Fix GL readback code to handle rowbytes correctly for non-32bit formats

tests/ReadWriteAlphaTest.cpp

Index: tests/ReadWriteAlphaTest.cpp
diff --git a/tests/ReadWriteAlphaTest.cpp b/tests/ReadWriteAlphaTest.cpp
index 0a8441797c2a4bfd657f2209294cd8082efbb4e2..4374d9cfca9881463c65b46ef22377abce80747f 100644
--- a/tests/ReadWriteAlphaTest.cpp
+++ b/tests/ReadWriteAlphaTest.cpp
@@ -17,13 +17,28 @@
 static const int X_SIZE = 13;
 static const int Y_SIZE = 13;
 
-DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
-    unsigned char alphaData[X_SIZE][Y_SIZE];
+static void validate_alpha_data(skiatest::Reporter* reporter, int w, int h, const uint8_t* actual,
+                                size_t actualRowBytes, const uint8_t* expected, SkString extraMsg) {
+    for (int y = 0; y < h; ++y) {
+        for (int x = 0; x < w; ++x) {
+            uint8_t a = actual[y * actualRowBytes + x];
+            uint8_t e = expected[y * w + x];
+            if (e != a) {
+                ERRORF(reporter,
+                       "Failed alpha readback. Expected: 0x%02x, Got: 0x%02x at (%d,%d), %s",
+                       e, a, x, y, extraMsg.c_str());
+                return;
+            }
+        }
+    }
+}
 
-    memset(alphaData, 0, X_SIZE * Y_SIZE);
+DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
+    unsigned char alphaData[X_SIZE * Y_SIZE];
 
     bool match;
-    unsigned char readback[X_SIZE][Y_SIZE];
+
+    static const size_t kRowBytes[] = {0, X_SIZE, X_SIZE + 1, 2 * X_SIZE - 1};
 
     for (int rt = 0; rt < 2; ++rt) {
         GrSurfaceDesc desc;
@@ -35,6 +50,7 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
         desc.fHeight    = Y_SIZE;
 
         // We are initializing the texture with zeros here
+        memset(alphaData, 0, X_SIZE * Y_SIZE);
         SkAutoTUnref<GrTexture> texture(
             context->textureProvider()->createTexture(desc, false, alphaData, 0));
         if (!texture) {
@@ -47,61 +63,59 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
         // 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;
-            }
-        }
-
-        // 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);
-
-        // 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;
-                }
+                alphaData[y * X_SIZE + x] = y*X_SIZE+x;
             }
         }
 
-        // 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;
+        for (auto rowBytes : kRowBytes) {
+            // upload the texture (do per-rowbytes iteration because we may overwrite below).
+            texture->writePixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+                                 alphaData, 0);
 
-            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;
+            size_t nonZeroRowBytes = rowBytes ? rowBytes : X_SIZE;
+            SkAutoTDeleteArray<uint8_t> readback(new uint8_t[nonZeroRowBytes * Y_SIZE]);
+            // clear readback to something non-zero so we can detect readback failures
+            memset(readback.get(), 0x1, nonZeroRowBytes * Y_SIZE);
 
-            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;
+            // read the texture back
+            texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig,
+                                readback.get(), rowBytes);
+
+            // make sure the original & read back versions match
+            SkString msg;
+            msg.printf("rt:%d, rb:%zd", rt, rowBytes);
+            validate_alpha_data(reporter, X_SIZE, Y_SIZE, readback.get(), nonZeroRowBytes,
+                                alphaData, msg);
+
+            // 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);
+
+                memset(readback.get(), 0x1, nonZeroRowBytes * Y_SIZE);
+                texture->readPixels(0, 0, desc.fWidth, desc.fHeight, desc.fConfig, readback.get(),
+                                    rowBytes);
+
+                match = true;
+                for (int y = 0; y < Y_SIZE && match; ++y) {
+                    for (int x = 0; x < X_SIZE && match; ++x) {
+                        uint8_t rbValue = readback.get()[y * nonZeroRowBytes + x];
+                        if (0xFF != rbValue) {
+                            ERRORF(reporter,
+                                   "Failed alpha readback after clear. Expected: 0xFF, Got: 0x%02x"
+                                   " at (%d,%d), rb:%zd", rbValue, x, y, rowBytes);
+                            match = false;
+                        }
                     }
                 }
             }
@@ -114,6 +128,12 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
         kSRGBA_8888_GrPixelConfig
     };
 
+    for (int y = 0; y < Y_SIZE; ++y) {
+        for (int x = 0; x < X_SIZE; ++x) {
+            alphaData[y * X_SIZE + x] = y*X_SIZE+x;
+        }
+    }
+
     // 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) {
@@ -124,11 +144,11 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
             desc.fWidth     = X_SIZE;
             desc.fHeight    = Y_SIZE;
 
-            uint32_t rgbaData[X_SIZE][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]);
+                    rgbaData[y * X_SIZE + x] = GrColorPackRGBA(6, 7, 8, alphaData[y * X_SIZE + x]);
                 }
             }
             SkAutoTUnref<GrTexture> texture(
@@ -141,27 +161,22 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(ReadWriteAlpha, reporter, context) {
                 continue;
             }
 
-            // clear readback to something non-zero so we can detect readback failures
-            memset(readback, 0x0, X_SIZE * Y_SIZE);
+            for (auto rowBytes : kRowBytes) {
+                size_t nonZeroRowBytes = rowBytes ? rowBytes : X_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;
-                    }
-                }
+                SkAutoTDeleteArray<uint8_t> readback(new uint8_t[nonZeroRowBytes * Y_SIZE]);
+                // Clear so we don't accidentally see values from previous iteration.
+                memset(readback.get(), 0x0, nonZeroRowBytes * Y_SIZE);
+
+                // read the texture back
+                texture->readPixels(0, 0, desc.fWidth, desc.fHeight, kAlpha_8_GrPixelConfig,
+                                    readback.get(), rowBytes);
+
+                // make sure the original & read back versions match
+                SkString msg;
+                msg.printf("rt:%d, rb:%zd", rt, rowBytes);
+                validate_alpha_data(reporter, X_SIZE, Y_SIZE, readback.get(), nonZeroRowBytes,
+                                    alphaData, msg);
             }
         }
     }