Old scrolling bug

[Duane Clark]

Howdy,

Another in my pattern of posting intermediate debugging results here, in 
case anyone can contribute some insight...

Looking into the bug that Dimitrie reported here:
http://www.winehq.com/hypermail/wine-devel/2002/09/0748.html

Here is what is happening (testing on the Listview Control Spy) when 
sliding the obscuring window. I changed a bunch of TRACE messages to 
ERR, and added a few. The window of interest, that the artifacts are 
appearing in is 0x10039 (the "Control Notifications" window):

err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 0,138 11x1
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 304,138 4x1
err:x11drv:X11DRV_Expose win 0x10039 (2e00032) 0,110 2x1
err:x11drv:X11DRV_Expose win 0x10039 (2e00033) 0,108 99x1
err:x11drv:X11DRV_Expose win 0x10040 (2e00041) 0,126 293x1
err:win:BeginPaint hwnd 0x10021 hdc = 0x9e8 box = (0,138 - 409,139)
err:win:EndPaint Here
err:win:BeginPaint hwnd 0x10039 hdc = 0x9e8 box = (0,108 - 99,109)
err:win:EndPaint Here
err:win:BeginPaint hwnd 0x10040 hdc = 0x9e8 box = (0,0 - 293,186)
err:win:EndPaint Here
err:win:BeginPaint hwnd 0x10047 hdc = 0x890 box = (0,109 - 277,110)
err:win:EndPaint Here

So an initial exposure occurred and was almost immediately painted. The 
obscuring window is now at y=109. The first expose of the pair is a 
validate, and the second is the invalidate. Then ScrollWindowEx is 
called, which eventually gets to X11DRV_ScrollDC, where the bitblt that 
scrolls the window is called.

err:bitblt:BitBlt hdcSrc=0x9e8 0,14 24 bpp->hdcDest=0x9e8 0,0 126x154x24 
rop=cc0020

After scrolling, X11DRV_EndGraphicsExposures is called, which checks 
pending exposure events as a result of the scroll.

err:x11drv:X11DRV_EndGraphicsExposures got 0,96 99x14 count 0

Note that the exposed part is the rectangle with y coordinates from 96 
to 110. That means that before the bitblt copy had occurred, the 
obscuring window had already moved down one pixel. The bitblt moved the 
previously obscured rectangle at (0,109 - 99,110) to (0,95 - 99,96), but 
that rectangle did not get into the update rectangle.

This is because the only pending events checked are those that are a 
direct result of exposure due to the copy in bitblt, and does not 
include any additional areas that were exposed by sliding the obscuring 
region.

err:scroll:X11DRV_ScrollWindowEx A hwnd 0x10039 rgn rect = (0,96,126,168)
err:win:GetUpdateRgn hrgnUpdate 0
err:scroll:X11DRV_ScrollWindowEx B hwnd 0x10039 rgn rect = (0,96,126,168)

It should be pointed out that X did not lose the exposure event due to 
sliding the obscuring window, because here it shows up in the next 
exposure event

err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 0,139 11x1
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 304,139 4x1
err:x11drv:X11DRV_Expose win 0x10039 (2e00032) 0,111 2x1
err:x11drv:X11DRV_Expose win 0x10039 (2e00033) 0,109 99x1
                                                  ^^^
Unfortunately, we have already handled the offset due to scrolling, so 
this event is put into the update region unshifted. The remaining 
exposures are new, so no shifting is needed.

err:x11drv:X11DRV_Expose win 0x10040 (2e00041) 0,127 293x1
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 0,140 11x3
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 304,140 4x3
err:x11drv:X11DRV_Expose win 0x10039 (2e00032) 0,112 2x3
err:x11drv:X11DRV_Expose win 0x10039 (2e00033) 0,110 99x3
err:x11drv:X11DRV_Expose win 0x10040 (2e00041) 0,128 293x3
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 0,143 11x1
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 304,143 4x1
err:x11drv:X11DRV_Expose win 0x10039 (2e00032) 0,115 2x1
err:x11drv:X11DRV_Expose win 0x10039 (2e00033) 0,113 99x1
err:x11drv:X11DRV_Expose win 0x10040 (2e00041) 0,131 293x1
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 0,144 11x2
err:x11drv:X11DRV_Expose win 0x10021 (2e00003) 304,144 4x2
err:x11drv:X11DRV_Expose win 0x10039 (2e00032) 0,116 2x2
err:x11drv:X11DRV_Expose win 0x10039 (2e00033) 0,114 99x2
err:x11drv:X11DRV_Expose win 0x10040 (2e00041) 0,132 293x2
err:win:BeginPaint hwnd 0x10021 hdc = 0x890 box = (0,139 - 409,146)
err:win:EndPaint Here

And finally the update region is painted. This update region includes 
the region exposed by the scroll, plus all the additional exposure 
events that occurred due to sliding the obscuring window.

err:win:BeginPaint hwnd 0x10039 hdc = 0x890 box = (0,96 - 126,168)
err:win:EndPaint Here

But there is a one pixel artifact at (0,95 - 99,96), because it is not 
in the update region.

Fundamentally, the problem is that the X events are handled out of 
order, because X11DRV_EndGraphicsExposures stripped out particular 
events (due to copying) without accounting for other pending events that 
might be relevant (plain old exposure).