Hi,
In my program, I'm trying to modify the coordinates of the texture in texture unit 0 based on the sum of values from texture units 1 and 2 (it's to simulate waves in slime based on two greyscale/GL_LUMINANCE waviness maps that scroll at right angles to one another).
How is this done? I have been reading Lighthouse3D and other sources, but I can't seem to find anywhere that changing the texcoords is explained. Here's what I have so far (apologies for newbishness, I've only just begun with GLSL)
| 1 | const char *vertex_prog_src = "\ |
| 2 | |
| 3 | varying vec2 uv_reflection; \ |
| 4 | varying vec2 uv_wavemap_1; \ |
| 5 | varying vec2 uv_wavemap_2; \ |
| 6 | \ |
| 7 | void main(void) \ |
| 8 | { \ |
| 9 | // don't modify vertex \ |
| 10 | gl_Position = ftransform(); \ |
| 11 | \ |
| 12 | // save position in texture for later \ |
| 13 | uv_reflection = gl_MultiTexCoord0.xy; \ |
| 14 | uv_wavemap_1 = gl_MultiTexCoord1.xy; \ |
| 15 | uv_wavemap_2 = gl_MultiTexCoord2.xy; \ |
| 16 | } \ |
| 17 | "; |
| 18 | |
| 19 | const char *fragment_prog_src = "\ |
| 20 | uniform sampler2D wavemap_1; \ |
| 21 | uniform sampler2D wavemap_2; \ |
| 22 | uniform sampler2D reflection_tex; \ |
| 23 | varying vec2 uv_reflection; \ |
| 24 | varying vec2 uv_wavemap_1; \ |
| 25 | varying vec2 uv_wavemap_2; \ |
| 26 | \ |
| 27 | void main() \ |
| 28 | { \ |
| 29 | // and this is where I'm stuck. \ |
| 30 | } \ |
| 31 | "; |
I know I need to sample wavemap_1 and wavemap_2, add them together (clamped or scaled as needed), and use those to tweak the 'u' of reflection_tex, then set 'gl_FragColor' to the result of that; I don't really know how to express that in GLSL or where to begin to look, though...
Edit:
I think this might be what I want:
| 1 | const char *frag_prog_src = "\ |
| 2 | uniform sampler2D wavemap_1; \ |
| 3 | uniform sampler2D wavemap_2; \ |
| 4 | uniform sampler2D reflection_tex; \ |
| 5 | varying vec2 uv_reflection; \ |
| 6 | varying vec2 uv_wavemap_1; \ |
| 7 | varying vec2 uv_wavemap_2; \ |
| 8 | \ |
| 9 | \ |
| 10 | void main() \ |
| 11 | { \ |
| 12 | float my_s; \ |
| 13 | float my_t; \ |
| 14 | vec2 warped_texcoord; \ |
| 15 | vec4 ref_colour; \ |
| 16 | \ |
| 17 | my_s = texture2D(wavemap_1,uv_wavemap_1).r / 2.0; \ |
| 18 | my_t = texture2D(wavemap_2,uv_wavemap_2).r / 2.0; \ |
| 19 | \ |
| 20 | warped_texcoord.x = uv_reflection.x + my_s; \ |
| 21 | warped_texcoord.y = uv_reflection.y + my_t; \ |
| 22 | \ |
| 23 | ref_colour = texture2D(reflection_tex,warped_texcoord).rgba; \ |
| 24 | \ |
| 25 | gl_FragColor = ref_colour; \ |
| 26 | } \ |
| 27 | "; |
Trying it now, will report back with results...
Edit the 2nd:
Nope, not quite. The wavemaps seem to get super-imposed over the texture in black, but that's not what I've told it to do (that I can see)...anyone out there got any ideas?
Edit the 3rd:
Fixed the above problem but the fragment program appears to do nothing; I changed 'ref_colour = texture2D(reflection_tex,warped_texcoord).rgba' to end with .rrrr instead, and there's no visible change in the reflection... 
