Add AlphaThreshold filter.

This is based on the Bitmap Alpha Threshold filter, and will be used by Chromium
to implement the window shape API.

R=bsalomon@chromium.org, wez@chromium.org, bsalomon@google.com, reed@google.com

Author: zork@chromium.org

Review URL: https://codereview.chromium.org/115633002

git-svn-id: http://skia.googlecode.com/svn/trunk@12935 2bbb7eff-a529-9590-31e7-b0007b416f81

gm/imagealphathreshold.cpp

@@ -0,0 +1,82 @@
+/*
+ * 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 "gm.h"
+#include "SkAlphaThresholdFilter.h"
+#include "SkRandom.h"
+
+#define WIDTH 500
+#define HEIGHT 500
+
+namespace skiagm {
+
+class ImageAlphaThresholdGM : public GM {
+public:
+    ImageAlphaThresholdGM() {
+        this->setBGColor(0xFFFFFFFF);
+    }
+
+protected:
+    virtual uint32_t onGetFlags() const SK_OVERRIDE {
+        return this->INHERITED::onGetFlags() | GM::kSkipTiled_Flag;
+    }
+
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("imagealphathreshold");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return make_isize(WIDTH, HEIGHT);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        SkIRect rects[2];
+        rects[0] = SkIRect::MakeXYWH(0, 150, WIDTH, HEIGHT - 300);
+        rects[1] = SkIRect::MakeXYWH(150, 0, WIDTH - 300, HEIGHT);
+        SkRegion region;
+        region.setRects(rects, 2);
+
+        SkMatrix matrix;
+        matrix.reset();
+        matrix.setTranslate(WIDTH * .1f, HEIGHT * .1f);
+        matrix.postScale(.8, .8);
+
+        canvas->concat(matrix);
+
+        SkPaint paint;
+        paint.setImageFilter(
+            SkAlphaThresholdFilter::Create(region, 0.2f, 0.7f))->unref();
+        canvas->saveLayer(NULL, &paint);
+        paint.setAntiAlias(true);
+
+        SkPaint rect_paint;
+        rect_paint.setColor(0xFF0000FF);
+        canvas->drawRect(SkRect::MakeXYWH(0, 0, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        rect_paint.setColor(0xBFFF0000);
+        canvas->drawRect(SkRect::MakeXYWH(WIDTH / 2, 0, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        rect_paint.setColor(0x3F00FF00);
+        canvas->drawRect(SkRect::MakeXYWH(0, HEIGHT / 2, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        rect_paint.setColor(0x00000000);
+        canvas->drawRect(SkRect::MakeXYWH(WIDTH / 2, HEIGHT / 2, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+
+        canvas->restore();
+    }
+
+private:
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* MyFactory(void*) { return new ImageAlphaThresholdGM; }
+static GMRegistry reg(MyFactory);
+
+}

gyp/effects.gypi

@@ -9,6 +9,7 @@
   'sources': [
     '<(skia_src_path)/effects/Sk1DPathEffect.cpp',
     '<(skia_src_path)/effects/Sk2DPathEffect.cpp',
+    '<(skia_src_path)/effects/SkAlphaThresholdFilter.cpp',
     '<(skia_src_path)/effects/SkArithmeticMode.cpp',
     '<(skia_src_path)/effects/SkAvoidXfermode.cpp',
     '<(skia_src_path)/effects/SkBicubicImageFilter.cpp',
@@ -80,6 +81,7 @@
     '<(skia_include_path)/effects/Sk1DPathEffect.h',
     '<(skia_include_path)/effects/Sk2DPathEffect.h',
     '<(skia_include_path)/effects/SkXfermodeImageFilter.h',
+    '<(skia_include_path)/effects/SkAlphaThresholdFilter.h',
     '<(skia_include_path)/effects/SkArithmeticMode.h',
     '<(skia_include_path)/effects/SkAvoidXfermode.h',
     '<(skia_include_path)/effects/SkBitmapSource.h',

gyp/gmslides.gypi

@@ -73,6 +73,7 @@
     '../gm/hairlines.cpp',
     '../gm/hairmodes.cpp',
     '../gm/hittestpath.cpp',
+    '../gm/imagealphathreshold.cpp',
     '../gm/imageblur.cpp',
     '../gm/imagemagnifier.cpp',
     '../gm/inversepaths.cpp',

