Fold alpha to the inner savelayer in savelayer-savelayer-restore patterns

gm/recordopts.cpp

Index: gm/recordopts.cpp
diff --git a/gm/recordopts.cpp b/gm/recordopts.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..08202111f5ea4ab308a0e53a07bb9afb0dfd99b7
--- /dev/null
+++ b/gm/recordopts.cpp
@@ -0,0 +1,218 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkCanvas.h"
+#include "SkPath.h"
+#include "SkPictureRecorder.h"
+#include "SkTableColorFilter.h"
+#include "SkColorFilterImageFilter.h"
+#include "SkPictureImageFilter.h"
+
+static const int kTestRectSize = 50;
+static const int kDetectorGreenValue = 50;
+
+// Below are few functions to install "detector" color filters. The filter is there to assert that
+// the color value it sees is the expected. It will trigger only with kDetectorGreenValue, and
+// turn that value into full green. The idea is that if an optimization incorrectly changes
+// kDetectorGreenValue and then the incorrect value is observable by some part of the drawing
+// pipeline, that pixel will remain empty.
+
+static SkColorFilter* make_detector_color_filter() {
+    uint8_t tableA[256] = { 0, };
+    uint8_t tableR[256] = { 0, };
+    uint8_t tableG[256] = { 0, };
+    uint8_t tableB[256] = { 0, };
+    tableA[255] = 255;
+    tableG[kDetectorGreenValue] = 255;
+    return SkTableColorFilter::CreateARGB(tableA, tableR, tableG, tableB);
+}
+
+// This detector detects that color filter phase of the pixel pipeline receives the correct value.
+static void install_detector_color_filter(SkPaint* drawPaint) {
+    drawPaint->setColorFilter(make_detector_color_filter())->unref();
+}
+
+// This detector detects that image filter phase of the pixel pipeline receives the correct value.
+static void install_detector_image_filter(SkPaint* drawPaint) {
+    SkAutoTUnref<SkColorFilter> colorFilter(make_detector_color_filter());
+    SkImageFilter* imageFilter =
+            SkColorFilterImageFilter::Create(colorFilter, drawPaint->getImageFilter());
+    drawPaint->setImageFilter(imageFilter)->unref();
+}
+
+static void no_detector_install(SkPaint*) {
+}
+
+typedef void(*InstallDetectorFunc)(SkPaint*);
+
+
+// Draws an pattern that can be optimized by alpha folding outer savelayer alpha value to
+// inner draw. Since we know that folding will happen to the inner draw, install a detector
+// to make sure that optimization does not change anything observable.
+static void draw_save_layer_draw_rect_restore_sequence(SkCanvas* canvas, SkColor shapeColor,
+                                                       InstallDetectorFunc installDetector) {
+    SkRect targetRect(SkRect::MakeWH(SkIntToScalar(kTestRectSize), SkIntToScalar(kTestRectSize)));
+    SkPaint layerPaint;
+    layerPaint.setColor(SkColorSetARGB(128, 0, 0, 0));
+    canvas->saveLayer(&targetRect, &layerPaint);
+        SkPaint drawPaint;
+        drawPaint.setColor(shapeColor);
+        installDetector(&drawPaint);
+        canvas->drawRect(targetRect, drawPaint);
+    canvas->restore();
+}
+
+// Draws an pattern that can be optimized by alpha folding outer savelayer alpha value to
+// inner draw. A variant where the draw is not uniform color.
+static void draw_save_layer_draw_bitmap_restore_sequence(SkCanvas* canvas, SkColor shapeColor,
+                                                         InstallDetectorFunc installDetector) {
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(kTestRectSize, kTestRectSize);
+    bitmap.eraseColor(shapeColor);
+    {
+        // Make the bitmap non-uniform color, so that it can not be optimized as uniform drawRect.
+        SkCanvas canvas(bitmap);
+        SkPaint p;
+        p.setColor(SK_ColorWHITE);
+        SkASSERT(shapeColor != SK_ColorWHITE);
+        canvas.drawRect(SkRect::MakeWH(SkIntToScalar(7), SkIntToScalar(7)), p);
+        canvas.flush();
+    }
+
+    SkRect targetRect(SkRect::MakeWH(SkIntToScalar(kTestRectSize), SkIntToScalar(kTestRectSize)));
+    SkPaint layerPaint;
+    layerPaint.setColor(SkColorSetARGB(129, 0, 0, 0));
+    canvas->saveLayer(&targetRect, &layerPaint);
+        SkPaint drawPaint;
+        installDetector(&drawPaint);
+        canvas->drawBitmap(bitmap, SkIntToScalar(0), SkIntToScalar(0), &drawPaint);
+    canvas->restore();
+}
+
+// Draws an pattern that can be optimized by alpha folding outer savelayer alpha value to
+// inner savelayer. We know that alpha folding happens to inner savelayer, so add detector there.
