Gecko:DisplayListBasedInvalidation: Difference between revisions

Gecko:DisplayListBasedInvalidation (view source)

Revision as of 04:47, 4 October 2012

826 bytes added , 4 October 2012

→‎Basic Outline

Mattwoodrow

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 = Basic Outline =
-* Display List changes
+There are 3 main components to DLBI: Frame invalidation, display list invalidation and layer tree invalidation.
-** We want to compare the new display to the old one and invalidate layer regions of anything that has changed.
-** We already cache most of the information that we need, and iterate over it in FrameLayerBuilder.
-*** We need to add the old bounds of the display item into the cached data
-*** Some items (e.g. borders) need two rectangles: an outer rect and an inner rect
-** Invalidating display items that no longer exist.
-*** How do we do this?
-*** We could iterate over the frames DisplayItemData at the end of nsFrame::BuildDisplayList, and send invalidations for any display item types that weren't just created.
-*** FrameLayerBuilder already detects items being added to or removed from a layer, so this won't be a problem if we do the processing in FrameLayerBuilder
-* Style and other changes
+== Frame Invalidation ==
-** These should invalidate all (?) display items for the frame, so we can just set a dirty bit on the frame and check this from FrameLayerBuilder
+Code lives in layout/generic/nsIFrame.h and layout/generic/nsFrame.cpp
+This is used when a frame has a major change that will affect rendering (such as a style change) and all display items belonging to this frame should redraw their content.
+nsIFrame::InvalidateFrame() marks the frame as invalid. You can also specify a rect using nsIFrame::InvalidateFrameWithRect, but note that this is a minimum, the display items created by this frame can still choose to invalidate further.
+== Display List Invalidation ==
+Compute the area of a ThebesLayer by comparing the current display list being drawn into the layer against the previous display list.
+Code lives in layout/base/FrameLayerBuilder.cpp, primarily in FrameLayerBuilder::InvalidateForLayerChange(). The nsDisplayItemGeometry classes in layout/base/nsDisplayListInvalidation.h, and layout/base/nsDisplayList.h - nsDisplayItem::AllocateGeometry(), nsDisplayItem::ComputeInvalidationRegion.
+Every display item is asked to allocate a geometry object that is retained between paints and then used to check for display item changes.
+When painting, it checks if it has been added or removed from the layer and invalidates the bounds of the display item if so.
+Items that exist between paints are asked to check for size changes using nsDisplayItem::ComputeInvalidationRegion and will compute the changed area (if any).
+== Layer Tree Invalidation ==
+Code lives in gfx/layers/LayerTreeInvalidation.{h,cpp}.
+Computes changes in layer trees and reports the invalid area.
+Used to find changes in inactive layer trees, compute widget dirty rects (BasicLayers only) and report MozAfterPaint events.
 = Potential Problems =