Are calls to glEnable/glDisable expensive?

Graphics and GPU Programming Programming

Started by My_Mind_Is_Going July 09, 2007 12:52 PM

4 comments, last by Pierrick 16 years, 9 months ago

132

Author

July 09, 2007 12:52 PM

For example to render my bitmap fonts correctly I have to disable lighting and textures and then re-enable them when I'm finished, is this a normal thing to have to do or should I be worried about making a lot of calls like this? Is this a ridiculous thing to be worried about?

ggp83

122

July 09, 2007 01:16 PM

heh.. you really shouldn't worry :)

finish your game/engine or whatever and then worry about function calls, and I bet in 99.999% of the cases it's your own functions you should worry about :)

rollo

366

July 09, 2007 02:45 PM

You are switching opengl state when you do that so it could be expensive. How much is hard to say without benchmarking it. Like ggp83 says though, don't worry about it too much.

If you do worry anyway, a good idea would be to makes sure you do all text rendering at the same time. Then you only have to switch state before and after all text rendering, instead of for each rendered text.

Stani R

1,070

July 09, 2007 02:53 PM

Like the posters above have said, first make it run, then make it run fast. Chances are, your font engine will not be the bottleneck.

V-man

813

July 10, 2007 05:40 AM

It's only a problem if you do it MANY times and you CPU and drivers are slow.
In general, the less calls to GL the better. And it depends very much on the actual call. glBindTexture is expensive, glUseProgram, etc...
glEnable and glDisable are less expensive

Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhLoadIdentityf2(matrix);
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhRotateAboutXf2(matrix, angleInRadians);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);

Pierrick

122

July 12, 2007 06:40 AM

profile your application with C/C++ profiler to find its bottlenecks. Then you'll know to improve your code. The results can be really impressive.

/P.

Are calls to glEnable/glDisable expensive?

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Are calls to glEnable/glDisable expensive?

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