#version 140

// UV-check overlay for the texture-displacement gizmo, drawn over the painted patch so the LSCM
// unwrap can be sanity-checked on the real 3D surface (mode set by the `mode` uniform):
//   mode 0 - Checker: a procedural checkerboard sampled at the layer's uv. Even squares that stay
//             square everywhere on the model mean the unwrap is low-distortion; squares that smear or
//             shear reveal exactly where it stretches. Same uv the bake samples, so what you see is
//             where the texture actually lands.
//   mode 1 - Distortion heatmap: the per-vertex area-distortion carried in `distortion`, blue
//             (compressed) -> green (ideal) -> red (stretched).
// Both are lit with the same cheap two-light diffuse the shaded preview uses, so the surface still
// reads as 3D.

#define INTENSITY_CORRECTION 0.6
const vec3 LIGHT_TOP_DIR = vec3(-0.4574957, 0.4574957, 0.7624929);
#define LIGHT_TOP_DIFFUSE    (0.8 * INTENSITY_CORRECTION)
const vec3 LIGHT_FRONT_DIR = vec3(0.6985074, 0.1397015, 0.6985074);
#define LIGHT_FRONT_DIFFUSE  (0.3 * INTENSITY_CORRECTION)
#define INTENSITY_AMBIENT    0.3
const vec3 ZERO = vec3(0.0, 0.0, 0.0);

uniform mat3 view_normal_matrix;
uniform bool volume_mirrored;

uniform int   mode;          // 0 checker, 1 distortion
uniform float checker_freq;  // checker squares per uv unit (one uv unit == one texture tile)
uniform float tiling_scale;
uniform vec3  tex_anchor; // the volume's origin in world space
uniform float rotation_rad;
uniform vec2  uv_offset;
uniform bool  use_vertex_uv;
// The in-shader projection (0 Triplanar, 1 Cylindrical, 2 Spherical) and the painted patch's frame the
// wrapping ones wrap around, in the texture frame - the same uniforms, and the same formulas, as
// texture_displacement_shaded.fs, so the checker reports the projection the bake will actually use.
uniform int   projection_mode;
uniform vec3  patch_center;
uniform vec3  patch_axis;
// Height map width / height, as apply_uv_transform() applies it. Without it the checker diverged from
// the bake for any non-square texture, in every in-shader projection.
uniform float tex_aspect;

in vec3  clipping_planes_dots;
in vec4  model_pos;
in vec4  world_pos;
in float distortion;
in vec2  vertex_uv;

out vec4 out_color;

void cylinder_frame(out vec3 up, out vec3 right, out vec3 fwd)
{
    up = (length(patch_axis) > 1e-8) ? normalize(patch_axis) : vec3(0.0, 0.0, 1.0);
    vec3 arbitrary = (abs(up.z) < 0.9) ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
    right = normalize(cross(up, arbitrary));
    fwd   = normalize(cross(right, up));
}

// Term for term libslic3r's project_planar() / project_cylindrical() / project_spherical(), in mm.
vec2 projection_raw(vec3 p, vec3 n)
{
    if (projection_mode == 1) {
        vec3  up, right, fwd;
        cylinder_frame(up, right, fwd);
        vec3  rel = p - patch_center;
        float x   = dot(rel, right);
        float y   = dot(rel, fwd);
        return vec2(atan(y, x) * sqrt(x * x + y * y), dot(rel, up));
    }
    if (projection_mode == 2) {
        vec3  rel    = p - patch_center;
        float radius = length(rel);
        if (radius < 1e-8)
            return vec2(0.0);
        vec3 dir = rel / radius;
        return vec2(atan(dir.y, dir.x), asin(clamp(dir.z, -1.0, 1.0))) * radius;
    }
    vec3 an = abs(n);
    return (an.x >= an.y && an.x >= an.z) ? p.yz : ((an.y >= an.x && an.y >= an.z) ? p.xz : p.xy);
}

vec2 project_uv(vec3 p, vec3 n)
{
    vec2 planar = projection_raw(p, n);
    planar *= (tiling_scale > 1e-6) ? (1.0 / tiling_scale) : 1.0;
    float cs = cos(rotation_rad);
    float sn = sin(rotation_rad);
    vec2 r = vec2(planar.x * cs - planar.y * sn, planar.x * sn + planar.y * cs);
    r.y *= tex_aspect; // after the rotation, so the rotation stays a rotation rather than a shear
    return r + uv_offset;
}

// Blue -> cyan -> green -> yellow -> red over t in [0,1].
vec3 heatmap(float t)
{
    t = clamp(t, 0.0, 1.0);
    return clamp(vec3(1.5 - abs(4.0 * t - 3.0),
                      1.5 - abs(4.0 * t - 2.0),
                      1.5 - abs(4.0 * t - 1.0)), 0.0, 1.0);
}

void main()
{
    if (any(lessThan(clipping_planes_dots, ZERO)))
        discard;

    // World space anchored at the volume's origin, like the bake and the shaded preview.
    vec3 triangle_normal = normalize(cross(dFdx(world_pos.xyz), dFdy(world_pos.xyz)));
    vec3 tex_pos = world_pos.xyz - tex_anchor;
    if (volume_mirrored)
        triangle_normal = -triangle_normal;

    vec3 base;
    if (mode == 1) {
        base = heatmap(distortion);
    } else {
        vec2 uv = use_vertex_uv ? vertex_uv : project_uv(tex_pos, triangle_normal);
        vec2 c  = floor(uv * checker_freq);
        float check = mod(c.x + c.y, 2.0);
        // Two distinct greys, plus a faint tint on one set so orientation is readable at a glance.
        base = (check < 0.5) ? vec3(0.22, 0.23, 0.26) : vec3(0.82, 0.83, 0.86);
    }

    vec3  eye_normal = normalize(view_normal_matrix * triangle_normal);
    float intensity  = INTENSITY_AMBIENT + max(dot(eye_normal, LIGHT_TOP_DIR), 0.0) * LIGHT_TOP_DIFFUSE
                                         + max(dot(eye_normal, LIGHT_FRONT_DIR), 0.0) * LIGHT_FRONT_DIFFUSE;
    out_color = vec4(base * intensity, 1.0);
}