Projective Texturing Help

Just to clarify, are you trying to do shadow mapping or something like projecting a torch onto the scene, like in Doom3?

I was originally trying to do shadow-mapping, but found out that projecting a texture created from the depth buffer from the lights point of view was how you did it...and i don't really know how to project textures....if this is wrong please let me know, or let me know i'm going at it in the wrong approach

thanks man

PS: i looked around for "decalling" too, is that the same thing?

Well for typical shadow mapping your first pass builds a depth texture and your second pass renders the scene and tests each pixels depth to that in the depth texture and then alters the pixel shaders output colour to be grey.

Dave

so shadow-mapping is not a fixed-function pipeline kind of thing?

No.

thanks, ok, so we have that down.....hmmmm, doing all this really got me thinking about projecting textures, so, forgetting about the whole shadow-mapping thing, i still want to be able to project a static image onto a flat plane....any advice?

I don't believe this is a shader only technique, but please let me know if it is

thanks

Projecting textures is done kinda similar.

Firstly the texture you are using must have atleast 1 pixel around its edge that is black. You set the texture sampling properties to CLAMP, this means that when you come to a pixel that would use a part of the texture that lies off the edge of the texture, it is not wrapped and you don't get your projected texture everywhere.

Transform the vertex position into the screen-space of the projector position, like you do for the light source in shadow mapping. Once this is done you simply sample the texture and blend the sampled colour with your output colour in the pixel shader.

Dave

hmmmmm, i'm still a little stumped here......anybody have any good insight for me? or words of wisdom?

I have been looking through this white paper:
http://www1.cs.columbia.edu/~ravir/6160/papers/shadow_mapping.pdf

I still feel like im missing something...

so i have an image or shadowmap i want to project onto a flat surface, how does the texture coordinates from the projector change into the coordinates that the camera sees?