Creating a 3d texture from data

OpenGL OpenGL: Advanced Coding
1

Hola,

I have been tinkering around with volume rendering to make volumetric clouds. I came across a decent nVidia demo on rendering to a 3d texture using FBOs and blending with ray marching in a shader program.

My goal is to make a 3d noise texture using libnoise and add that into the blending equation. The problem I’m having is when I create my 3d noise texture, it’s only filling up about 1/3 of what it should (the block in the picture):

Here’s how I go about creating it…it’s using the same dimensions as the textures used to make the rest of the volume, but I am uncertain about the [widthheightdepth*4] part.

T* texPtr = new T[width*height*depth*4];   // it's templated
int x, y, z;
unsigned nPointsInSlice = width*height;

for (z = 0; z < depth; ++z)
{
	for (y = 0; y < height; ++y)
	{
		for (x = 0; x < width; ++x)
		{
			T noise = (T)scaleBias.GetValue(x, y, z);
			texPtr[(z*nPointsInSlice + y*width + x)] = noise; 
		}
	}
}

GLuint id;
glGenTextures(1, &id);

glActiveTextureARB(texUnit);
glBindTexture(GL_TEXTURE_3D, id);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_REPEAT);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

glTexImage3D(GL_TEXTURE_3D, 0, GL_RGBA16F_ARB, width,
	height, depth, 0, GL_RGBA, dataType, texPtr);

I looked all over, but all I’ve found assumes that what I’m missing is simple I guess.

Thanks in advance.

2

I think your are only filling one fourth of your texture - you should do something like that in your loops:


for (z = 0; z < depth; ++z)
{
for (y = 0; y < height; ++y)
{
for (x = 0; x < width; ++x)
{
T noise = (T)scaleBias.GetValue(x, y, z);
texPtr[(z*nPointsInSlice + y*width + x)*4+0] = noise;
texPtr[(z*nPointsInSlice + y*width + x)*4+1] = noise;
texPtr[(z*nPointsInSlice + y*width + x)*4+2] = noise;
texPtr[(z*nPointsInSlice + y*width + x)*4+3] = noise;
}
}
}

Apart from that, if you only need one noise value per texel, you don’t have to use GLRGBA15F, you can simply use GL_R32F and create your texture memory with the dimension widthheightdepth.
And I you don’t need those nested loops - just loop over each texel linearly (using one loop) and fill it with a noise value.

3

Well thank you…that was very concise. I will give it a shot. I knew that I wasn’t using the most efficient method, so thank you for that as well.