Fix scaling issue with translation

bug:5684832

Change-Id: I57fd4cddd480f6d8d5e3bebdf9a63bcab59e02c5

1 files changed, 14 insertions, 1 deletions

diff --git a/Source/WebCore/platform/graphics/android/ShaderProgram.cpp b/Source/WebCore/platform/graphics/android/ShaderProgram.cpp
index b09701b..74a74e1 100644
--- a/Source/WebCore/platform/graphics/android/ShaderProgram.cpp
+++ b/Source/WebCore/platform/graphics/android/ShaderProgram.cpp
@@ -385,7 +385,20 @@ void ShaderProgram::setupDrawing(const IntRect& viewRect, const SkRect& visibleR
     TransformationMatrix ortho;
     GLUtils::setOrthographicMatrix(ortho, visibleRect.fLeft, visibleRect.fTop,
                                    visibleRect.fRight, visibleRect.fBottom, -1000, 1000);
-    m_projectionMatrix = ortho;
+    // In most case , visibleRect / viewRect * scale should 1.0, but for the
+    // translation case, the scale factor can be 1 but visibleRect is smaller
+    // than viewRect, we need to tune in this factor to make sure we scale them
+    // right. Conceptually, that means, no matter how animation affects the
+    // visibleRect, the scaling should respect the viewRect if zoomScale is 1.0.
+    // Note that at TiledPage, we already scale the tile size inversely to make
+    // zooming animation right.
+    float orthoScaleX = scale * visibleRect.width() / viewRect.width();
+    float orthoScaleY = scale * visibleRect.height() / viewRect.height();
+
+    TransformationMatrix orthoScale;
+    orthoScale.scale3d(orthoScaleX, orthoScaleY, 1.0);
+
+    m_projectionMatrix = ortho * orthoScale;
     m_viewport = visibleRect;
     m_currentScale = scale;