Concatenate matrices when GrMatrixEffect wraps another GrMatrixEffect

Bug: skia:11844
Change-Id: I13165fb17b06371854a4911c5d91bf2415d4df2a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/396017
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

src/gpu/effects/GrMatrixEffect.cpp

@@ -35,6 +35,23 @@ private:
     UniformHandle fMatrixVar;
 };
 
+std::unique_ptr<GrFragmentProcessor> GrMatrixEffect::Make(
+        const SkMatrix& matrix, std::unique_ptr<GrFragmentProcessor> child) {
+    if (matrix.isIdentity()) {
+        return child;
+    }
+    if (child->classID() == kGrMatrixEffect_ClassID) {
+        auto me = static_cast<GrMatrixEffect*>(child.get());
+        // registerChild's sample usage records whether the matrix used has perspective or not,
+        // so we can't add perspective to 'me' if it doesn't already have it.
+        if (me->matrix().hasPerspective() || !matrix.hasPerspective()) {
+            me->fMatrix.preConcat(matrix);
+            return child;
+        }
+    }
+    return std::unique_ptr<GrFragmentProcessor>(new GrMatrixEffect(matrix, std::move(child)));
+}
+
 std::unique_ptr<GrGLSLFragmentProcessor> GrMatrixEffect::onMakeProgramImpl() const {
     return std::make_unique<GrGLSLMatrixEffect>();
 }

src/gpu/effects/GrMatrixEffect.h

@@ -16,12 +16,7 @@
 class GrMatrixEffect : public GrFragmentProcessor {
 public:
     static std::unique_ptr<GrFragmentProcessor> Make(const SkMatrix& matrix,
-                                                     std::unique_ptr<GrFragmentProcessor> child) {
+                                                     std::unique_ptr<GrFragmentProcessor> child);
-        if (matrix.isIdentity()) {
-            return child;
-        }
-        return std::unique_ptr<GrFragmentProcessor>(new GrMatrixEffect(matrix, std::move(child)));
-    }
 
     std::unique_ptr<GrFragmentProcessor> clone() const override;
     const char* name() const override { return "MatrixEffect"; }