2 files changed, 43 insertions, 0 deletions
diff --git a/src/gpu/effects/GrBicubicEffect.cpp b/src/gpu/effects/GrBicubicEffect.cpp
index 89124ff667..9c6d1a3f8c 100644
--- a/src/gpu/effects/GrBicubicEffect.cpp
+++ b/src/gpu/effects/GrBicubicEffect.cpp
@@ -177,3 +177,36 @@ GrEffectRef* GrBicubicEffect::TestCreate(SkRandom* random,
     }
     return GrBicubicEffect::Create(textures[texIdx], coefficients);
 }
+
+//////////////////////////////////////////////////////////////////////////////
+
+bool GrBicubicEffect::ShouldUseBicubic(const SkMatrix& matrix,
+                                       GrTextureParams::FilterMode* filterMode) {
+    if (matrix.isIdentity()) {
+        *filterMode = GrTextureParams::kNone_FilterMode;
+        return false;
+    }
+
+    SkScalar scales[2];
+    if (!matrix.getMinMaxScales(scales) || scales[0] < SK_Scalar1) {
+        // Bicubic doesn't handle arbitrary minimization well, as src texels can be skipped
+        // entirely,
+        *filterMode = GrTextureParams::kMipMap_FilterMode;
+        return false;
+    }
+    // At this point if scales[1] == SK_Scalar1 then the matrix doesn't do any scaling.
+    if (scales[1] == SK_Scalar1) {
+        if (matrix.rectStaysRect() && SkScalarIsInt(matrix.getTranslateX()) &&
+            SkScalarIsInt(matrix.getTranslateY())) {
+            *filterMode = GrTextureParams::kNone_FilterMode;
+        } else {
+            // Use bilerp to handle rotation or fractional translation.
+            *filterMode = GrTextureParams::kBilerp_FilterMode;
+        }
+        return false;
+    }
+    // When we use the bicubic filtering effect each sample is read from the texture using
+    // nearest neighbor sampling.
+    *filterMode = GrTextureParams::kNone_FilterMode;
+    return true;
+}
diff --git a/src/gpu/effects/GrBicubicEffect.h b/src/gpu/effects/GrBicubicEffect.h
index cc8b120863..1998e68780 100644
--- a/src/gpu/effects/GrBicubicEffect.h
+++ b/src/gpu/effects/GrBicubicEffect.h
@@ -78,6 +78,16 @@ public:
         return CreateEffectRef(effect);
     }
 
+    /**
+     * Determines whether the bicubic effect should be used based on the transformation from the
+     * local coords to the device. Returns true if the bicubic effect should be used. filterMode
+     * is set to appropriate filtering mode to use regardless of the return result (e.g. when this
+     * returns false it may indicate that the best fallback is to use kMipMap, kBilerp, or
+     * kNearest).
+     */
+    static bool ShouldUseBicubic(const SkMatrix& localCoordsToDevice,
+                                 GrTextureParams::FilterMode* filterMode);
+
 private:
     GrBicubicEffect(GrTexture*, const SkScalar coefficients[16],
                     const SkMatrix &matrix, const SkShader::TileMode tileModes[2]);