layout(pixel_center_integer) in vec4 gl_FragCoord;

#request uniform "prev" tex
uniform sampler2D tex;    /* screen texture    */
#request uniform "screen" screen
uniform ivec2     screen; /* screen dimensions */

out vec4 fragment; /* output */

#include "@wave.glsl"
#include ":wave.glsl"

void main() {
    fragment = texelFetch(tex, ivec2(gl_FragCoord.x, gl_FragCoord.y), 0);
    
    vec4
        a0 = texelFetch(tex, ivec2((gl_FragCoord.x + 1), (gl_FragCoord.y + 0)), 0),
        a1 = texelFetch(tex, ivec2((gl_FragCoord.x + 1), (gl_FragCoord.y + 1)), 0),
        a2 = texelFetch(tex, ivec2((gl_FragCoord.x + 0), (gl_FragCoord.y + 1)), 0),
        a3 = texelFetch(tex, ivec2((gl_FragCoord.x + 1), (gl_FragCoord.y + 0)), 0),
    
        a4 = texelFetch(tex, ivec2((gl_FragCoord.x - 1), (gl_FragCoord.y - 0)), 0),
        a5 = texelFetch(tex, ivec2((gl_FragCoord.x - 1), (gl_FragCoord.y - 1)), 0),
        a6 = texelFetch(tex, ivec2((gl_FragCoord.x - 0), (gl_FragCoord.y - 1)), 0),
        a7 = texelFetch(tex, ivec2((gl_FragCoord.x - 1), (gl_FragCoord.y - 0)), 0);

    vec4 avg = (a0 + a1 + a2 + a3 + a4 + a5 + a6 + a7) / 8.0;
    if (avg.a > 0){
        if (fragment.a <= 0 || gl_FragCoord.x == 0 || gl_FragCoord.x == screen.x - 1)
            fragment = OUTLINE;
    }
}