New analytic AA scan converter using delta (I call it DAA for now)

DAA is:

1. Much simpler than AAA.
   SkScan_AAAPath.cpp is about 1700 lines.
   SkScan_DAAPath.cpp is about 300 lines.
   The whole DAA CL is only about 800 lines.

2. Much faster than AAA for complicated paths.
   The speedup applies to GL backend (including ccpr)!
   Here's the frame time of 'SampleApp --slide Chart' on macbook pro:
     AAA-raster: 33ms
     DAA-raster: 21ms
     AAA-gl:     30ms
     DAA-gl:     20ms
     AAA-ccpr:   18ms
     DAA-ccpr:   12ms
   My linux desktop doesn't have SSE3 so the speedup is smaller
   (~25% for Chart). I believe that DAA is so fast that I can enable
   it for any paths (AAA is not enabled by default for complicated
   paths because it is slow; hence our older supersampling scan
   converter is used for stroking on Chart for AAA-xxx config.)

3. The SkCoverageDelta is suitable for threaded backend with
   out-of-order concurrent scan conversion as commented in the source
   code. Maybe we can also just send deltas to GPU.

4. Similar to most analytic path renderers, the quality is on the best
   ground-truth level, unless there are intersections within a pixel.
   The intersections look good to my eyes although theoretically that
   could be arbitrary far from the ground truth (see my AAA slides).

5. For simple paths, such as circle, triangle, rrect, etc., DAA is
   slower than AAA. But DAA is faster than our older supersampling
   scan converter in most cases. As those simple paths usually don't
   constitute the bottleneck of a picture (skp or svg), I strongly
   recommend use DAA.

6. DAA also heavily favors blitMask so it may work quite well with
   SkRasterPipeline and SkRasterPipelineBlitter.

Finally, please check https://skia-review.googlesource.com/c/22420/
which accelerate DAA by specializing blitCoverageDeltas for
SkARGB32_Blitter and SkARGB32_Black_Blitter. It brings a little(<5%)
speedup. But I couldn't figure out how to reduce the duplicate code
so I don't intend to land it.

Bug: skia:
Change-Id: I3b7ed6a727447922e645b1acb737a506e7c09a4c
Reviewed-on: https://skia-review.googlesource.com/19666
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index 196cb220d0..798dd0d727 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -1199,7 +1199,11 @@ int main(int argc, char** argv) {
     }
 
     gSkUseAnalyticAA = FLAGS_analyticAA;
+    gSkUseDeltaAA = FLAGS_deltaAA;
 
+    if (FLAGS_forceDeltaAA) {
+        gSkForceDeltaAA = true;
+    }
     if (FLAGS_forceAnalyticAA) {
         gSkForceAnalyticAA = true;
     }