#version 330

// ── Gradient border shader for picom ─────────────────────────────────────────
// Blends a diagonal gradient (top-left → bottom-right) over the window border.
//
// COLOR_A : top-left colour  — #7B2FBE (purple)
// COLOR_B : bottom-right     — #2FB8BE (teal)
//
// To change colours: convert hex → float by dividing each channel by 255.

// ── Tuneable constants ────────────────────────────────────────────────────────

const float BORDER_WIDTH   = 4.0;   // Border band thickness in pixels
const float BORDER_OPACITY = 0.95;  // How strongly the gradient is applied

// COLOR_A: #7B2FBE  (vibrant purple)
const vec3 COLOR_A = vec3(0.106,  0.992,  0.612);

// COLOR_B: #2FB8BE  (cyan-teal)
const vec3 COLOR_B = vec3(0.651,  1.0,  0.788);

// ── Picom-provided ────────────────────────────────────────────────────────────

in vec2 texcoord;           // Fragment texture coordinate (in pixels)
uniform sampler2D tex;      // Window texture

// Picom's built-in post-processing (opacity, rounded corners, etc.)
vec4 default_post_processing(vec4 c);

// ── Entry point ───────────────────────────────────────────────────────────────

vec4 window_shader() {
    // Sample the original window pixel
    vec4 c = texelFetch(tex, ivec2(texcoord), 0);

    // Derive texture size from the sampler
    vec2 size = vec2(textureSize(tex, 0));

    // Normalised UV (0,0) top-left → (1,1) bottom-right
    vec2 uv = texcoord / size;

    // Diagonal gradient factor
    float t = (uv.x + uv.y) * 0.5;
    vec3 gradient = mix(COLOR_A, COLOR_B, t);

    // Border mask: 1.0 on the edge band, 0.0 in the interior
    float left   = smoothstep(0.0, BORDER_WIDTH, texcoord.x);
    float right  = smoothstep(0.0, BORDER_WIDTH, size.x - texcoord.x);
    float top    = smoothstep(0.0, BORDER_WIDTH, texcoord.y);
    float bottom = smoothstep(0.0, BORDER_WIDTH, size.y - texcoord.y);
    float mask   = 1.0 - (left * right * top * bottom);

    // Blend gradient onto border region only
    c.rgb = mix(c.rgb, gradient, mask * BORDER_OPACITY);

    // Let picom handle opacity, rounded corners, etc.
    return default_post_processing(c);
}