RHI::CullMode::None);
+    pipelineDesc.rasterizerState.frontFace = static_cast<uint32_t>(RHI::FrontFace::CounterClockwise);
+    pipelineDesc.rasterizerState.depthClipEnable = true;
+
+    pipelineDesc.blendState.blendEnable = false;
+    pipelineDesc.blendState.colorWriteMask = static_cast<uint8_t>(RHI::ColorWriteMask::All);
+
+    pipelineDesc.depthStencilState.depthTestEnable = true;
+    pipelineDesc.depthStencilState.depthWriteEnable = false;
+    pipelineDesc.depthStencilState.depthFunc = static_cast<uint32_t>(RHI::ComparisonFunc::LessEqual);
+
+    const Resources::ShaderBackend backend = ::XCEngine::Rendering::Detail::ToShaderBackend(backendType);
+    if (const Resources::ShaderStageVariant* vertexVariant =
+            shader.FindVariant(passName, Resources::ShaderType::Vertex, backend)) {
+        ::XCEngine::Rendering::Detail::ApplyShaderStageVariant(*vertexVariant, pipelineDesc.vertexShader);
+    }
+    if (const Resources::ShaderStageVariant* fragmentVariant =
+            shader.FindVariant(passName, Resources::ShaderType::Fragment, backend)) {
+        ::XCEngine::Rendering::Detail::ApplyShaderStageVariant(*fragmentVariant, pipelineDesc.fragmentShader);
+    }
+
+    return pipelineDesc;
+}
+
 } // namespace
 
 BuiltinForwardPipeline::BuiltinForwardPipeline() {
     m_passSequence.AddPass(std::make_unique<Detail::BuiltinForwardOpaquePass>(*this));
+    m_passSequence.AddPass(std::make_unique<Detail::BuiltinForwardSkyboxPass>(*this));
     m_passSequence.AddPass(std::make_unique<Detail::BuiltinForwardTransparentPass>(*this));
 }
 
@@ -145,6 +229,11 @@ bool BuiltinForwardPipeline::Render(
     return m_passSequence.Execute(passContext);
 }
 
+bool BuiltinForwardPipeline::HasProceduralSkybox(const RenderSceneData& sceneData) const {
+    return sceneData.environment.HasProceduralSkybox() &&
+           sceneData.cameraData.perspectiveProjection;
+}
+
 bool BuiltinForwardPipeline::BeginForwardScenePass(const RenderPassContext& passContext) {
     const RenderContext& context = passContext.renderContext;
     const RenderSurface& surface = passContext.surface;
@@ -200,7 +289,8 @@ bool BuiltinForwardPipeline::BeginForwardScenePass(const RenderPassContext& pass
         ? surface.GetClearColorOverride()
         : sceneData.cameraData.clearColor;
     const float clearValues[4] = { clearColor.r, clearColor.g, clearColor.b, clearColor.a };
-    if (HasRenderClearFlag(sceneData.cameraData.clearFlags, RenderClearFlags::Color)) {
+    if (HasRenderClearFlag(sceneData.cameraData.clearFlags, RenderClearFlags::Color) &&
+        !HasProceduralSkybox(sceneData)) {
         for (RHI::RHIResourceView* renderTarget : renderTargets) {
             if (renderTarget != nullptr) {
                 commandList->ClearRenderTarget(renderTarget, clearValues, 1, clearRects);
@@ -256,6 +346,51 @@ bool BuiltinForwardPipeline::ExecuteForwardOpaquePass(const RenderPassContext& p
     return DrawVisibleItems(context, sceneData, false);
 }
 
