sksl: Add a "sk_Clockwise" built-in

This allows us to identify clockwise-winding triangles, in terms of
Skia device space, in all backends and with all render target origins.

Bug: skia:
Change-Id: I220e1c459e0129d1cc4dee6458ef94277fbedd21
Reviewed-on: https://skia-review.googlesource.com/142662
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

10 files changed, 52 insertions, 33 deletions

diff --git a/src/gpu/GrProcessor.h b/src/gpu/GrProcessor.h
index 4afc928da7..5d83ce3ddb 100644
--- a/src/gpu/GrProcessor.h
+++ b/src/gpu/GrProcessor.h
@@ -71,6 +71,7 @@ public:
         kButtCapStrokedCircleGeometryProcessor_ClassID,
         kCircleGeometryProcessor_ClassID,
         kCircularRRectEffect_ClassID,
+        kClockwiseTestProcessor_ClassID,
         kColorMatrixEffect_ClassID,
         kColorTableEffect_ClassID,
         kComposeOneFragmentProcessor_ClassID,
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 18ff4c670f..e04a40d8ab 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -359,9 +359,9 @@ void GrGLGpu::onResetContext(uint32_t resetBits) {
 
         // We don't use face culling.
         GL_CALL(Disable(GR_GL_CULL_FACE));
-        // We do use separate stencil. Our algorithms don't care which face is front vs. back so
-        // just set this to the default for self-consistency.
-        GL_CALL(FrontFace(GR_GL_CCW));
+
+        // Setting the front face keeps gl_FrontFacing consistent in device space.
+        fHWFrontFace = GR_GL_NONE;
 
         fHWBufferState[kTexel_GrBufferType].invalidate();
         fHWBufferState[kDrawIndirect_GrBufferType].invalidate();
@@ -1704,6 +1704,7 @@ bool GrGLGpu::flushGLState(const GrPrimitiveProcessor& primProc,
     fHWProgram->setData(primProc, pipeline);
 
     GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(pipeline.renderTarget());
+    GrSurfaceOrigin origin = pipeline.proxy()->origin();
     GrStencilSettings stencil;
     if (pipeline.isStencilEnabled()) {
         // TODO: attach stencil and create settings during render target flush.
@@ -1715,16 +1716,16 @@ bool GrGLGpu::flushGLState(const GrPrimitiveProcessor& primProc,
     if (pipeline.isScissorEnabled()) {
         static constexpr SkIRect kBogusScissor{0, 0, 1, 1};
         GrScissorState state(fixedDynamicState ? fixedDynamicState->fScissorRect : kBogusScissor);
-        this->flushScissor(state, glRT->getViewport(), pipeline.proxy()->origin());
+        this->flushScissor(state, glRT->getViewport(), origin);
     } else {
         this->disableScissor();
     }
-    this->flushWindowRectangles(pipeline.getWindowRectsState(), glRT, pipeline.proxy()->origin());
+    this->flushWindowRectangles(pipeline.getWindowRectsState(), glRT, origin);
     this->flushHWAAState(glRT, pipeline.isHWAntialiasState(), !stencil.isDisabled());
 
     // This must come after textures are flushed because a texture may need
     // to be msaa-resolved (which will modify bound FBO state).
-    this->flushRenderTarget(glRT);
+    this->flushRenderTarget(glRT, origin);
 
     return true;
 }
@@ -1856,9 +1857,9 @@ void GrGLGpu::clear(const GrFixedClip& clip, GrColor color,
     GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(target);
 
     if (clip.scissorEnabled()) {
-        this->flushRenderTarget(glRT, origin, clip.scissorRect());
+        this->flushRenderTarget(glRT, origin, &clip.scissorRect());
     } else {
-        this->flushRenderTarget(glRT);
+        this->flushRenderTarget(glRT, origin);
     }
     this->flushScissor(clip.scissorState(), glRT->getViewport(), origin);
     this->flushWindowRectangles(clip.windowRectsState(), glRT, origin);
@@ -2121,14 +2122,17 @@ GrGpuTextureCommandBuffer* GrGLGpu::createCommandBuffer(GrTexture* texture,
 }
 
 void GrGLGpu::flushRenderTarget(GrGLRenderTarget* target, GrSurfaceOrigin origin,
-                                const SkIRect& bounds) {
+                                const SkIRect* bounds) {
     this->flushRenderTargetNoColorWrites(target);
-    this->didWriteToSurface(target, origin, &bounds);
-}
 
-void GrGLGpu::flushRenderTarget(GrGLRenderTarget* target) {
-    this->flushRenderTargetNoColorWrites(target);
-    this->didWriteToSurface(target, kTopLeft_GrSurfaceOrigin, nullptr);
+    // A triangle is front-facing if it winds clockwise in device space.
+    GrGLenum frontFace = (kBottomLeft_GrSurfaceOrigin == origin) ? GR_GL_CW : GR_GL_CCW;
+    if (frontFace != fHWFrontFace) {
+        GL_CALL(FrontFace(frontFace));
+        fHWFrontFace = frontFace;
+    }
+
+    this->didWriteToSurface(target, origin, bounds);
 }
 
 void GrGLGpu::flushRenderTargetNoColorWrites(GrGLRenderTarget* target) {
@@ -3360,7 +3364,7 @@ void GrGLGpu::clearStencilClipAsDraw(const GrFixedClip& clip, bool insideStencil
     }
 
     GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(rt->asRenderTarget());
-    this->flushRenderTarget(glRT);
+    this->flushRenderTarget(glRT, origin);
 
     this->flushProgram(fStencilClipClearProgram);
 
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 78ae024306..3e6dbaad29 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -341,9 +341,7 @@ private:
 
     // The passed bounds contains the render target's color values that will subsequently be
     // written.
-    void flushRenderTarget(GrGLRenderTarget*, GrSurfaceOrigin, const SkIRect& bounds);
-    // This version has an implicit bounds of the entire render target.
-    void flushRenderTarget(GrGLRenderTarget*);
+    void flushRenderTarget(GrGLRenderTarget*, GrSurfaceOrigin, const SkIRect* bounds = nullptr);
     // This version can be used when the render target's colors will not be written.
     void flushRenderTargetNoColorWrites(GrGLRenderTarget*);
 
@@ -560,6 +558,7 @@ private:
     GrStencilSettings                       fHWStencilSettings;
     TriState                                fHWStencilTestEnabled;
 
+    GrGLenum                                fHWFrontFace;
 
     TriState                                fHWWriteToColor;
     GrGpuResource::UniqueID                 fHWBoundRenderTargetUniqueID;
diff --git a/src/gpu/gl/GrGLPathRendering.cpp b/src/gpu/gl/GrGLPathRendering.cpp
index 85c129f8b0..8a53f88b2c 100644
--- a/src/gpu/gl/GrGLPathRendering.cpp
+++ b/src/gpu/gl/GrGLPathRendering.cpp
@@ -88,11 +88,12 @@ void GrGLPathRendering::onStencilPath(const StencilPathArgs& args, const GrPath*
     gpu->flushColorWrite(false);
 
     GrGLRenderTarget* rt = static_cast<GrGLRenderTarget*>(args.fProxy->priv().peekRenderTarget());
+    GrSurfaceOrigin origin = args.fProxy->origin();
     SkISize size = SkISize::Make(rt->width(), rt->height());
-    this->setProjectionMatrix(*args.fViewMatrix, size, args.fProxy->origin());
-    gpu->flushScissor(*args.fScissor, rt->getViewport(), args.fProxy->origin());
+    this->setProjectionMatrix(*args.fViewMatrix, size, origin);
+    gpu->flushScissor(*args.fScissor, rt->getViewport(), origin);
     gpu->flushHWAAState(rt, args.fUseHWAA, true);
-    gpu->flushRenderTarget(rt);
+    gpu->flushRenderTarget(rt, origin);
 
     const GrGLPath* glPath = static_cast<const GrGLPath*>(path);
 
diff --git a/src/gpu/vk/GrVkPipeline.cpp b/src/gpu/vk/GrVkPipeline.cpp
index 60e7f43259..6cdfc4eff9 100644
--- a/src/gpu/vk/GrVkPipeline.cpp
+++ b/src/gpu/vk/GrVkPipeline.cpp
@@ -436,7 +436,9 @@ static void setup_raster_state(const GrPipeline& pipeline,
     rasterInfo->polygonMode = caps->wireframeMode() ? VK_POLYGON_MODE_LINE
                                                     : VK_POLYGON_MODE_FILL;
     rasterInfo->cullMode = VK_CULL_MODE_NONE;
-    rasterInfo->frontFace = VK_FRONT_FACE_COUNTER_CLOCKWISE;
+    // A triangle is front-facing if it winds clockwise in device space.
+    rasterInfo->frontFace = (kTopLeft_GrSurfaceOrigin == pipeline.proxy()->origin())
+        ? VK_FRONT_FACE_CLOCKWISE : VK_FRONT_FACE_COUNTER_CLOCKWISE;
     rasterInfo->depthBiasEnable = VK_FALSE;
     rasterInfo->depthBiasConstantFactor = 0.0f;
     rasterInfo->depthBiasClamp = 0.0f;
diff --git a/src/gpu/vk/GrVkPipelineStateBuilder.cpp b/src/gpu/vk/GrVkPipelineStateBuilder.cpp
index 91685c6016..bcccbc0c17 100644
--- a/src/gpu/vk/GrVkPipelineStateBuilder.cpp
+++ b/src/gpu/vk/GrVkPipelineStateBuilder.cpp
@@ -204,19 +204,23 @@ GrVkPipelineState* GrVkPipelineStateBuilder::finalize(const GrStencilSettings& s
 
