Screenspace AA tessellated path rendering.

src/gpu/batches/GrTessellatingPathRenderer.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrTessellatingPathRenderer.h"
 
 #include "GrAuditTrail.h"
 #include "GrBatchFlushState.h"
 #include "GrBatchTest.h"
 #include "GrClip.h"
 #include "GrDefaultGeoProcFactory.h"
+#include "GrDrawTarget.h"
 #include "GrMesh.h"
 #include "GrPathUtils.h"
 #include "GrPipelineBuilder.h"
 #include "GrResourceCache.h"
 #include "GrResourceProvider.h"
 #include "GrTessellator.h"
 #include "SkGeometry.h"
 
 #include "batches/GrVertexBatch.h"
 
 #include <stdio.h>
 
+#define SK_DISABLE_SCREENSPACE_TESS_AA_PATH_RENDERER
+
 /*
- * This path renderer tessellates the path into triangles using GrTessellator, uploads the triangles
- * to a vertex buffer, and renders them with a single draw call. It does not currently do
- * antialiasing, so it must be used in conjunction with multisampling.
+ * This path renderer tessellates the path into triangles using GrTessellator, uploads the
+ * triangles to a vertex buffer, and renders them with a single draw call. It can do screenspace
+ * antialiasing with a one-pixel coverage ramp.
  */
 namespace {
 
 struct TessInfo {
     SkScalar  fTolerance;
     int       fCount;
 };
 
 // When the SkPathRef genID changes, invalidate a corresponding GrResource described by key.
 class PathInvalidator : public SkPathRef::GenIDChangeListener {
@@ skipping 16 matching lines @@
     const TessInfo* info = static_cast<const TessInfo*>(data->data());
     if (info->fTolerance == 0 || info->fTolerance < 3.0f * tol) {
         *actualCount = info->fCount;
         return true;
     }
     return false;
 }
 
 class StaticVertexAllocator : public GrTessellator::VertexAllocator {
 public:
-    StaticVertexAllocator(GrResourceProvider* resourceProvider, bool canMapVB)
-      : fResourceProvider(resourceProvider)
+    StaticVertexAllocator(size_t stride, GrResourceProvider* resourceProvider, bool canMapVB)
+      : VertexAllocator(stride)
+      , fResourceProvider(resourceProvider)
       , fCanMapVB(canMapVB)
       , fVertices(nullptr) {
     }
-    SkPoint* lock(int vertexCount) override {
-        size_t size = vertexCount * sizeof(SkPoint);
+    void* lock(int vertexCount) override {
+        size_t size = vertexCount * stride();
         fVertexBuffer.reset(fResourceProvider->createBuffer(
             size, kVertex_GrBufferType, kStatic_GrAccessPattern, 0));
         if (!fVertexBuffer.get()) {
             return nullptr;
         }
         if (fCanMapVB) {
-            fVertices = static_cast<SkPoint*>(fVertexBuffer->map());
+            fVertices = fVertexBuffer->map();
         } else {
-            fVertices = new SkPoint[vertexCount];
+            fVertices = sk_malloc_throw(vertexCount * stride());
         }
         return fVertices;
     }
     void unlock(int actualCount) override {
         if (fCanMapVB) {
             fVertexBuffer->unmap();
         } else {
-            fVertexBuffer->updateData(fVertices, actualCount * sizeof(SkPoint));
-            delete[] fVertices;
+            fVertexBuffer->updateData(fVertices, actualCount * stride());
+            sk_free(fVertices);
         }
         fVertices = nullptr;
     }
     GrBuffer* vertexBuffer() { return fVertexBuffer.get(); }
 private:
     SkAutoTUnref<GrBuffer> fVertexBuffer;
     GrResourceProvider* fResourceProvider;
     bool fCanMapVB;
-    SkPoint* fVertices;
+    void* fVertices;
+};
+
+class DynamicVertexAllocator : public GrTessellator::VertexAllocator {
+public:
+    DynamicVertexAllocator(size_t stride, GrVertexBatch::Target* target)
+      : VertexAllocator(stride)
+      , fTarget(target)
+      , fVertexBuffer(nullptr)
+      , fVertices(nullptr) {
+    }
+    void* lock(int vertexCount) override {
+        fVertexCount = vertexCount;
+        fVertices = fTarget->makeVertexSpace(stride(), vertexCount, &fVertexBuffer, &fFirstVertex);
+        return fVertices;
+    }
+    void unlock(int actualCount) override {
+        fTarget->putBackVertices(fVertexCount - actualCount, stride());
+        fVertices = nullptr;
+    }
+    const GrBuffer* vertexBuffer() const { return fVertexBuffer; }
+    int firstVertex() const { return fFirstVertex; }
+private:
+    GrVertexBatch::Target* fTarget;
+    const GrBuffer* fVertexBuffer;
+    int fVertexCount;
+    int fFirstVertex;
+    void* fVertices;
 };
 
