Clamp ScrollbarLayer's texture size to GL_MAX_TEXTURE_SIZE.

When a scale transformation is applied to a scrollbar, its texture size
can be larger than the GL maximum.  Limit the value of contentsScale to
avoid this.

Picked up from original patch at https://codereview.chromium.org/11419140/

BUG=161029


Review URL: https://chromiumcodereview.appspot.com/11428042

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@169869 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 28 insertions, 0 deletions

diff --git a/cc/scrollbar_layer.cc b/cc/scrollbar_layer.cc
index 392369f..09c4e7f 100644
--- a/cc/scrollbar_layer.cc
+++ b/cc/scrollbar_layer.cc
@@ -40,6 +40,32 @@ ScrollbarLayer::~ScrollbarLayer()
 {
 }
 
+int ScrollbarLayer::maxTextureSize() {
+    DCHECK(layerTreeHost());
+    return layerTreeHost()->rendererCapabilities().maxTextureSize;
+}
+
+float ScrollbarLayer::clampScaleToMaxTextureSize(float scale) {
+    // If the scaled contentBounds() is bigger than the max texture size of the
+    // device, we need to clamp it by rescaling, since contentBounds() is used
+    // below to set the texture size.
+    gfx::Size scaledBounds = computeContentBoundsForScale(scale, scale);
+    if (scaledBounds.width() > maxTextureSize() || scaledBounds.height() > maxTextureSize()) {
+         if (scaledBounds.width() > scaledBounds.height())
+             return (maxTextureSize() - 1) / static_cast<float>(bounds().width());
+         else
+             return (maxTextureSize() - 1) / static_cast<float>(bounds().height());
+   }
+    return scale;
+}
+
+void ScrollbarLayer::setContentsScale(float contentsScale) {
+    contentsScale = clampScaleToMaxTextureSize(contentsScale);
+    ContentsScalingLayer::setContentsScale(contentsScale);
+    DCHECK_LE(contentBounds().width(), maxTextureSize());
+    DCHECK_LE(contentBounds().height(), maxTextureSize());
+}
+
 void ScrollbarLayer::pushPropertiesTo(LayerImpl* layer)
 {
     ContentsScalingLayer::pushPropertiesTo(layer);
@@ -235,6 +261,8 @@ void ScrollbarLayer::setTexturePriorities(const PriorityCalculator&)
 {
     if (contentBounds().IsEmpty())
         return;
+    DCHECK_LE(contentBounds().width(), maxTextureSize());
+    DCHECK_LE(contentBounds().height(), maxTextureSize());
 
     createUpdaterIfNeeded();