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

src/gpu/effects/GrTextureDomain.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrTextureDomainEffect_DEFINED
 #define GrTextureDomainEffect_DEFINED
 
@@ skipping 51 matching lines @@
         SkScalar hInv = SK_Scalar1 / texture->height();
         SkRect result = {
             texelRect.fLeft * wInv,
             texelRect.fTop * hInv,
             texelRect.fRight * wInv,
             texelRect.fBottom * hInv
         };
         return result;
     }
 
+    static const SkRect MakeTexelDomainForMode(const GrTexture* texture, const SkIRect& texelRect, Mode mode) {
+        // For Clamp mode, inset by half a texel.
+        SkScalar wInv = SK_Scalar1 / texture->width();
+        SkScalar hInv = SK_Scalar1 / texture->height();
+        SkScalar inset = (mode == kClamp_Mode && !texelRect.isEmpty()) ? SK_ScalarHalf : 0;
+        return SkRect::MakeLTRB(
+            (texelRect.fLeft + inset) * wInv,
+            (texelRect.fTop + inset) * hInv,
+            (texelRect.fRight - inset) * wInv,
+            (texelRect.fBottom - inset) * hInv
+        );
+    }
+
     bool operator== (const GrTextureDomain& that) const {
         return fMode == that.fMode && (kIgnore_Mode == fMode || fDomain == that.fDomain);
     }
 
     /**
      * A GrGLProcessor subclass that corresponds to a GrProcessor subclass that uses GrTextureDomain
      * should include this helper. It generates the texture domain GLSL, produces the part of the
      * effect key that reflects the texture domain code, and performs the uniform uploads necessary
      * for texture domains.
      */
@@ skipping 93 matching lines @@
     bool onIsEqual(const GrFragmentProcessor&) const override;
 
     void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
 
     GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
 
     typedef GrSingleTextureEffect INHERITED;
 };
 
 #endif