uniform sampler2D map;

uniform float width;
uniform float height;
uniform float nearClipping, farClipping;
uniform float pointSize;
uniform float boxSize;
uniform float cameraIndex;
uniform float numCameras;

uniform mat4 c2wm;
uniform mat4 prjm;

varying vec2 vUv;
varying vec2 vUv1pxOffset;
varying float paintfordiscard;

void main() {

    vUv = vec2( position.x / width, position.y / height );  
    vUv1pxOffset = vec2( 1.0 / width, 1.0 / height ) * 2.0;
    int skipctr = 0;
    int skipthreshold = 1;

    for (float xoff = -1.0; xoff < 2.0; xoff++) {
        for (float yoff = -1.0; yoff < 2.0; yoff++) {
            vec2 thisUv = vUv + (vec2(xoff, yoff) * vUv1pxOffset);
            vec4 color = texture2D(map, thisUv*vec2(1.0/numCameras,(1.0/3.0))+vec2(cameraIndex/numCameras,(1.0/3.0)));
            float depth = ( color.r + color.g + color.b ) / 3.0;
            if (depth < 0.01) {
                skipctr++;
            }
        }
    }

    paintfordiscard = float(skipctr > skipthreshold);
    vec4 color = texture2D( map, vUv*vec2(1.0/numCameras,(1.0/3.0))+vec2(cameraIndex/numCameras,(1.0/3.0)));

    float depth = ( color.r + color.g + color.b ) / 3.0;

    vec4 pos = vec4(
        2.*(position.x / float(width))  - 1., 
        2.*(position.y / float(height)) - 1., 
        mix(1., -1., depth), 
        1.0
    );

    // First undo projection, then undo view, then below model is undone; flip the Y and Z vectors since WebGL is right handed
    vec4 pos2 = c2wm * inverse(prjm) * pos; // order matters here! Parentheses do not

    pos2.xyz *= boxSize;
    gl_PointSize = pointSize;
    gl_Position = projectionMatrix * modelViewMatrix * pos2;
    if (depth  <.01 || (paintfordiscard != 0.0))  { // move this point out of the view box if the depth is nearly zero
        gl_Position = vec4(-1., -1., -1., -1.);
    }
}