Pre-crop filled rects to avoid scissor

Updates GrDrawContext to crop filled rects to the clip bounds before
creating batches for them. Also adds clipping logic to ignore scissor
when the draw falls completely inside. These two changes combined
reduce API traffic and improve batching.

In the future this can and should be improved by switching to floating
point clip boundaries, thus allowing us to throw out non pixel aligned
rectangle clips as well.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2132073002

Committed: https://skia.googlesource.com/skia/+/7969838702135b9f127bd738728da61bc49b050a
Review-Url: https://codereview.chromium.org/2132073002

1 files changed, 108 insertions, 0 deletions

diff --git a/gm/croppedrects.cpp b/gm/croppedrects.cpp
new file mode 100644
index 0000000000..5c36c54815
--- /dev/null
+++ b/gm/croppedrects.cpp
@@ -0,0 +1,108 @@
+/*
+ * Copyright 2016 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 "SkPath.h"
+#include "SkRandom.h"
+#include "SkRRect.h"
+#include "SkSurface.h"
+
+namespace skiagm {
+
+constexpr SkRect kSrcImageClip{75, 75, 275, 275};
+
+/*
+ * The purpose of this test is to exercise all three codepaths in GrDrawContext (drawFilledRect,
+ * fillRectToRect, fillRectWithLocalMatrix) that pre-crop filled rects based on the clip.
+ *
+ * The test creates an image of a green square surrounded by red background, then draws this image
+ * in various ways with the red clipped out. The test is successful if there is no visible red
+ * background, scissor is never used, and ideally, all the rectangles draw in one batch.
+ */
+class CroppedRectsGM : public GM {
+private:
+    SkString onShortName() override final { return SkString("croppedrects"); }
+    SkISize onISize() override { return SkISize::Make(500, 500); }
+
+    void onOnceBeforeDraw() override {
+        sk_sp<SkSurface> srcSurface = SkSurface::MakeRasterN32Premul(500, 500);
+        SkCanvas* srcCanvas = srcSurface->getCanvas();
+
+        srcCanvas->clear(SK_ColorRED);
+
+        SkPaint paint;
+        paint.setColor(0xff00ff00);
+        srcCanvas->drawRect(kSrcImageClip, paint);
+
+        constexpr SkScalar kStrokeWidth = 10;
+        SkPaint stroke;
+        stroke.setStyle(SkPaint::kStroke_Style);
+        stroke.setStrokeWidth(kStrokeWidth);
+        stroke.setColor(0xff008800);
+        srcCanvas->drawRect(kSrcImageClip.makeInset(kStrokeWidth / 2, kStrokeWidth / 2), stroke);
+
+        fSrcImage = srcSurface->makeImageSnapshot(SkBudgeted::kYes, SkSurface::kNo_ForceUnique);
+        fSrcImageShader = fSrcImage->makeShader(SkShader::kClamp_TileMode,
+                                                SkShader::kClamp_TileMode);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        canvas->clear(SK_ColorWHITE);
+
+        {
+            // GrDrawContext::drawFilledRect.
+            SkAutoCanvasRestore acr(canvas, true);
+            SkPaint paint;
+            paint.setShader(fSrcImageShader);
+            paint.setFilterQuality(kNone_SkFilterQuality);
+            canvas->clipRect(kSrcImageClip);
+            canvas->drawPaint(paint);
+        }
+
+        {
+            // GrDrawContext::fillRectToRect.
+            SkAutoCanvasRestore acr(canvas, true);
+            SkPaint paint;
+            paint.setFilterQuality(kNone_SkFilterQuality);
+            SkRect drawRect = SkRect::MakeXYWH(350, 100, 100, 300);
+            canvas->clipRect(drawRect);
+            canvas->drawImageRect(fSrcImage.get(),
+                                  kSrcImageClip.makeOutset(0.5f * kSrcImageClip.width(),
+                                                           kSrcImageClip.height()),
+                                  drawRect.makeOutset(0.5f * drawRect.width(), drawRect.height()),
+                                  &paint);
+        }
+
+        {
+            // GrDrawContext::fillRectWithLocalMatrix.
+            SkAutoCanvasRestore acr(canvas, true);
+            SkPath path;
+            path.moveTo(kSrcImageClip.fLeft - kSrcImageClip.width(), kSrcImageClip.centerY());
+            path.lineTo(kSrcImageClip.fRight + 3 * kSrcImageClip.width(), kSrcImageClip.centerY());
+            SkPaint paint;
+            paint.setStyle(SkPaint::kStroke_Style);
+            paint.setStrokeWidth(2 * kSrcImageClip.height());
+            paint.setShader(fSrcImageShader);
+            paint.setFilterQuality(kNone_SkFilterQuality);
+            canvas->translate(-90, 263);
+            canvas->scale(300 / kSrcImageClip.width(), 100 / kSrcImageClip.height());
+            canvas->clipRect(kSrcImageClip);
+            canvas->drawPath(path, paint);
+        }
+
+        // TODO: assert the draw target only has one batch in the post-MDB world.
+    }
+
+    sk_sp<SkImage> fSrcImage;
+    sk_sp<SkShader> fSrcImageShader;
+
+    typedef GM INHERITED;
+};
+
+DEF_GM( return new CroppedRectsGM(); )
+
+}