gyp/public_headers.gypi

@@ -72,6 +72,7 @@
       'effects/SkMorphologyImageFilter.h',
       'effects/Sk2DPathEffect.h',
       'effects/SkXfermodeImageFilter.h',
+      'effects/SkAlphaThresholdFilter.h',
       'effects/SkArithmeticMode.h',
       'effects/SkMergeImageFilter.h',
       'effects/SkPerlinNoiseShader.h',

include/effects/SkAlphaThresholdFilter.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkAlphaThresholdFilter_DEFINED
+#define SkAlphaThresholdFilter_DEFINED
+
+#include "SkRegion.h"
+#include "SkImageFilter.h"
+
+class SK_API SkAlphaThresholdFilter {
+public:
+    /**
+     * Creates an image filter that samples a region. If the sample is inside the
+     * region the alpha of the image is boosted up to a threshold value. If it is
+     * outside the region then the alpha is decreased to the threshold value.
+     * The 0,0 point of the region corresponds to the upper left corner of the
+     * source image.
+     */
+    static SkImageFilter* Create(const SkRegion& region, SkScalar innerThreshold, SkScalar outerThreshold);
+};
+
+#endif

src/effects/SkAlphaThresholdFilter.cpp

@@ -0,0 +1,367 @@
+/*
+ * 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 "SkAlphaThresholdFilter.h"
+#include "SkBitmap.h"
+#include "SkFlattenableBuffers.h"
+#include "SkRegion.h"
+
+class SK_API SkAlphaThresholdFilterImpl : public SkImageFilter {
+public:
+    SkAlphaThresholdFilterImpl(const SkRegion& region, SkScalar innerThreshold, SkScalar outerThreshold);
+
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkAlphaThresholdFilterImpl)
+
+protected:
+    explicit SkAlphaThresholdFilterImpl(SkFlattenableReadBuffer& buffer);
+    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
+
+    virtual bool onFilterImage(Proxy*, const SkBitmap& src, const SkMatrix&,
+                               SkBitmap* result, SkIPoint* offset) SK_OVERRIDE;
+#if SK_SUPPORT_GPU
+    virtual bool asNewEffect(GrEffectRef** effect, GrTexture* texture,
+                             const SkMatrix& matrix, const SkIRect& bounds) const SK_OVERRIDE;
+#endif
+
+private:
+    SkRegion fRegion;
+    SkScalar fInnerThreshold;
+    SkScalar fOuterThreshold;
+    typedef SkImageFilter INHERITED;
+};
+
+SkImageFilter* SkAlphaThresholdFilter::Create(const SkRegion& region,
+                                              SkScalar innerThreshold,
+                                              SkScalar outerThreshold) {
+    return SkNEW_ARGS(SkAlphaThresholdFilterImpl, (region, innerThreshold, outerThreshold));
+}
+
+#if SK_SUPPORT_GPU
+#include "GrContext.h"
+#include "GrCoordTransform.h"
+#include "GrEffect.h"
+#include "gl/GrGLEffect.h"
+#include "GrTBackendEffectFactory.h"
+#include "GrTextureAccess.h"
+
+#include "SkGr.h"
+
+class GrGLAlphaThresholdEffect;
+
+class AlphaThresholdEffect : public GrEffect {
+
+public:
+    static GrEffectRef* Create(GrTexture* texture,
+                               GrTexture* maskTexture,
+                               float innerThreshold,
+                               float outerThreshold) {
+        AutoEffectUnref effect(SkNEW_ARGS(AlphaThresholdEffect, (texture,
+                                                                 maskTexture,
+                                                                 innerThreshold,
+                                                                 outerThreshold)));
+        return CreateEffectRef(effect);
+    }
+
+    virtual ~AlphaThresholdEffect() {};
+
+    static const char* Name() { return "Alpha Threshold"; }
+
+    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE;
+    virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const SK_OVERRIDE;
+
+    float innerThreshold() const { return fInnerThreshold; }
+    float outerThreshold() const { return fOuterThreshold; }
+
+    typedef GrGLAlphaThresholdEffect GLEffect;
+
+private:
+    AlphaThresholdEffect(GrTexture* texture,
+                         GrTexture* maskTexture,
+                         float innerThreshold,
+                         float outerThreshold)
+        : fInnerThreshold(innerThreshold)
+        , fOuterThreshold(outerThreshold)
