#ifdef GL_ES
precision mediump float;
#endif

uniform sampler2D u_Tex0;  
uniform sampler2D u_Tex1;    
uniform vec2 u_WalkOffset;    
varying vec2 v_TexCoord;   

const vec2 zoom = vec2(5.0, 5.0);
const vec3 overlayColor = vec3(0.0, 0.0, 0.0);
const float overlayOpacity = 0.3;
void main(void)
{
    vec2 offset = (u_WalkOffset + v_TexCoord) * zoom;
    offset = fract(offset);
    offset.y = 1.0 - offset.y;

    vec3 bgcol  = texture2D(u_Tex0, v_TexCoord).rgb;
    vec3 fogcol = texture2D(u_Tex1, offset).rgb;
    vec3 finalFog = mix(fogcol, overlayColor, 0.4 - overlayOpacity);

    vec3 col = bgcol * finalFog;

    gl_FragColor = vec4(col, 1.0);
}