Simple GLSL Spotlight Shader

I need help with a simple spotlight shader. All vertices inside the cone should be colored yellow, all vertices outside the cone should be colored black. I just can't get it work. I asume it has something to do with the transformation from world into eye coordinates. Vertex Shader: ``` uniform vec4 lightPositionOC; // in object coordinates uniform vec3 spotDirectionOC; // in object coordinates uniform float spotCutoff; // in degrees void main(void) { vec3 lightPosition; vec3 spotDirection; vec3 lightDirection; float angle; gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex; // Transforms light position and direction into eye coordinates lightPosition = (lightPositionOC * gl_ModelViewMatrix).xyz; spotDirection = normalize(spotDirectionOC * gl_NormalMatrix); // Calculates the light vector (vector from light position to vertex) vec4 vertex = gl_ModelViewMatrix * gl_Vertex; lightDirection = normalize(vertex.xyz - lightPosition.xyz); // Calculates the angle between the spot light direction vector and the light vector angle = dot( normalize(spotDirection), -normalize(lightDirection)); angle = max(angle,0); // Test whether vertex is located in the cone if(angle > radians(spotCutoff)) gl_FrontColor = vec4(1,1,0,1); // lit (yellow) else gl_FrontColor = vec4(0,0,0,1); // unlit(black) } ``` Fragment Shader: ``` void main(void) { gl_FragColor = gl_Color; } ``` Edit: Tim is right. This ``` if(angle > radians(spotCutoff)) ``` should be: ``` if(acos(angle) < radians(spotCutoff)) ``` New question: The light seems not to stay at a fixed position in the scene, instead it seems to move relative to my camera as the cone gets smaller or bigger when I move forward or backward.