GLSL: sampler3D in vertex shader, texture appears blank - opengl

Question

EDIT: Think I've narrowed down the problem. Skip to the running section.
I'm trying to sample a 3d texture in my vertex shader, I'm going to use the texel values as corner value in Marching Cubes. The issue I'm having is that no matter what method I use to sample it, I always get (0,0,0,0). I've tried using texelFetch and texture3D and neither seem to work.
I'm also using transform feedback, but as far as I'm aware that shouldn't cause this issue.
Shader setup:
glEnable(GL_TEXTURE_3D);
Shader vertListTriangles(GL_VERTEX_SHADER_ARB);
vertListTriangles.setSource(lst_tri_vert); //Util to load from file.
vertListTriangles.compile();
vertListTriangles.errorCheck(); //Prints errors to console if they exist - shader compiles fine.
Shader geomListTriangles(GL_GEOMETRY_SHADER_ARB);
geomListTriangles.setSource(lst_tri_geom); //Util to load from file
geomListTriangles.compile();
geomListTriangles.errorCheck(); //Prints errors to console if they exist - shader compiles fine.
program.attach(vertListTriangles);
program.attach(geomListTriangles);
//Setup transform feedback varyings, also works as expected.
const GLchar* varyings1[1];
varyings1[0] = "gTriangle";
glTransformFeedbackVaryings(program.getID(), 1, varyings1, GL_INTERLEAVED_ATTRIBS);
program.link();
program.checkLink(); //Prints link errors to console - program links fine aparently.
Texture setup:
glBindTexture(GL_TEXTURE_3D, textureID);
errorCheck("texture bind"); //<- Detects GL errors, I actually get a GL_INVALID_OPERATION here, not sure if its the cause of the problem though as all subsuquent binds go smoothly.
if(!(glIsTexture(textureID)==GL_TRUE)) consolePrint("Texture Binding Failed."); //Oddly the texture never registers as failed despite the previous error message.
//Generate Texture
GLfloat volumeData[32768*3];
for(int z = 0; z < 32; z++)
{
for(int y = 0; y < 32; y++)
{
for(int x = 0; x < 32; x++)
{
//Set all 1s for testing purposes
volumeData[(x*3)+(y*96)+(z*3072)] = 1.0f;
volumeData[(x*3)+(y*96)+(z*3072)+1] = 1.0f;
volumeData[(x*3)+(y*96)+(z*3072)+2] = 1.0f;
}
}
}
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAX_LEVEL, 0);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_BASE_LEVEL, 0);
glTexImage3D(GL_TEXTURE_3D, 0, GL_RGB8, 32, 32, 32, 0, GL_RGB,
GL_FLOAT, volumeData);
glBindTexture(GL_TEXTURE_3D, 0);
Running Shader:
EDIT: Here it gets interesting. If I specify an incorrect uniform name or comment out the below lines it appears to work.
program.use();
//Disable Rastering
glEnable(GL_RASTERIZER_DISCARD);
//Input buffer: Initial vertices
glBindBuffer(GL_ARRAY_BUFFER, mInitialDataBuffer);
glEnableVertexAttribArray(0);
glVertexAttribIPointer(0, 1, GL_UNSIGNED_INT, 0, 0); //Initial input is array of uints
//Output buffer: Triangles
glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, mTriangleBuffer); //Triangle Markers, in the form of uints. NOT actual triangles.
//Texture setup
//If I comment out from here....
GLint sampler = glGetUniformLocation(program.getID(), "densityVol");
glUniform1i(sampler, GL_TEXTURE0);
glActiveTexture(GL_TEXTURE0);
//To here. It appears to work.
glBindTexture(GL_TEXTURE_3D, textureID);
//Just using this to debug texture.
//test is all 1s, so the texture is uploading correctly.
GLfloat test[32768*3];
memset(test, 0, sizeof(test));
glGetTexImage(GL_TEXTURE_3D, 0, GL_RGB, GL_FLOAT, test);
//Transform Feedback and Draw
glBeginTransformFeedback(GL_POINTS);
glDrawArrays(GL_POINTS, 0, 29790);
glEndTransformFeedback();
//Re-enable Rastering and cleanup
glDisable(GL_RASTERIZER_DISCARD);
glDisableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
My code is a little more spread out in reality, but I hope I managed to edit it into something cohesive. Anyway if I map to the output buffer it does indeed output some information, however it processes as if all the texture data is 0s. I hacked the shader to just output some test results instead but I can't find any evidence the shader is using the texture correctly:
#version 410
#extension GL_EXT_gpu_shader4 : require
layout (location = 0) in int x_y_z;
uniform sampler3D densityVol;
out Voxel
{
/*
Each triangle is the edges it joins. There are 12 edges and so we need 12 bits. 4 For each edge.
There are up to 32 voxels, which means we need 6 bits for each coord, which is 18.
30 bits total.
int format 00xxxxxxyyyyyyzzzzzz111122223333
*/
uint triangles[5];
uint triangleCount;
} vVoxel;
//... Omitted some huge ref tables.
void main()
{
vec4 sample0 = texture3D(densityVol, vec3(0.1,0.1,0.1) );
vec4 sample1 = texture3D(densityVol, vec3(0.9,0.9,0.9) );
vec4 sample2 = texture3D(densityVol, vec3(0.1,0.1,0.9) );
vec4 sample3 = texture3D(densityVol, vec3(0.9,0.9,0.1) );
if(sample0.r > 0.0f)
{
vVoxel.triangles[1] = 1;
}
if(sample1.r > 0.0f)
{
vVoxel.triangles[2] = 2;
}
if(sample2.r > 0.0f)
{
vVoxel.triangles[3] = 3;
}
if(sample3.r > 0.0f)
{
vVoxel.triangles[4] = 4;
}
vVoxel.triangleCount = 5;
}
Not the best designed test, but I didn't want to write something from scratch. If I change the if clauses to if(true) the test outputs correctly. When the shader is compiled as above, the buffer is blank. I'm using a GS for pass through.
Can anyone see an obvious mistake in there? I've been stumped for about 2 hours now and I can't see what I'm doing different from many of the GLSL texturing tutorials.

Answer 1

Okay figured it out.
glUniform1i(sampler, GL_TEXTURE0);
The GL_TEXTURE0 is incorrect here.
glUniform1i(sampler, 0);
Is how it should be.