alpha threshold bitmap shader

src/effects/SkBitmapAlphaThresholdShader.cpp

Index: src/effects/SkBitmapAlphaThresholdShader.cpp
diff --git a/src/effects/SkBitmapAlphaThresholdShader.cpp b/src/effects/SkBitmapAlphaThresholdShader.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..c9275883e3ae61cf22cfccceecc51f7b39a81a7e
--- /dev/null
+++ b/src/effects/SkBitmapAlphaThresholdShader.cpp
@@ -0,0 +1,311 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmapAlphaThresholdShader.h"
+
+class BATShader : public SkShader {
+public:
+    SK_DECLARE_INST_COUNT(SkThresholdShader);
+
+    BATShader(const SkBitmap& bitmap, SkRegion region, U8CPU);
+    BATShader(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {
+        // We should probably do something here.
+    }
+    
+    
+    virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE {};
+    
+#if SK_SUPPORT_GPU
+    virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint& paint) const SK_OVERRIDE;
+#endif
+    
+    SK_DEVELOPER_TO_STRING();
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(BATShader)
+    
+private:
+    SkBitmap fBitmap;
+    SkRegion fRegion;
+    U8CPU    fThreshold;
+    
+    typedef SkShader INHERITED;
+};
+
+SkShader* SkBitmapAlphaThresholdShader::Create(const SkBitmap& bitmap,
+                                               const SkRegion& region,
+                                               U8CPU threshold) {
+    SkASSERT(threshold < 256);
+    return SkNEW_ARGS(BATShader, (bitmap, region, threshold));
+}
+
+BATShader::BATShader(const SkBitmap& bitmap, SkRegion region, U8CPU threshold)
+: fBitmap(bitmap)
+, fRegion(region)
+, fThreshold(threshold) {
+};
+
+
+#ifdef SK_DEVELOPER
+void BATShader::toString(SkString* str) const {
+    str->append("BATShader: (");
+
+    fBitmap.toString(str);
+
+    this->INHERITED::toString(str);
+
+    str->append(")");
+}
+#endif
+
+#if SK_SUPPORT_GPU
+#include "GrContext.h"
+#include "GrEffect.h"
+#include "gl/GrGLEffect.h"
+#include "gl/GrGLEffectMatrix.h"
+#include "GrTBackendEffectFactory.h"
+#include "GrTextureAccess.h"
+
+#include "SkGr.h"
+
+/**
+ * Could create specializations for some simple cases:
+ *  - The region is empty.
+ *  - The region fully contains the bitmap.
+ *  - The regions is 1 rect (or maybe a small number of rects).
+ */
+class ThresholdEffect : public GrEffect {
+public:
+    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE {
+        return GrTBackendEffectFactory<ThresholdEffect>::getInstance();
+    }
+
+    static GrEffectRef* Create(GrTexture* bmpTexture, const SkMatrix& bmpMatrix,
+                               GrTexture* maskTexture, const SkMatrix& maskMatrix,
+                               U8CPU threshold) {
+        SkScalar thresh = SkIntToScalar(threshold) / 255;
+
+        AutoEffectUnref effect(SkNEW_ARGS(ThresholdEffect, (bmpTexture, bmpMatrix,
+                                                            maskTexture, maskMatrix,
+                                                            thresh)));
+        return CreateEffectRef(effect);
+    }
+
+    virtual void getConstantColorComponents(GrColor* color,
+                                            uint32_t* validFlags) const SK_OVERRIDE {
+        if ((kA_GrColorComponentFlag & *validFlags) && 0 == GrColorUnpackA(*color)) {
+            return;
+        }
+        *validFlags = 0;
+        return;
+    }
+
+    static const char* Name() { return "Bitmap Alpha Threshold"; }
+
+    class GLEffect : public GrGLEffect {
+    public:
+        GLEffect(const GrBackendEffectFactory& factory,
+                    const GrDrawEffect& e)
+        : GrGLEffect(factory)
+        , fBmpMatrix(GrEffect::kLocal_CoordsType)
+        , fMaskMatrix(GrEffect::kLocal_CoordsType)
+        , fPrevThreshold(-SK_Scalar1) {
+        }
+
+        virtual void emitCode(GrGLShaderBuilder* builder,
+                                const GrDrawEffect& drawEffect,
+                                EffectKey key,
+                                const char* outputColor,
+                                const char* inputColor,
