Add stencil light shaders by Lauri Peltonen (Zan).

Please Note:

There is a problem with this implementation when the light cone crosses
the near/far camera boundary.

Shaders/light-cone.frag

@@ -0,0 +1,9 @@
+varying float fogCoord;
+
+void main()
+{
+    vec4 fragColor = gl_FrontMaterial.ambient;
+//    float fogFactor = exp(-gl_Fog.density * gl_Fog.density * fogCoord * fogCoord);
+//    gl_FragColor = mix(gl_Fog.color, fragColor, fogFactor);
+    gl_FragColor = fragColor;
+}

Shaders/light-cone.vert

@@ -0,0 +1,9 @@
+varying float fogCoord;
+
+void main()
+{
+    vec3 ecPosition = vec3(gl_ModelViewMatrix * gl_Vertex);
+
+    gl_Position = ftransform();
+    fogCoord = abs(ecPosition.z);
+}

Shaders/terrain-default.frag

@@ -0,0 +1,58 @@
+// -*-C++-*-
+
+varying vec4 diffuse, constantColor;
+varying vec3 normal, lightDir, halfVector;
+varying float fogCoord, alpha;
+
+uniform sampler2D texture;
+uniform sampler3D noise;
+
+float luminance(vec3 color)
+{
+    return dot(vec3(0.212671, 0.715160, 0.072169), color);
+}
+
+void main()
+{
+    vec3 n, halfV;
+    float NdotL, NdotHV, fogFactor;
+    vec4 color = constantColor;
+    vec4 texel;
+    vec4 fragColor;
+    vec4 specular = vec4(0.0);
+
+    n = normalize(normal);
+    if (!gl_FrontFacing)
+        n = -n;
+    NdotL = max(dot(n, lightDir), 0.0);
+    if (NdotL > 0.0) {
+        color += diffuse * NdotL;
+        halfV = normalize(halfVector);
+        NdotHV = max(dot(n, halfV), 0.0);
+        if (gl_FrontMaterial.shininess > 0.0)
+            specular.rgb = (gl_FrontMaterial.specular.rgb
+                            * gl_LightSource[0].specular.rgb
+                            * pow(NdotHV, gl_FrontMaterial.shininess));
+    }
+    color.a = alpha;
+
+
+    // This shouldn't be necessary, but our lighting becomes very
+    // saturated. Clamping the color before modulating by the texture
+    // is closer to what the OpenGL fixed function pipeline does.
+    color = clamp(color, 0.0, 1.0);
+    texel = texture2D(texture, gl_TexCoord[0].st);
+    fragColor = color * texel + specular;
+
+    // Store pixel's luminance in the alpha value
+    if(alpha > 0.95) {
+      float lum = 1.0 - (luminance(fragColor.rgb) * 3.0);
+      float tex_lum = luminance(texel.rgb);
+      fragColor.a = tex_lum * clamp(lum, 0.01, 1.0);
+    }
+
+    fogFactor = exp(-gl_Fog.density * gl_Fog.density * fogCoord * fogCoord);
+    gl_FragColor = mix(gl_Fog.color, fragColor, fogFactor);
+
+}
+