// world.gdshader
// shader for earth globe with heightmap and color texture
shader_type spatial;

uniform sampler2D height_map : hint_default_white;
uniform sampler2D earth_texture : hint_default_white;
uniform float height_scale : hint_range(0.0, 0.2) = 0.02;
uniform bool apply_height = true;
uniform bool show_height_debug = false;

// convert point on unit sphere to lat/lon uv coordinates
vec2 point_to_uv(vec3 point) {
float latitude = asin(point.y);
float longitude = atan(point.x, -point.z);
// optional : move seam by rotating longitude (0 = current)
float lon_offset = 0.0;
longitude += lon_offset;
float u = (longitude + PI) / (2.0 * PI);
float v = (latitude + PI / 2.0) / PI;

return vec2(u, v);
}

void vertex() {
// get point on unit sphere (normalized vertex position)
vec3 sphere_point = normalize(VERTEX);
// convert to uv using lat/lon projection
vec2 tex_coord = point_to_uv(sphere_point);
// sample heightmap
// apply height displacement along normal
if (apply_height) {
float height = texture(height_map, tex_coord).r;
VERTEX = sphere_point * (1.0 + height * height_scale);
NORMAL = normalize(VERTEX);
}
// pass uv to fragment shader
UV = tex_coord;
}

void fragment() {
// sample earth texture using lat/lon uv
vec4 earth_color = texture(earth_texture, UV);
if (show_height_debug) {
// debug: show heightmap as grayscale
float height = texture(height_map, UV).r;
ALBEDO = vec3(height);
} else {
// normal rendering: show earth texture
ALBEDO = earth_color.rgb;
}
// basic lighting
ROUGHNESS = 0.8;
METALLIC = 0.0;
}