simple.glsl

/* simple.glsl

simple diffuse lighting based on laberts cosine law; see e.g.:
    http://en.wikipedia.org/wiki/Lambertian_reflectance
    http://en.wikipedia.org/wiki/Lambert%27s_cosine_law
*/
---VERTEX SHADER-------------------------------------------------------
#ifdef GL_ES
    precision highp float;
#endif

attribute vec3 v_pos;
attribute vec3 v_normal;

uniform mat4 modelview_mat;
uniform mat4 projection_mat;

varying vec4 normal_vec;
varying vec4 vertex_pos;

void main(void) {
    // Compute vertex position in eye_sapce and normalize normal vector
    vec4 pos = modelview_mat * vec4(v_pos, 1.0);
    vertex_pos = pos;
    normal_vec = vec4(v_normal, 0.0);
    gl_Position = projection_mat * pos;
}


---FRAGMENT SHADER-----------------------------------------------------
#ifdef GL_ES
    precision highp float;
#endif

varying vec4 normal_vec;
varying vec4 vertex_pos;

uniform mat4 normal_mat;

void main(void) {
    // Correct normal, and compute light vector (assume light at the eye)
    vec4 v_normal = normalize(normal_mat * normal_vec);
    vec4 v_light = normalize(vec4(0, 0, 0, 1) - vertex_pos);
    // Reflectance based on lamberts law of cosine
    float theta = clamp(dot(v_normal, v_light), 0.0, 1.0);
    gl_FragColor = vec4(theta, theta, theta, 1.0);
}