+                                const TextureSamplerArray& samplers) SK_OVERRIDE {
+            SkString bmpCoord;
+            SkString maskCoord;
+
+            GrSLType bmpCoordType = fBmpMatrix.emitCode(builder, key, &bmpCoord, NULL, "Bmp");
+            EffectKey maskMatrixKey = key >> GrGLEffectMatrix::kKeyBits;
+            GrSLType maskCoordType = fMaskMatrix.emitCode(builder,
+                                                          maskMatrixKey,
+                                                          &maskCoord,
+                                                          NULL,
+                                                          "Mask");
+
+            // put bitmap color in "color"
+            builder->fsCodeAppend("\t\tvec4 color = ");
+            builder->fsAppendTextureLookup(samplers[0], bmpCoord.c_str(), bmpCoordType);
+            builder->fsCodeAppend(";\n");
+
+            // put alpha from mask texture in "mask"
+            builder->fsCodeAppend("\t\tfloat mask = ");
+            builder->fsAppendTextureLookup(samplers[1], maskCoord.c_str(), maskCoordType);
+            builder->fsCodeAppend(".a;\n");
+
+            const char* threshold;
+
+            fThresholdUniHandle = builder->addUniform(GrGLShaderBuilder::kFragment_Visibility,
+                                                      kFloat_GrSLType,
+                                                      "threshold",
+                                                      &threshold);
+            builder->fsCodeAppendf("\t\tfloat thresh = %s;\n", threshold);
+
+            builder->fsCodeAppend("\t\tif (mask < 0.5) {\n"
+                                    "\t\t\tif (color.a > thresh) {\n"
+                                    "\t\t\t\tfloat scale = thresh / color.a;\n"
+                                    "\t\t\t\tcolor.rgb *= scale;\n"
+                                    "\t\t\t\tcolor.a = thresh;\n"
+                                    "\t\t\t}\n"
+                                    "\t\t} else if (color.a < thresh) {\n"
+                                    "\t\t\tfloat scale = thresh / color.a;\n"
+                                    "\t\t\tcolor.rgb *= scale;\n"
+                                    "\t\t\tcolor.a = thresh;\n"
+                                    "\t\t}\n");
+
+            builder->fsCodeAppend("color = ");
+            SkString outStr;
+            outStr.appendf("\t\t%s = ", outputColor);
+            GrGLSLModulatef<4>(&outStr, inputColor, "color");
+            outStr.append(";\n");
+            builder->fsCodeAppend(outStr.c_str());
+        }
+
+        virtual void setData(const GrGLUniformManager& uman, const GrDrawEffect& e) SK_OVERRIDE {
+            const ThresholdEffect& effect = e.castEffect<ThresholdEffect>();
+            fBmpMatrix.setData(uman, effect.fBmpMatrix, e, effect.fBmpAccess.getTexture());
+            fMaskMatrix.setData(uman, effect.fMaskMatrix, e, effect.fMaskAccess.getTexture());
+            if (fPrevThreshold != effect.fThreshold) {
+                uman.set1f(fThresholdUniHandle, effect.fThreshold);
+            }
+        }
+
+        static inline EffectKey GenKey(const GrDrawEffect& e, const GrGLCaps&) {
+            const ThresholdEffect& effect = e.castEffect<ThresholdEffect>();
+
+            EffectKey bmpMKey = GrGLEffectMatrix::GenKey(effect.fBmpMatrix,
+                                                         e,
+                                                         GrEffect::kLocal_CoordsType,
+                                                         effect.fBmpAccess.getTexture());
+            EffectKey maskMKey = GrGLEffectMatrix::GenKey(effect.fMaskMatrix,
+                                                          e,
+                                                          GrEffect::kLocal_CoordsType,
+                                                          effect.fMaskAccess.getTexture());
+            return bmpMKey | (maskMKey << GrGLEffectMatrix::kKeyBits);
+        }
+
+    private:
+        GrGLEffectMatrix fBmpMatrix;
