Make A8 readback work in more cases and improve testing.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1584563002

Review URL: https://codereview.chromium.org/1584563002

src/gpu/gl/GrGLCaps.cpp

@@ -637,7 +637,22 @@ bool GrGLCaps::readPixelsSupported(const GrGLInterface* intf,
     }
 
     if (kGL_GrGLStandard == intf->fStandard) {
-        // All of our renderable configs can be converted to each other by glReadPixels in OpenGL.
+        // Some OpenGL implementations allow GL_ALPHA as a format to glReadPixels. However,
+        // the manual (https://www.opengl.org/sdk/docs/man/) says only these formats are allowed:
+        // GL_STENCIL_INDEX, GL_DEPTH_COMPONENT, GL_DEPTH_STENCIL, GL_RED, GL_GREEN, GL_BLUE,
+        // GL_RGB, GL_BGR, GL_RGBA, and GL_BGRA. We check for the subset that we would use.
+        if (readFormat != GR_GL_RED && readFormat != GR_GL_RGB && readFormat != GR_GL_RGBA &&
+            readFormat != GR_GL_BGRA) {
+            return false;
+        }
+        // There is also a set of allowed types, but all the types we use are in the set:
+        // GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT,
+        // GL_HALF_FLOAT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
+        // GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4,
+        // GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
+        // GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,GL_UNSIGNED_INT_10_10_10_2,
+        // GL_UNSIGNED_INT_2_10_10_10_REV, GL_UNSIGNED_INT_24_8, GL_UNSIGNED_INT_10F_11F_11F_REV,
+        // GL_UNSIGNED_INT_5_9_9_9_REV, or GL_FLOAT_32_UNSIGNED_INT_24_8_REV.
         return true;
     }
 
@@ -1051,6 +1066,17 @@ bool GrGLCaps::getExternalFormat(GrPixelConfig surfaceConfig, GrPixelConfig memo
     *externalFormat = fConfigTable[memoryConfig].fFormats.fExternalFormat[usage];
     *externalType = fConfigTable[memoryConfig].fFormats.fExternalType;
 
+    // When GL_RED is supported as a texture format, our alpha-only textures are stored using
+    // GL_RED and we swizzle in order to map all components to 'r'. However, in this case the
+    // surface is not alpha-only and we want alpha to really mean the alpha component of the
+    // texture, not the red component.
+    if (memoryIsAlphaOnly && !surfaceIsAlphaOnly) {
+        if (this->textureRedSupport()) {
+            SkASSERT(GR_GL_RED == *externalFormat);
+            *externalFormat = GR_GL_ALPHA;
+        }
+    }
+
     return true;
 }
 

src/gpu/gl/GrGLGpu.cpp

@@ -1951,7 +1951,8 @@ bool GrGLGpu::onGetReadPixelsInfo(GrSurface* srcSurface, int width, int height,
                                   ReadPixelTempDrawInfo* tempDrawInfo) {
     // This subclass can only read pixels from a render target. We could use glTexSubImage2D on
     // GL versions that support it but we don't today.
-    if (!srcSurface->asRenderTarget()) {
+    GrRenderTarget* srcAsRT = srcSurface->asRenderTarget();
+    if (!srcAsRT) {
         ElevateDrawPreference(drawPreference, kRequireDraw_DrawPreference);
     }
 
@@ -1992,13 +1993,20 @@ bool GrGLGpu::onGetReadPixelsInfo(GrSurface* srcSurface, int width, int height,
         tempDrawInfo->fTempSurfaceDesc.fConfig = kRGBA_8888_GrPixelConfig;
         tempDrawInfo->fSwapRAndB = true;
         ElevateDrawPreference(drawPreference, kRequireDraw_DrawPreference);
+    } else if (kRequireDraw_DrawPreference == *drawPreference &&
+               readConfig == kAlpha_8_GrPixelConfig &&
+               !this->caps()->isConfigRenderable(kAlpha_8_GrPixelConfig, false)) {
+        // On some GLs there is no renderable single channel format. In that case we fall back
+        // to rendering to a RGBA and then will extract the alpha from that.
+        if (this->caps()->isConfigRenderable(kRGBA_8888_GrPixelConfig, false)) {
+            tempDrawInfo->fTempSurfaceDesc.fConfig = kRGBA_8888_GrPixelConfig;
+        } else {
+            return false;
+        }
     }
 
-    GrRenderTarget* srcAsRT = srcSurface->asRenderTarget();
+    if (srcAsRT && read_pixels_pays_for_y_flip(srcAsRT, this->glCaps(), width, height, readConfig,
-    if (!srcAsRT) {
+                                               rowBytes)) {
-        ElevateDrawPreference(drawPreference, kRequireDraw_DrawPreference);
-    } else if (read_pixels_pays_for_y_flip(srcAsRT, this->glCaps(), width, height, readConfig,
-                                           rowBytes)) {
         ElevateDrawPreference(drawPreference, kGpuPrefersDraw_DrawPreference);
     }
 