+        , fImageCoordTransform(kLocal_GrCoordSet, MakeDivByTextureWHMatrix(texture), texture)
+        , fImageTextureAccess(texture)
+        , fMaskCoordTransform(kLocal_GrCoordSet, MakeDivByTextureWHMatrix(maskTexture), maskTexture)
+        , fMaskTextureAccess(maskTexture) {
+        this->addCoordTransform(&fImageCoordTransform);
+        this->addTextureAccess(&fImageTextureAccess);
+        this->addCoordTransform(&fMaskCoordTransform);
+        this->addTextureAccess(&fMaskTextureAccess);
+    }
+
+    virtual bool onIsEqual(const GrEffect&) const SK_OVERRIDE;
+
+    GR_DECLARE_EFFECT_TEST;
+
+    float fInnerThreshold;
+    float fOuterThreshold;
+    GrCoordTransform fImageCoordTransform;
+    GrTextureAccess  fImageTextureAccess;
+    GrCoordTransform fMaskCoordTransform;
+    GrTextureAccess  fMaskTextureAccess;
+
+    typedef GrEffect INHERITED;
+};
+
+class GrGLAlphaThresholdEffect : public GrGLEffect {
+public:
+    GrGLAlphaThresholdEffect(const GrBackendEffectFactory&, const GrDrawEffect&);
+
+    virtual void emitCode(GrGLShaderBuilder*,
+                          const GrDrawEffect&,
+                          EffectKey,
+                          const char* outputColor,
+                          const char* inputColor,
+                          const TransformedCoordsArray&,
+                          const TextureSamplerArray&) SK_OVERRIDE;
+
+    virtual void setData(const GrGLUniformManager&, const GrDrawEffect&) SK_OVERRIDE;
+
+private:
+
+    GrGLUniformManager::UniformHandle       fInnerThresholdVar;
+    GrGLUniformManager::UniformHandle       fOuterThresholdVar;
+
+    typedef GrGLEffect INHERITED;
+};
+
+GrGLAlphaThresholdEffect::GrGLAlphaThresholdEffect(const GrBackendEffectFactory& factory, const GrDrawEffect&)
+    : INHERITED(factory) {
+}
+
+void GrGLAlphaThresholdEffect::emitCode(GrGLShaderBuilder* builder,
+                                        const GrDrawEffect&,
+                                        EffectKey key,
+                                        const char* outputColor,
+                                        const char* inputColor,
+                                        const TransformedCoordsArray& coords,
+                                        const TextureSamplerArray& samplers) {
+    SkString coords2D = builder->ensureFSCoords2D(coords, 0);
+    SkString maskCoords2D = builder->ensureFSCoords2D(coords, 1);
+    fInnerThresholdVar = builder->addUniform(
+        GrGLShaderBuilder::kFragment_Visibility,
+        kFloat_GrSLType, "inner_threshold");
+    fOuterThresholdVar = builder->addUniform(
+        GrGLShaderBuilder::kFragment_Visibility,
+        kFloat_GrSLType, "outer_threshold");
+
+    builder->fsCodeAppendf("\t\tvec2 coord = %s;\n", coords2D.c_str());
+    builder->fsCodeAppendf("\t\tvec2 mask_coord = %s;\n", maskCoords2D.c_str());
+    builder->fsCodeAppend("\t\tvec4 input_color = ");
+    builder->fsAppendTextureLookup(samplers[0], "coord");
+    builder->fsCodeAppend(";\n");
+    builder->fsCodeAppend("\t\tvec4 mask_color = ");
+    builder->fsAppendTextureLookup(samplers[1], "mask_coord");
+    builder->fsCodeAppend(";\n");
+
+    builder->fsCodeAppendf("\t\tfloat inner_thresh = %s;\n",
+                           builder->getUniformCStr(fInnerThresholdVar));
+    builder->fsCodeAppendf("\t\tfloat outer_thresh = %s;\n",
+                           builder->getUniformCStr(fOuterThresholdVar));
+    builder->fsCodeAppend("\t\tfloat mask = mask_color.a;\n");
+
+    builder->fsCodeAppend("vec4 color = input_color;\n");
+    builder->fsCodeAppend("\t\tif (mask < 0.5) {\n"
+                          "\t\t\tif (color.a > outer_thresh) {\n"
+                          "\t\t\t\tfloat scale = outer_thresh / color.a;\n"
+                          "\t\t\t\tcolor.rgb *= scale;\n"
+                          "\t\t\t\tcolor.a = outer_thresh;\n"
+                          "\t\t\t}\n"
+                          "\t\t} else if (color.a < inner_thresh) {\n"
+                          "\t\t\tfloat scale = inner_thresh / max(0.001, color.a);\n"
+                          "\t\t\tcolor.rgb *= scale;\n"
+                          "\t\t\tcolor.a = inner_thresh;\n"
