add gamma stage

Until now we've been using 3 separate parametric stages to apply
gamma to r,g,b.  That works fine, but is kind of unnecessarily
slow, and again less clear in a stack trace than seeing "gamma".

The new bench runs in about 60% of the time the old one does
on my Trashcan.

BUG=skia:6939

Change-Id: I079698d3009b081f1c23a2e27fc26e373b439610
Reviewed-on: https://skia-review.googlesource.com/32721
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

bench/SkRasterPipelineBench.cpp

@@ -113,9 +113,12 @@ static SkColorSpaceTransferFn gamma(float g) {
 
 class SkRasterPipeline_2dot2 : public Benchmark {
 public:
+    SkRasterPipeline_2dot2(bool parametric) : fParametric(parametric) {}
+
     bool isSuitableFor(Backend backend) override { return backend == kNonRendering_Backend; }
     const char* onGetName() override {
-        return "SkRasterPipeline_2dot2";
+        return fParametric ? "SkRasterPipeline_2dot2_parametric"
+                           : "SkRasterPipeline_2dot2_gamma";
     }
 
     void onDraw(int loops, SkCanvas*) override {
@@ -126,19 +129,27 @@ public:
         SkSTArenaAlloc<256> alloc;
         SkRasterPipeline p(&alloc);
         p.append_constant_color(&alloc, c);
-        p.append(SkRasterPipeline::parametric_r, &from_2dot2);
-        p.append(SkRasterPipeline::parametric_g, &from_2dot2);
-        p.append(SkRasterPipeline::parametric_b, &from_2dot2);
-        p.append(SkRasterPipeline::parametric_r, &  to_2dot2);
-        p.append(SkRasterPipeline::parametric_g, &  to_2dot2);
-        p.append(SkRasterPipeline::parametric_b, &  to_2dot2);
+        if (fParametric) {
+            p.append(SkRasterPipeline::parametric_r, &from_2dot2);
+            p.append(SkRasterPipeline::parametric_g, &from_2dot2);
+            p.append(SkRasterPipeline::parametric_b, &from_2dot2);
+            p.append(SkRasterPipeline::parametric_r, &  to_2dot2);
+            p.append(SkRasterPipeline::parametric_g, &  to_2dot2);
+            p.append(SkRasterPipeline::parametric_b, &  to_2dot2);
+        } else {
+            p.append(SkRasterPipeline::gamma, &from_2dot2.fG);
+            p.append(SkRasterPipeline::gamma, &  to_2dot2.fG);
+        }
 
         while (loops --> 0) {
             p.run(0,0,N,1);
         }
     }
+private:
+    bool fParametric;
 };
-DEF_BENCH( return (new SkRasterPipeline_2dot2); )
+DEF_BENCH( return (new SkRasterPipeline_2dot2( true)); )
+DEF_BENCH( return (new SkRasterPipeline_2dot2(false)); )
 
 class SkRasterPipelineToSRGB : public Benchmark {
 public:

src/core/SkColorSpacePriv.h

@@ -170,6 +170,16 @@ static inline bool is_almost_linear(const SkColorSpaceTransferFn& coeffs) {
     return linearExp || linearFn;
 }
 
+static inline bool is_just_gamma(const SkColorSpaceTransferFn& coeffs) {
+    return transfer_fn_almost_equal(coeffs.fA, 1.0f)
+        && transfer_fn_almost_equal(coeffs.fB, 0.0f)
+        && transfer_fn_almost_equal(coeffs.fC, 0.0f)
+        && transfer_fn_almost_equal(coeffs.fD, 0.0f)
+        && transfer_fn_almost_equal(coeffs.fE, 0.0f)
+        && transfer_fn_almost_equal(coeffs.fF, 0.0f);
+}
+
+
 static inline void value_to_parametric(SkColorSpaceTransferFn* coeffs, float exponent) {
     coeffs->fA = 1.0f;
     coeffs->fB = 0.0f;

src/core/SkColorSpaceXform.cpp

@@ -588,17 +588,13 @@ bool SkColorSpaceXform_XYZ<kCSM>
     }
 
     TablesContext tables;
-    SkColorSpaceTransferFn to_2dot2 = {0,0,0,0,0,0,0};
-    to_2dot2.fG = 1/2.2f;
-    to_2dot2.fA = 1;
+    float to_2dot2 = 1/2.2f;
     switch (fDstGamma) {
         case kSRGB_DstGamma:
             pipeline.append(SkRasterPipeline::to_srgb);
             break;
         case k2Dot2_DstGamma:
-            pipeline.append(SkRasterPipeline::parametric_r, &to_2dot2);
-            pipeline.append(SkRasterPipeline::parametric_g, &to_2dot2);
-            pipeline.append(SkRasterPipeline::parametric_b, &to_2dot2);
+            pipeline.append(SkRasterPipeline::gamma, &to_2dot2);
             break;
         case kTable_DstGamma:
             tables.fR = fDstGammaTables[0];

src/core/SkColorSpaceXform_A2B.cpp

@@ -149,9 +149,13 @@ SkColorSpaceXform_A2B::SkColorSpaceXform_A2B(SkColorSpace_A2B* srcSpace,
                 auto fn = fAlloc.make<SkColorSpaceTransferFn>();
                 SkAssertResult(named_to_parametric(fn, e.gammaNamed()));
 
