glBindTexture

dave05

Unregistered

Post: #1

Jun 13, 2005 — 04:28 PM

Currently in my code, the way it's structured, when I draw the same sprite 8 times in a row, for example, I call glBindTexture every single one of those 8 times.

ie, here is the routine that i call

Code:

void    OGL_DrawImageInRectWithOriginRotation(

                GLuint img, CGRect imgRect, int centerX, int centerY, int rotation)

{

    glPushMatrix();

        glTranslatef(centerX, centerY, 0);

        glRotatef(rotation,0,0,1);

        glBindTexture( GL_TEXTURE_2D, img );

        glBegin(GL_QUADS);

            glTexCoord2f(    0.0f,    0.0f);

            glVertex2i(    imgRect.origin.x,    imgRect.origin.y );

            glTexCoord2f(    1.0f,    0.0f);

            glVertex2i(    imgRect.size.width+imgRect.origin.x,

                        imgRect.origin.y);

            glTexCoord2f(    1.0f,    1.0f);

            glVertex2i(    imgRect.size.width+imgRect.origin.x, 

                        imgRect.size.height+imgRect.origin.y);

            glTexCoord2f(    0.0f,    1.0f);

            glVertex2i(    imgRect.origin.x,

                        imgRect.size.height+imgRect.origin.y);

        glEnd();

    glPopMatrix();

}

now, I was just wondering if it's faster to draw repeatedly without rebinding.. ie, should I create a separate function that does the binding, then draw several quads before binding the next sprite...?

NitroPye

Member

Posts: 28
Joined: 2005.04

Post: #2

Jun 13, 2005 — 09:04 PM

dave05 Wrote:Currently in my code, the way it's structured, when I draw the same sprite 8 times in a row, for example, I call glBindTexture every single one of those 8 times.
...
now, I was just wondering if it's faster to draw repeatedly without rebinding.. ie, should I create a separate function that does the binding, then draw several quads before binding the next sprite...?

I am going to say of course it would be faster, less calls to glBindTexture, but I have no idea how much overhead there is, so how much of a speed hit? I have no idea. You will have to use OpenGL Profiler to find out.

Remember optimization is cool, but it takes a good programmer to know when and where to optimize, if calling glBindTexture a million times, creates litteraly no overhead, then dont bother the time it will take you to re-implement that. Stick to the expensive places first, and toss in a nice

Code:

#warning glBindTexture is being called a lot, possible optimization here

to get a nice little flag every time you build. Just my 2cents.

kelvin

Member

Posts: 469
Joined: 2002.10

Post: #3

Jun 13, 2005 — 09:23 PM

throwing all those state calls will slow you down. If you've got all your GL wrapped up in good OOP, it shouldn't be a problem to cache that part of the state. Another thing I like to cache is the current context. I know in NSGL (not sure about here) -makeCurrentContext is ghastly slow.

---Kelvin--
15.4" MacBook Pro revA
1.83GHz/2GB/250GB

kelvin

Member

Posts: 469
Joined: 2002.10

Post: #4

Jun 13, 2005 — 09:24 PM

Oh yeah, and besides, if you've got a good rendering pipeline, you can coalesce all those immediate mode calls into a single vertex array and get lots and lots of speed up.

---Kelvin--
15.4" MacBook Pro revA
1.83GHz/2GB/250GB

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