+                          "\t\t}\n");
+
+    builder->fsCodeAppendf("%s = %s;\n", outputColor,
+                           (GrGLSLExpr4(inputColor) * GrGLSLExpr4("color")).c_str());
+}
+
+void GrGLAlphaThresholdEffect::setData(const GrGLUniformManager& uman,
+                                  const GrDrawEffect& drawEffect) {
+    const AlphaThresholdEffect& alpha_threshold =
+        drawEffect.castEffect<AlphaThresholdEffect>();
+    uman.set1f(fInnerThresholdVar, alpha_threshold.innerThreshold());
+    uman.set1f(fOuterThresholdVar, alpha_threshold.outerThreshold());
+}
+
+/////////////////////////////////////////////////////////////////////
+
+GR_DEFINE_EFFECT_TEST(AlphaThresholdEffect);
+
+GrEffectRef* AlphaThresholdEffect::TestCreate(SkRandom* random,
+                                              GrContext* context,
+                                              const GrDrawTargetCaps&,
+                                              GrTexture** textures) {
+    GrTexture* bmpTex = textures[GrEffectUnitTest::kSkiaPMTextureIdx];
+    GrTexture* maskTex = textures[GrEffectUnitTest::kAlphaTextureIdx];
+    float inner_thresh = random->nextUScalar1();
+    float outer_thresh = random->nextUScalar1();
+    return AlphaThresholdEffect::Create(bmpTex, maskTex, inner_thresh, outer_thresh);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+const GrBackendEffectFactory& AlphaThresholdEffect::getFactory() const {
+    return GrTBackendEffectFactory<AlphaThresholdEffect>::getInstance();
+}
+
+bool AlphaThresholdEffect::onIsEqual(const GrEffect& sBase) const {
+    const AlphaThresholdEffect& s = CastEffect<AlphaThresholdEffect>(sBase);
+    return (this->texture(0) == s.texture(0) &&
+            this->fInnerThreshold == s.fInnerThreshold &&
+            this->fOuterThreshold == s.fOuterThreshold);
+}
+
+void AlphaThresholdEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
+    if ((*validFlags & kA_GrColorComponentFlag) && 0xFF == GrColorUnpackA(*color) &&
+        GrPixelConfigIsOpaque(this->texture(0)->config())) {
+        *validFlags = kA_GrColorComponentFlag;
+    } else {
+        *validFlags = 0;
+    }
+}
+
+#endif
+
+SkAlphaThresholdFilterImpl::SkAlphaThresholdFilterImpl(SkFlattenableReadBuffer& buffer)
+  : INHERITED(1, buffer) {
+    fInnerThreshold = buffer.readScalar();
+    fOuterThreshold = buffer.readScalar();
+    buffer.readRegion(&fRegion);
+}
+
+SkAlphaThresholdFilterImpl::SkAlphaThresholdFilterImpl(const SkRegion& region,
+                                                       SkScalar innerThreshold,
+                                                       SkScalar outerThreshold)
+    : INHERITED(0)
+    , fRegion(region)
+    , fInnerThreshold(innerThreshold)
+    , fOuterThreshold(outerThreshold) {
+}
+
+#if SK_SUPPORT_GPU
+bool SkAlphaThresholdFilterImpl::asNewEffect(GrEffectRef** effect, GrTexture* texture,
+                                             const SkMatrix& in_matrix, const SkIRect&) const {
+    if (effect) {
+        GrContext* context = texture->getContext();
+        GrTextureDesc maskDesc;
+        if (context->isConfigRenderable(kAlpha_8_GrPixelConfig, false)) {
+            maskDesc.fConfig = kAlpha_8_GrPixelConfig;
+        } else {
+            maskDesc.fConfig = kRGBA_8888_GrPixelConfig;
+        }
+        maskDesc.fFlags = kRenderTarget_GrTextureFlagBit | kNoStencil_GrTextureFlagBit;
+        // Add one pixel of border to ensure that clamp mode will be all zeros
+        // the outside.
+        maskDesc.fWidth = texture->width();
+        maskDesc.fHeight = texture->height();
+        GrAutoScratchTexture ast(context, maskDesc, GrContext::kApprox_ScratchTexMatch);
+        GrTexture*  maskTexture = ast.texture();
+        if (NULL == maskTexture) {
+            return false;
+        }
+
+        {
+            GrContext::AutoRenderTarget art(context, ast.texture()->asRenderTarget());
+            GrPaint grPaint;
+            grPaint.setBlendFunc(kOne_GrBlendCoeff, kZero_GrBlendCoeff);
+            SkRegion::Iterator iter(fRegion);
+            context->clear(NULL, 0x0, true);
+
+            SkMatrix old_matrix = context->getMatrix();
