Refactor bilerp a little.

  1) rename to bilerp_xy, for x,y in {n[egative], p[ositive};
  2) pull out a save_xy stage to save off the original x,y;
  3) also calculate the fractional x,y fx,fy once instead of 4 times.

1) is a pure refactor;
2) adds a stage but otherwise is nothing different;
3) changes images a little bit (fractional parts can vary a bit around powers of two).

This extends naturally to naive bicubic using 16 bicubic_xy stages.

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: I666de5c21e978abb4feb6e3225e5b5920ba6c5b9
Reviewed-on: https://skia-review.googlesource.com/5550
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>

2 files changed, 12 insertions, 16 deletions

diff --git a/src/image/SkImageShader.cpp b/src/image/SkImageShader.cpp
index d2ddc95744..719bced4f5 100644
--- a/src/image/SkImageShader.cpp
+++ b/src/image/SkImageShader.cpp
@@ -358,26 +358,20 @@ bool SkImageShader::onAppendStages(SkRasterPipeline* p, SkColorSpace* dst, SkFal
         }
     };
 
-    if (quality == kNone_SkFilterQuality) {
-        append_tiling_and_gather();
-
-    } else {
-        p->append(SkRasterPipeline::top_left, ctx);
-        append_tiling_and_gather();
-        p->append(SkRasterPipeline::accumulate, ctx);
-
-        p->append(SkRasterPipeline::top_right, ctx);
-        append_tiling_and_gather();
-        p->append(SkRasterPipeline::accumulate, ctx);
-
-        p->append(SkRasterPipeline::bottom_left, ctx);
+    auto sample = [&](SkRasterPipeline::StockStage sampler) {
+        p->append(sampler, ctx);
         append_tiling_and_gather();
         p->append(SkRasterPipeline::accumulate, ctx);
+    };
 
-        p->append(SkRasterPipeline::bottom_right, ctx);
+    if (quality == kNone_SkFilterQuality) {
         append_tiling_and_gather();
-        p->append(SkRasterPipeline::accumulate, ctx);
-
+    } else {
+        p->append(SkRasterPipeline::save_xy, ctx);
+        sample(SkRasterPipeline::bilinear_nn);
+        sample(SkRasterPipeline::bilinear_np);
+        sample(SkRasterPipeline::bilinear_pn);
+        sample(SkRasterPipeline::bilinear_pp);
         p->append(SkRasterPipeline::move_dst_src);
     }
 
diff --git a/src/image/SkImageShaderContext.h b/src/image/SkImageShaderContext.h
index 7e50286072..b0652900dd 100644
--- a/src/image/SkImageShaderContext.h
+++ b/src/image/SkImageShaderContext.h
@@ -28,6 +28,8 @@ struct SkImageShaderContext {
     float         matrix[9];
     float         x[8];
     float         y[8];
+    float         fx[8];
+    float         fy[8];
     float         scale[8];
 };