-                fElementsPipeline.append(SkRasterPipeline::parametric_r, fn);
-                fElementsPipeline.append(SkRasterPipeline::parametric_g, fn);
-                fElementsPipeline.append(SkRasterPipeline::parametric_b, fn);
+                if (is_just_gamma(*fn)) {
+                    fElementsPipeline.append(SkRasterPipeline::gamma, &fn->fG);
+                } else {
+                    fElementsPipeline.append(SkRasterPipeline::parametric_r, fn);
+                    fElementsPipeline.append(SkRasterPipeline::parametric_g, fn);
+                    fElementsPipeline.append(SkRasterPipeline::parametric_b, fn);
+                }
                 break;
             }
             case SkColorSpace_A2B::Element::Type::kGammas: {
@@ -236,13 +240,7 @@ SkColorSpaceXform_A2B::SkColorSpaceXform_A2B(SkColorSpace_A2B* srcSpace,
             // do nothing
             break;
         case k2Dot2Curve_SkGammaNamed: {
-            SkColorSpaceTransferFn fn = {0,0,0,0,0,0,0};
-            fn.fG = 1/2.2f;
-            fn.fA = 1;
-            auto to_2dot2 = this->copy(fn);
-            fElementsPipeline.append(SkRasterPipeline::parametric_r, to_2dot2);
-            fElementsPipeline.append(SkRasterPipeline::parametric_g, to_2dot2);
-            fElementsPipeline.append(SkRasterPipeline::parametric_b, to_2dot2);
+            fElementsPipeline.append(SkRasterPipeline::gamma, this->copy(1/2.2f));
             break;
         }
         case kSRGB_SkGammaNamed:

src/core/SkConvertPixels.cpp

@@ -7,6 +7,7 @@
 
 #include "SkColorSpaceXform_Base.h"
 #include "SkColorSpaceXformPriv.h"
+#include "SkColorSpacePriv.h"
 #include "SkColorTable.h"
 #include "SkConvertPixels.h"
 #include "SkHalf.h"
@@ -255,9 +256,13 @@ static void convert_with_pipeline(const SkImageInfo& dstInfo, void* dstRow, size
         pipeline.append_from_srgb(premulState);
     } else if (isColorAware && !srcInfo.colorSpace()->gammaIsLinear()) {
         SkAssertResult(srcInfo.colorSpace()->isNumericalTransferFn(&srcFn));
-        pipeline.append(SkRasterPipeline::parametric_r, &srcFn);
-        pipeline.append(SkRasterPipeline::parametric_g, &srcFn);
-        pipeline.append(SkRasterPipeline::parametric_b, &srcFn);
+        if (is_just_gamma(srcFn)) {
+            pipeline.append(SkRasterPipeline::gamma, &srcFn.fG);
+        } else {
+            pipeline.append(SkRasterPipeline::parametric_r, &srcFn);
+            pipeline.append(SkRasterPipeline::parametric_g, &srcFn);
+            pipeline.append(SkRasterPipeline::parametric_b, &srcFn);
+        }
     }
 
     float matrix[12];
@@ -283,9 +288,13 @@ static void convert_with_pipeline(const SkImageInfo& dstInfo, void* dstRow, size
     } else if (isColorAware && !dstInfo.colorSpace()->gammaIsLinear()) {
         SkAssertResult(dstInfo.colorSpace()->isNumericalTransferFn(&dstFn));
         dstFn = dstFn.invert();
-        pipeline.append(SkRasterPipeline::parametric_r, &dstFn);
-        pipeline.append(SkRasterPipeline::parametric_g, &dstFn);
-        pipeline.append(SkRasterPipeline::parametric_b, &dstFn);
+        if (is_just_gamma(dstFn)) {
+            pipeline.append(SkRasterPipeline::gamma, &dstFn.fG);
+        } else {
+            pipeline.append(SkRasterPipeline::parametric_r, &dstFn);
+            pipeline.append(SkRasterPipeline::parametric_g, &dstFn);
+            pipeline.append(SkRasterPipeline::parametric_b, &dstFn);
+        }
     }
 
     if (kUnpremul_SkAlphaType == premulState && kPremul_SkAlphaType == dat &&

src/core/SkRasterPipeline.h

@@ -71,7 +71,7 @@ struct SkJumper_Engine;
     M(matrix_2x3) M(matrix_3x4) M(matrix_4x5) M(matrix_4x3)      \
     M(matrix_perspective)                                        \
     M(parametric_r) M(parametric_g) M(parametric_b)              \
-    M(parametric_a)                                              \
+    M(parametric_a) M(gamma)                                     \
     M(table_r) M(table_g) M(table_b) M(table_a)                  \
     M(lab_to_xyz)                                                \
     M(clamp_x)   M(mirror_x)   M(repeat_x)                       \

src/jumper/SkJumper_stages.cpp

@@ -836,6 +836,13 @@ STAGE(parametric_g) { g = parametric(g, ctx); }
 STAGE(parametric_b) { b = parametric(b, ctx); }
 STAGE(parametric_a) { a = parametric(a, ctx); }
 
+STAGE(gamma) {
+    float G = *(const float*)ctx;
+    r = approx_powf(r,G);
+    g = approx_powf(g,G);
+    b = approx_powf(b,G);
+}
+
 STAGE(lab_to_xyz) {
     F L = r * 100.0f,
       A = g * 255.0f - 128.0f,