Revert "low-hanging bilerp_clamp_8888 wins"

This reverts commit f946b41643e049f3b81f40316373ad22e1518818.

Reason for revert: nervous diffs

Original change's description:
> low-hanging bilerp_clamp_8888 wins
> 
>    - support sampling bgra too
>    - lowp impl
> 
> Bug: skia:7810
> 
> Change-Id: I21db805483f612024802f2b508c140c42a029c54
> Reviewed-on: https://skia-review.googlesource.com/121582
> Commit-Queue: Mike Klein <mtklein@google.com>
> Reviewed-by: Florin Malita <fmalita@chromium.org>

TBR=mtklein@chromium.org,mtklein@google.com,fmalita@chromium.org

Change-Id: Id91d583151091a082a2d3f301d85f3acb12f4b19
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:7810
Reviewed-on: https://skia-review.googlesource.com/121589
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

2 files changed, 8 insertions, 67 deletions

diff --git a/src/opts/SkRasterPipeline_opts.h b/src/opts/SkRasterPipeline_opts.h
index 8332e4c12e..5a2c5b26a0 100644
--- a/src/opts/SkRasterPipeline_opts.h
+++ b/src/opts/SkRasterPipeline_opts.h
@@ -2264,7 +2264,7 @@ STAGE(gauss_a_to_rgba, Ctx::None) {
 }
 
 // A specialized fused image shader for clamp-x, clamp-y, non-sRGB sampling.
-STAGE(bilerp_clamp_8888, const SkJumper_GatherCtx* ctx) {
+STAGE(bilerp_clamp_8888, SkJumper_GatherCtx* ctx) {
     // (cx,cy) are the center of our sample.
     F cx = r,
       cy = g;
@@ -2600,7 +2600,6 @@ SI F floor_(F x) {
     return roundtrip - if_then_else(roundtrip > x, F(1), F(0));
 #endif
 }
-SI F fract(F x) { return x - floor_(x); }
 SI F abs_(F x) { return bit_cast<F>( bit_cast<I32>(x) & 0x7fffffff ); }
 
 // ~~~~~~ Basic / misc. stages ~~~~~~ //
@@ -3321,59 +3320,6 @@ STAGE_PP(srcover_bgra_8888, const SkJumper_MemoryCtx* ctx) {
     store_8888_(ptr, tail, b,g,r,a);
 }
 
-#if defined(SK_DISABLE_LOWP_BILERP_CLAMP_CLAMP_STAGE)
-    static void(*bilerp_clamp_8888)(void) = nullptr;
-#else
-STAGE_GP(bilerp_clamp_8888, const SkJumper_GatherCtx* ctx) {
-    // (cx,cy) are the center of our sample.
-    F cx = x,
-      cy = y;
-
-    // All sample points are at the same fractional offset (fx,fy).
-    // They're the 4 corners of a logical 1x1 pixel surrounding (x,y) at (0.5,0.5) offsets.
-    F fx = fract(cx + 0.5f),
-      fy = fract(cy + 0.5f);
-
-    // We'll accumulate the color of all four samples into {r,g,b,a} directly.
-    r = g = b = a = 0;
-
-    for (float dy = -0.5f; dy <= +0.5f; dy += 1.0f)
-    for (float dx = -0.5f; dx <= +0.5f; dx += 1.0f) {
-        // (x,y) are the coordinates of this sample point.
-        F x = cx + dx,
-          y = cy + dy;
-
-        // ix_and_ptr() will clamp to the image's bounds for us.
-        const uint32_t* ptr;
-        U32 ix = ix_and_ptr(&ptr, ctx, x,y);
-
-        U16 sr,sg,sb,sa;
-        from_8888(gather<U32>(ptr, ix), &sr,&sg,&sb,&sa);
-
-        // In bilinear interpolation, the 4 pixels at +/- 0.5 offsets from the sample pixel center
-        // are combined in direct proportion to their area overlapping that logical query pixel.
-        // At positive offsets, the x-axis contribution to that rectangle is fx,
-        // or (1-fx) at negative x.  Same deal for y.
-        F sx = (dx > 0) ? fx : 1.0f - fx,
-          sy = (dy > 0) ? fy : 1.0f - fy;
-
-        // The sum of the four sx*sy products will add up to 1.0, so we can keep up to
-        // 8 bits of fractional precision here and not worry about overflowing 16-bit.
-        U16 area = cast<U16>(sx * sy * 256);
-
-        r += sr * area;
-        g += sg * area;
-        b += sb * area;
-        a += sa * area;
-    }
-
-    r /= 256;
-    g /= 256;
-    b /= 256;
-    a /= 256;
-}
-#endif
-
 // Now we'll add null stand-ins for stages we haven't implemented in lowp.
 // If a pipeline uses these stages, it'll boot it out of lowp into highp.
 
@@ -3414,7 +3360,8 @@ static NotImplemented
         alter_2pt_conical_unswap,
         mask_2pt_conical_nan,
         mask_2pt_conical_degenerates,
-        apply_vector_mask;
+        apply_vector_mask,
+        bilerp_clamp_8888;
 
 #endif//defined(JUMPER_IS_SCALAR) controlling whether we build lowp stages
 }  // namespace lowp
diff --git a/src/shaders/SkImageShader.cpp b/src/shaders/SkImageShader.cpp
index 8ef647f5c9..1838e9e498 100644
--- a/src/shaders/SkImageShader.cpp
+++ b/src/shaders/SkImageShader.cpp
@@ -416,19 +416,13 @@ bool SkImageShader::onAppendStages(const StageRec& rec) const {
         return true;
     };
 
-    // We've got a fast path for 8888 bilinear clamp/clamp non-color-managed sampling.
-    auto ct = info.colorType();
-    if (true
-        && (ct == kRGBA_8888_SkColorType || ct == kBGRA_8888_SkColorType)
-        && quality == kLow_SkFilterQuality
-        && fTileModeX == SkShader::kClamp_TileMode
-        && fTileModeY == SkShader::kClamp_TileMode
-        && !is_srgb) {
+    if (quality == kLow_SkFilterQuality            &&
+        info.colorType() == kRGBA_8888_SkColorType &&
+        fTileModeX == SkShader::kClamp_TileMode    &&
+        fTileModeY == SkShader::kClamp_TileMode    &&
+        !is_srgb) {
 
         p->append(SkRasterPipeline::bilerp_clamp_8888, gather);
-        if (ct == kBGRA_8888_SkColorType) {
-            p->append(SkRasterPipeline::swap_rb);
-        }
         return append_misc();
     }