Depth Buffer in MATLAB

Question

I am trying to reconstruct world coordinates from the depth buffer in MATLAB and was wondering if someone could please help me figure out a way to get depth buffer values from a rendered image in MATLAB as there are no built-in functions that can accomplish this.

Answer 1

It seems that the best way to do this is via an MEX interface to openGL function calls. Thanks to Twerdster he has written a cross platform MEX file for this.

#include "mex.h"   

#define GL_VIEWPORT                       0x0BA2
#define GL_DEPTH_COMPONENT                0x1902
#define GL_FLOAT                          0x1406

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
    int viewport[4], i, x, y;
    int colLen;
    float *data;
    double *matrix;

    glGetIntegerv(GL_VIEWPORT, viewport);
    data = (float*)malloc(viewport[2] * viewport[3] * sizeof(float));
    glReadPixels(0, 0, viewport[2], viewport[3], GL_DEPTH_COMPONENT, GL_FLOAT, data);

    plhs[0] = mxCreateNumericMatrix(viewport[3], viewport[2], mxDOUBLE_CLASS, mxREAL);
    matrix = mxGetPr(plhs[0]);
    colLen = mxGetM(plhs[0]);

    for(x = 0; x < viewport[2]; ++ x) {
        for(y = 0; y < viewport[3]; ++ y)
            matrix[x * colLen + y] = data[x + (viewport[3] - 1 - y) * viewport[2]];
    }

    free(data);
    return;
 }

The only errors I get is glReadPixels and glGetIntegerv identifier not found

This is most likely because the library is not being linked correctly during compilation.

Assuming you are using this MEX file (the compilation will be the same method for whatever other MEX you have written); to compile this MEX file open the MATLAB command prompt / terminal and enter the following commands (Assuming you have saved your MEX file as getDepth.c) :

Windows: mex getDepth.c "path to OpenGL32.lib"

Unix: mex getDepth.c "path to opengl32.a"

This will compile this C code into an MEX callable function to be ran in MATLAB. Example:

depthData=getDepth;
figure
imshow(depthData);

I hope this helps.