GLSL Basics

attribute float Accessibility;varying vec4 ShadowCoord;// Ambient and diffuse scale factors.const float As = 1.0 / 1.5;const float Ds = 1.0 / 3.0;void main(){    vec4 ecPosition = gl_ModelViewMatrix * gl_Vertex;    vec3 ecPosition3 = (vec3(ecPosition)) / ecPosition.w;    vec3 VP = vec3(gl_LightSource[0].position) - ecPosition3;    VP = normalize(VP);    vec3 normal = normalize(gl_NormalMatrix * gl_Normal);    float diffuse = max(0.0, dot(normal, VP));    float scale = min(1.0, Accessibility * As + diffuse * Ds);    vec4 texCoord = gl_TextureMatrix[1] * gl_Vertex;    ShadowCoord   = texCoord / texCoord.w;    gl_FrontColor  = vec4(scale * gl_Color.rgb, gl_Color.a);    gl_Position    = ftransform();}Fragment Shaderuniform sampler2DShadow ShadowMap;uniform float Epsilon;varying vec4 ShadowCoord;float lookup(float x, float y){    float depth = shadow2DProj(ShadowMap,                      ShadowCoord + vec3(x, y, 0) * Epsilon).x;    return depth != 1.0 ? 0.75 : 1.0;}void main(){    float shadeFactor = lookup(0.0, 0.0);    gl_FragColor = vec4(shadeFactor * gl_Color.rgb, gl_Color.a);}