+static void draw_svg_opacity_and_filter_layer_sequence(SkCanvas* canvas, SkColor shapeColor,
+                                                       InstallDetectorFunc installDetector) {
+
+    SkRect targetRect(SkRect::MakeWH(SkIntToScalar(kTestRectSize), SkIntToScalar(kTestRectSize)));
+    SkAutoTUnref<SkPicture> shape;
+    {
+        SkPictureRecorder recorder;
+        SkCanvas* canvas = recorder.beginRecording(SkIntToScalar(kTestRectSize + 2),
+                                                   SkIntToScalar(kTestRectSize + 2));
+        SkPaint shapePaint;
+        shapePaint.setColor(shapeColor);
+        canvas->drawRect(targetRect, shapePaint);
+        shape.reset(recorder.endRecordingAsPicture());
+    }
+
+    SkPaint layerPaint;
+    layerPaint.setColor(SkColorSetARGB(130, 0, 0, 0));
+    canvas->saveLayer(&targetRect, &layerPaint);
+        canvas->save();
+            canvas->clipRect(targetRect);
+            SkPaint drawPaint;
+            drawPaint.setImageFilter(SkPictureImageFilter::Create(shape))->unref();
+            installDetector(&drawPaint);
+            canvas->saveLayer(&targetRect, &drawPaint);
+            canvas->restore();
+        canvas->restore();
+    canvas->restore();
+}
+
+// Draws two columns of rectangles. The test is correct when:
+//  - Left and right columns always identical
+//  - First 3 rows are green, with a white dent in the middle row
+//  - Next 6 rows are green, with a grey dent in the middle row
+//    (the grey dent is from the color filter removing everything but the "good" green, see below)
+//  - Last 6 rows are grey
+DEF_SIMPLE_GM(recordopts, canvas, (kTestRectSize+1)*2, (kTestRectSize+1)*15) {
+    canvas->clear(SK_ColorTRANSPARENT);
+
+    typedef void (*TestVariantSequence)(SkCanvas*, SkColor, InstallDetectorFunc);
+    TestVariantSequence funcs[] = {
+        draw_save_layer_draw_rect_restore_sequence,
+        draw_save_layer_draw_bitmap_restore_sequence,
+        draw_svg_opacity_and_filter_layer_sequence,
+    };
+
+    // Draw layer-related sequences that can be optimized by folding the opacity layer alpha to
+    // the inner draw operation. This tries to trigger the optimization, and relies on gm diffs
+    // to keep the color value correct over time.
+
+    // Draws two green rects side by side: one is without the optimization, the other is with
+    // the optimization applied.
+
+    SkColor shapeColor = SkColorSetARGB(255, 0, 255, 0);
+    for (size_t k = 0; k < SK_ARRAY_COUNT(funcs); ++k) {
+        canvas->save();
+
+        TestVariantSequence drawTestSequence = funcs[k];
+        drawTestSequence(canvas, shapeColor, no_detector_install);
+        canvas->flush();
+        canvas->translate(SkIntToScalar(kTestRectSize) + SkIntToScalar(1), SkIntToScalar(0));
+        {
+            SkPictureRecorder recorder;
+            drawTestSequence(recorder.beginRecording(SkIntToScalar(kTestRectSize),
+                                                     SkIntToScalar(kTestRectSize)),
+                             shapeColor, no_detector_install);
+            SkAutoTUnref<SkPicture> optimizedPicture(recorder.endRecordingAsPicture());
+            optimizedPicture->playback(canvas);
+            canvas->flush();
+        }
+        canvas->restore();
+        canvas->translate(SkIntToScalar(0), SkIntToScalar(kTestRectSize) + SkIntToScalar(1));
+    }
+
+    // Draw the same layer related sequences, but manipulate the sequences so that the result is
+    // incorrect if the alpha is folded or folded incorrectly. These test the observable state
+    // throughout the pixel pipeline, and thus may turn off the optimizations (this is why we
+    // trigger the optimizations above).
+
+    // Draws two green rects side by side: one is without the optimization, the other is with
+    // the possibility that optimization is applied.
+    // At the end, draws the same patterns in translucent black. This tests that the detectors
+    // work, eg. that if the value the detector sees is wrong, the resulting image shows this.
+    SkColor shapeColors[] = {
+        SkColorSetARGB(255, 0, kDetectorGreenValue, 0),
+        SkColorSetARGB(255, 0, kDetectorGreenValue + 1, 0) // This tests that detectors work.
+    };
+
+    InstallDetectorFunc detectorInstallFuncs[] = {
+        install_detector_image_filter,
+        install_detector_color_filter
+    };
+
+    for (size_t i = 0; i < SK_ARRAY_COUNT(shapeColors); ++i) {
+        shapeColor = shapeColors[i];
+        for (size_t j = 0; j < SK_ARRAY_COUNT(shapeColors); ++j) {
+            InstallDetectorFunc detectorInstallFunc = detectorInstallFuncs[j];
+            for (size_t k = 0; k < SK_ARRAY_COUNT(funcs); ++k) {
+                TestVariantSequence drawTestSequence = funcs[k];
+                canvas->save();
+                drawTestSequence(canvas, shapeColor, detectorInstallFunc);
+                canvas->flush();
+                canvas->translate(SkIntToScalar(kTestRectSize) + SkIntToScalar(1), SkIntToScalar(0));
+                {
+                    SkPictureRecorder recorder;
+                    drawTestSequence(recorder.beginRecording(SkIntToScalar(kTestRectSize),
+                                                             SkIntToScalar(kTestRectSize)),
+                                     shapeColor, detectorInstallFunc);
+                    SkAutoTUnref<SkPicture> optimizedPicture(recorder.endRecordingAsPicture());
+                    optimizedPicture->playback(canvas);
+                    canvas->flush();
+                }
+
+                canvas->restore();
+                canvas->translate(SkIntToScalar(0), SkIntToScalar(kTestRectSize) + SkIntToScalar(1));
+            }
+
+        }
+    }
+}
+