// missing_texture.glsl

extern float scale = 16.0;

vec4 effect(vec4 color, Image texture, vec2 uv, vec2 screen_coords)
{
    vec4 tex = Texel(texture, uv);

    // checker pattern
    float cx = floor(screen_coords.x / scale);
    float cy = floor(screen_coords.y / scale);

    float checker = mod(cx + cy, 2.0);

    vec3 magenta = vec3(1.0, 0.0, 1.0);
    vec3 black   = vec3(0.0, 0.0, 0.0);

    vec3 pattern = mix(magenta, black, checker);

    return vec4(pattern, tex.a) * color;
}