 }  // namespace
 
 GrTessellatingPathRenderer::GrTessellatingPathRenderer() {
 }
 
 bool GrTessellatingPathRenderer::onCanDrawPath(const CanDrawPathArgs& args) const {
-    // This path renderer can draw fill styles but does not do antialiasing. It can do convex and
-    // concave paths, but we'll leave the convex ones to simpler algorithms. We pass on paths that
-    // have styles, though they may come back around after applying the styling information to the
-    // geometry to create a filled path. We also skip paths that don't have a key since the real
-    // advantage of this path renderer comes from caching the tessellated geometry.
+    // This path renderer can draw fill styles, and can do screenspace antialiasing via a
+    // one-pixel coverage ramp. It can do convex and concave paths, but we'll leave the convex
+    // ones to simpler algorithms. We pass on paths that have styles, though they may come back
+    // around after applying the styling information to the geometry to create a filled path. In
+    // the non-AA case, We skip paths thta don't have a key since the real advantage of this path
+    // renderer comes from caching the tessellated geometry. In the AA case, we do not cache, so we
+    // accept paths without keys.
+    if (args.fAntiAlias) {
+#ifdef SK_DISABLE_SCREENSPACE_TESS_AA_PATH_RENDERER
+        return false;
+#else
+        SkPath path;
+        args.fShape->asPath(&path);

[bsalomon, 2016/08/31 14:19:19]

If the path has a path effect or is stroked this only reflects the verb count of
the original path. Perhaps we should check the that the style is simple fill
first?

[Stephen White, 2016/08/31 15:16:38]

Good idea; done.

+        if (path.countVerbs() > 10) {
+            return false;
+        }
+#endif
+    } else if (!args.fShape->hasUnstyledKey()) {
+        return false;
+    }
     return !args.fShape->style().applies() && args.fShape->style().isSimpleFill() &&

[bsalomon, 2016/08/31 14:19:19]

I realize that this is pre-existing (probably done by me) but the .applies()
isn't needed given the check for .isSimpleFill().

[Stephen White, 2016/08/31 15:16:38]

Done.

-           !args.fAntiAlias && args.fShape->hasUnstyledKey() && !args.fShape->knownToBeConvex();
+           !args.fShape->knownToBeConvex();
 }
 
 class TessellatingPathBatch : public GrVertexBatch {
 public:
     DEFINE_BATCH_CLASS_ID
 
     static GrDrawBatch* Create(const GrColor& color,
                                const GrShape& shape,
                                const SkMatrix& viewMatrix,
-                               SkRect clipBounds) {
-        return new TessellatingPathBatch(color, shape, viewMatrix, clipBounds);
+                               SkIRect devClipBounds,
+                               bool antiAlias) {
+        return new TessellatingPathBatch(color, shape, viewMatrix, devClipBounds, antiAlias);
     }
 
     const char* name() const override { return "TessellatingPathBatch"; }
 
     void computePipelineOptimizations(GrInitInvariantOutput* color,
                                       GrInitInvariantOutput* coverage,
                                       GrBatchToXPOverrides* overrides) const override {
         color->setKnownFourComponents(fColor);
         coverage->setUnknownSingleComponent();
     }
 
 private:
     void initBatchTracker(const GrXPOverridesForBatch& overrides) override {
         // Handle any color overrides
         if (!overrides.readsColor()) {
             fColor = GrColor_ILLEGAL;
         }
         overrides.getOverrideColorIfSet(&fColor);
         fPipelineInfo = overrides;
     }
 
