Frontiers/Shaders/terrain.gdshader

shader_type canvas_item;

// Textures
uniform sampler2D height_map : filter_nearest;

// Thresholds
uniform float water_threshold = 0.0;
uniform float rock_threshold = 0.05;
uniform float snow_height_threshold = 0.8;
uniform float desert_temperature_threshold = 0.7;
uniform float desert_moisture_threshold = 0.3;

// Noise parameters
uniform float temperature_noise_frequency = 0.01;
uniform float temperature_noise_amplitude = 0.1;
uniform float moisture_noise_frequency = 0.01;
uniform float moisture_noise_amplitude = 0.1;

// Debug mode
uniform int debug_type = 0; // 0=None, 1=Slope, 2=Height, 3=Temperature, 4=Moisture

// Colors
const vec3 COLOR_WATER = vec3(0.263, 0.502, 0.690);     // #4380b0
const vec3 COLOR_GRASS = vec3(0.745, 0.835, 0.541);     // #bed58a
const vec3 COLOR_DESERT = vec3(0.929, 0.788, 0.686);    // #edc9af
const vec3 COLOR_BEACH = vec3(0.502, 0.502, 0.502);     // #808080
const vec3 COLOR_SNOW = vec3(0.957, 0.957, 0.957);      // #f4f4f4
const vec3 COLOR_ROCK = vec3(0.894, 0.827, 0.651);      // #e4d3a6

// Better hash function for noise
vec2 hash22(vec2 p, float seed) {
    vec3 p3 = fract(vec3(p.xyx) * vec3(443.897, 441.423, 437.195));
    p3 += dot(p3, p3.yzx + 19.19 + seed);
    return fract((p3.xx + p3.yz) * p3.zy);
}

float hash12(vec2 p, float seed) {
    vec3 p3 = fract(vec3(p.xyx) * 0.1031);
    p3 += dot(p3, p3.yzx + 33.33 + seed);
    return fract((p3.x + p3.y) * p3.z);
}

// Perlin noise
float perlin_noise(vec2 p, float seed) {
    vec2 i = floor(p);
    vec2 f = fract(p);

    // Quintic interpolation
    vec2 u = f * f * f * (f * (f * 6.0 - 15.0) + 10.0);

    // Get gradients
    float a = hash12(i + vec2(0.0, 0.0), seed);
    float b = hash12(i + vec2(1.0, 0.0), seed);
    float c = hash12(i + vec2(0.0, 1.0), seed);
    float d = hash12(i + vec2(1.0, 1.0), seed);

    // Mix
    return mix(mix(a, b, u.x), mix(c, d, u.x), u.y) * 2.0 - 1.0;
}

// FBM with 12 octaves
float fbm(vec2 p, float freq, float seed) {
    float value = 0.0;
    float amplitude = 0.5;
    float frequency = freq;

    for(int i = 0; i < 12; i++) {
        value += amplitude * perlin_noise(p * frequency, seed);
        frequency *= 2.0;
        amplitude *= 0.5;
    }

    return value;
}

// Get height at UV coordinates
float get_height(vec2 uv) {
    return texture(height_map, uv).r;
}

// Get heat value with latitude falloff
float get_heat(vec2 uv) {
    vec2 heightmap_size = vec2(textureSize(height_map, 0));
    vec2 heightmap_coords = uv * heightmap_size;

    // Original C# uses 1/frequency for FastNoiseLite, so we invert
    float actualFreq = 1.0 / temperature_noise_frequency;
    float heat = fbm(heightmap_coords, actualFreq, 1738.0);
    heat *= temperature_noise_amplitude;

    // Latitude falloff (sine wave from poles to equator)
    float latitude_factor = sin(3.14159265 * uv.y);
    heat = latitude_factor + heat;

    return heat;
}

// Get moisture value with latitude falloff
float get_moisture(vec2 uv) {
    vec2 heightmap_size = vec2(textureSize(height_map, 0));
    vec2 heightmap_coords = uv * heightmap_size;

    // Original C# uses 1/frequency for FastNoiseLite, so we invert
    float actualFreq = 1.0 / moisture_noise_frequency;
    float moisture = fbm(heightmap_coords, actualFreq, 1337.0);
    moisture *= moisture_noise_amplitude;

    // Latitude falloff (sine wave from poles to equator)
    float latitude_factor = sin(3.14159265 * uv.y);
    moisture = latitude_factor + moisture;

    return moisture;
}

// Check if position is sea
bool is_sea(vec2 uv) {
    return get_height(uv) <= water_threshold;
}

// Check if position is desert
bool is_desert(vec2 uv, float heat, float moisture) {
    return moisture < desert_moisture_threshold && heat > desert_temperature_threshold;
}

// Calculate max height difference with neighbors (for slope)
float get_max_slope(vec2 uv) {
    vec2 heightmap_size = vec2(textureSize(height_map, 0));
    vec2 texel_size = 1.0 / heightmap_size;

    float center_height = get_height(uv);
    float max_diff = 0.0;

    // Check 8 neighbors
    for(int x = -1; x <= 1; x++) {
        for(int y = -1; y <= 1; y++) {
            if(x == 0 && y == 0) continue;

            vec2 neighbor_uv = uv + vec2(float(x), float(y)) * texel_size;
            float neighbor_height = get_height(neighbor_uv);
            float diff = abs(center_height - neighbor_height);
            max_diff = max(max_diff, diff);
        }
    }

    return max_diff;
}

// Check if any neighbor is sea (for beach detection)
bool borders_sea(vec2 uv) {
    vec2 heightmap_size = vec2(textureSize(height_map, 0));
    vec2 texel_size = 1.0 / heightmap_size;

    for(int x = -1; x <= 1; x++) {
        for(int y = -1; y <= 1; y++) {
            if(x == 0 && y == 0) continue;

            vec2 neighbor_uv = uv + vec2(float(x), float(y)) * texel_size;
            if(is_sea(neighbor_uv)) {
                return true;
            }
        }
    }

    return false;
}

void fragment() {
    vec2 uv = UV;

    float height_value = get_height(uv);
    float heat_value = get_heat(uv);
    float moisture_value = get_moisture(uv);
    float slope = get_max_slope(uv);

    vec3 color = COLOR_GRASS; // Default

    if(debug_type == 0) {
        // Normal rendering

        // Water
        if(is_sea(uv)) {
            color = COLOR_WATER;
        }
        // Desert
        else if(is_desert(uv, heat_value, moisture_value)) {
            color = COLOR_DESERT;
        }
        // Beach (borders sea)
        else if(borders_sea(uv)) {
            color = COLOR_BEACH;
        }
        // Snow (high altitude, not desert)
        else if(height_value > snow_height_threshold && !is_desert(uv, heat_value, moisture_value)) {
            color = COLOR_SNOW;
        }

        // Rock (steep areas) - override everything except water
        if(slope > rock_threshold && !is_sea(uv)) {
            color = COLOR_ROCK;
        }
    }
    else if(debug_type == 1) {
        // Slope debug
        float gray = slope * 5.0;
        color = vec3(gray);
    }
    else if(debug_type == 2) {
        // Height debug
        color = vec3(height_value);
    }
    else if(debug_type == 3) {
        // Temperature debug
        color = vec3(heat_value);
    }
    else if(debug_type == 4) {
        // Moisture debug
        color = vec3(moisture_value);
    }

    COLOR = vec4(color, 1.0);
}