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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>
<p>
Mesa can use either an X Pixmap or XImage as the backbuffer when in
double buffer mode. Using GLX, the default is to use an XImage. The
<b>MESA_BACK_BUFFER</b> environment variable can override this. 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).
Mesa can use either an X Pixmap or XImage as the back color buffer when in
double-buffer mode.
The default is to use an XImage.
The <b>MESA_BACK_BUFFER</b> environment variable can override this.
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>
A pixmap is faster when drawing simple lines and polygons while an
XImage is faster when Mesa has to do pixel-by-pixel rendering. If you
need depth buffering the XImage will almost surely be faster.
Using XImage is almost always faster than a Pixmap since it resides in
the application's address space.
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
for your application.
</p>