Object aligned slice based volume rendering

I just finished 2D texture slices based volume rendering today. Here are the snapshots of the application. Its damn fast. I will be adding some transfer function editing facility into it tomorrow.

A cool idea though will now work on transfer functions and then view aligned slicing of 3D texture.

Implementation details:

I used glut and OpenGL for this b/c I think its much more fast to develop applications in OpenGL and glut. First I determine the current view direction vector which is simply obtained using the following code

   GLfloat matView[16];
   glGetFloatv(GL_MODELVIEW_MATRIX, matView);
   GLfloat viewDir[3]={ -matView[2], -matView[6], -matView[10]};

Next a 3d texture is loaded from the CT/MRI scans and then using this code, object space quad slices are generated. Here I am only giving the code for the PosZ axis. A slight modification is needed for the other axes.

void DrawSliceZPos()
{
   float zPos = 0.5;
   float zAmt = -1.0f/zSlices;

   glBindTexture(GL_TEXTURE_3D,textureID);
   glBegin(GL_QUADS);

   //offset the slice so its in the middle
   zPos += zAmt/2.0f;
   for(int i=zSlices-1;i>=0;i--)
   {
      float tex = (((float)i)/zSlices);
      glTexCoord3f(0,0,tex); glVertex3f(-0.5, -0.5, zPos);
      glTexCoord3f(0,1,tex); glVertex3f(-0.5,  0.5, zPos);
      glTexCoord3f(1,1,tex); glVertex3f( 0.5,  0.5, zPos);
      glTexCoord3f(1,0,tex); glVertex3f( 0.5, -0.5, zPos);
      zPos += zAmt;
   }
   glEnd();
}

The appropriate slices are drawn based on the maximum abs value of the current view direction as

switch(GetMaxDim(viewDir))
{
   case 0:
      if(viewDir[maxDim] > 0.0f)
         DrawSlicePosX();
      else
         DrawSliceNegX();
   break;
   ...
   case n: ... and so on
}

Thats it and finally the result is blended to produce the rendering as shown above.