+bool BuiltinForwardPipeline::ExecuteForwardSkyboxPass(const RenderPassContext& passContext) {
+    const RenderContext& context = passContext.renderContext;
+    const RenderSurface& surface = passContext.surface;
+    const RenderSceneData& sceneData = passContext.sceneData;
+
+    if (!HasProceduralSkybox(sceneData)) {
+        return true;
+    }
+    if (surface.GetDepthAttachment() == nullptr) {
+        return true;
+    }
+
+    if (!EnsureSkyboxResources(context) ||
+        m_skyboxPipelineLayout == nullptr ||
+        m_skyboxPipelineState == nullptr ||
+        m_skyboxConstantSet == nullptr) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline skybox pass failed to initialize runtime skybox resources");
+        return false;
+    }
+
+    SkyboxConstants constants = {};
+    constants.topColor = sceneData.environment.skybox.topColor.ToVector4();
+    constants.horizonColor = sceneData.environment.skybox.horizonColor.ToVector4();
+    constants.bottomColor = sceneData.environment.skybox.bottomColor.ToVector4();
+    constants.cameraRightAndTanHalfFov = Math::Vector4(
+        sceneData.cameraData.worldRight,
+        std::tan(sceneData.cameraData.verticalFovRadians * 0.5f));
+    constants.cameraUpAndAspect = Math::Vector4(
+        sceneData.cameraData.worldUp,
+        sceneData.cameraData.aspectRatio);
+    constants.cameraForwardAndUnused = Math::Vector4(sceneData.cameraData.worldForward, 0.0f);
+
+    m_skyboxConstantSet->WriteConstant(0, &constants, sizeof(constants));
+
+    RHI::RHICommandList* commandList = context.commandList;
+    commandList->SetPrimitiveTopology(RHI::PrimitiveTopology::TriangleList);
+    commandList->SetPipelineState(m_skyboxPipelineState);
+    RHI::RHIDescriptorSet* descriptorSets[] = { m_skyboxConstantSet };
+    commandList->SetGraphicsDescriptorSets(0, 1, descriptorSets, m_skyboxPipelineLayout);
+    commandList->Draw(3, 1, 0, 0);
+    return true;
+}
+
 bool BuiltinForwardPipeline::ExecuteForwardTransparentPass(const RenderPassContext& passContext) {
     const RenderContext& context = passContext.renderContext;
     const RenderSceneData& sceneData = passContext.sceneData;
@@ -345,6 +480,15 @@ bool BuiltinForwardPipeline::CreatePipelineResources(const RenderContext& contex
         return false;
     }
 
+    m_builtinSkyboxShader = Resources::ResourceManager::Get().Load<Resources::Shader>(
+        Resources::GetBuiltinSkyboxShaderPath());
+    if (!m_builtinSkyboxShader.IsValid()) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline failed to load builtin skybox shader resource");
+        return false;
+    }
+
     RHI::SamplerDesc samplerDesc = {};
     samplerDesc.filter = static_cast<uint32_t>(RHI::FilterMode::Linear);
     samplerDesc.addressU = static_cast<uint32_t>(RHI::TextureAddressMode::Clamp);
@@ -396,6 +540,123 @@ bool BuiltinForwardPipeline::CreatePipelineResources(const RenderContext& contex
     return true;
 }
 
