Fix SkXfermodeImageFilter when an input is cropped out.

tests/ImageFilterTest.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBicubicImageFilter.h"
 #include "SkBitmap.h"
 #include "SkBitmapDevice.h"
@@ skipping 299 matching lines @@
     canvas.drawSprite(bitmap, 0, 0, &paint);
 }
 
 DEF_TEST(HugeBlurImageFilter, reporter) {
     SkBitmap temp;
     temp.allocN32Pixels(100, 100);
     SkBitmapDevice device(temp);
     test_huge_blur(&device, reporter);
 }
 
+static void test_xfermode_cropped_input(SkBaseDevice* device, skiatest::Reporter* reporter) {
+    SkCanvas canvas(device);
+    canvas.clear(0);
+
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(1, 1);
+    bitmap.eraseARGB(255, 255, 255, 255);
+
+    SkAutoTUnref<SkColorFilter> green(
+        SkColorFilter::CreateModeFilter(SK_ColorGREEN, SkXfermode::kSrcIn_Mode));
+    SkAutoTUnref<SkColorFilterImageFilter> greenFilter(
+        SkColorFilterImageFilter::Create(green.get()));
+    SkImageFilter::CropRect cropRect(SkRect::MakeEmpty());
+    SkAutoTUnref<SkColorFilterImageFilter> croppedOut(
+        SkColorFilterImageFilter::Create(green.get(), NULL, &cropRect));
+
+    // Check that an xfermode image filter whose input has been cropped out still draws the other
+    // input. Also check that drawing with both inputs cropped out doesn't cause a GPU warning.
+    SkXfermode* mode = SkXfermode::Create(SkXfermode::kSrcOver_Mode);
+    SkAutoTUnref<SkImageFilter> xfermodeNoFg(
+        SkXfermodeImageFilter::Create(mode, greenFilter, croppedOut));
+    SkAutoTUnref<SkImageFilter> xfermodeNoBg(
+        SkXfermodeImageFilter::Create(mode, croppedOut, greenFilter));
+    SkAutoTUnref<SkImageFilter> xfermodeNoFgNoBg(
+        SkXfermodeImageFilter::Create(mode, croppedOut, croppedOut));
+
+    SkPaint paint;
+    paint.setImageFilter(xfermodeNoFg);
+    canvas.drawSprite(bitmap, 0, 0, &paint);
+
+    uint32_t pixel;
+    SkImageInfo info = SkImageInfo::MakeN32Premul(1, 1);
+    canvas.readPixels(info, &pixel, 4, 0, 0);
+    REPORTER_ASSERT(reporter, pixel == SK_ColorGREEN);
+
+    paint.setImageFilter(xfermodeNoBg);
+    canvas.drawSprite(bitmap, 0, 0, &paint);
+    canvas.readPixels(info, &pixel, 4, 0, 0);
+    REPORTER_ASSERT(reporter, pixel == SK_ColorGREEN);
+
+    paint.setImageFilter(xfermodeNoFgNoBg);
+    canvas.drawSprite(bitmap, 0, 0, &paint);
+    canvas.readPixels(info, &pixel, 4, 0, 0);
+    REPORTER_ASSERT(reporter, pixel == SK_ColorGREEN);
+}
+
+DEF_TEST(XfermodeImageFilterCroppedInput, reporter) {
+    SkBitmap temp;
+    temp.allocN32Pixels(100, 100);
+    SkBitmapDevice device(temp);
+    test_xfermode_cropped_input(&device, reporter);
+}
 
 #if SK_SUPPORT_GPU
 DEF_GPUTEST(ImageFilterCropRectGPU, reporter, factory) {
     GrContext* context = factory->get(static_cast<GrContextFactory::GLContextType>(0));
     SkAutoTUnref<SkGpuDevice> device(SkGpuDevice::Create(context,
                                                          SkImageInfo::MakeN32Premul(100, 100),
                                                          0));
     test_crop_rects(device, reporter);
 }
 
 DEF_GPUTEST(HugeBlurImageFilterGPU, reporter, factory) {
     GrContext* context = factory->get(static_cast<GrContextFactory::GLContextType>(0));
     SkAutoTUnref<SkGpuDevice> device(SkGpuDevice::Create(context,
                                                          SkImageInfo::MakeN32Premul(100, 100),
                                                          0));
     test_huge_blur(device, reporter);
 }
+
+DEF_GPUTEST(XfermodeImageFilterCroppedInputGPU, reporter, factory) {
+    GrContext* context = factory->get(static_cast<GrContextFactory::GLContextType>(0));
+    SkAutoTUnref<SkGpuDevice> device(SkGpuDevice::Create(context,
+                                                         SkImageInfo::MakeN32Premul(1, 1),
+                                                         0));
+    test_xfermode_cropped_input(device, reporter);
+}
 #endif