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hksduhksdu

OpenGL glDrawElements vs. glVertex3f

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hksduhksdu    122
Hi all, I have an opengl book that has an example of small game engine, and it is using glVertex3f() to draw all triangles. However, in one of the chapters, it says that glDrawElements() is more efficient and powerful. So which one is more efficient? Assume that glVertex3f() is drawing from vertex array. Thanks, Andy

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Wingman    167
Using glVertex*() functions is called immediate mode and is NOT a good idea for rendering lots of stuff.
glDrawElements (and other vertex array functions) really are faster and it's a good idea to get used to using vertex arrays.
For even better performance, you could try Vertex Buffer Objects (if your card supports them).

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nts    968

Vertex arrays (glDrawElements) will always be faster to immediate mode (glVertex3f).

your book probably explains why, might want to take a look at VBO's too.

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Ademan555    361
your indicies are incorrect, or something similar, lemme guess, its an access violation right? you or openGL is trying to read outside the bounds of your arrays, which is bad, hence the violation, just make sure you pass the right sizes and stuff, and make sure your indicies (if ur using them) dont point to vertices outside of the bounds of the arrays ur using (ie: you have a vertex array, and a texture coordinate array, both have 256 elements, if you have one of ur indices asking for element 257, (or even 256 since its base 0) you should get an access violation, hope that helps
-Dan

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Ademan555    361
I didnt say too much about how to fix it, if you need help just post it here (i also forgot that your pointers that your passing might be NULL also)
-Dan

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vincoof    514
Quote:
Original post by nts

Vertex arrays (glDrawElements) will always be faster to immediate mode (glVertex3f).

As to "always", that's a false assumption. I'd rather say it will be faster in "most cases".
For instance when you have to render a quad over the whole screen (for post-rendering effects for instance) it's faster to call glVertex four times rather than enabling client states, specifying pointers etc to the vertex array.

Quote:
Original post by Ademan555
I didnt say too much about how to fix it, if you need help just post it here (i also forgot that your pointers that your passing might be NULL also)
-Dan

Hey, with VBO's NULL is a valid pointer ;)

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hksduhksdu    122
vincoof, so you mean that if I render static model or model that will be tranformed, I better use glDrawElements, if I render something like special effects, I better use glVertex3f?

:)

Andy

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_the_phantom_    11250
its all a matter of balance.
If the object is REALLY simple, such as the Quad example, then the overhead of doing all the state setting and building the array just isnt worth it.
For the majority of cases in a med to large application Vertex Arrays and VBOs will be faster and the best method, the trick is to spot when using vertex3f et al is the right time.

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