From 4c1166372f98119a449492f16f6ea62b89557c0a Mon Sep 17 00:00:00 2001
From: Vladimir Vukicevic <vladimir@pobox.com>
Date: Mon, 19 Jul 2010 14:54:17 -0700
Subject: [PATCH] b=579696; BasicTextureImage doesn't handle partial updates
 properly; r=cjones

---
 gfx/layers/opengl/ThebesLayerOGL.cpp | 33 ++++++++++++++++++----------
 gfx/thebes/GLContext.cpp             | 14 ++++++++----
 2 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/gfx/layers/opengl/ThebesLayerOGL.cpp b/gfx/layers/opengl/ThebesLayerOGL.cpp
index c63607224f38..4fe59ec85586 100644
--- a/gfx/layers/opengl/ThebesLayerOGL.cpp
+++ b/gfx/layers/opengl/ThebesLayerOGL.cpp
@@ -142,25 +142,36 @@ ThebesLayerOGL::RenderLayer(int aPreviousFrameBuffer,
   nsIntRegion rgnToPaint = mVisibleRegion;
   rgnToPaint.Sub(rgnToPaint, mValidRegion);
   PRBool textureBound = PR_FALSE;
-  if (!rgnToPaint.IsEmpty())
-  {
+  if (!rgnToPaint.IsEmpty()) {
     nsIntRect visibleRect = mVisibleRegion.GetBounds();
-    // translate repaint region to texture-buffer space
-    nsIntRegion bufRgnToPaint = rgnToPaint;
-    bufRgnToPaint.MoveBy(-visibleRect.x, -visibleRect.y);
-    nsRefPtr<gfxContext> ctx = mTexImage->BeginUpdate(bufRgnToPaint);
-    if (!ctx)
-    {
+
+    // Offset rgnToPaint by our visible region's origin, before
+    // passing to BeginUpdate.  The TextureImage has no concept of an
+    // origin, only a size, so it always represents a 0,0 origin area.
+    // The layer however has a position, represented by its visible
+    // region.  So we have to move things around so that we can
+    // interact with the TextureImage.
+    rgnToPaint.MoveBy(-visibleRect.TopLeft());
+
+    // BeginUpdate is allowed to modify the given region,
+    // if it wants more to be repainted than we request.
+    nsRefPtr<gfxContext> ctx = mTexImage->BeginUpdate(rgnToPaint);
+    if (!ctx) {
       NS_WARNING("unable to get context for update");
       return;
     }
-    // and translate update context back to screen space
+
+    // Move rgnToPaint back into position so that the thebes callback
+    // gets the right coordintes.
+    rgnToPaint.MoveBy(visibleRect.TopLeft());
+
+    // Translate the context so that we're matching the layer's
+    // origin, not the 0,0-based TextureImage
     ctx->Translate(-gfxPoint(visibleRect.x, visibleRect.y));
 
     TextureImage::ContentType contentType = mTexImage->GetContentType();
     //ClipToRegion(ctx, rgnToDraw);
-    if (gfxASurface::CONTENT_COLOR_ALPHA == contentType)
-    {
+    if (gfxASurface::CONTENT_COLOR_ALPHA == contentType) {
       ctx->SetOperator(gfxContext::OPERATOR_CLEAR);
       ctx->Paint();
       ctx->SetOperator(gfxContext::OPERATOR_OVER);
diff --git a/gfx/thebes/GLContext.cpp b/gfx/thebes/GLContext.cpp
index 4cf2f2e77c21..0a927a2a6123 100644
--- a/gfx/thebes/GLContext.cpp
+++ b/gfx/thebes/GLContext.cpp
@@ -413,8 +413,7 @@ BasicTextureImage::BeginUpdate(nsIntRegion& aRegion)
     aRegion = nsIntRegion(mUpdateRect);
         
     nsIntSize rgnSize = mUpdateRect.Size();
-    if (!nsIntRect(nsIntPoint(0, 0), mSize).Contains(mUpdateRect))
-    {
+    if (!nsIntRect(nsIntPoint(0, 0), mSize).Contains(mUpdateRect)) {
         NS_ERROR("update outside of image");
         return NULL;
     }
@@ -428,6 +427,8 @@ BasicTextureImage::BeginUpdate(nsIntRegion& aRegion)
     if (!updateSurface)
         return NULL;
 
+    updateSurface->SetDeviceOffset(gfxPoint(-mUpdateRect.x, -mUpdateRect.y));
+
     mUpdateContext = new gfxContext(updateSurface);
     return mUpdateContext;
 }
@@ -438,8 +439,13 @@ BasicTextureImage::EndUpdate()
     NS_ASSERTION(!!mUpdateContext, "EndUpdate() without BeginUpdate()?");
 
     // FIXME: this is the slow boat.  Make me fast (with GLXPixmap?).
-    nsRefPtr<gfxImageSurface> uploadImage =
-        GetImageForUpload(mUpdateContext->OriginalSurface());
+    nsRefPtr<gfxASurface> originalSurface = mUpdateContext->OriginalSurface();
+
+    // Undo the device offset that BeginUpdate set; doesn't much matter for us here,
+    // but important if we ever do anything directly with the surface.
+    originalSurface->SetDeviceOffset(gfxPoint(0, 0));
+
+    nsRefPtr<gfxImageSurface> uploadImage = GetImageForUpload(originalSurface);
     if (!uploadImage)
         return PR_FALSE;