Shader mask

/* GLSL */

// fragmentShader:
#ifdef GL_ES
precision mediump float;
#endif

varying vec4 v_color;
varying vec2 v_texCoords;
uniform sampler2D u_texture;
uniform sampler2D u_maskTexture;

void main() {
    vec4 color = v_color texture2D( u_texture, v_texCoords );
    vec2 maskCoords = vec2(v_texCoords.x 2.0, v_texCoords.y 12.0);
    vec3 mask_color = texture2D(u_maskTexture, maskCoords).rgb;
    if( color.a == 0.0 ) gl_FragColor = vec4( color.r, color.g, color.b, color.a );
    else gl_FragColor = vec4( mask_color.r, mask_color.g, mask_color.b, color.a );
}

// vertexShader:
attribute vec4 a_position;
attribute vec4 a_color;
attribute vec2 a_texCoord0;
attribute vec3 a_maskTexture;

uniform mat4 u_projTrans;

varying vec3 v_maskTexture;
varying vec4 v_color;
varying vec2 v_texCoords;

void main() {
    v_color = a_color;
    v_maskTexture = a_maskTexture;
    v_texCoords = a_texCoord0;
    gl_Position = u_projTrans a_position;
}