558350 - [OOPP] CoreGraphics stops receiving InvalidateRect when the object is on a subpixel

Status: RESOLVED FIXED

(Core Graveyard :: Plug-ins, defect)

Description

[Benoit Girard (:BenWa)]

When the browser window is above a certain size (above 720 lines) it appears that the Flash stops sending invalidatingRect. Resizing the screen down causes these events to start firing again.

Comment 1

[Benoit Girard (:BenWa)]

So I traced back the problem to nsDisplayPlugin::mVisibleRect. When redrawing the plug-in I get:
Plugin Rect (272, 50, 640, 385)
Dirty Rect (271, 95, 1, 270)

We get an empty intersection so the plug-in does keeps waiting for the NPCocoaEventDraw and stops refreshing. Also the X coordinate in the dirty rect is off by 1 for nearly every call. It is likely that this bug is causing the white vertical lines when repainting.

Comment 2

[Josh Aas]

I think bug 556052 is the bug about the off-by-one rect.

Comment 3

[Benoit Girard (:BenWa)]

The cause of the problem is:
http://mxr.mozilla.org/mozilla-central/source/gfx/public/nsRect.h#341

When the window is larger we are dealing with larger values of X. The conversion from AppUnitsPerPixel must be a bit lower then the true value thus for large values of X the error become significant. Thus when we take the floor :
NSToIntFloor(NSAppUnitsToFloatPixels(x, float(aAppUnitsPerPixel)));
we end up clipping one pixel lower. nsRect::ToOutsidePixels is used to calculate the dirty rect but since the value x value is off by -1, the x+width is also off by -1 causing bug 556052. 

This bug here is caused when we try to draw a rect of width 1, since x+width is off by -1 it is completely outside the range we want to draw. When we take the intersection of the content rect and dirty rect we get a redraw region of width 0. Sending a NPCocoaEventDraw with width 0 causes the plug-in to stop firing InvalidateRect, presumably waiting for a correct NPCocoaEventDraw.

Comment 5

[Benoit Girard (:BenWa)]

The fix for bug 556052 landed yesterday. This bug no longer occurs on the nightly.

Comment 6

[Benoit Girard (:BenWa)]

I've ran into this problem again so in case someone else is seeing this, is it likely that the user is running an older version of the Flash Beta.