114082 - the ViewManager always requests an offscreen as large as the widget

Status: RESOLVED FIXED

(Core Graveyard :: GFX, defect)

Description

[Kevin McCluskey (gone)]

On each paint event the VM requests an offscreen as large as the widget. The VM
should request an offscreen only as large as the damaged area. 

The current code always bitblits from (0,0) and relies on setting a clip rect to
limit the bitblt to the damaged area.  This is a very inefficient use of the
offscreen. Instead, the viewmanager should request an offscreen the same size as
the damaged area and translate the rendering context to (-damage.x, -damage.y)
before rendering to the backbuffer. When copying forward the backbuffer should
be translated back to (damage.x, damage.y) to place the offscreen in the correct
position.

This bug is important to fix because IFRAMES can be given an arbitrary width and
height which forces the VM to create a backbuffer at least as large as the
IFRAMES size.

In addition, when bug 95952 is fixed this bug will become more important because
the backbuffer will be allocated/deallocated on each paint request, so making
smaller reguests will be more important.

Comment 1

[Kevin McCluskey (gone)]

Attachment: Patch which renders to backbuffer sized to the damaged region instead of always rendering to a region the size of the widget

Comment 2

[Kevin McCluskey (gone)]

Attachment: Updated patch - which requests an offscreen the size of the damage rect.

Comment 3

[Kevin McCluskey (gone)]

I tested patch 61803 on WIN32, Linux, and Mac. I haven't seen any regressions. I
have between running with the patch installed on WIN32 for the last two days as
dogfood.

Comment 4

[dcone (gone)]

r=dcone

Comment 5

[Marc Attinasi]

Comment on attachment 61803 [details] [diff] [review]
Updated patch - which requests an offscreen the size of the damage rect.

sr=attinasi

Comment 6

[Kevin McCluskey (gone)]

Fix checked in