Re: [Dri-devel] Re: [Dri-patches] CVS Update: xc (branch: trunk)

[Jens Owen]

Keith wrote:

Jens wrote:

Michel wrote:

>>> This doesn't help mixed OpenGL and X11 rendering in the same
>>> window, but that supposedly doesn't work with the traditional
>>> method of drawing to the back buffer and then copying it over
>>> the front buffer either, so enable page flipping by default.
>>

What "clobbering" is allowed can be inferred from the GLX specification. If you overlook DBE for a second, I believe we are meeting the requirements of the spec, so I wouldn't say we're "broken".

This isn't true.

I'll clarify my statement...the traditional non-page flipping code is not broken.

Consider when a diagonal line is drawn by Xlib across the active GL window, with pages flipped.

--> Xlib draws in the "back buffer"

It's my interpretation that this step alone doesn't comply with the GLX spec for the page flipping case, but it does work with the traditional code.

Assuming the active GL window is double buffered, the X server should render to *only* the front buffer (unless DBE is being used).

--> Shadow copies the bounding box of the line to the front buffer, including *all* of the backbuffer.

What you really want is just a line to be drawn in the front buffer, but in fact you get a whole lot of garbage with it.

Right. Just a line in the front buffer and no rendering in the back buffer (for the double buffered GLX window).

A common place things like this occur is in opaque window moves -- if you move the 3d window when pages are flipped, its contents are replaced with whatever's in the backbuffer.

A solution to this is to get Xlib and GL to agree which is the front buffer and always have Xlib draw into that & copy to the backbuffer.

I'll add that we should only copy to the backbuffer if it's not being used by OpenGL or DBE as a double buffered window.

Based on Keith's insights and other follow ups to this thread, it looks like there is more work to be done before page flipping will work correctly.

Michel, I suggest you turn off page flipping by default until these issues are resolved.

--
/\
Jens Owen / \/\ _
[EMAIL PROTECTED] / \ \ \ Steamboat Springs, Colorado



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