make alpha read back of bgra/rgba work

src/gpu/gl/GrGLGpu.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGLGpu.h"
 #include "GrGLGLSL.h"
@@ skipping 1576 matching lines @@
         return false;
     }
 
     GrGLuint programID = program->programID();
     if (fHWProgramID != programID) {
         GL_CALL(UseProgram(programID));
         fHWProgramID = programID;
     }
 
     if (blendInfo.fWriteColor) {
-        this->flushBlend(blendInfo);
+        this->flushBlend(blendInfo, SkToBool(args.fDesc->header().fSwapDstRedAndAlpha));
     }
 
     SkSTArray<8, const GrTextureAccess*> textureAccesses;
     program->setData(*args.fPrimitiveProcessor, pipeline, &textureAccesses);
 
     int numTextureAccesses = textureAccesses.count();
     for (int i = 0; i < numTextureAccesses; i++) {
         this->bindTexture(i, textureAccesses[i]->getParams(),
                           static_cast<GrGLTexture*>(textureAccesses[i]->getTexture()));
     }
@@ skipping 458 matching lines @@
             this->onResolveRenderTarget(tgt);
             // we don't track the state of the READ FBO ID.
             fStats.incRenderTargetBinds();
             GL_CALL(BindFramebuffer(GR_GL_READ_FRAMEBUFFER,
                                     tgt->textureFBOID()));
             break;
         default:
             SkFAIL("Unknown resolve type");
     }
 
+    // This must be called after the RT is bound as the FBO above.
+    if (!this->glCaps().readPixelsSupported(this->glInterface(), format, type, tgt->config())) {
+        // We fail except the special case of reading back just the alpha channel of a RGBA/BGRA
+        // target.
+        if ((tgt->config() == kRGBA_8888_GrPixelConfig ||
+             tgt->config() == kBGRA_8888_GrPixelConfig) &&
+            kAlpha_8_GrPixelConfig == config) {
+            SkDebugf("");
+            SkAutoTDeleteArray<uint32_t> temp(new uint32_t[width * height * 4]);
+            if (this->onReadPixels(surface, left, top, width, height, tgt->config(), temp.get(),
+                                   width*4)) {
+                uint8_t* dst = reinterpret_cast<uint8_t*>(buffer);
+                for (int j = 0; j < height; ++j) {
+                    for (int i = 0; i < width; ++i) {
+                        dst[j*rowBytes + i] = (0xFF000000U & temp[j*width+i]) >> 24;
+                    }
+                }
+                SkDebugf("rowBytes: %d\n", rowBytes);
+                return true;
+            }            
+        }
+        return false;
+    }
+
     const GrGLIRect& glvp = tgt->getViewport();
 
     // the read rect is viewport-relative
     GrGLIRect readRect;
     readRect.setRelativeTo(glvp, left, top, width, height, tgt->origin());
 
     size_t tightRowBytes = GrBytesPerPixel(config) * width;
 
     size_t readDstRowBytes = tightRowBytes;
     void* readDst = buffer;
@@ skipping 329 matching lines @@
             }
         } else {
             if (kNo_TriState != fMSAAEnabled) {
                 GL_CALL(Disable(GR_GL_MULTISAMPLE));
                 fMSAAEnabled = kNo_TriState;
             }
         }
     }
 }
 
-void GrGLGpu::flushBlend(const GrXferProcessor::BlendInfo& blendInfo) {
+void GrGLGpu::flushBlend(const GrXferProcessor::BlendInfo& blendInfo, bool swapConstRedAndAlpha) {
     // Any optimization to disable blending should have already been applied and
     // tweaked the equation to "add" or "subtract", and the coeffs to (1, 0).
 
     GrBlendEquation equation = blendInfo.fEquation;
     GrBlendCoeff srcCoeff = blendInfo.fSrcBlend;
     GrBlendCoeff dstCoeff = blendInfo.fDstBlend;
     bool blendOff = (kAdd_GrBlendEquation == equation || kSubtract_GrBlendEquation == equation) &&
                     kOne_GrBlendCoeff == srcCoeff && kZero_GrBlendCoeff == dstCoeff;
     if (blendOff) {
         if (kNo_TriState != fHWBlendState.fEnabled) {
@@ skipping 33 matching lines @@
 
     if (fHWBlendState.fSrcCoeff != srcCoeff ||
         fHWBlendState.fDstCoeff != dstCoeff) {
         GL_CALL(BlendFunc(gXfermodeCoeff2Blend[srcCoeff],
                           gXfermodeCoeff2Blend[dstCoeff]));
         fHWBlendState.fSrcCoeff = srcCoeff;
         fHWBlendState.fDstCoeff = dstCoeff;
     }
 
