GLSL for reconstructing depth from HSL image

gistfile1.txt

//Convert an RGB vec3 to an HSL vec3. We use the HUE value to encode depth, while SATURATION and BRIGHTNESS are always maxed out

vec3 rgb2hsl( vec3 _input ){
  float h = 0.0;
	float s = 0.0;
	float l = 0.0;
	float r = _input.r;
	float g = _input.g;
	float b = _input.b;
	float cMin = min( r, min( g, b ) );
	float cMax = max( r, max( g, b ) );
 
	l = ( cMax + cMin ) / 2.0;
	if ( cMax > cMin ) {
		float cDelta = cMax - cMin;
        
		s = l < .05 ? cDelta / ( cMax + cMin ) : cDelta / ( 2.0 - ( cMax + cMin ) );
 
		// hue
		if ( r == cMax ) {
			h = ( g - b ) / cDelta;
		} else if ( g == cMax ) {
			h = 2.0 + ( b - r ) / cDelta;
		} else {
			h = 4.0 + ( r - g ) / cDelta;
		}
 
		if ( h < 0.0) {
			h += 6.0;
		}
		h = h / 6.0;
	}
	return vec3( h, s, l );
}

//sample the texture at depth position, get the Hue value (R component after conversion) and then map it between min & max

float depthValueFromSample( vec2 depthPos){
    vec2  halfvec = vec2(.5,.5);
    float depth = rgb2hsl( texture2DRect(texture, floor(depthPos) + halfvec ).xyz ).r;
    return depth * ( maxDepth - minDepth ) + minDepth;
}
  
vec2 samplePos = gl_Vertex.xy;
  vec2 depthPos = samplePos + depthRect.xy;
  float depth = depthValueFromSample( depthPos );

	// Reconstruct the 3D point position
  vec4 pos = vec4((samplePos.x - depthPP.x) * depth / depthFOV.x,
                  (samplePos.y - depthPP.y) * depth / depthFOV.y,
                  depth,                1.0);


The XML that we export looks like this:
<depth>
    <fovx>570.342224121</fovx>
    <fovy>570.342224121</fovy>
    <ppx>320.000000000</ppx>
    <ppy>240.000000000</ppy>
    <width>640.000000000</width>
    <height>480.000000000</height>
    <minDepth>0.000000000</minDepth>
    <maxDepth>5999.999511719</maxDepth>
</depth>