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I went through the google I/O video but did not get exactly how to do it. If somebody could point me to a simple 3D texture implementation using webgl, it would be helpful.

i basically have a volume, a cube, i want to fill it up with pixel data, which comes from a stack of images along the x-y axis. How do i do that?

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1 Answer

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Here's the GLSL function copied directly from the Google I/O talk

vec4 sampleAs3DTexture(sampler2D tex, vec3 texCoord, float size) {
   float sliceSize = 1.0 / size;                         // space of 1 slice
   float slicePixelSize = sliceSize / size;              // space of 1 pixel
   float sliceInnerSize = slicePixelSize * (size - 1.0); // space of size pixels
   float zSlice0 = min(floor(texCoord.z * size), size - 1.0);
   float zSlice1 = min(zSlice0 + 1.0, size - 1.0);
   float xOffset = slicePixelSize * 0.5 + texCoord.x * sliceInnerSize;
   float s0 = xOffset + (zSlice0 * sliceSize);
   float s1 = xOffset + (zSlice1 * sliceSize);
   vec4 slice0Color = texture2D(tex, vec2(s0, texCoord.y));
   vec4 slice1Color = texture2D(tex, vec2(s1, texCoord.y));
   float zOffset = mod(texCoord.z * size, 1.0);
   return mix(slice0Color, slice1Color, zOffset);
}

https://code.google.com/p/webglsamples/source/browse/color-adjust/color-adjust.html

If you want a 8x8x8 3D texture you'd make 64x8 texture and put each slice of the cube across the texture 

[slice0][slice1][slice2]....[slice7]

Then make a sampler2D uniform in your shader and call 

sampleAs3DTexture(yourSampler, your3DTexCoord, size)

where size the size of your cube (in the example size = 8)

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thanks @gman for your answer! how is it possible to change the code, so that we can have a e.g. 8x8x5 texture instead? It seems that this doesn't work properly: ` vec4 sampleAs3DTexture(sampler2D tex, vec3 texCoord, float size, vec2 texDimensions) { float sliceSize = 1.0 / size; float slicePixelSize = sliceSize / texDimensions.x; float sliceInnerSize = slicePixelSize * (texDimensions.x - 1.0);` Or what does "space of size pixels" mean? – dforce Jan 16 at 13:33
if you make your slices 8x5 so that your cube is 8x5x8 and your 2D version of that texture is width=8*8, height=5 it should just work. No Changes. – gman Jan 17 at 19:23

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