@@ -2049,6 +2057,28 @@ bool GrGLGpu::onReadPixels(GrSurface* surface,
             SkFAIL("Unknown resolve type");
     }
 
+    // We have a special case fallback for reading alpha from a RGBA/BGRA surface. We will read
+    // back all the channels as RGBA and then extract A.
+    // This must be called after the RT is bound as the FBO above.
+    if (!this->glCaps().readPixelsSupported(this->glInterface(), config, tgt->config())) {
+        if ((tgt->config() == kRGBA_8888_GrPixelConfig ||
+             tgt->config() == kBGRA_8888_GrPixelConfig) &&
+            kAlpha_8_GrPixelConfig == config) {
+            SkAutoTDeleteArray<uint32_t> temp(new uint32_t[width * height * 4]);
+            if (this->onReadPixels(surface, left, top, width, height, kRGBA_8888_GrPixelConfig,
+                                   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;
+                    }
+                }
+                return true;
+            }
+        }
+        return false;
+    }
+
     const GrGLIRect& glvp = tgt->getViewport();
 
     // the read rect is viewport-relative

tests/ReadWriteAlphaTest.cpp

@@ -8,7 +8,7 @@
 #include "Test.h"
 
 // This test is specific to the GPU backend.
-#if SK_SUPPORT_GPU && !defined(SK_BUILD_FOR_ANDROID)
+#if SK_SUPPORT_GPU
 
 #include "GrContext.h"
 #include "SkGpuDevice.h"
@@ -18,88 +18,147 @@ static const int X_SIZE = 13;
 static const int Y_SIZE = 13;
 
 DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
-    unsigned char textureData[X_SIZE][Y_SIZE];
+    unsigned char alphaData[X_SIZE][Y_SIZE];
 
-    memset(textureData, 0, X_SIZE * Y_SIZE);
+    memset(alphaData, 0, X_SIZE * Y_SIZE);
-
-    GrSurfaceDesc desc;
-
-    // let Skia know we will be using this texture as a render target
-    desc.fFlags     = kRenderTarget_GrSurfaceFlag;
-    // it is a single channel texture
-    desc.fConfig    = kAlpha_8_GrPixelConfig;
-    desc.fWidth     = X_SIZE;
-    desc.fHeight    = Y_SIZE;
-
-    // We are initializing the texture with zeros here
-    GrTexture* texture = context->textureProvider()->createTexture(desc, false, textureData, 0);
-    if (!texture) {
-        return;
-    }
-
-    SkAutoTUnref<GrTexture> au(texture);
-
-    // create a distinctive texture
-    for (int y = 0; y < Y_SIZE; ++y) {
-        for (int x = 0; x < X_SIZE; ++x) {
-            textureData[x][y] = x*Y_SIZE+y;
-        }
-    }
-
-    // upload the texture
-    texture->writePixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
-                         textureData, 0);
 
+    bool match;
     unsigned char readback[X_SIZE][Y_SIZE];
 
-    // clear readback to something non-zero so we can detect readback failures
+    for (int rt = 0; rt < 2; ++rt) {
-    memset(readback, 0x1, X_SIZE * Y_SIZE);
+        GrSurfaceDesc desc;
+        // let Skia know we will be using this texture as a render target
+        desc.fFlags     = rt ? kRenderTarget_GrSurfaceFlag : kNone_GrSurfaceFlags;
+        // it is a single channel texture
+        desc.fConfig    = kAlpha_8_GrPixelConfig;
+        desc.fWidth     = X_SIZE;
+        desc.fHeight    = Y_SIZE;
 
-    // read the texture back
+        // We are initializing the texture with zeros here
-    texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+        SkAutoTUnref<GrTexture> texture(
-                        readback, 0);
+            context->textureProvider()->createTexture(desc, false, alphaData, 0));
+        if (!texture) {
+            if (!rt) {
+                ERRORF(reporter, "Could not create alpha texture.");
+            }
+            continue;
+        }
 
-    // make sure the original & read back versions match
+        // create a distinctive texture
-    bool match = true;
+        for (int y = 0; y < Y_SIZE; ++y) {
+            for (int x = 0; x < X_SIZE; ++x) {
+                alphaData[x][y] = x*Y_SIZE+y;
+            }
+        }
 
