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

Review-Url: https://codereview.chromium.org/2132073002

1 files changed, 20 insertions, 0 deletions

diff --git a/include/gpu/GrClip.h b/include/gpu/GrClip.h
index e58528114e..b63f2130da 100644
--- a/include/gpu/GrClip.h
+++ b/include/gpu/GrClip.h
@@ -109,6 +109,26 @@ public:
                        const SkRect* devBounds, GrAppliedClip*) const = 0;
 
     virtual ~GrClip() {}
+
+protected:
+    /**
+     * Returns true if a clip can safely disable its scissor test for a particular draw.
+     */
+    static bool CanIgnoreScissor(const SkIRect& scissorRect, const SkRect& drawBounds) {
+        // This is the maximum distance that a draw may extend beyond a clip's scissor and still
+        // count as inside. We use a sloppy compare because the draw may have chosen its bounds in a
+        // different coord system. The rationale for 1e-3 is that in the coverage case (and barring
+        // unexpected rounding), as long as coverage stays below 0.5 * 1/256 we ought to be OK.
+        constexpr SkScalar fuzz = 1e-3f;
+        SkASSERT(!scissorRect.isEmpty());
+        SkASSERT(!drawBounds.isEmpty());
+        return scissorRect.fLeft <= drawBounds.fLeft + fuzz &&
+               scissorRect.fTop <= drawBounds.fTop + fuzz &&
+               scissorRect.fRight >= drawBounds.fRight - fuzz &&
+               scissorRect.fBottom >= drawBounds.fBottom - fuzz;
+    }
+
+    friend class GrClipMaskManager;
 };
 
 /**