refactor: route builtin infinite grid through shader assets

engine/src/Resources/BuiltinResources.cpp

@@ -26,6 +26,7 @@ constexpr const char* kBuiltinTexturePrefix = "builtin://textures/";
 constexpr const char* kBuiltinDefaultPrimitiveMaterialPath = "builtin://materials/default-primitive";
 constexpr const char* kBuiltinForwardLitShaderPath = "builtin://shaders/forward-lit";
 constexpr const char* kBuiltinObjectIdShaderPath = "builtin://shaders/object-id";
+constexpr const char* kBuiltinInfiniteGridShaderPath = "builtin://shaders/infinite-grid";
 constexpr const char* kBuiltinDefaultPrimitiveTexturePath = "builtin://textures/default-primitive-albedo";
 constexpr float kPi = 3.14159265358979323846f;
 
@@ -308,6 +309,152 @@ void main() {
 }
 )";
 
+const char kBuiltinInfiniteGridHlsl[] = R"(
+cbuffer GridConstants : register(b0) {
+    float4x4 gViewProjectionMatrix;
+    float4 gCameraPositionAndScale;
+    float4 gCameraRightAndFade;
+    float4 gCameraUpAndTanHalfFov;
+    float4 gCameraForwardAndAspect;
+    float4 gViewportNearFar;
+    float4 gGridTransition;
+};
+
+struct VSOutput {
+    float4 position : SV_POSITION;
+};
+
+VSOutput MainVS(uint vertexId : SV_VertexID) {
+    static const float2 positions[3] = {
+        float2(-1.0, -1.0),
+        float2(-1.0,  3.0),
+        float2( 3.0, -1.0)
+    };
+
+    VSOutput output;
+    output.position = float4(positions[vertexId], 0.0, 1.0);
+    return output;
+}
+
+float PristineGridLine(float2 uv) {
+    float2 deriv = max(fwidth(uv), float2(1e-6, 1e-6));
+    float2 uvMod = frac(uv);
+    float2 uvDist = min(uvMod, 1.0 - uvMod);
+    float2 distInPixels = uvDist / deriv;
+    float2 lineAlpha = 1.0 - smoothstep(0.0, 1.0, distInPixels);
+    float density = max(deriv.x, deriv.y);
+    float densityFade = 1.0 - smoothstep(0.5, 1.0, density);
+    return max(lineAlpha.x, lineAlpha.y) * densityFade;
+}
+
+float AxisLineAA(float coord, float deriv) {
+    float distInPixels = abs(coord) / max(deriv, 1e-6);
+    return 1.0 - smoothstep(0.0, 1.5, distInPixels);
+}
+
+struct GridLayer {
+    float minor;
+    float major;
+};
+
+GridLayer SampleGridLayer(float2 worldPos2D, float baseScale) {
+    GridLayer layer;
+    const float2 gridCoord1 = worldPos2D / baseScale;
+    const float2 gridCoord10 = worldPos2D / (baseScale * 10.0);
+    const float grid1 = PristineGridLine(gridCoord1);
+    const float grid10 = PristineGridLine(gridCoord10);
+    const float2 deriv1 = fwidth(gridCoord1);
+    const float lodFactor = smoothstep(0.3, 0.6, max(deriv1.x, deriv1.y));
+
+    layer.major = max(grid10, grid1 * 0.35);
+    layer.minor = grid1 * (1.0 - lodFactor);
+    return layer;
+}
+
+struct PSOutput {
+    float4 color : SV_TARGET0;
+    float depth : SV_Depth;
+};
+
+PSOutput MainPS(VSOutput input) {
+    const float2 viewportSize = max(gViewportNearFar.xy, float2(1.0, 1.0));
+    const float scale = max(gCameraPositionAndScale.w, 1e-4);
+    const float fadeDistance = max(gCameraRightAndFade.w, scale * 10.0);
+    const float tanHalfFov = max(gCameraUpAndTanHalfFov.w, 1e-4);
+    const float aspect = max(gCameraForwardAndAspect.w, 1e-4);
+    const float transitionBlend = saturate(gGridTransition.x);
+    const float nearClip = gViewportNearFar.z;
+    const float sceneFarClip = gViewportNearFar.w;
+
+    const float2 ndc = float2(
+        (input.position.x / viewportSize.x) * 2.0 - 1.0,
+        1.0 - (input.position.y / viewportSize.y) * 2.0);
+
+    const float3 cameraPosition = gCameraPositionAndScale.xyz;
+    const float3 rayDirection = normalize(
+        gCameraForwardAndAspect.xyz +
+        ndc.x * aspect * tanHalfFov * gCameraRightAndFade.xyz +
+        ndc.y * tanHalfFov * gCameraUpAndTanHalfFov.xyz);
+
+    if (abs(rayDirection.y) < 1e-5) {
+        discard;
+    }
+
+    const float t = -cameraPosition.y / rayDirection.y;
+    if (t <= nearClip) {
+        discard;
+    }
+
+    const float3 worldPosition = cameraPosition + rayDirection * t;
+    float depth = 0.999999;
+    if (t < sceneFarClip) {
+        const float4 clipPosition = mul(gViewProjectionMatrix, float4(worldPosition, 1.0));
+        if (clipPosition.w <= 1e-6) {
+            discard;
+        }
+
+        depth = clipPosition.z / clipPosition.w;
+        if (depth <= 0.0 || depth >= 1.0) {
+            discard;
+        }
+    }
+
+    const float radialFade =
+        1.0 - smoothstep(fadeDistance * 0.3, fadeDistance, length(worldPosition - cameraPosition));
+    const float normalFade = smoothstep(0.0, 0.15, abs(rayDirection.y));
+    const float fadeFactor = radialFade * normalFade;
+    if (fadeFactor < 1e-3) {
+        discard;
+    }
+
+    const float2 worldPos2D = worldPosition.xz;
+    const GridLayer baseLayer = SampleGridLayer(worldPos2D, scale);
+    const GridLayer nextLayer = SampleGridLayer(worldPos2D, scale * 10.0);
+    const float minorGridIntensity = lerp(baseLayer.minor, nextLayer.minor, transitionBlend);
+    const float majorGridIntensity = lerp(baseLayer.major, nextLayer.major, transitionBlend);
+    float3 finalColor = float3(0.56, 0.56, 0.56);
+    float finalAlpha = max(
+        0.13 * minorGridIntensity * fadeFactor,
+        0.28 * majorGridIntensity * fadeFactor);
+
+    const float2 worldDeriv = max(fwidth(worldPos2D), float2(1e-6, 1e-6));
+    const float xAxisAlpha = AxisLineAA(worldPos2D.y, worldDeriv.y) * fadeFactor;
+    const float zAxisAlpha = AxisLineAA(worldPos2D.x, worldDeriv.x) * fadeFactor;
+
+    const float axisAlpha = max(xAxisAlpha, zAxisAlpha);
+    finalAlpha = max(finalAlpha, 0.34 * saturate(axisAlpha));
+
+    if (finalAlpha < 1e-3) {
+        discard;
+    }
+
+    PSOutput output;
+    output.color = float4(finalColor, finalAlpha);
+    output.depth = depth;
+    return output;
+}
+)";
+
 Math::Bounds ComputeBounds(const std::vector<StaticMeshVertex>& vertices) {
     if (vertices.empty()) {
         return Math::Bounds();
@@ -943,6 +1090,41 @@ Shader* BuildBuiltinObjectIdShader(const Containers::String& path) {
     return shader;
 }
 