+        GrGLEffectMatrix fMaskMatrix;
+
+        GrGLUniformManager::UniformHandle fThresholdUniHandle;
+        SkScalar                          fPrevThreshold;
+    };
+
+    GR_DECLARE_EFFECT_TEST;
+
+private:
+    ThresholdEffect(GrTexture* bmpTexture, const SkMatrix& bmpMatrix,
+                    GrTexture* maskTexture, const SkMatrix& maskMatrix,
+                    SkScalar threshold)
+    : fBmpAccess(bmpTexture, GrTextureParams())
+    , fMaskAccess(maskTexture, GrTextureParams())
+    , fBmpMatrix(bmpMatrix)
+    , fMaskMatrix(maskMatrix)
+    , fThreshold(threshold) {
+        this->addTextureAccess(&fBmpAccess);
+        this->addTextureAccess(&fMaskAccess);
+    }
+
+    virtual bool onIsEqual(const GrEffect& other) const SK_OVERRIDE {
+        const ThresholdEffect& e = CastEffect<ThresholdEffect>(other);
+        return e.fBmpAccess.getTexture() == fBmpAccess.getTexture() &&
+               e.fMaskAccess.getTexture() == fMaskAccess.getTexture() &&
+               e.fBmpMatrix == fBmpMatrix &&
+               e.fMaskMatrix == fMaskMatrix &&
+               e.fThreshold == fThreshold;
+    }
+
+    GrTextureAccess fBmpAccess;
+    GrTextureAccess fMaskAccess;
+
+    SkMatrix fBmpMatrix;
+    SkMatrix fMaskMatrix;
+
+    SkScalar fThreshold;
+};
+
+GR_DEFINE_EFFECT_TEST(ThresholdEffect);
+
+GrEffectRef* ThresholdEffect::TestCreate(SkMWCRandom* rand,
+                                         GrContext*,
+                                         const GrDrawTargetCaps&,
+                                         GrTexture* textures[]) {
+    GrTexture* bmpTex = textures[GrEffectUnitTest::kSkiaPMTextureIdx];
+    GrTexture* maskTex = textures[GrEffectUnitTest::kAlphaTextureIdx];
+    U8CPU thresh = rand->nextU() % 0xff;
+    return ThresholdEffect::Create(bmpTex, SkMatrix::I(), maskTex, SkMatrix::I(), thresh);
+}
+
+GrEffectRef* BATShader::asNewEffect(GrContext* context, const SkPaint& paint) const {
+    SkMatrix localInverse;
+    if (!this->getLocalMatrix().invert(&localInverse)) {
+        return NULL;
+    }
+
+    GrTextureDesc maskDesc;
+    if (context->isConfigRenderable(kAlpha_8_GrPixelConfig)) {
+        maskDesc.fConfig = kAlpha_8_GrPixelConfig;
+    } else {
+        maskDesc.fConfig = kRGBA_8888_GrPixelConfig;
+    }
+    maskDesc.fFlags = kRenderTarget_GrTextureFlagBit | kNoStencil_GrTextureFlagBit;
+    const SkIRect& bounds = fRegion.getBounds();
+    // Add one pixel of border to ensure that clamp mode will be all zeros
+    // the outside.
+    maskDesc.fWidth = bounds.width() + 2;
+    maskDesc.fHeight = bounds.height() + 2;
+    GrAutoScratchTexture ast(context, maskDesc, GrContext::kApprox_ScratchTexMatch);
+    GrTexture*  maskTexture = ast.texture();
+    if (NULL == maskTexture) {
+        return NULL;
+    }
+
+    GrPaint grPaint;
+    grPaint.setBlendFunc(kOne_GrBlendCoeff, kZero_GrBlendCoeff);
+    SkRegion::Iterator iter(fRegion);
+    context->setRenderTarget(maskTexture->asRenderTarget());
+    context->clear(NULL, 0x0);
+
+    // offset to ensure border is zero on top/left
+    SkMatrix matrix;
+    matrix.setTranslate(SK_Scalar1, SK_Scalar1);
+    context->setMatrix(matrix);
+
+    while (!iter.done()) {
+        SkRect rect = SkRect::MakeFromIRect(iter.rect());
+        context->drawRect(grPaint, rect);
+        iter.next();
+    }
+
+    GrTexture* bmpTexture = GrLockAndRefCachedBitmapTexture(context, fBitmap, NULL);
+    if (NULL == bmpTexture) {
+        return NULL;
+    }
+
+    SkMatrix bmpMatrix = localInverse;
+    bmpMatrix.postIDiv(bmpTexture->width(), bmpTexture->height());
+
+    SkMatrix maskMatrix = localInverse;
+    // compensate for the border
+    maskMatrix.postTranslate(SK_Scalar1, SK_Scalar1);
+    maskMatrix.postIDiv(maskTexture->width(), maskTexture->height());
+
+    GrEffectRef* effect = ThresholdEffect::Create(bmpTexture, bmpMatrix,
+                                                  maskTexture, maskMatrix,
+                                                  fThreshold);
+
+    GrUnlockAndUnrefCachedBitmapTexture(bmpTexture);
+
+    return effect;
+}
+
+#endif