Fix drawVertices() texture mapping in the presence of a local matrix

Change-Id: I6379f2e7c030d7d1e0fcb2bd6ecc7d81c8a4eec5
Reviewed-on: https://skia-review.googlesource.com/8502
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

1 files changed, 57 insertions, 3 deletions

diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index 4ec48952eb..4182ef3a72 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -1855,7 +1855,56 @@ void SkTriColorShader::toString(SkString* str) const {
 }
 #endif
 
-static sk_sp<SkShader> MakeTextureShader(const VertState& state, const SkPoint verts[],
+namespace {
+
+// Similar to SkLocalMatrixShader, but composes the local matrix with the CTM (instead
+// of composing with the inherited local matrix):
+//
+//   rec' = {rec.ctm x localMatrix, rec.localMatrix}
+//
+// (as opposed to rec' = {rec.ctm, rec.localMatrix x localMatrix})
+//
+class SkLocalInnerMatrixShader final : public SkShader {
+public:
+    SkLocalInnerMatrixShader(sk_sp<SkShader> proxy, const SkMatrix& localMatrix)
+    : INHERITED(&localMatrix)
+    , fProxyShader(std::move(proxy)) {}
+
+    Factory getFactory() const override {
+        SkASSERT(false);
+        return nullptr;
+    }
+
+protected:
+    void flatten(SkWriteBuffer&) const override {
+        SkASSERT(false);
+    }
+
+    Context* onMakeContext(const ContextRec& rec, SkArenaAlloc* alloc) const override {
+        SkMatrix adjustedCTM = SkMatrix::Concat(*rec.fMatrix, this->getLocalMatrix());
+        ContextRec newRec(rec);
+        newRec.fMatrix = &adjustedCTM;
+        return fProxyShader->makeContext(newRec, alloc);
+    }
+
+    bool onAppendStages(SkRasterPipeline* p, SkColorSpace* cs, SkArenaAlloc* alloc,
+                        const SkMatrix& ctm, const SkPaint& paint,
+                        const SkMatrix* localM) const override {
+        // We control the shader graph ancestors, so we know there's no local matrix being
+        // injected before this.
+        SkASSERT(!localM);
+
+        SkMatrix adjustedCTM = SkMatrix::Concat(ctm, this->getLocalMatrix());
+        return fProxyShader->appendStages(p, cs, alloc, adjustedCTM, paint);
+    }
+
+private:
+    sk_sp<SkShader> fProxyShader;
+
+    typedef SkShader INHERITED;
+};
+
+sk_sp<SkShader> MakeTextureShader(const VertState& state, const SkPoint verts[],
                                          const SkPoint texs[], const SkPaint& paint,
                                          SkColorSpace* dstColorSpace,
                                          SkArenaAlloc* alloc) {
@@ -1868,9 +1917,12 @@ static sk_sp<SkShader> MakeTextureShader(const VertState& state, const SkPoint v
     if (p0 != p1 || p0 != p2) {
         // Common case (non-collapsed texture coordinates).
         // Map the texture to vertices using a local transform.
+
+        // We cannot use a plain SkLocalMatrix shader, because we need the texture matrix
+        // to compose next to the CTM.
         SkMatrix localMatrix;
         return texture_to_matrix(state, verts, texs, &localMatrix)
-            ? alloc->makeSkSp<SkLocalMatrixShader>(paint.refShader(), localMatrix)
+            ? alloc->makeSkSp<SkLocalInnerMatrixShader>(paint.refShader(), localMatrix)
             : nullptr;
     }
 
@@ -1901,6 +1953,8 @@ static sk_sp<SkShader> MakeTextureShader(const VertState& state, const SkPoint v
     return alloc->makeSkSp<SkColorShader>(SkUnPreMultiply::PMColorToColor(pmColor));
 }
 
+} // anonymous ns
+
 void SkDraw::drawVertices(SkCanvas::VertexMode vmode, int count,
                           const SkPoint vertices[], const SkPoint textures[],
                           const SkColor colors[], SkBlendMode bmode,
@@ -1978,7 +2032,7 @@ void SkDraw::drawVertices(SkCanvas::VertexMode vmode, int count,
             //
             static constexpr size_t kAllocSize =
                 sizeof(SkAutoBlitterChoose) + sizeof(SkComposeShader) +
-                SkTMax(sizeof(SkLocalMatrixShader), sizeof(SkColorShader));
+                SkTMax(sizeof(SkLocalInnerMatrixShader), sizeof(SkColorShader));
             char allocBuffer[kAllocSize];
             SkArenaAlloc alloc(allocBuffer);