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updated Pixmap vs. XImage info

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Brian Paul 2006-06-07 14:01:31 +00:00
parent 37474eca68
commit 808809b061
1 changed files with 17 additions and 8 deletions
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docs/xlibdriver.html
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@ -70,17 +70,26 @@ Here are some examples:
<H2>Double Buffering</H2> <H2>Double Buffering</H2>
<p> <p>
Mesa can use either an X Pixmap or XImage as the backbuffer when in Mesa can use either an X Pixmap or XImage as the back color buffer when in
double buffer mode. Using GLX, the default is to use an XImage. The double-buffer mode.
<b>MESA_BACK_BUFFER</b> environment variable can override this. The valid The default is to use an XImage.
values for <b>MESA_BACK_BUFFER</b> are: <b>Pixmap</b> and <b>XImage</b> The <b>MESA_BACK_BUFFER</b> environment variable can override this.
(only the first letter is checked, case doesn't matter). The valid values for <b>MESA_BACK_BUFFER</b> are: <b>Pixmap</b> and
<b>XImage</b> (only the first letter is checked, case doesn't matter).
</p> </p>
<p> <p>
A pixmap is faster when drawing simple lines and polygons while an Using XImage is almost always faster than a Pixmap since it resides in
XImage is faster when Mesa has to do pixel-by-pixel rendering. If you the application's address space.
need depth buffering the XImage will almost surely be faster. When glXSwapBuffers() is called, XPutImage() or XShmPutImage() is used
to transfer the XImage to the on-screen window.
</p>
<p>
A Pixmap may be faster when doing remote rendering of a simple scene.
Some OpenGL features will be very slow with a Pixmap (for example, blending
will require a round-trip message for pixel readback.)
</p>
<p>
Experiment with the MESA_BACK_BUFFER variable to see which is faster Experiment with the MESA_BACK_BUFFER variable to see which is faster
for your application. for your application.
</p> </p>