-    void draw(Target* target, const GrGeometryProcessor* gp) const {
-        GrResourceProvider* rp = target->resourceProvider();
-        SkScalar screenSpaceTol = GrPathUtils::kDefaultTolerance;
-        SkScalar tol = GrPathUtils::scaleToleranceToSrc(screenSpaceTol, fViewMatrix,
-                                                        fShape.bounds());
-
+    SkPath getPath() const {
         SkPath path;

[bsalomon, 2016/08/31 14:19:19]

I think this can be:
fShape.applyStyle(GrStyle::Apply::kPathEffectAndStrokeRec,
styleScale).asPath(&path);

Or to maintain the assert:
GrShape shape = fShape.applyStyle(GrStyle::Apply::kPathEffectAndStrokeRec,
styleScale);
SkASSERT(shape.style().isSimpleFill());
shape.asPath(&path);

[Stephen White, 2016/08/31 15:16:38]

Actually, given that onCanDrawPath() checks that
!args.fShape->style().applies(), I think this code can be
removed. I've replaced it with an assert.

I must admit I'm a little unclear on the difference between 
isSimpleFill() and !style().applies(). Is the former a superset 
of the latter?

[bsalomon, 2016/08/31 15:29:48]

Agreed.
!style().applies() will also be true for hairlines.

         fShape.asPath(&path);
-        bool inverseFill = path.isInverseFillType();
+        if (fShape.style().applies()) {
+            SkScalar styleScale = GrStyle::MatrixToScaleFactor(fViewMatrix);
+            SkStrokeRec::InitStyle fill;
+            SkAssertResult(fShape.style().applyToPath(&path, &fill, path, styleScale));
+            SkASSERT(SkStrokeRec::kFill_InitStyle == fill);
+        }
+        return path;
+    }
+
+    void draw(Target* target, const GrGeometryProcessor* gp) const {
+        SkASSERT(!fAntiAlias);
+        GrResourceProvider* rp = target->resourceProvider();
+        bool inverseFill = fShape.inverseFilled();
         // construct a cache key from the path's genID and the view matrix
         static const GrUniqueKey::Domain kDomain = GrUniqueKey::GenerateDomain();
         GrUniqueKey key;
-        static constexpr int kClipBoundsCnt = sizeof(fClipBounds) / sizeof(uint32_t);
+        static constexpr int kClipBoundsCnt = sizeof(fDevClipBounds) / sizeof(uint32_t);
         int shapeKeyDataCnt = fShape.unstyledKeySize();
         SkASSERT(shapeKeyDataCnt >= 0);
         GrUniqueKey::Builder builder(&key, kDomain, shapeKeyDataCnt + kClipBoundsCnt);
         fShape.writeUnstyledKey(&builder[0]);
         // For inverse fills, the tessellation is dependent on clip bounds.
         if (inverseFill) {
-            memcpy(&builder[shapeKeyDataCnt], &fClipBounds, sizeof(fClipBounds));
+            memcpy(&builder[shapeKeyDataCnt], &fDevClipBounds, sizeof(fDevClipBounds));
         } else {
-            memset(&builder[shapeKeyDataCnt], 0, sizeof(fClipBounds));
+            memset(&builder[shapeKeyDataCnt], 0, sizeof(fDevClipBounds));
         }
         builder.finish();
         SkAutoTUnref<GrBuffer> cachedVertexBuffer(rp->findAndRefTByUniqueKey<GrBuffer>(key));
         int actualCount;
+        SkScalar tol = GrPathUtils::kDefaultTolerance;
+        tol = GrPathUtils::scaleToleranceToSrc(tol, fViewMatrix, fShape.bounds());
         if (cache_match(cachedVertexBuffer.get(), tol, &actualCount)) {
             this->drawVertices(target, gp, cachedVertexBuffer.get(), 0, actualCount);
             return;
         }
 
