#version 300 es
precision highp float;

uniform sampler2D u_texture;
uniform vec2 u_resolution;
uniform float u_time;
in vec2 v_texCoord;
out vec4 fragColor;

const float EDGE_STRENGTH = 0.2;  // Adjust edge brightness
const float EDGE_THRESHOLD = 0.01; // Minimum edge strength to display

void main() {
    vec2 uv = gl_FragCoord.xy/u_resolution.xy;
    vec2 texel = 1.0 / u_resolution.xy;

    // Sample the neighboring pixels
    vec3 top    = texture(u_texture, uv + vec2(0.0,  texel.y)).rgb;
    vec3 bottom = texture(u_texture, uv + vec2(0.0, -texel.y)).rgb;
    vec3 left   = texture(u_texture, uv + vec2(-texel.x, 0.0)).rgb;
    vec3 right  = texture(u_texture, uv + vec2(texel.x,  0.0)).rgb;
    vec3 center = texture(u_texture, uv).rgb * 4.0;

    // Apply Laplacian kernel
    vec3 laplacian = -center + top + bottom + left + right;

    // Convert to grayscale
    float edge = dot(abs(laplacian), vec3(0.2126, 0.7152, 0.0722));

    // Apply threshold and adjust strength
    edge = smoothstep(EDGE_THRESHOLD, EDGE_THRESHOLD + 0.01, edge) * EDGE_STRENGTH;

    fragColor = vec4(vec3(edge), 1.0);
}