Fix recursive computation of filter bounds for drop shadow,

morphology, blur.

Because we're computing "backwards" from a clip rect of destination
pixels to be filled to the required source pixels, we should use tail
recursion rather than head recursion in onFilterBounds().

This actually only makes a difference for drop-shadow, where
the computation is non-commutative. Blur and morphology commute, but I
moved them to tail recursion anyway for clarity (so all onFilterBounds
use tail recursion).

BUG=skia:
R=bsalomon@google.com

Author: senorblanco@chromium.org

Review URL: https://codereview.chromium.org/481273005

src/effects/SkBlurImageFilter.cpp

@@ -253,13 +253,13 @@ void SkBlurImageFilter::computeFastBounds(const SkRect& src, SkRect* dst) const
 bool SkBlurImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                        SkIRect* dst) const {
     SkIRect bounds = src;
-    if (getInput(0) && !getInput(0)->filterBounds(src, ctm, &bounds)) {
-        return false;
-    }
     SkVector sigma = SkVector::Make(fSigma.width(), fSigma.height());
     ctm.mapVectors(&sigma, 1);
     bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
                   SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
+    if (getInput(0) && !getInput(0)->filterBounds(bounds, ctm, &bounds)) {
+        return false;
+    }
     *dst = bounds;
     return true;
 }

src/effects/SkDropShadowImageFilter.cpp

@@ -121,9 +121,6 @@ void SkDropShadowImageFilter::computeFastBounds(const SkRect& src, SkRect* dst)
 bool SkDropShadowImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                              SkIRect* dst) const {
     SkIRect bounds = src;
-    if (getInput(0) && !getInput(0)->filterBounds(src, ctm, &bounds)) {
-        return false;
-    }
     SkVector offsetVec = SkVector::Make(fDx, fDy);
     ctm.mapVectors(&offsetVec, 1);
     bounds.offset(-SkScalarCeilToInt(offsetVec.x()),
@@ -133,6 +130,9 @@ bool SkDropShadowImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix&
     bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
                   SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
     bounds.join(src);
+    if (getInput(0) && !getInput(0)->filterBounds(bounds, ctm, &bounds)) {
+        return false;
+    }
     *dst = bounds;
     return true;
 }

src/effects/SkMorphologyImageFilter.cpp

@@ -248,13 +248,13 @@ void SkMorphologyImageFilter::computeFastBounds(const SkRect& src, SkRect* dst)
 bool SkMorphologyImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                              SkIRect* dst) const {
     SkIRect bounds = src;
-    if (getInput(0) && !getInput(0)->filterBounds(src, ctm, &bounds)) {
-        return false;
-    }
     SkVector radius = SkVector::Make(SkIntToScalar(this->radius().width()),
                                      SkIntToScalar(this->radius().height()));
     ctm.mapVectors(&radius, 1);
     bounds.outset(SkScalarCeilToInt(radius.x()), SkScalarCeilToInt(radius.y()));
+    if (getInput(0) && !getInput(0)->filterBounds(bounds, ctm, &bounds)) {
+        return false;
+    }
     *dst = bounds;
     return true;
 }

tests/ImageFilterTest.cpp

@@ -469,6 +469,50 @@ DEF_TEST(ImageFilterDrawMatrixBBH, reporter) {
     }
 }
 
+static SkImageFilter* makeBlur(SkImageFilter* input = NULL) {
+    return SkBlurImageFilter::Create(SK_Scalar1, SK_Scalar1, input);
+}
+
+static SkImageFilter* makeDropShadow(SkImageFilter* input = NULL) {
+    return SkDropShadowImageFilter::Create(
+        SkIntToScalar(100), SkIntToScalar(100),
+        SkIntToScalar(10), SkIntToScalar(10),
+        SK_ColorBLUE, input);
+}
+
+DEF_TEST(ImageFilterBlurThenShadowBounds, reporter) {
+    SkAutoTUnref<SkImageFilter> filter1(makeBlur());
+    SkAutoTUnref<SkImageFilter> filter2(makeDropShadow(filter1.get()));
+
+    SkIRect bounds = SkIRect::MakeXYWH(0, 0, 100, 100);
+    SkIRect expectedBounds = SkIRect::MakeXYWH(-133, -133, 236, 236);
+    filter2->filterBounds(bounds, SkMatrix(), &bounds);
+
+    REPORTER_ASSERT(reporter, bounds == expectedBounds);
+}
+
+DEF_TEST(ImageFilterShadowThenBlurBounds, reporter) {
+    SkAutoTUnref<SkImageFilter> filter1(makeDropShadow());
+    SkAutoTUnref<SkImageFilter> filter2(makeBlur(filter1.get()));
+
+    SkIRect bounds = SkIRect::MakeXYWH(0, 0, 100, 100);
+    SkIRect expectedBounds = SkIRect::MakeXYWH(-133, -133, 236, 236);
+    filter2->filterBounds(bounds, SkMatrix(), &bounds);
+
+    REPORTER_ASSERT(reporter, bounds == expectedBounds);
+}
+
+DEF_TEST(ImageFilterDilateThenBlurBounds, reporter) {
+    SkAutoTUnref<SkImageFilter> filter1(SkDilateImageFilter::Create(2, 2));
+    SkAutoTUnref<SkImageFilter> filter2(makeDropShadow(filter1.get()));
+
+    SkIRect bounds = SkIRect::MakeXYWH(0, 0, 100, 100);
+    SkIRect expectedBounds = SkIRect::MakeXYWH(-132, -132, 234, 234);
+    filter2->filterBounds(bounds, SkMatrix(), &bounds);
+
+    REPORTER_ASSERT(reporter, bounds == expectedBounds);
+}
+
 static void drawBlurredRect(SkCanvas* canvas) {
     SkAutoTUnref<SkImageFilter> filter(SkBlurImageFilter::Create(SkIntToScalar(8), 0));
     SkPaint filterPaint;