 //////////////////////////////////////////////////////////////////////////////
 
-uint32_t get_blend_info_key(const GrPipeline& pipeline) {
-    GrXferProcessor::BlendInfo blendInfo;
-    pipeline.getXferProcessor().getBlendInfo(&blendInfo);
-
-    static const uint32_t kBlendWriteShift = 1;
+uint32_t get_pipeline_info_key(const GrPipeline& pipeline) {
     static const uint32_t kBlendCoeffShift = 5;
     GR_STATIC_ASSERT(kLast_GrBlendCoeff < (1 << kBlendCoeffShift));
     GR_STATIC_ASSERT(kFirstAdvancedGrBlendEquation - 1 < 4);
 
-    uint32_t key = blendInfo.fWriteColor;
-    key |= (blendInfo.fSrcBlend << kBlendWriteShift);
-    key |= (blendInfo.fDstBlend << (kBlendWriteShift + kBlendCoeffShift));
-    key |= (blendInfo.fEquation << (kBlendWriteShift + 2 * kBlendCoeffShift));
+    GrXferProcessor::BlendInfo blendInfo;
+    pipeline.getXferProcessor().getBlendInfo(&blendInfo);
+
+    GrSurfaceOrigin origin = pipeline.proxy()->origin();
+    SkASSERT(0 == origin || 1 == origin);
+
+    uint32_t key;
+    key = blendInfo.fEquation;
+    key = blendInfo.fDstBlend | (key << kBlendCoeffShift);
+    key = blendInfo.fSrcBlend | (key << kBlendCoeffShift);
+    key = (int)blendInfo.fWriteColor | (key << 1);
+    key = origin | (key << 1);
 
     return key;
 }
@@ -238,7 +242,7 @@ bool GrVkPipelineStateBuilder::Desc::Build(Desc* desc,
 
     stencil.genKey(&b);
 
-    b.add32(get_blend_info_key(pipeline));
+    b.add32(get_pipeline_info_key(pipeline));
 
     b.add32((uint32_t)primitiveType);
 
diff --git a/src/sksl/README b/src/sksl/README
index bb2dd05396..dd0af9825f 100644
--- a/src/sksl/README
+++ b/src/sksl/README
@@ -45,6 +45,8 @@ Differences from GLSL
 * use sk_InstanceID instead of gl_InstanceID
 * the fragment coordinate is sk_FragCoord, and is always relative to the upper
   left.
+* use sk_Clockwise instead of gl_FrontFacing. This is always relative to an
+  upper left origin.
 * you do not need to include ".0" to make a number a float (meaning that
   "float2(x, y) * 4" is perfectly legal in SkSL, unlike GLSL where it would
   often have to be expressed "float2(x, y) * 4.0". There is no performance
@@ -149,4 +151,4 @@ Creating a new .fp file
 7. At this point you can reference the new fragment processor from within Skia.
 
 Once you have done this initial setup, simply re-build Skia to pick up any
-changes to the .fp file.
\ No newline at end of file
+changes to the .fp file.
diff --git a/src/sksl/SkSLCompiler.h b/src/sksl/SkSLCompiler.h
index b55bf405bd..c840bd800f 100644
--- a/src/sksl/SkSLCompiler.h
+++ b/src/sksl/SkSLCompiler.h
@@ -27,6 +27,7 @@
 #define SK_OUT_BUILTIN                 10007
 #define SK_LASTFRAGCOLOR_BUILTIN       10008
 #define SK_FRAGCOORD_BUILTIN              15
+#define SK_CLOCKWISE_BUILTIN              17
 #define SK_VERTEXID_BUILTIN               42
 #define SK_INSTANCEID_BUILTIN             43
 #define SK_CLIPDISTANCE_BUILTIN            3
diff --git a/src/sksl/SkSLGLSLCodeGenerator.cpp b/src/sksl/SkSLGLSLCodeGenerator.cpp
index 3c697d8e4b..d08c9135e1 100644
--- a/src/sksl/SkSLGLSLCodeGenerator.cpp
+++ b/src/sksl/SkSLGLSLCodeGenerator.cpp
@@ -689,6 +689,9 @@ void GLSLCodeGenerator::writeVariableReference(const VariableReference& ref) {
         case SK_FRAGCOORD_BUILTIN:
             this->writeFragCoord();
             break;
+        case SK_CLOCKWISE_BUILTIN:
+            this->write("gl_FrontFacing");
+            break;
         case SK_VERTEXID_BUILTIN:
             this->write("gl_VertexID");
             break;
diff --git a/src/sksl/sksl_frag.inc b/src/sksl/sksl_frag.inc
index 429d05a73e..202747a815 100644
--- a/src/sksl/sksl_frag.inc
+++ b/src/sksl/sksl_frag.inc
@@ -2,7 +2,9 @@ STRINGIFY(
 
 // defines built-in interfaces supported by SkiaSL fragment shaders
 
+// See "enum SpvBuiltIn_" in ./spirv.h
 layout(builtin=15) in float4 sk_FragCoord;
+layout(builtin=17) in bool sk_Clockwise;  // Similar to gl_FrontFacing, but defined in device space.
 layout(builtin=3) float sk_ClipDistance[1];
 
 // 9999 is a temporary value that causes us to ignore these declarations beyond