Hi, Manu
Cant comment on performance gain with pure gl, but you can write small test to see possible gain. Osg dont share fbos with cameras and dont keep track of vbo's binded so most of gain would be from reducing number of glBindFramebuffer...(..) calls and geometry setup (vertex\index\texcoord arrays\pointers).
It is possible to create whatever objects you need inside renderImplementation, also you need to info osg::State about all gl state that osg::State keep track of, that you change with opengl calls (look at osg::State::haveApplied...(...) ), or use osg::State functionality instead of opengl calls (look at applyMode(..)/applyAttribute(..)), though not all gl calls can be done through osg::State interface. Instead you can use pure gl and call osg::State::dirtyAll...() afterwards. Dont forget to restore fbo used by osg if you change fbo binding inside drawImplementation(). Also there could be issues with multiple opengl contexts handling if you use multiple screens, so you may need to track current contextID and create\store opengl handles for each contextID used, and pick right handles for current contextID.
Also with pure gl approach you can get rid of fbo and drawBuffers switch if you can use NV_texture_barrier extension - you can create texture array with two textures, reading from one layer and writing to another based on uniform value or instanceID if you use instanced drawing for sqreen aligned quads.
Cheers,
Sergey.
23.09.2011, 15:50, "Emmanuel Roche" <[email protected]>:
Thanks Sergey,
Right now I'm using multiple cameras rendered one after another... but I have the feeling the performances are not too good (with 17 pre render cameras...). Do you think I'm right to assume I could really improve the performances by using pure GL code instead and create only one FBO ?
as a matter of fact, my second idea would be to encapsulate all this using approximately the code snippet of the previous mail in a special drawable. But i'm wondering if this will not lead to other issues (I'm not that familiar with pure GL code and creating special drawables): is it possible to allocate by FBO and everything I could need from within the renderImplementation of a drawable ? Could somebody predict a big issue doing this ?
Cheers,
Manu.2011/9/23 Sergey Polischuk <[email protected]>Hi, ManuThere are no convenient support for renderbuffer ping-ponging. You can either use pure gl, graph with lots of cameras setup with correct render order and output textures, or osgppu graph with chain of unitsCheers,Sergey.22.09.2011, 16:28, "Emmanuel Roche" <[email protected]>:Hi everyone,
I have a question regarding FBO usage and Draw/Read buffer changes:
- I have one pre render camera using FBO and with 2 textures attached (to COLOR_BUFFER0 and COLOR_BUFFER1)
- Under that camera I would like to add multiple screen aligned quads that would use the attached textures this way: (call them tex0 and tex1):
- quad0 would using the tex0 as input and draw on tex1
- quad1 would then use tex1 as input and draw on tex0
- quad2 would using the tex0 as input and draw on tex1
- quad3 would then use tex1 as input and draw on tex0
- etc.
This is possible in pure OpenGL using something like that:
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fftFbo2);
glUseProgram(fftx->program);
glUniform1i(glGetUniformLocation(fftx->program, "nLayers"), choppy ? 5 : 3);
for (int i = 0; i < PASSES; ++i) {
glUniform1f(glGetUniformLocation(fftx->program, "pass"), float(i + 0.5) / PASSES);
if (i%2 == 0) {
glUniform1i(glGetUniformLocation(fftx->program, "imgSampler"), FFT_A_UNIT);
glDrawBuffer(GL_COLOR_ATTACHMENT1_EXT);
} else {
glUniform1i(glGetUniformLocation(fftx->program, "imgSampler"), FFT_B_UNIT);
glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);
}
drawQuad();
}
glUseProgram(ffty->program);
glUniform1i(glGetUniformLocation(ffty->program, "nLayers"), choppy ? 5 : 3);
for (int i = PASSES; i < 2 * PASSES; ++i) {
glUniform1f(glGetUniformLocation(ffty->program, "pass"), float(i - PASSES + 0.5) / PASSES);
if (i%2 == 0) {
glUniform1i(glGetUniformLocation(ffty->program, "imgSampler"), FFT_A_UNIT);
glDrawBuffer(GL_COLOR_ATTACHMENT1_EXT);
} else {
glUniform1i(glGetUniformLocation(ffty->program, "imgSampler"), FFT_B_UNIT);
glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);
}
drawQuad();
}
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
.. but I can't figure out how to do something equivalent to the internal calls to glDrawBuffer in the previous snippet when I have a single camera. (as calling setDrawBuffer() is done once and for all before rendering anything... Any idea what could be worth trying here ?
Cheers,
Manu._______________________________________________
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