Add texture displacement bump and UV-check shaders

resources/shaders/140/texture_displacement_uvcheck.fs

@@ -0,0 +1,83 @@
+#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 bump 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 float rotation_rad;
+uniform vec2  uv_offset;
+uniform bool  use_vertex_uv;
+
+in vec3  clipping_planes_dots;
+in vec4  model_pos;
+in vec4  world_pos;
+in float distortion;
+in vec2  vertex_uv;
+
+out vec4 out_color;
+
+vec2 project_uv(vec3 p, vec3 n)
+{
+    vec3 an = abs(n);
+    vec2 planar = (an.x >= an.y && an.x >= an.z) ? p.yz : ((an.y >= an.x && an.y >= an.z) ? p.xz : p.xy);
+    planar *= (tiling_scale > 1e-6) ? (1.0 / tiling_scale) : 1.0;
+    float cs = cos(rotation_rad);
+    float sn = sin(rotation_rad);
+    return vec2(planar.x * cs - planar.y * sn, planar.x * sn + planar.y * cs) + 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;
+
+    vec3 triangle_normal = normalize(cross(dFdx(model_pos.xyz), dFdy(model_pos.xyz)));
+    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(model_pos.xyz, 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);
+}