+        SkRect clipBounds = SkRect::Make(fDevClipBounds);
+
+        SkMatrix vmi;
+        if (!fViewMatrix.invert(&vmi)) {
+            return;
+        }
+        vmi.mapRect(&clipBounds);
         bool isLinear;
         bool canMapVB = GrCaps::kNone_MapFlags != target->caps().mapBufferFlags();
-        StaticVertexAllocator allocator(rp, canMapVB);
-        int count = GrTessellator::PathToTriangles(path, tol, fClipBounds, &allocator, &isLinear);
+        StaticVertexAllocator allocator(gp->getVertexStride(), rp, canMapVB);
+        int count = GrTessellator::PathToTriangles(getPath(), tol, clipBounds, &allocator,
+                                                   false, GrColor(), false, &isLinear);
         if (count == 0) {
             return;
         }
         this->drawVertices(target, gp, allocator.vertexBuffer(), 0, count);
         TessInfo info;
         info.fTolerance = isLinear ? 0 : tol;
         info.fCount = count;
         key.setCustomData(SkData::MakeWithCopy(&info, sizeof(info)));
         rp->assignUniqueKeyToResource(key, allocator.vertexBuffer());
     }
 
+    void drawAA(Target* target, const GrGeometryProcessor* gp) const {
+        SkASSERT(fAntiAlias);
+        SkPath path = getPath();
+        if (path.isEmpty()) {
+            return;
+        }
+        SkRect clipBounds = SkRect::Make(fDevClipBounds);
+        path.transform(fViewMatrix);
+        SkScalar tol = GrPathUtils::kDefaultTolerance;
+        bool isLinear;
+        DynamicVertexAllocator allocator(gp->getVertexStride(), target);
+        bool canTweakAlphaForCoverage = fPipelineInfo.canTweakAlphaForCoverage();
+        int count = GrTessellator::PathToTriangles(path, tol, clipBounds, &allocator,
+                                                   true, fColor, canTweakAlphaForCoverage,
+                                                   &isLinear);
+        if (count == 0) {
+            return;
+        }
+        drawVertices(target, gp, allocator.vertexBuffer(), allocator.firstVertex(), count);
+    }
+
     void onPrepareDraws(Target* target) const override {
         sk_sp<GrGeometryProcessor> gp;
         {
             using namespace GrDefaultGeoProcFactory;
 
             Color color(fColor);
             LocalCoords localCoords(fPipelineInfo.readsLocalCoords() ?
                                     LocalCoords::kUsePosition_Type :
                                     LocalCoords::kUnused_Type);
             Coverage::Type coverageType;
-            if (fPipelineInfo.readsCoverage()) {
+            if (fAntiAlias) {
+                color = Color(Color::kAttribute_Type);
+                if (fPipelineInfo.canTweakAlphaForCoverage()) {
+                    coverageType = Coverage::kSolid_Type;
+                } else {
+                    coverageType = Coverage::kAttribute_Type;
+                }
+            } else if (fPipelineInfo.readsCoverage()) {
                 coverageType = Coverage::kSolid_Type;
             } else {
                 coverageType = Coverage::kNone_Type;
             }
             Coverage coverage(coverageType);
-            gp = GrDefaultGeoProcFactory::Make(color, coverage, localCoords, fViewMatrix);
+            if (fAntiAlias) {
+                gp = GrDefaultGeoProcFactory::MakeForDeviceSpace(color, coverage, localCoords,
+                                                                 fViewMatrix);
+            } else {
+                gp = GrDefaultGeoProcFactory::Make(color, coverage, localCoords, fViewMatrix);
+            }
         }
-        this->draw(target, gp.get());
+        if (fAntiAlias) {
+            this->drawAA(target, gp.get());
+        } else {
+            this->draw(target, gp.get());
+        }
     }
 
     void drawVertices(Target* target, const GrGeometryProcessor* gp, const GrBuffer* vb,
                       int firstVertex, int count) const {
-        SkASSERT(gp->getVertexStride() == sizeof(SkPoint));
-
         GrPrimitiveType primitiveType = TESSELLATOR_WIREFRAME ? kLines_GrPrimitiveType
                                                               : kTriangles_GrPrimitiveType;
         GrMesh mesh;
         mesh.init(primitiveType, vb, firstVertex, count);
         target->draw(gp, mesh);
     }
 
