More than one lightmap

[Leyder Dylan]

Hi,

I've a question :

How do you when you have more than one lightmap on a polygon ?

I've tryed to render the 2 lightmaps but only one is displayed. If I display the number 1 or 2 alone, no problem.

I'm almost sure that's is because I use only 1 texture unit and the same one for rendering each lightmap.

So, how do you do for rendering more than one lightmap ?

So, if I've 6 lightmap, should I use 6 texture units ? It has no sense, not ?


Thanks,


LEYDER Dylan


[This message has been edited by Leyder Dylan (edited 10-23-2003).]

[gator]

If I understand your question, it's either single-pass multi-texturing if you have the
hardware to do it, or multi-pass multi-texturing if you don't.

This will tell you how many texture units your card has:

#include <GL/glext.h>

INT max_texture_units;
glGetIntegerv( GL_MAX_TEXTURE_UNITS_ARB, &max_texture_units );

But I'm sure you already know all of this? It is a very basic mult-texturing question.


[This message has been edited by gator (edited 10-23-2003).]

[Obli]

Originally posted by Leyder Dylan:
...
So, how do you do for rendering more than one lightmap ?

So, if I've 6 lightmap, should I use 6 texture units ? It has no sense, not ?
...

Lightmaps are usually melt togheter at compile time by adding them. So for example, each light which is static is combined in the same lightmap, each light which pulsates at a certain rithm is another lightmap (which also contains all the other lights with the same rithm) and so go on.

Now, what you do really depends from the architecture of your engine and from the target machine. Fragment programming facilities are somewhat helpful here but keeping on the topic...

First point is to accumulate all the lights. In standard multitexturing this will take a tex unit foreach lightmap. Every other lightmap is added. After every lightmap has been added, it's just time to multiply. Sounds easy? It's not.
In case you don't have so much texture units (but I guess you can do interesting things with just 5 lightmaps and a 3 base textures and some cards will let you do that) I'm afraid you will have to use the so-dreaded multipass rendering using blendfuncs. Ack.
Some time ago, I took in consideration the idea to do ping-pong rendering using a special texture. It turns out that context switching is so expensive that it really kills **a lot** of performance so it does not pay so much if you're running low resolution.

[gator]

Ah, if he means putting multiple OpenGL lights in a scene, then that is a different question altogether.

[Leyder Dylan]

Hi,

Here's a screenshot, you'll understand :
http://users.skynet.be/fa550206/Slug...p/Lightmap.jpg

Sorry but the forum doesn't include the image in the message, don't know why.

Yes I'm using Multitexturing and my GeForce 4 Ti 4200 has only 4 texture units. Damned ...

First point is to accumulate all the lights

Is it possible, for static lightmap to create only one texture with all lightmaps ?

What about the fragment program ?



[This message has been edited by Leyder Dylan (edited 10-23-2003).]

[jwatte]

This only barely qualifies as "advanced" and only barely qualifies as "OpenGL," but what the hey. There is no "basic rendering questions" board that I know of, except flipcode/gamedev...

Here's one way of doing arbitrary numbers of light maps with a simple diffuse color texture per object:

1) clear framebuffer to ambient light color
2) Enable(BLEND); BlendFunc(ONE,ONE);
3) for each lightmap
3.1) for each object within radius of that light
3.1.1) render the object with the light map
4) BlendFunc(ZERO,SRC_COLOR);
5) for each object
5.1) render the object with full-bright diffuse color map

[Leyder Dylan]

I can render the lightmap. My question was : How can I render more than one lightmap if I only use one texture unit with ARB multitexturing.

I can do that with the polygon offset ? How it's a wrong way ... ?

[Ysaneya]

This is confusing as hell. Why would you want more than one lightmap per triangle ? Unless you are working with advanced hybrid techniques, more than one lightmap per triangle is not needed...

How can I render more than one lightmap if I only use one texture unit with ARB multitexturing.

Sorry ? You're not making any sense at all here. If you only use one texture unit... you're not doing any MULTItexturing at all.

Y.


[This message has been edited by Ysaneya (edited 10-24-2003).]

[Tom Nuydens]

Originally posted by Ysaneya:
This is confusing as hell. Why would you want more than one lightmap per triangle ? Unless you are working with advanced hybrid techniques, more than one lightmap per triangle is not needed...

I recall from one of his previous posts that he uses the term "(dynamic) lightmapping" to describe what is actually attenuation mapping.

The answer to the problem is exactly what jwatte posted. Also note that the very first pass should not use blending, because that one will need to lay down the Z-buffer. You also need to switch to DepthMask(FALSE) and DepthFunc(GL_EQUAL) after the first pass.

-- Tom

[Leyder Dylan]

Oups, sorry jwatte to haven't followed your advice.

Kick my ass.

That's work.