+Shader* BuildBuiltinInfiniteGridShader(const Containers::String& path) {
+    auto* shader = new Shader();
+    IResource::ConstructParams params;
+    params.name = Containers::String("Builtin Infinite Grid");
+    params.path = path;
+    params.guid = ResourceGUID::Generate(path);
+    params.memorySize = 0;
+    shader->Initialize(params);
+
+    const Containers::String passName("InfiniteGrid");
+    shader->SetPassTag(passName, "LightMode", "InfiniteGrid");
+
+    AddBuiltinShaderStageVariant(
+        *shader,
+        passName,
+        ShaderType::Vertex,
+        ShaderLanguage::HLSL,
+        ShaderBackend::D3D12,
+        kBuiltinInfiniteGridHlsl,
+        "MainVS",
+        "vs_5_0");
+    AddBuiltinShaderStageVariant(
+        *shader,
+        passName,
+        ShaderType::Fragment,
+        ShaderLanguage::HLSL,
+        ShaderBackend::D3D12,
+        kBuiltinInfiniteGridHlsl,
+        "MainPS",
+        "ps_5_0");
+
+    shader->m_memorySize = CalculateBuiltinShaderMemorySize(*shader);
+    return shader;
+}
+
 Material* BuildDefaultPrimitiveMaterial(const Containers::String& path) {
     auto* material = new Material();
     IResource::ConstructParams params;
@@ -1049,6 +1231,10 @@ Containers::String GetBuiltinObjectIdShaderPath() {
     return Containers::String(kBuiltinObjectIdShaderPath);
 }
 
+Containers::String GetBuiltinInfiniteGridShaderPath() {
+    return Containers::String(kBuiltinInfiniteGridShaderPath);
+}
+
 Containers::String GetBuiltinDefaultPrimitiveTexturePath() {
     return Containers::String(kBuiltinDefaultPrimitiveTexturePath);
 }
@@ -1141,6 +1327,8 @@ LoadResult CreateBuiltinShaderResource(const Containers::String& path) {
         shader = BuildBuiltinForwardLitShader(path);
     } else if (path == GetBuiltinObjectIdShaderPath()) {
         shader = BuildBuiltinObjectIdShader(path);
+    } else if (path == GetBuiltinInfiniteGridShaderPath()) {
+        shader = BuildBuiltinInfiniteGridShader(path);
     } else {
         return LoadResult(Containers::String("Unknown builtin shader: ") + path);
     }