Implement approx-match support in image filter saveLayer() offscreen.

src/effects/SkMagnifierImageFilter.cpp

Index: src/effects/SkMagnifierImageFilter.cpp
diff --git a/src/effects/SkMagnifierImageFilter.cpp b/src/effects/SkMagnifierImageFilter.cpp
index 622713d796f1f0be7cc240ffdff51ddfcf13ac7f..6d2ee01d5263e82ad4e7e4efbfb6248c6aa7a426 100644
--- a/src/effects/SkMagnifierImageFilter.cpp
+++ b/src/effects/SkMagnifierImageFilter.cpp
@@ -25,6 +25,7 @@ class GrMagnifierEffect : public GrSingleTextureEffect {
 
 public:
     static GrFragmentProcessor* Create(GrTexture* texture,
+                                       const SkRect& bounds,
                                        float xOffset,
                                        float yOffset,
                                        float xInvZoom,
@@ -32,6 +33,7 @@ public:
                                        float xInvInset,
                                        float yInvInset) {
         return SkNEW_ARGS(GrMagnifierEffect, (texture,
+                                              bounds,
                                               xOffset,
                                               yOffset,
                                               xInvZoom,
@@ -48,15 +50,22 @@ public:
 
     GrGLFragmentProcessor* createGLInstance() const override;
 
+    const SkRect& bounds() const { return fBounds; }    // Bounds of source image.
+    // Offset to apply to zoomed pixels, (srcRect position / texture size).
     float x_offset() const { return fXOffset; }
     float y_offset() const { return fYOffset; }
+
+    // Scale to apply to zoomed pixels (srcRect size / bounds size).
     float x_inv_zoom() const { return fXInvZoom; }
     float y_inv_zoom() const { return fYInvZoom; }
+
+    // 1/radius over which to transition from unzoomed to zoomed pixels (bounds size / inset).
     float x_inv_inset() const { return fXInvInset; }
     float y_inv_inset() const { return fYInvInset; }
 
 private:
     GrMagnifierEffect(GrTexture* texture,
+                      const SkRect& bounds,
                       float xOffset,
                       float yOffset,
                       float xInvZoom,
@@ -64,6 +73,7 @@ private:
                       float xInvInset,
                       float yInvInset)
         : GrSingleTextureEffect(texture, GrCoordTransform::MakeDivByTextureWHMatrix(texture))
+        , fBounds(bounds)
         , fXOffset(xOffset)
         , fYOffset(yOffset)
         , fXInvZoom(xInvZoom)
@@ -79,6 +89,7 @@ private:
 
     GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
 
+    SkRect fBounds;
     float fXOffset;
     float fYOffset;
     float fXInvZoom;
@@ -109,6 +120,7 @@ private:
     UniformHandle       fOffsetVar;
     UniformHandle       fInvZoomVar;
     UniformHandle       fInvInsetVar;
+    UniformHandle       fBoundsVar;
 
     typedef GrGLFragmentProcessor INHERITED;
 };
@@ -134,6 +146,10 @@ void GrGLMagnifierEffect::emitCode(GrGLFPBuilder* builder,
         GrGLProgramBuilder::kFragment_Visibility |
         GrGLProgramBuilder::kVertex_Visibility,
         kVec2f_GrSLType, kDefault_GrSLPrecision, "InvInset");
+    fBoundsVar = builder->addUniform(
+        GrGLProgramBuilder::kFragment_Visibility |
+        GrGLProgramBuilder::kVertex_Visibility,
+        kVec4f_GrSLType, kDefault_GrSLPrecision, "Bounds");
 
     GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
     SkString coords2D = fsBuilder->ensureFSCoords2D(coords, 0);
@@ -142,9 +158,9 @@ void GrGLMagnifierEffect::emitCode(GrGLFPBuilder* builder,
                            builder->getUniformCStr(fOffsetVar),
                            coords2D.c_str(),
                            builder->getUniformCStr(fInvZoomVar));
-
-    fsBuilder->codeAppend("\t\tvec2 delta = min(coord, vec2(1.0, 1.0) - coord);\n");
-
+    const char* bounds = builder->getUniformCStr(fBoundsVar);
+    fsBuilder->codeAppendf("\t\tvec2 delta = (coord - %s.xy) * %s.zw;\n", bounds, bounds);
+    fsBuilder->codeAppendf("\t\tdelta = min(delta, vec2(1.0, 1.0) - delta);\n");
     fsBuilder->codeAppendf("\t\tdelta = delta * %s;\n", builder->getUniformCStr(fInvInsetVar));
 