     bool onCombineIfPossible(GrBatch*, const GrCaps&) override { return false; }
 
     TessellatingPathBatch(const GrColor& color,
                           const GrShape& shape,
                           const SkMatrix& viewMatrix,
-                          const SkRect& clipBounds)
+                          const SkIRect& devClipBounds,
+                          bool antiAlias)
       : INHERITED(ClassID())
       , fColor(color)
       , fShape(shape)
-      , fViewMatrix(viewMatrix) {
-        const SkRect& pathBounds = shape.bounds();
-        fClipBounds = clipBounds;
-        // Because the clip bounds are used to add a contour for inverse fills, they must also
-        // include the path bounds.
-        fClipBounds.join(pathBounds);
-        const SkRect& srcBounds = shape.inverseFilled() ? fClipBounds : pathBounds;
-        this->setTransformedBounds(srcBounds, viewMatrix, HasAABloat::kNo, IsZeroArea::kNo);
+      , fViewMatrix(viewMatrix)
+      , fDevClipBounds(devClipBounds)
+      , fAntiAlias(antiAlias) {
+        SkRect devBounds;
+        viewMatrix.mapRect(&devBounds, shape.bounds());
+        if (shape.inverseFilled()) {
+            // Because the clip bounds are used to add a contour for inverse fills, they must also
+            // include the path bounds.
+            devBounds.join(SkRect::Make(fDevClipBounds));
+        }
+        this->setBounds(devBounds, HasAABloat::kNo, IsZeroArea::kNo);
     }
 
     GrColor                 fColor;
     GrShape                 fShape;
     SkMatrix                fViewMatrix;
-    SkRect                  fClipBounds; // in source space
+    SkIRect                 fDevClipBounds;
+    bool                    fAntiAlias;
     GrXPOverridesForBatch   fPipelineInfo;
 
     typedef GrVertexBatch INHERITED;
 };
 
 bool GrTessellatingPathRenderer::onDrawPath(const DrawPathArgs& args) {
     GR_AUDIT_TRAIL_AUTO_FRAME(args.fDrawContext->auditTrail(),
                               "GrTessellatingPathRenderer::onDrawPath");
-    SkASSERT(!args.fAntiAlias);
-
     SkIRect clipBoundsI;
     args.fClip->getConservativeBounds(args.fDrawContext->width(), args.fDrawContext->height(),
                                       &clipBoundsI);
-    SkRect clipBounds = SkRect::Make(clipBoundsI);
-    SkMatrix vmi;
-    if (!args.fViewMatrix->invert(&vmi)) {
-        return false;
-    }
-    vmi.mapRect(&clipBounds);
-    SkPath path;
-    args.fShape->asPath(&path);
     SkAutoTUnref<GrDrawBatch> batch(TessellatingPathBatch::Create(args.fPaint->getColor(),
                                                                   *args.fShape,
-                                                                  *args.fViewMatrix, clipBounds));
+                                                                  *args.fViewMatrix,
+                                                                  clipBoundsI,
+                                                                  args.fAntiAlias));
 
     GrPipelineBuilder pipelineBuilder(*args.fPaint, args.fDrawContext->mustUseHWAA(*args.fPaint));
     pipelineBuilder.setUserStencil(args.fUserStencilSettings);
 
     args.fDrawContext->drawBatch(pipelineBuilder, *args.fClip, batch);
 
     return true;
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 #ifdef GR_TEST_UTILS
 
 DRAW_BATCH_TEST_DEFINE(TesselatingPathBatch) {
     GrColor color = GrRandomColor(random);
     SkMatrix viewMatrix = GrTest::TestMatrixInvertible(random);
     SkPath path = GrTest::TestPath(random);
-    SkRect clipBounds = GrTest::TestRect(random);
-    SkMatrix vmi;
-    bool result = viewMatrix.invert(&vmi);
-    if (!result) {
-        SkFAIL("Cannot invert matrix\n");
-    }
-    vmi.mapRect(&clipBounds);
+    SkIRect devClipBounds = SkIRect::MakeXYWH(
+        random->nextU(), random->nextU(), random->nextU(), random->nextU());
+    bool antiAlias = random->nextBool();
     GrStyle style;
     do {
         GrTest::TestStyle(random, &style);
     } while (style.strokeRec().isHairlineStyle());
     GrShape shape(path, style);
-    return TessellatingPathBatch::Create(color, shape, viewMatrix, clipBounds);
+    return TessellatingPathBatch::Create(color, shape, viewMatrix, devClipBounds, antiAlias);
 }
 
 #endif