I was wondering if its actually possible to do bump mapping with 2 normal maps... I have tried doing it this way however I get a function overload on max and dot. uniform sampler2D n_mapTex; uniform sampler2D n_mapTex2; uniform sampler2D refTex; varying mediump vec2 TexCoord; varying mediump float vTime; void main() { mediump vec4 wave = texture2D(n_mapTex, TexCoord - vTime); mediump vec4 wave2 = texture2D(n_mapTex2, TexCoord + vTime); mediump vec4 bump = mix(wave2, wave, 0.5); //this extracts the normals from the combined normal maps mediump vec4 normal = normalize(bump.xyzw * 2.0 - 1.0); //determines light position mediump vec3 lightPos = normalize(vec3(0.0, 1.0, 3.0)); mediump float diffuse = max(dot(normal, lightPos),0.0); gl_FragColor = mix(texture2D(refTex, TexCoord), bump, 0.5); }