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View Full Version : Technical reason why polygon stipple is slow on ATI?



Joseph19
09-02-2004, 03:42 AM
Is there a technical reason why GL_POLYGON_STIPPLE doesn't slow down rendering at all on my geforceFX at home, but at school on my ATI FireGL X1 it makes rendering very very slow?

I want polygon dithering :)

09-02-2004, 07:32 AM
do you want dithering or stippling? two different things.

i any case, it could be any number of things. it could be some combination of states thats forcing a software path, and so on.

try to be more specific about the conditions, post code, etc.

Joseph19
09-03-2004, 10:08 PM
Ok, I thought that dithering was when a polygon is displayed like this:

http://pages.cpsc.ucalgary.ca/~cherlin/glboard.png

But either way that is the effect I want. Perhaps you could give me the correct name of this as well?

As for code, well, It is just like:

glEnable(GL_POLYGON_STIPPLE);
(render some models via GL_TRIANGLE_STRIP)
glDisable(GL_POLYGON_STIPPLE)
(render some models via GL_TRIANGLE_STRIP)
glEnable(GL_POLYGON_STIPPLE);
(render some models via GL_TRIANGLE_STRIP)
etc

However, I have vertex and fragment shaders running using during all of this

09-04-2004, 01:33 AM
Joseph, i dont know what to tell you about the speed hit. probably a software path on that fire gl, dunno, not familiar with that card.

dithering is briefly discussed in the redbook (chapter 5, skip down a bit):
http://www.parallab.uib.no/SGI_bookshelves/SGI_Developer/books/OpenGL_PG/sgi_html/ch05.html

basically it allows for an increase in percieved color resolution.

09-04-2004, 01:35 AM
oh, as for the name thing, im thinking "contour", but im not sure what youre after.

Joseph19
09-04-2004, 06:16 AM
Doubt it is a software path since the shader still works and it is not possible that the shader is being done in software.

--Joseph

09-04-2004, 10:23 PM
vp/fp can be emulated in software. just try disabling dithering -- see what happens. try diabling stenciling -- see what happens. compare card specs. how many instructions do your shaders have? what's the maximum number on that card? glGet* is your friend. experiment! :)

heres a site that gives all kinds of info on various cards: www.delphi3d.com (http://www.delphi3d.com)

hope this helps!

:)

09-04-2004, 11:38 PM
oooooops! its www.delphi3d.net (http://www.delphi3d.net)