let's not forget the actual shader

pkg/base/shader/post_stereo.lua

@@ -0,0 +1,97 @@
+return shader_new{name="post_stereo", vert=[=[
+// Vertex shader
+
+void main()
+{
+	gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
+	gl_TexCoord[0] = gl_MultiTexCoord0;
+}
+
+]=], frag=[=[
+// Fragment shader
+
+uniform sampler2D tex0;
+uniform sampler2D tex1;
+uniform vec2 soffs;
+uniform float time;
+uniform float fog;
+uniform float depth_A;
+uniform float depth_B;
+
+float getdepth(float buf)
+{
+	/*
+	const float f = 127.5;
+	const float n = 0.05;
+	// TODO: fetch correct fog and zoom
+
+	// d = (Az+B)/(Cz+D)
+	// d(Cz+D) = (Az+B)
+	// Czd+Dd = Az+B
+	// Czd-Az = B-Dd
+	// z(Cd-A) = B-Dd
+	// z = (B-Dd)/(Cd-A)
+
+	// Note, commented code is correct
+	//const float A = (f+n)/(f-n);
+	//const float B = -(2.0*f*n)/(f-n);
+	//const float C = 1.0;
+	//return B/(C*buf-A);
+	//return (B/C)/(buf-(A/C)); // saves a calculation step
+
+	const float A = (f+n)/(f-n);
+	const float B = -(2.0*f*n)/(f-n);
+	return B/(buf-A);
+	*/
+
+	// Hypothetically faster when f,n not precalced
+	/*
+	const float A = (f+n);
+	const float B = -(2.0*f*n);
+	return B/((f-n)*buf-A);
+	*/
+
+	return depth_B/(buf-depth_A);
+	// get 1/z
+	//return (buf-depth_A)/depth_B;
+}
+
+void main()
+{
+	vec2 tc = gl_TexCoord[0].st;
+	float dbval = texture2D(tex1, tc).x;
+	float db = getdepth(dbval);
+	vec2 tc0 = tc;
+	vec2 tc1 = tc;
+	float sep = min(0.1,0.1/db);
+	tc0.x -= sep;
+	tc1.x += sep;
+	vec4 color0 = texture2D(tex0, tc0);
+	vec4 color1 = texture2D(tex0, tc1);
+
+	// mild desaturation
+	float lum0 = dot(color0.rgb, vec3(0.3,0.5,0.2));
+	float lum1 = dot(color1.rgb, vec3(0.3,0.5,0.2));
+	color0 -= lum0;
+	color1 -= lum1;
+	color0 *= 0.5;
+	color1 *= 0.5;
+	color0 += lum0;
+	color1 += lum1;
+
+	vec4 color = vec4(
+		color0.r,
+		color1.g,
+		color1.b,
+		1.0);
+
+	float distamp = length((tc*2.0-1.0)*(soffs.x/soffs)); // TODO: get correct FOV
+	float realdist = (1.0/db)*length(vec2(1.0, distamp));
+	float fog_strength = min(1.0, realdist/fog);
+	fog_strength *= fog_strength;
+	gl_FragColor = color * (1.0 - fog_strength)
+		+ gl_Fog.color * fog_strength;
+}
+
+]=]}
+