-    for (int y = 0; y < Y_SIZE; ++y) {
+        // upload the texture
-        for (int x = 0; x < X_SIZE; ++x) {
+        texture->writePixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
-            if (textureData[x][y] != readback[x][y]) {
+                             alphaData, 0);
-                match = false;
+
+        // clear readback to something non-zero so we can detect readback failures
+        memset(readback, 0x1, X_SIZE * Y_SIZE);
+
+        // read the texture back
+        texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+                            readback, 0);
+
+        // make sure the original & read back versions match
+        match = true;
+
+        for (int y = 0; y < Y_SIZE && match; ++y) {
+            for (int x = 0; x < X_SIZE && match; ++x) {
+                if (alphaData[x][y] != readback[x][y]) {
+                    SkDebugf("Failed alpha readback. Expected: 0x%02x, "
+                             "Got: 0x%02x at (%d,%d), rt: %d", alphaData[x][y], readback[x][y], x,
+                             y, rt);
+                    match = false;
+                }
+            }
+        }
+
+        // Now try writing on the single channel texture (if we could create as a RT).
+        if (texture->asRenderTarget()) {
+            SkSurfaceProps props(SkSurfaceProps::kLegacyFontHost_InitType);
+            SkAutoTUnref<SkBaseDevice> device(SkGpuDevice::Create(
+                texture->asRenderTarget(), &props, SkGpuDevice::kUninit_InitContents));
+            SkCanvas canvas(device);
+
+            SkPaint paint;
+
+            const SkRect rect = SkRect::MakeLTRB(-10, -10, X_SIZE + 10, Y_SIZE + 10);
+
+            paint.setColor(SK_ColorWHITE);
+
+            canvas.drawRect(rect, paint);
+
+            texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig, readback, 0);
+
+            match = true;
+
+            for (int y = 0; y < Y_SIZE && match; ++y) {
+                for (int x = 0; x < X_SIZE && match; ++x) {
+                    if (0xFF != readback[x][y]) {
+                        ERRORF(reporter,
+                               "Failed alpha readback after clear. Expected: 0xFF, Got: 0x%02x at "
+                               "(%d,%d)", readback[x][y], x, y);
+                        match = false;
+                    }
+                }
             }
         }
     }
 
-    REPORTER_ASSERT(reporter, match);
+    // Attempt to read back just alpha from a RGBA/BGRA texture. Once with a texture-only src and
+    // once with a render target.
+    for (int cfg = 0; cfg < 2; ++cfg) {
+        for (int rt = 0; rt < 2; ++rt) {
+            GrSurfaceDesc desc;
+            desc.fFlags     = rt ? kRenderTarget_GrSurfaceFlag : kNone_GrSurfaceFlags;
+            desc.fConfig    = cfg ? kBGRA_8888_GrPixelConfig : kRGBA_8888_GrPixelConfig;
+            desc.fWidth     = X_SIZE;
+            desc.fHeight    = Y_SIZE;
 
-    // Now try writing on the single channel texture
+            uint32_t rgbaData[X_SIZE][Y_SIZE];
-    SkSurfaceProps props(SkSurfaceProps::kLegacyFontHost_InitType);
+            // Make the alpha channel of the rgba texture come from alphaData.
-    SkAutoTUnref<SkBaseDevice> device(SkGpuDevice::Create(texture->asRenderTarget(), &props,
+            for (int y = 0; y < Y_SIZE; ++y) {
-                                                          SkGpuDevice::kUninit_InitContents));
+                for (int x = 0; x < X_SIZE; ++x) {
-    SkCanvas canvas(device);
+                    rgbaData[x][y] = GrColorPackRGBA(6, 7, 8, alphaData[x][y]);
+                }
+            }
+            SkAutoTUnref<GrTexture> texture(
+                context->textureProvider()->createTexture(desc, false, rgbaData, 0));
+            if (!texture) {
+                // We always expect to be able to create a RGBA texture
+                if (!rt  && kRGBA_8888_GrPixelConfig == desc.fConfig) {
+                    ERRORF(reporter, "Failed to create RGBA texture.");
+                }
+                continue;
+            }
 
-    SkPaint paint;
+            // clear readback to something non-zero so we can detect readback failures
+            memset(readback, 0x0, X_SIZE * Y_SIZE);
 
-    const SkRect rect = SkRect::MakeLTRB(-10, -10, X_SIZE + 10, Y_SIZE + 10);
+            // read the texture back
+            texture->readPixels(0, 0, desc.fWidth, desc.fHeight, kAlpha_8_GrPixelConfig, readback,
+                                0);
 
-    paint.setColor(SK_ColorWHITE);
+            match = true;
 
-    canvas.drawRect(rect, paint);
+            for (int y = 0; y < Y_SIZE && match; ++y) {
-
+                for (int x = 0; x < X_SIZE && match; ++x) {
-    texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+                    if (alphaData[x][y] != readback[x][y]) {
-                        readback, 0);
+                        texture->readPixels(0, 0, desc.fWidth, desc.fHeight,
-
+                                            kAlpha_8_GrPixelConfig, readback, 0);
-    match = true;
+                        ERRORF(reporter,
-
+                               "Failed alpha readback from cfg %d. Expected: 0x%02x, Got: 0x%02x at "
-    for (int y = 0; y < Y_SIZE; ++y) {
+                               "(%d,%d), rt:%d", desc.fConfig, alphaData[x][y], readback[x][y], x,
-        for (int x = 0; x < X_SIZE; ++x) {
+                               y, rt);
-            if (0xFF != readback[x][y]) {
+                        match = false;
-                match = false;
+                    }
+                }
             }
         }
     }
-
-    REPORTER_ASSERT(reporter, match);
 }
 
 #endif