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GPU ray casting (single pass) with 3d textures in polar coordinates

HomeCategory: stackoverflowGPU ray casting (single pass) with 3d textures in polar coordinates
john asked 3 weeks ago

i’ am implementing an algorithm of volume rendering “GPU ray casting single pass”. For this, i used a float array of intensity values as 3d textures ( this 3d textures describes a regular grid in polar coordinates ).

Here there are example of array values:


the dimensions of polar grid are (r,theta,phi)=(368,15,768), and this is the input format for load textures:

glTexImage3D(GL_TEXTURE_3D, 0, GL_R16F, 256, 256, 256, 0, GL_RED, GL_FLOAT, dataPtr)

And This is an image of my visualization:


The problem is that the visuization should be a disk, or at least a similar form.

i think that the problme is i do not specify correctly the coordinates for textures( in polar coordinates).

this is the vertex shader code:

  #version 330 core

layout(location = 0) in vec3 vVertex; //object space vertex position

 uniform mat4 MVP;   //combined modelview projection matrix

 smooth out vec3 vUV; //3D texture coordinates for texture lookup in   the fragment shader

void main()
    //get the clipspace position 
     gl_Position = MVP*vec4(,1);

    //get the 3D texture coordinates by adding (0.5,0.5,0.5) to the object space 
    //vertex position. Since the unit cube is at origin (min: (-0.5,-0.5,-0.5) and max: (0.5,0.5,0.5))
    //adding (0.5,0.5,0.5) to the unit cube object space position gives us values from (0,0,0) to 
    vUV = vVertex + vec3(0.5);

and this is the fragmen shader code:

  #version 330 core

layout(location = 0) out vec4 vFragColor;   //fragment shader output

smooth in vec3 vUV;             //3D texture coordinates  form vertex shader 
                                 //interpolated by rasterizer

uniform sampler3D   volume;     //volume dataset
uniform vec3        camPos;     //camera position
uniform vec3        step_size;  //ray step size 

const int MAX_SAMPLES = 300;    //total samples for each ray march step
const vec3 texMin = vec3(0);    //minimum texture access coordinate
const vec3 texMax = vec3(1);    //maximum texture access coordinate

    vec4 colour_transfer(float intensity)

    vec3 high = vec3(100.0, 20.0, 10.0);
   // vec3 low = vec3(0.0, 0.0, 0.0);
   float alpha = (exp(intensity) - 1.0) / (exp(1.0) - 1.0);
   return vec4(intensity * high, alpha);


void main()
//get the 3D texture coordinates for lookup into the volume dataset
vec3 dataPos = vUV;

//Getting the ray marching direction:
//get the object space position by subracting 0.5 from the
//3D texture coordinates. Then subtraact it from camera position
//and normalize to get the ray marching direction
vec3 geomDir = normalize((vUV-vec3(0.5)) - camPos); 

//multiply the raymarching direction with the step size to get the
//sub-step size we need to take at each raymarching step
vec3 dirStep = geomDir * step_size; 

//flag to indicate if the raymarch loop should terminate
bool stop = false; 

//for all samples along the ray
for (int i = 0; i < MAX_SAMPLES; i++) {
    // advance ray by dirstep
    dataPos = dataPos + dirStep;

    stop = dot(sign(dataPos-texMin),sign(texMax-dataPos)) < 3.0;

    //if the stopping condition is true we brek out of the ray marching loop
    if (stop) 
    // data fetching from the red channel of volume texture
    float sample = texture(volume, dataPos).r;  

     vec4 c = colour_transfer(sample);

    vFragColor.rgb = c.a * c.rgb + (1 - c.a) * vFragColor.a * vFragColor.rgb;
    vFragColor.a = c.a + (1 - c.a) * vFragColor.a;

    //early ray termination
    //if the currently composited colour alpha is already fully saturated
    //we terminated the loop
    if( vFragColor.a>0.99)


How can i specific the coordinates for i will visualize the information in the 3d textures, in polar cordinates?

1 Answers
Best Answer
Arben answered 3 weeks ago
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