+bool BuiltinForwardPipeline::EnsureSkyboxResources(const RenderContext& context) {
+    if (m_skyboxPipelineLayout != nullptr &&
+        m_skyboxPipelineState != nullptr &&
+        m_skyboxConstantPool != nullptr &&
+        m_skyboxConstantSet != nullptr) {
+        return true;
+    }
+
+    DestroySkyboxResources();
+    return CreateSkyboxResources(context);
+}
+
+bool BuiltinForwardPipeline::CreateSkyboxResources(const RenderContext& context) {
+    if (!context.IsValid() || !m_builtinSkyboxShader.IsValid()) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline skybox resources require a valid context and loaded shader");
+        return false;
+    }
+
+    const Resources::ShaderBackend backend = ::XCEngine::Rendering::Detail::ToShaderBackend(m_backendType);
+    const Resources::ShaderPass* skyboxPass =
+        FindCompatibleSkyboxPass(*m_builtinSkyboxShader.Get(), backend);
+    if (skyboxPass == nullptr) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline could not resolve a valid skybox shader pass");
+        return false;
+    }
+
+    RHI::DescriptorSetLayoutBinding constantBinding = {};
+    constantBinding.binding = 0;
+    constantBinding.type = static_cast<uint32_t>(RHI::DescriptorType::CBV);
+    constantBinding.count = 1;
+    constantBinding.visibility = static_cast<uint32_t>(RHI::ShaderVisibility::All);
+
+    RHI::DescriptorSetLayoutDesc constantLayout = {};
+    constantLayout.bindings = &constantBinding;
+    constantLayout.bindingCount = 1;
+
+    RHI::RHIPipelineLayoutDesc pipelineLayoutDesc = {};
+    pipelineLayoutDesc.setLayouts = &constantLayout;
+    pipelineLayoutDesc.setLayoutCount = 1;
+    m_skyboxPipelineLayout = m_device->CreatePipelineLayout(pipelineLayoutDesc);
+    if (m_skyboxPipelineLayout == nullptr) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline failed to create skybox pipeline layout");
+        DestroySkyboxResources();
+        return false;
+    }
+
+    RHI::DescriptorPoolDesc constantPoolDesc = {};
+    constantPoolDesc.type = RHI::DescriptorHeapType::CBV_SRV_UAV;
+    constantPoolDesc.descriptorCount = 1;
+    constantPoolDesc.shaderVisible = false;
+    m_skyboxConstantPool = m_device->CreateDescriptorPool(constantPoolDesc);
+    if (m_skyboxConstantPool == nullptr) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline failed to create skybox descriptor pool");
+        DestroySkyboxResources();
+        return false;
+    }
+
+    m_skyboxConstantSet = m_skyboxConstantPool->AllocateSet(constantLayout);
+    if (m_skyboxConstantSet == nullptr) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline failed to allocate skybox descriptor set");
+        DestroySkyboxResources();
+        return false;
+    }
+
+    m_skyboxPipelineState = m_device->CreatePipelineState(
+        CreateSkyboxPipelineDesc(
+            m_backendType,
+            m_skyboxPipelineLayout,
+            *m_builtinSkyboxShader.Get(),
+            skyboxPass->name));
+    if (m_skyboxPipelineState == nullptr || !m_skyboxPipelineState->IsValid()) {
+        Debug::Logger::Get().Error(
+            Debug::LogCategory::Rendering,
+            "BuiltinForwardPipeline failed to create skybox graphics pipeline state");
+        DestroySkyboxResources();
+        return false;
+    }
+
+    return true;
+}
+
+void BuiltinForwardPipeline::DestroySkyboxResources() {
+    if (m_skyboxPipelineState != nullptr) {
+        m_skyboxPipelineState->Shutdown();
+        delete m_skyboxPipelineState;
+        m_skyboxPipelineState = nullptr;
+    }
+
+    if (m_skyboxConstantSet != nullptr) {
+        m_skyboxConstantSet->Shutdown();
+        delete m_skyboxConstantSet;
+        m_skyboxConstantSet = nullptr;
+    }
+
+    if (m_skyboxConstantPool != nullptr) {
+        m_skyboxConstantPool->Shutdown();
+        delete m_skyboxConstantPool;
+        m_skyboxConstantPool = nullptr;
+    }
+
+    if (m_skyboxPipelineLayout != nullptr) {
+        m_skyboxPipelineLayout->Shutdown();
+        delete m_skyboxPipelineLayout;
+        m_skyboxPipelineLayout = nullptr;
+    }
+}
+
 void BuiltinForwardPipeline::DestroyPipelineResources() {
     m_resourceCache.Shutdown();
 
@@ -423,6 +684,8 @@ void BuiltinForwardPipeline::DestroyPipelineResources() {
         m_fallbackTextureView = nullptr;
     }
 