     GrColor blendConst = blendInfo.fBlendConstant;
-    if ((BlendCoeffReferencesConstant(srcCoeff) ||
-         BlendCoeffReferencesConstant(dstCoeff)) &&
-        (!fHWBlendState.fConstColorValid ||
-         fHWBlendState.fConstColor != blendConst)) {
-        GrGLfloat c[4];
-        GrColorToRGBAFloat(blendConst, c);
-        GL_CALL(BlendColor(c[0], c[1], c[2], c[3]));
-        fHWBlendState.fConstColor = blendConst;
-        fHWBlendState.fConstColorValid = true;
+    if ((BlendCoeffReferencesConstant(srcCoeff) || BlendCoeffReferencesConstant(dstCoeff))) {
+        if (swapConstRedAndAlpha) {
+            blendConst = GrColorPackRGBA(GrColorUnpackA(blendConst), GrColorUnpackG(blendConst),
+                                         GrColorUnpackB(blendConst), GrColorUnpackR(blendConst));
+        }
+        if (!fHWBlendState.fConstColorValid || fHWBlendState.fConstColor != blendConst) {
+            GrGLfloat c[4];
+            GrColorToRGBAFloat(blendConst, c);
+            GL_CALL(BlendColor(c[0], c[1], c[2], c[3]));
+            fHWBlendState.fConstColor = blendConst;
+            fHWBlendState.fConstColorValid = true;
+        }
     }
 }
 
 static inline GrGLenum tile_to_gl_wrap(SkShader::TileMode tm) {
     static const GrGLenum gWrapModes[] = {
         GR_GL_CLAMP_TO_EDGE,
         GR_GL_REPEAT,
         GR_GL_MIRRORED_REPEAT
     };
     GR_STATIC_ASSERT(SkShader::kTileModeCount == SK_ARRAY_COUNT(gWrapModes));
@@ skipping 825 matching lines @@
     GrGLAttribArrayState* attribs =
         fHWGeometryState.bindArrayAndBufferToDraw(this, fWireRectArrayBuffer);
     attribs->set(this, 0, fWireRectArrayBuffer, 2, GR_GL_FLOAT, false, 2 * sizeof(GrGLfloat), 0);
     attribs->disableUnusedArrays(this, 0x1);
 
     GL_CALL(Uniform4fv(fWireRectProgram.fRectUniform, 1, edges));
     GL_CALL(Uniform4fv(fWireRectProgram.fColorUniform, 1, channels));
 
     GrXferProcessor::BlendInfo blendInfo;
     blendInfo.reset();
-    this->flushBlend(blendInfo);
+    this->flushBlend(blendInfo, false);
     this->flushColorWrite(true);
     this->flushDrawFace(GrPipelineBuilder::kBoth_DrawFace);
     this->flushHWAAState(glRT, false);
     this->disableScissor();
     GrStencilSettings stencil;
     stencil.setDisabled();
     this->flushStencil(stencil);
 
     GL_CALL(DrawArrays(GR_GL_LINE_LOOP, 0, 4));
 }
@@ skipping 50 matching lines @@
         sy1 = 1.f - sy1;
     }
 
     GL_CALL(Uniform4f(fCopyPrograms[progIdx].fPosXformUniform, dx1 - dx0, dy1 - dy0, dx0, dy0));
     GL_CALL(Uniform4f(fCopyPrograms[progIdx].fTexCoordXformUniform,
                       sx1 - sx0, sy1 - sy0, sx0, sy0));
     GL_CALL(Uniform1i(fCopyPrograms[progIdx].fTextureUniform, 0));
 
     GrXferProcessor::BlendInfo blendInfo;
     blendInfo.reset();
-    this->flushBlend(blendInfo);
+    this->flushBlend(blendInfo, false);
     this->flushColorWrite(true);
     this->flushDrawFace(GrPipelineBuilder::kBoth_DrawFace);
     this->flushHWAAState(dstRT, false);
     this->disableScissor();
     GrStencilSettings stencil;
     stencil.setDisabled();
     this->flushStencil(stencil);
 
     GL_CALL(DrawArrays(GR_GL_TRIANGLE_STRIP, 0, 4));
 }
@@ skipping 234 matching lines @@
             this->setVertexArrayID(gpu, 0);
         }
         int attrCount = gpu->glCaps().maxVertexAttributes();
         if (fDefaultVertexArrayAttribState.count() != attrCount) {
             fDefaultVertexArrayAttribState.resize(attrCount);
         }
         attribState = &fDefaultVertexArrayAttribState;
     }
     return attribState;
 }