     fsBuilder->codeAppend("\t\tfloat weight = 0.0;\n");
@@ -175,6 +191,8 @@ void GrGLMagnifierEffect::setData(const GrGLProgramDataManager& pdman,
     pdman.set2f(fOffsetVar, zoom.x_offset(), zoom.y_offset());
     pdman.set2f(fInvZoomVar, zoom.x_inv_zoom(), zoom.y_inv_zoom());
     pdman.set2f(fInvInsetVar, zoom.x_inv_inset(), zoom.y_inv_inset());
+    pdman.set4f(fBoundsVar, zoom.bounds().x(), zoom.bounds().y(),
+                            zoom.bounds().width(), zoom.bounds().height());
 }
 
 /////////////////////////////////////////////////////////////////////
@@ -206,6 +224,7 @@ GrFragmentProcessor* GrMagnifierEffect::TestCreate(SkRandom* random,
 
     GrFragmentProcessor* effect = GrMagnifierEffect::Create(
         texture,
+        SkRect::MakeWH(SkIntToScalar(kMaxWidth), SkIntToScalar(kMaxHeight)),
         (float) width / texture->width(),
         (float) height / texture->height(),
         texture->width() / (float) x,
@@ -220,7 +239,8 @@ GrFragmentProcessor* GrMagnifierEffect::TestCreate(SkRandom* random,
 
 bool GrMagnifierEffect::onIsEqual(const GrFragmentProcessor& sBase) const {
     const GrMagnifierEffect& s = sBase.cast<GrMagnifierEffect>();
-    return (this->fXOffset == s.fXOffset &&
+    return (this->fBounds == s.fBounds &&
+            this->fXOffset == s.fXOffset &&
             this->fYOffset == s.fYOffset &&
             this->fXInvZoom == s.fXInvZoom &&
             this->fYInvZoom == s.fYInvZoom &&
@@ -258,18 +278,27 @@ SkMagnifierImageFilter::SkMagnifierImageFilter(const SkRect& srcRect, SkScalar i
 
 #if SK_SUPPORT_GPU
 bool SkMagnifierImageFilter::asFragmentProcessor(GrFragmentProcessor** fp, GrTexture* texture,
-                                                 const SkMatrix&, const SkIRect&) const {
+                                                 const SkMatrix&, const SkIRect&bounds) const {
     if (fp) {
-        SkScalar yOffset = (texture->origin() == kTopLeft_GrSurfaceOrigin) ? fSrcRect.y() :
-                           (texture->height() - (fSrcRect.y() + fSrcRect.height()));
+        SkScalar yOffset = texture->origin() == kTopLeft_GrSurfaceOrigin ? fSrcRect.y() :
+           texture->height() - fSrcRect.height() * texture->height() / bounds.height()
+                             - fSrcRect.y();
+        int boundsY = (texture->origin() == kTopLeft_GrSurfaceOrigin) ? bounds.y() :
+                      (texture->height() - bounds.height());
+        SkRect effectBounds = SkRect::MakeXYWH(
+            SkIntToScalar(bounds.x()) / texture->width(),
+            SkIntToScalar(boundsY) / texture->height(),
+            SkIntToScalar(texture->width()) / bounds.width(),
+            SkIntToScalar(texture->height()) / bounds.height());
         SkScalar invInset = fInset > 0 ? SkScalarInvert(fInset) : SK_Scalar1;
         *fp = GrMagnifierEffect::Create(texture,
+                                        effectBounds,
                                         fSrcRect.x() / texture->width(),
                                         yOffset / texture->height(),
-                                        fSrcRect.width() / texture->width(),
-                                        fSrcRect.height() / texture->height(),
-                                        texture->width() * invInset,
-                                        texture->height() * invInset);
+                                        fSrcRect.width() / bounds.width(),
+                                        fSrcRect.height() / bounds.height(),
+                                        bounds.width() * invInset,
+                                        bounds.height() * invInset);
     }
     return true;
 }