Make A8 readbacks work from non-A8 surfaces

tests/ReadWriteAlphaTest.cpp

Index: tests/ReadWriteAlphaTest.cpp
diff --git a/tests/ReadWriteAlphaTest.cpp b/tests/ReadWriteAlphaTest.cpp
index 1ee6b09a995d29ce5514dd571a315ceec1332f9b..0a8441797c2a4bfd657f2209294cd8082efbb4e2 100644
--- a/tests/ReadWriteAlphaTest.cpp
+++ b/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 +18,153 @@ 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);
+    bool match;
+    unsigned char readback[X_SIZE][Y_SIZE];
 
-    // 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;
+    for (int rt = 0; rt < 2; ++rt) {
+        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;
+
+        // We are initializing the texture with zeros here
+        SkAutoTUnref<GrTexture> texture(
+            context->textureProvider()->createTexture(desc, false, alphaData, 0));
+        if (!texture) {
+            if (!rt) {
+                ERRORF(reporter, "Could not create alpha texture.");
+            }
+            continue;
         }
-    }
 
-    // upload the texture
-    texture->writePixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
-                         textureData, 0);
+        // create a distinctive texture
+        for (int y = 0; y < Y_SIZE; ++y) {
+            for (int x = 0; x < X_SIZE; ++x) {
+                alphaData[x][y] = y*X_SIZE+x;
+            }
+        }
 
-    unsigned char readback[X_SIZE][Y_SIZE];
+        // upload the texture
+        texture->writePixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+                             alphaData, 0);
 
-    // clear readback to something non-zero so we can detect readback failures
-    memset(readback, 0x1, X_SIZE * Y_SIZE);
+        // 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);
+        // read the texture back
+        texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+                            readback, 0);
 
-    // make sure the original & read back versions match
-    bool match = true;
+        // make sure the original & read back versions match
+        match = true;
 
-    for (int y = 0; y < Y_SIZE; ++y) {
-        for (int x = 0; x < X_SIZE; ++x) {
-            if (textureData[x][y] != readback[x][y]) {
-                match = false;
+        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;
+                }
             }
         }
-    }
-
-    REPORTER_ASSERT(reporter, match);
 
-    // Now try writing on the single channel texture
-    SkSurfaceProps props(SkSurfaceProps::kLegacyFontHost_InitType);
-    SkAutoTUnref<SkBaseDevice> device(SkGpuDevice::Create(texture->asRenderTarget(), &props,
-                                                          SkGpuDevice::kUninit_InitContents));
-    SkCanvas canvas(device);
+        // 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;
+            SkPaint paint;
 
-    const SkRect rect = SkRect::MakeLTRB(-10, -10, X_SIZE + 10, Y_SIZE + 10);
+            const SkRect rect = SkRect::MakeLTRB(-10, -10, X_SIZE + 10, Y_SIZE + 10);
 
-    paint.setColor(SK_ColorWHITE);
+            paint.setColor(SK_ColorWHITE);
 
-    canvas.drawRect(rect, paint);
+            canvas.drawRect(rect, paint);
 
-    texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
-                        readback, 0);
+            texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig, readback, 0);
 
-    match = true;
+            match = true;
 
-    for (int y = 0; y < Y_SIZE; ++y) {
-        for (int x = 0; x < X_SIZE; ++x) {
-            if (0xFF != readback[x][y]) {
-                match = false;
+            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);
+    static const GrPixelConfig kRGBAConfigs[] {
+        kRGBA_8888_GrPixelConfig,
+        kBGRA_8888_GrPixelConfig,
+        kSRGBA_8888_GrPixelConfig
+    };
+
+    // Attempt to read back just alpha from a RGBA/BGRA texture. Once with a texture-only src and
+    // once with a render target.
+    for (auto cfg : kRGBAConfigs) {
+        for (int rt = 0; rt < 2; ++rt) {
+            GrSurfaceDesc desc;
+            desc.fFlags     = rt ? kRenderTarget_GrSurfaceFlag : kNone_GrSurfaceFlags;
+            desc.fConfig    = cfg;
+            desc.fWidth     = X_SIZE;
+            desc.fHeight    = Y_SIZE;
+
+            uint32_t rgbaData[X_SIZE][Y_SIZE];
+            // Make the alpha channel of the rgba texture come from alphaData.
+            for (int y = 0; y < Y_SIZE; ++y) {
+                for (int x = 0; x < X_SIZE; ++x) {
+                    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;
+            }
+
+            // clear readback to something non-zero so we can detect readback failures
+            memset(readback, 0x0, X_SIZE * Y_SIZE);
+
+            // read the texture back
+            texture->readPixels(0, 0, desc.fWidth, desc.fHeight, kAlpha_8_GrPixelConfig, readback,
+                                0);
+
+            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]) {
+                        texture->readPixels(0, 0, desc.fWidth, desc.fHeight,
+                                            kAlpha_8_GrPixelConfig, readback, 0);
+                        ERRORF(reporter,
+                               "Failed alpha readback from cfg %d. Expected: 0x%02x, Got: 0x%02x at"
+                               " (%d,%d), rt:%d", desc.fConfig, alphaData[x][y], readback[x][y], x,
+                               y, rt);
+                        match = false;
+                    }
+                }
+            }
+        }
+    }
 }
 
 #endif