Texture Switching vs Bandwidth

WarAmp · 2004-05-28T16:19:55

Ok, I know this question is best answered by experimentation, but given my current render setup, alot of code would need to be rewritten to test it, so i'm turning to you kind folks for advice. My current terrain rendering system does this: For each texture layer { Bind Texture For each terrain chunk (33x33 vertices, 24 Bytes/Vertex) { glVertexPointer, glColorPointer, glTexCoordpointer glDrawElements() } } Now as you can see, this results in me sending each terrain chunk to the card for each texture layer being used (300 chunks * 4 Layers) == Lots of bandwidth a frame. How expensive is texture state changing? Would it be faster for me to send each chunk once, and texture switch 300 * 4 times instead? Waramp. "Before you insult a man, walk a mile in his shoes. That way, when you do insult him, you'll be a mile away, and you'll have his shoes." [edited by - waramp on May 19, 2004 1:16:25 PM] [edited by - waramp on May 19, 2004 1:33:18 PM]

Graphics and GPU Programming Programming

Started by WarAmp May 19, 2004 12:15 PM

11 comments, last by WarAmp 19 years, 10 months ago

_the_phantom_

11,263

May 20, 2004 02:48 AM

quote:Original post by WarAmp
Oh it has 2 Texture Units, but each vertex has up to 8 textures (t0..t7), and so that means 8 weights (w0..w7).
(note that the sum of all weights == 1.0)

ie: Final Vertex Color = w0*t0 + w1*t1 + .. + w7*t7.

so I would need to be able to do wn*tn + w(n+1)*t(n+1) in 2 units, and I can''t figure out how without the use of the combine4_nv extension.

If you know of a way to do ab + cd with 2 units with ARB extensions only, please let me know.

Yeah, i see what you mean, NV_com4 has a nice little a0a2 + a1a3 version of GL_ADD you can use and it seems no amount of messing with the GL_INTERPOLATE_ARB (a0a2 + a1(1-a2) tex_env_combine function will let it work :|

Granted you could do it with the NV_com4 extension on NV cards and ATI''s fragment_shader extension on ATI cards, but as you want to stick with ARB stuff thats not much use

WarAmp

750

Author

May 20, 2004 09:22 AM

SimmerD: They are all uniqe textures, its based off Yann''s Terrain Texturing thread on here.

I don''t think I explained myself clearly, a gf2MX cannot do:
Tex0 * a + Tex1 * b in one pass. (Using ARB extensions).

Waramp.

Before you insult a man, walk a mile in his shoes.
That way, when you do insult him, you''ll be a mile away, and you''ll have his shoes.

Waramp.Before you insult a man, walk a mile in his shoes.That way, when you do insult him, you'll be a mile away, and you'll have his shoes.

WarAmp

750

Author

May 28, 2004 04:07 PM

Sorry to pseudo-necro this thread, but I figured a way to do AB + CD in 2 texture units.

A, B = Textures 0 and 1.
x, y = Texture Weights 0 and 1.

in order to do Ax + By in 2 units with OpenGL1.1 + ARB:

note that if y == 0, then don't bother with the divide.
Primary Color(x/y, x/y, x/y, y);

Texture 0: RGB: Modulate(Primary Color, A), Alpha: Anything.
Texture 1: RGB: Add(Previous, B), Alpha: Replace(Primary Color.Alpha)

glBlendFunc(SRC_ALPHA, ONE (or whatever you need))

This ends up being: (A(x/y) + B)y = Ax + By.

yay!

Waramp.

Before you insult a man, walk a mile in his shoes.
That way, when you do insult him, you'll be a mile away, and you'll have his shoes.

[edited by - waramp on May 28, 2004 5:19:55 PM]

Waramp.Before you insult a man, walk a mile in his shoes.That way, when you do insult him, you'll be a mile away, and you'll have his shoes.

Texture Switching vs Bandwidth

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