precision highp float;

varying vec2 v_TexCoords;
uniform mat4 u_STMatrix;

uniform sampler2D u_Texture;
uniform sampler2D u_Mask;
uniform float featureX;
uniform float featureY;
uniform float scale;

void main() {
  vec2 uv = (u_STMatrix * vec4(v_TexCoords.x, v_TexCoords.y, 0.0, 1.0)).xy;
	vec2 ap;
	ap.x = featureX;  			
	ap.y = featureY;
	vec2 uvTweek = (uv - ap) * (1.0/scale) + ap;  	// subtract anchor pt., do scale, then add anchor point back
	vec4 feed = texture2D(u_Texture, uv);
	vec4 mouth = texture2D(u_Texture, uvTweek);
	vec4 mask = texture2D(u_Mask, uvTweek);
	gl_FragColor = mix(feed, mouth, mask.r);
}