Memory managment?

OpenGL OpenGL: Advanced Coding
1

What percent of a Video Cards memory should be used by textures? In order to leave room for the depth buffer, and vertex information? I mean if you have a 8 meg video card, how many megs should be dedicated to texture use?? Or if you have a 64 meg vid card, what percent of that one should be used for textures/?

2

I think it depends of your app, you have to compute the size of your back & front buffer + z buffer and maybe stencil : for example if those 4 buffer have a 16bits per pixel precision and with = 800x600 resolution then it use 3,84 Mo. So with a 8Mo video card it give you 4Mo for texture. Over those 4Mo other texture are in aperture, a memory allocated in the RAM to download quickly texture in memory via AGP. Aperture can be parameterized.

3

Ok then does this sound right?

If i have a 1024768 window, and i am using 32Bit buffers. I have 3 buffers in use, the front buffer, the back buffer, and the Depth buffer. I would have (1024768)329;

Because I have 1024*768 pixels = 786432 Pixels. 32Bits per pixel. And 9 32Bit values for each pixel (2 sets of RGBA (front back buffers taking 4 values a piece per pixel) and 1 set of 32bit float values for the depth buffer) Making a grand total of
226492416Bits for the buffers all togeather?

4

no, the format that you describe is 32bit per color component (red green blue alpha) a 128 bit per pixel

i think when you talk about RGBA 32 bits per pixels, you mean
8 bits for red component
8 bits for green component
8 bits for blue component
8 bits for alpha component

and not 32 bits for red component etc…

so back buffer + front buffer =
(1024 * 768 * 32) * 2

  • 32 bit z buffer

  • (1024 * 768 * 32)

finaly : 75 497 472 MBits
also 9 437 184 Mbytes

5

Ok, one more quick question. How can i choose my depth buffer value? Like if wanted a 16bit, or a 32bit value. Is there a way i can set this value, or is it just created without me being able to set it??

6

It depends, if you use OpenGL under windows without glut, you can specifie the zbuffer precision in the PIXELFORMATDESCRIPTOR structure set the member cDepthBits to 16 or 32. With glut i don t know the way to change precision but to know which precision is used you can call
GLint bitPrecision;
glGetIntegerv(GL_DEPTH_BITS,&bitPrecision)

result is in bitPrecision.

7

you can set it in the PIXELFORMATDESCRIPTOR