src/third_party/skia/src/effects/SkLumaColorFilter.cpp

   1 /*
   2  * Copyright 2013 Google Inc.
   3  *
   4  * Use of this source code is governed by a BSD-style license that can be
   5  * found in the LICENSE file.
   6  */
   7
   8 #include "SkLumaColorFilter.h"
   9
  10 #include "SkColorPriv.h"
  11 #include "SkString.h"
  12
  13 #if SK_SUPPORT_GPU
  14 #include "gl/GrGLProcessor.h"
  15 #include "gl/builders/GrGLProgramBuilder.h"
  16 #include "GrContext.h"
  17 #include "GrTBackendProcessorFactory.h"
  18 #endif
  19
  20 void SkLumaColorFilter::filterSpan(const SkPMColor src[], int count,
  21                                    SkPMColor dst[]) const {
  22     for (int i = 0; i < count; ++i) {
  23         SkPMColor c = src[i];
  24
  25         /*
  26          * While LuminanceToAlpha is defined to operate on un-premultiplied
  27          * inputs, due to the final alpha scaling it can be computed based on
  28          * premultipled components:
  29          *
  30          *   LumA = (k1 * r / a + k2 * g / a + k3 * b / a) * a
  31          *   LumA = (k1 * r + k2 * g + k3 * b)
  32          */
  33         unsigned luma = SkComputeLuminance(SkGetPackedR32(c),
  34                                            SkGetPackedG32(c),
  35                                            SkGetPackedB32(c));
  36         dst[i] = SkPackARGB32(luma, 0, 0, 0);
  37     }
  38 }
  39
  40 SkColorFilter* SkLumaColorFilter::Create() {
  41     return SkNEW(SkLumaColorFilter);
  42 }
  43
  44 SkLumaColorFilter::SkLumaColorFilter() : INHERITED() {}
  45
  46 #ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
  47 SkLumaColorFilter::SkLumaColorFilter(SkReadBuffer& buffer) : INHERITED(buffer) {}
  48 #endif
  49
  50 SkFlattenable* SkLumaColorFilter::CreateProc(SkReadBuffer&) {
  51     return SkNEW(SkLumaColorFilter);
  52 }
  53
  54 void SkLumaColorFilter::flatten(SkWriteBuffer&) const {}
  55
  56 #ifndef SK_IGNORE_TO_STRING
  57 void SkLumaColorFilter::toString(SkString* str) const {
  58     str->append("SkLumaColorFilter ");
  59 }
  60 #endif
  61
  62 #if SK_SUPPORT_GPU
  63 class LumaColorFilterEffect : public GrFragmentProcessor {
  64 public:
  65     static GrFragmentProcessor* Create() {
  66         GR_CREATE_STATIC_PROCESSOR(gLumaEffect, LumaColorFilterEffect, ());
  67         return SkRef(gLumaEffect);
  68     }
  69
  70     static const char* Name() { return "Luminance-to-Alpha"; }
  71
  72     virtual const GrBackendFragmentProcessorFactory& getFactory() const SK_OVERRIDE {
  73         return GrTBackendFragmentProcessorFactory<LumaColorFilterEffect>::getInstance();
  74     }
  75
  76     class GLProcessor : public GrGLFragmentProcessor {
  77     public:
  78         GLProcessor(const GrBackendProcessorFactory& factory,
  79                     const GrProcessor&)
  80         : INHERITED(factory) {
  81         }
  82
  83         static void GenKey(const GrProcessor&, const GrGLCaps&, GrProcessorKeyBuilder* b) {}
  84
  85         virtual void emitCode(GrGLFPBuilder* builder,
  86                               const GrFragmentProcessor&,
  87                               const GrProcessorKey&,
  88                               const char* outputColor,
  89                               const char* inputColor,
  90                               const TransformedCoordsArray&,
  91                               const TextureSamplerArray&) SK_OVERRIDE {
  92             if (NULL == inputColor) {
  93                 inputColor = "vec4(1)";
  94             }
  95
  96             GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
  97             fsBuilder->codeAppendf("\tfloat luma = dot(vec3(%f, %f, %f), %s.rgb);\n",
  98                                    SK_ITU_BT709_LUM_COEFF_R,
  99                                    SK_ITU_BT709_LUM_COEFF_G,
 100                                    SK_ITU_BT709_LUM_COEFF_B,
 101                                    inputColor);
 102             fsBuilder->codeAppendf("\t%s = vec4(0, 0, 0, luma);\n",
 103                                    outputColor);
 104
 105         }
 106
 107     private:
 108         typedef GrGLFragmentProcessor INHERITED;
 109     };
 110
 111 private:
 112     virtual bool onIsEqual(const GrFragmentProcessor&) const SK_OVERRIDE { return true; }
 113
 114     virtual void onComputeInvariantOutput(InvariantOutput* inout) const SK_OVERRIDE {
 115         // The output is always black. The alpha value for the color passed in is arbitrary.
 116         inout->setToOther(kRGB_GrColorComponentFlags, GrColorPackRGBA(0, 0, 0, 0),
 117                           InvariantOutput::kWill_ReadInput);
 118     }
 119 };
 120
 121 GrFragmentProcessor* SkLumaColorFilter::asFragmentProcessor(GrContext*) const {
 122     return LumaColorFilterEffect::Create();
 123 }
 124 #endif