GLSL Vertex Shader lookup-table question

Question

I've got some difficulty debugging my program. I'm trying use an array as a lookup table to offset the vertex location in my vertex shader, but I can't even tell if I'm linking my array correctly. The offset factor always ends up zero (flattening my vectors, rather than giving them a shape), so either I'm accessing the texture1D coordinates wrong or the array isn't binding right to the texture.

Frankly, I don't know which coordinates I should be using to get the values from a 1D texture... but I've tried all the combinations.

Here I setup the array and bind it to the shader:

//FISH
GLfloat fish_coords[100];
for (int i = 0; i < 50; i++){fish_coords[i] = 0;}
for (int i = 50; i < 100; i++){fish_coords[i] = 1;}
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

glGenTextures(1, &fishtexture);  
glBindTexture(GL_TEXTURE_1D, fishtexture);
glTexImage1D(GL_TEXTURE_1D, 0, 1, 128,0,GL_RGBA, GL_UNSIGNED_BYTE, &fish_coords);

switch(shadow_selection){
case 0: 
    vertexShader = "fish.vert";
    fragmentShader = "fish.frag";
    setShaders();

    GLint loc1;
    loc1 = glGetUniformLocation(shaderProgram,"fish_coords");
    glUniform1i(loc1,0);

And my vertex shader:

uniform float spec_factor;
uniform sampler1D fish_coords;

varying vec3 lightDir,normal;

void main()
{

    vec4 v_pos;
    vec3 ldir;

    gl_TexCoord[0] = gl_MultiTexCoord0;

    v_pos = gl_ModelViewMatrix * gl_Vertex;
    ldir = vec3(gl_LightSource[0].position-v_pos);
    lightDir = normalize(ldir);
    normal = normalize(gl_NormalMatrix * gl_Normal);

    vec4 offset;
    offset = texture1D(fish_coords, gl_TexCoord[0].r);

    vec4 fish_shape;
    fish_shape.xz = gl_Vertex.xz;
    fish_shape.y = gl_Vertex.y * offset.x;
    fish_shape.w = 1;

    gl_Position = gl_ModelViewProjectionMatrix * fish_shape;
}

The quick answer is: That's not how you load a texture. Bind selects a texture by id that you want to operate on. You allocate ids with glGenTextures, bind them, load them (eg with glTexImage1D) and then use them. — Ben Jackson
ah, I thought lookup tables were a kind of hack with the textures so that's why I wasn't doing that. thanks. — jakev

Dr. Snoopy Dr. Snoopy · Accepted Answer · 2010-11-05T13:03:52

There are two problems in your texture loading code:

1.- The default MIN filter uses mipmaps, so with that setup the texture incomplete. Set the MIN/MAG filters after binding the texture to GL_NEAREST. 2.- Your texture data is floats, but you say to GL they are unsigned bytes, change that to GL_FLOAT.

After this changes your texture should appear.

GLSL Vertex Shader lookup-table question

2 Answers