Bug 1279611 - Document and test the fact that SurfacePipe::WriteEmpty…

…Row() overwrites the entire row. r=njn
dothq · Jun 17, 2016 · bf26782 · bf26782
1 parent 0b6af32
commit bf26782
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Showing 2 changed files with 54 additions and 2 deletions.
diff --git a/image/SurfacePipe.h b/image/SurfacePipe.h
@@ -320,7 +320,8 @@ class SurfaceFilter
   }
 
   /**
-   * Write an empty row to the surface.
+   * Write an empty row to the surface. If some pixels have already been written
+   * to this row, they'll be discarded.
    *
    * @return WriteState::FINISHED if the entire surface has been written to.
    *         Otherwise, returns WriteState::NEED_MORE_DATA.
@@ -575,7 +576,8 @@ class SurfacePipe
   }
 
   /**
-   * Write an empty row to the surface.
+   * Write an empty row to the surface. If some pixels have already been written
+   * to this row, they'll be discarded.
    *
    * @see SurfaceFilter::WriteEmptyRow() for the canonical documentation.
    */

diff --git a/image/test/gtest/TestSurfaceSink.cpp b/image/test/gtest/TestSurfaceSink.cpp
@@ -375,6 +375,31 @@ TEST(ImageSurfaceSink, SurfaceSinkWriteEmptyRow)
 
     ResetForNextPass(aSink);
 
+    {
+      // Write a partial row before we begin calling WriteEmptyRow(). We check
+      // that the generated image is entirely transparent, which is to be
+      // expected since WriteEmptyRow() overwrites the current row even if some
+      // data has already been written to it.
+      uint32_t count = 0;
+      auto result = aSink->WritePixels<uint32_t>([&]() -> NextPixel<uint32_t> {
+        if (count == 50) {
+          return AsVariant(WriteState::NEED_MORE_DATA);
+        }
+        ++count;
+        return AsVariant(BGRAColor::Green().AsPixel());
+      });
+
+      EXPECT_EQ(WriteState::NEED_MORE_DATA, result);
+      EXPECT_EQ(50u, count);
+      EXPECT_FALSE(aSink->IsSurfaceFinished());
+
+      CheckIterativeWrite(aDecoder, aSink, IntRect(0, 0, 0, 0), [&]{
+        return aSink->WriteEmptyRow();
+      });
+    }
+
+    ResetForNextPass(aSink);
+
     {
       // Create a buffer the same size as one row of the surface, containing all
       // green pixels.
@@ -931,6 +956,31 @@ TEST(ImageSurfaceSink, PalettedSurfaceSinkWriteEmptyRow)
 
     ResetForNextPass(aSink);
 
+    {
+      // Write a partial row before we begin calling WriteEmptyRow(). We check
+      // that the generated image is entirely 0, which is to be expected since
+      // WriteEmptyRow() overwrites the current row even if some data has
+      // already been written to it.
+      uint32_t count = 0;
+      auto result = aSink->WritePixels<uint8_t>([&]() -> NextPixel<uint8_t> {
+        if (count == 50) {
+          return AsVariant(WriteState::NEED_MORE_DATA);
+        }
+        ++count;
+        return AsVariant(uint8_t(255));
+      });
+
+      EXPECT_EQ(WriteState::NEED_MORE_DATA, result);
+      EXPECT_EQ(50u, count);
+      EXPECT_FALSE(aSink->IsSurfaceFinished());
+
+      CheckPalettedIterativeWrite(aDecoder, aSink, IntRect(0, 0, 0, 0), [&]{
+        return aSink->WriteEmptyRow();
+      });
+    }
+
+    ResetForNextPass(aSink);
+
     {
       // Create a buffer the same size as one row of the surface, containing all
       // 255 pixels.