+    DestroySkyboxResources();
+
     if (m_fallbackTexture != nullptr) {
         m_fallbackTexture->Shutdown();
         delete m_fallbackTexture;
@@ -445,6 +708,7 @@ void BuiltinForwardPipeline::DestroyPipelineResources() {
     m_initialized = false;
     m_builtinForwardShader.Reset();
     m_builtinUnlitShader.Reset();
+    m_builtinSkyboxShader.Reset();
 }
 
 } // namespace Pipelines

engine/src/Resources/BuiltinResources.cpp

@@ -32,6 +32,7 @@ constexpr const char* kBuiltinUnlitShaderPath = "builtin://shaders/unlit";
 constexpr const char* kBuiltinDepthOnlyShaderPath = "builtin://shaders/depth-only";
 constexpr const char* kBuiltinShadowCasterShaderPath = "builtin://shaders/shadow-caster";
 constexpr const char* kBuiltinObjectIdShaderPath = "builtin://shaders/object-id";
+constexpr const char* kBuiltinSkyboxShaderPath = "builtin://shaders/skybox";
 constexpr const char* kBuiltinDefaultPrimitiveTexturePath = "builtin://textures/default-primitive-albedo";
 constexpr float kPi = 3.14159265358979323846f;
 
@@ -52,6 +53,8 @@ constexpr const char* kBuiltinShadowCasterShaderManifestRelativePath =
     "engine/assets/builtin/shaders/shadow-caster/shadow-caster.shader";
 constexpr const char* kBuiltinObjectIdShaderManifestRelativePath =
     "engine/assets/builtin/shaders/object-id/object-id.shader";
+constexpr const char* kBuiltinSkyboxShaderManifestRelativePath =
+    "engine/assets/builtin/shaders/skybox/skybox.shader";
 
 Containers::String NormalizeBuiltinAssetPath(const std::filesystem::path& path) {
     return Containers::String(path.lexically_normal().generic_string().c_str());
@@ -130,6 +133,9 @@ const char* GetBuiltinShaderManifestRelativePath(const Containers::String& built
     if (builtinShaderPath == Containers::String(kBuiltinObjectIdShaderPath)) {
         return kBuiltinObjectIdShaderManifestRelativePath;
     }
+    if (builtinShaderPath == Containers::String(kBuiltinSkyboxShaderPath)) {
+        return kBuiltinSkyboxShaderManifestRelativePath;
+    }
 
     return nullptr;
 }
@@ -670,6 +676,10 @@ Shader* BuildBuiltinObjectIdShader(const Containers::String& path) {
     return TryLoadBuiltinShaderFromManifest(path);
 }
 
+Shader* BuildBuiltinSkyboxShader(const Containers::String& path) {
+    return TryLoadBuiltinShaderFromManifest(path);
+}
+
 Material* BuildDefaultPrimitiveMaterial(const Containers::String& path) {
     auto* material = new Material();
     IResource::ConstructParams params;
@@ -788,6 +798,10 @@ Containers::String GetBuiltinObjectIdShaderPath() {
     return Containers::String(kBuiltinObjectIdShaderPath);
 }
 
+Containers::String GetBuiltinSkyboxShaderPath() {
+    return Containers::String(kBuiltinSkyboxShaderPath);
+}
+
 Containers::String GetBuiltinDefaultPrimitiveTexturePath() {
     return Containers::String(kBuiltinDefaultPrimitiveTexturePath);
 }
@@ -886,6 +900,8 @@ LoadResult CreateBuiltinShaderResource(const Containers::String& path) {
         shader = BuildBuiltinShadowCasterShader(path);
     } else if (path == GetBuiltinObjectIdShaderPath()) {
         shader = BuildBuiltinObjectIdShader(path);
+    } else if (path == GetBuiltinSkyboxShaderPath()) {
+        shader = BuildBuiltinSkyboxShader(path);
     } else {
         return LoadResult(Containers::String("Unknown builtin shader: ") + path);
     }