source: downloads/Samples/Media/materials/programs/DepthShadowmapCasterFp.glsl @ 1

varying vec2 depth;

void main()
{
#if LINEAR_RANGE
        float finalDepth = depth.x;
#else
        float finalDepth = depth.x / depth.y;
#endif
        // just smear across all components 
        // therefore this one needs high individual channel precision
        gl_FragColor = vec4(finalDepth, finalDepth, finalDepth, 1);

}