static void
AdjustDisplayPortForScrollDelta(mozilla::layers::FrameMetrics& aFrameMetrics,
const CSSPoint& aActualScrollOffset)
{
// Correct the display-port by the difference between the requested scroll
// offset and the resulting scroll offset after setting the requested value.
LayerPoint shift =
(aFrameMetrics.GetScrollOffset() - aActualScrollOffset) *
aFrameMetrics.LayersPixelsPerCSSPixel();
LayerMargin margins = aFrameMetrics.GetDisplayPortMargins();
margins.left -= shift.x;
margins.right += shift.x;
margins.top -= shift.y;
margins.bottom += shift.y;
aFrameMetrics.SetDisplayPortMargins(margins);
}
static void
MaybeAlignAndClampDisplayPort(mozilla::layers::FrameMetrics& aFrameMetrics,
const CSSPoint& aActualScrollOffset)
{
// Correct the display-port by the difference between the requested scroll
// offset and the resulting scroll offset after setting the requested value.
CSSRect& displayPort = aFrameMetrics.mDisplayPort;
displayPort += aFrameMetrics.mScrollOffset - aActualScrollOffset;
// Expand the display port to the next tile boundaries, if tiled thebes layers
// are enabled.
if (gfxPlatform::GetPrefLayersEnableTiles()) {
displayPort =
ExpandDisplayPortToTileBoundaries(displayPort + aActualScrollOffset,
aFrameMetrics.LayersPixelsPerCSSPixel())
- aActualScrollOffset;
}
// Finally, clamp the display port to the expanded scrollable rect.
CSSRect scrollableRect = aFrameMetrics.GetExpandedScrollableRect();
displayPort = scrollableRect.Intersect(displayPort + aActualScrollOffset)
- aActualScrollOffset;
}