Flatshading GLSL Example

flatshaded_frag.glsl

#extension GL_OES_standard_derivatives : enable
precision highp float;
precision highp int;

varying vec3 vViewPos;

vec3 normals_1_0(vec3 pos) {
    vec3 fdx = dFdx(pos);
    vec3 fdy = dFdy(pos);
    return normalize(cross(fdx, fdy));
}
void main() {
    vec3 lightDir = vec3(1.0, 0.0, 0.0);
    vec3 normal = normals_1_0(vViewPos);
    vec3 lightColor = vec3(0.9, 0.9, 0.8);
    vec3 materialColor = vec3(0.8, 0.6, 0.6);
    vec3 ambientColor = vec3(0.2, 0.2, 0.2);
    
    float cosTheta = clamp(dot(normal, lightDir), 0.0, 1.0);
    vec3 ambientLight = ambientColor * materialColor;
    
    gl_FragColor.rgb = ambientLight + lightColor * materialColor * cosTheta;
    gl_FragColor.a = 1.0;
}

flatshaded_vert.glsl

precision highp float;
precision highp int;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
attribute vec3 position;
varying vec3 vViewPos;
void main() {
    vec4 pos = vec4(position, 1.0);
    vec4 mpos = modelViewMatrix * pos;
    gl_Position = projectionMatrix * mpos;
    vViewPos = -mpos.xyz;
}