strange texture size

OpenGL OpenGL: Advanced Coding
1

Hello,

in my app i got a lightmap texture which is about 9000 x 9000 texels in size, giving a total of 81,000,000 texels. it is stored in RGB format, so i guess it uses one byte each for the R, G and B component, giving it a total size of 81 000 000 x 3 = 243,000,000 bytes, which are 237305 kb, which are about 231 mb. But my graphics card only has a memory of 64 mb, and there also is other data, such as 100 display lists which cover a terrain with about 240,000 triangles, several objects etc. but still, the program runs absolutely smooth and fast. How is this possible? Am i getting something wrong? If a lot of texture swapping between graphic board memory and main memory would happen, one surely would notice this?

Jan

2

Your video card only supports 4096x4096 textures at best. Older cards only support 2048x2048 or less. Presumably you’re using gluBuild2DMipmaps() to upload your image – this function automatically scales your image down if it is too large (it uses the proxy texture mechanism).

To see for yourself that this is indeed what’s happening, draw a couple of lines on your texture that are one pixel apart, and see how they look in your app.

– Tom

3

thanks, you are right .

Jan