+            context->setMatrix(in_matrix);
+
+            while (!iter.done()) {
+                SkRect rect = SkRect::Make(iter.rect());
+                context->drawRect(grPaint, rect);
+                iter.next();
+            }
+            context->setMatrix(old_matrix);
+        }
+
+        *effect = AlphaThresholdEffect::Create(texture,
+                                               maskTexture,
+                                               fInnerThreshold,
+                                               fOuterThreshold);
+    }
+    return true;
+}
+#endif
+
+void SkAlphaThresholdFilterImpl::flatten(SkFlattenableWriteBuffer& buffer) const {
+    this->INHERITED::flatten(buffer);
+    buffer.writeScalar(fInnerThreshold);
+    buffer.writeScalar(fOuterThreshold);
+    buffer.writeRegion(fRegion);
+}
+
+bool SkAlphaThresholdFilterImpl::onFilterImage(Proxy*, const SkBitmap& src,
+                                               const SkMatrix& matrix, SkBitmap* dst,
+                                               SkIPoint* offset) {
+    SkASSERT(src.config() == SkBitmap::kARGB_8888_Config);
+
+    if (src.config() != SkBitmap::kARGB_8888_Config) {
+      return false;
+    }
+
+    SkMatrix localInverse;
+    if (!matrix.invert(&localInverse)) {
+        return NULL;
+    }
+
+    SkAutoLockPixels alp(src);
+    SkASSERT(src.getPixels());
+    if (!src.getPixels() || src.width() <= 0 || src.height() <= 0) {
+      return false;
+    }
+
+    dst->setConfig(src.config(), src.width(), src.height());
+    dst->allocPixels();
+    if (!dst->getPixels()) {
+        return false;
+    }
+
+    U8CPU innerThreshold = fInnerThreshold * 0xFF;
+    U8CPU outerThreshold = fOuterThreshold * 0xFF;
+    SkColor* sptr = src.getAddr32(0, 0);
+    SkColor* dptr = dst->getAddr32(0, 0);
+    int width = src.width(), height = src.height();
+    for (int y = 0; y < height; ++y) {
+        for (int x = 0; x < width; ++x) {
+            const SkColor& source = sptr[y * width + x];
+            SkColor output_color(source);
+            SkPoint position;
+            localInverse.mapXY(x, y, &position);
+            if (fRegion.contains(position.x(), position.y())) {
+                if (SkColorGetA(source) < innerThreshold) {
+                    U8CPU alpha = SkColorGetA(source);
+                    if (alpha == 0)
+                        alpha = 1;
+                    float scale = (float)innerThreshold / alpha;
+                    output_color = SkColorSetARGB(innerThreshold,
+                                                  SkColorGetR(source) * scale,
+                                                  SkColorGetG(source) * scale,
+                                                  SkColorGetB(source) * scale);
+                }
+            } else {
+                if (SkColorGetA(source) > outerThreshold) {
+                    float scale = (float)outerThreshold / SkColorGetA(source);
+                    output_color = SkColorSetARGB(outerThreshold,
+                                                  SkColorGetR(source) * scale,
+                                                  SkColorGetG(source) * scale,
+                                                  SkColorGetB(source) * scale);
+                }
+            }
+            dptr[y * dst->width() + x] = output_color;
+        }
+    }
+
+    return true;
+}

tests/GLProgramsTest.cpp

@@ -251,6 +251,7 @@ DEFINE_GPUTESTCLASS("GLPrograms", GLProgramsTestClass, GLProgramsTest)
 // in the unit that could pass pointers to functions from the unit out to other translation units!
 // We force some of the effects that would otherwise be discarded to link here.
 
+#include "SkAlphaThresholdFilter.h"
 #include "SkLightingImageFilter.h"
 #include "SkMagnifierImageFilter.h"
 #include "SkColorMatrixFilter.h"
@@ -259,6 +260,7 @@ void forceLinking();
 
 void forceLinking() {
     SkLightingImageFilter::CreateDistantLitDiffuse(SkPoint3(0,0,0), 0, 0, 0);
+    SkAlphaThresholdFilter::Create(SkRegion(), .5, .5);
     SkMagnifierImageFilter mag(SkRect::MakeWH(SK_Scalar1, SK_Scalar1), SK_Scalar1);
     GrConfigConversionEffect::Create(NULL,
                                      false,