added water

src/app.rs

@@ -369,6 +369,12 @@ impl TerrainApp {
             &mut self.params.snowline_height,
             0..=255,
         );
+        labeled_int_slider(
+            ui,
+            "Water Table Height",
+            &mut self.params.water_table_height,
+            0..=255,
+        );
         labeled_float_slider(
             ui,
             "Rock Slope Angle",

src/generator.rs

@@ -22,6 +22,7 @@ pub struct GenerationParams {
     pub erosion_detail: f32,
     pub erosion_octaves: usize,
     pub snowline_height: u8,
+    pub water_table_height: u8,
     pub rock_slope_angle_degrees: f32,
 }
 
@@ -38,6 +39,7 @@ impl Default for GenerationParams {
             erosion_detail: 1.5,
             erosion_octaves: 5,
             snowline_height: 220,
+            water_table_height: 0,
             rock_slope_angle_degrees: 15.0,
         }
     }
@@ -54,6 +56,8 @@ pub struct GeneratedImages {
     #[allow(dead_code)]
     pub grass_mask_image: GrayImage,
     #[allow(dead_code)]
+    pub water_mask_image: GrayImage,
+    #[allow(dead_code)]
     pub rock_mask_image: GrayImage,
     #[allow(dead_code)]
     pub snow_mask_image: GrayImage,
@@ -135,6 +139,10 @@ fn clamp01(x: f32) -> f32 {
     clamp(x, 0.0, 1.0)
 }
 
+fn mix_u8(a: u8, b: u8, t: f32) -> u8 {
+    mix(a as f32, b as f32, clamp01(t)).round() as u8
+}
+
 fn hash22(p: Vec2, random_seed: u64) -> Vec2 {
     let scrambled_x = splitmix64(random_seed ^ 0x9E37_79B9_7F4A_7C15);
     let scrambled_y = splitmix64(random_seed ^ 0xBF58_476D_1CE4_E5B9);
@@ -401,10 +409,15 @@ pub fn generate(params: &GenerationParams) -> GeneratedImages {
         width,
         height,
         params.snowline_height,
+        params.water_table_height,
         params.rock_slope_angle_degrees,
     );
-    let terrain_composite_image =
-        build_soft_light_composite(&terrain_layers.terrain_color_image, &bumpmap_image);
+    let terrain_composite_image = build_soft_light_composite(
+        &terrain_layers.terrain_color_image,
+        &bumpmap_image,
+        &heightmap_image,
+        &terrain_layers.water_mask_image,
+    );
 
     GeneratedImages {
         width,
@@ -414,6 +427,7 @@ pub fn generate(params: &GenerationParams) -> GeneratedImages {
         terrain_color_image: terrain_layers.terrain_color_image,
         terrain_composite_image,
         grass_mask_image: terrain_layers.grass_mask_image,
+        water_mask_image: terrain_layers.water_mask_image,
         rock_mask_image: terrain_layers.rock_mask_image,
         snow_mask_image: terrain_layers.snow_mask_image,
     }
@@ -422,6 +436,7 @@ pub fn generate(params: &GenerationParams) -> GeneratedImages {
 struct TerrainLayers {
     terrain_color_image: RgbaImage,
     grass_mask_image: GrayImage,
+    water_mask_image: GrayImage,
     rock_mask_image: GrayImage,
     snow_mask_image: GrayImage,
 }
@@ -460,22 +475,28 @@ fn build_terrain_layers(
     width: usize,
     height: usize,
     snowline_height: u8,
+    water_table_height: u8,
     rock_slope_angle_degrees: f32,
 ) -> TerrainLayers {
     let mut terrain_color_image = RgbaImage::new(width as u32, height as u32);
     let mut grass_mask_image = GrayImage::new(width as u32, height as u32);
+    let mut water_mask_image = GrayImage::new(width as u32, height as u32);
     let mut rock_mask_image = GrayImage::new(width as u32, height as u32);
     let mut snow_mask_image = GrayImage::new(width as u32, height as u32);
 
-    let grass_color = Rgba([92, 140, 66, 255]);
+    let low_grass_color = [78, 146, 64];
+    let high_grass_color = [150, 156, 88];
+    let water_color = Rgba([40, 70, 150, 255]);
+    let sand_color = [210, 195, 145];
     let rock_color = Rgba([122, 112, 98, 255]);
-    let snow_color = Rgba([245, 248, 252, 255]);
+    let snow_color = Rgba([255, 250, 250, 255]);
     let slope_threshold_radians = rock_slope_angle_degrees.clamp(0.0, 89.9).to_radians();
 
     for y in 0..height {
         for x in 0..width {
             let idx = y * width + x;
             let height_value = heightmap[idx].clamp(0.0, 1.0);
+            let u8_height = (height_value * 255.0).round() as u8;
 
             let left = sample_height(heightmap, width, height, x.saturating_sub(1), y);
             let right = sample_height(heightmap, width, height, (x + 1).min(width - 1), y);
@@ -486,26 +507,56 @@ fn build_terrain_layers(
             let dy = (down - up) * 0.5 * height as f32;
             let slope_angle = dx.hypot(dy).atan();
 
+            let grass_t = clamp01((height_value - 0.08) / 0.52);
+            let grass_color = [
+                mix_u8(low_grass_color[0], high_grass_color[0], grass_t),
+                mix_u8(low_grass_color[1], high_grass_color[1], grass_t),
+                mix_u8(low_grass_color[2], high_grass_color[2], grass_t),
+            ];
+            let is_water = if water_table_height == 0 {
+                false
+            } else {
+                u8_height < water_table_height
+            };
+
+            let sand_width = 4.0;
+            let sand_t = if water_table_height == 0 || is_water {
+                0.0
+            } else {
+                let diff = (u8_height - water_table_height) as f32;
+                (1.0 - (diff / sand_width)).clamp(0.0, 1.0)
+            };
+
+            let base_color = Rgba([
+                mix_u8(grass_color[0], sand_color[0], sand_t),
+                mix_u8(grass_color[1], sand_color[1], sand_t),
+                mix_u8(grass_color[2], sand_color[2], sand_t),
+                255,
+            ]);
+
             let is_snow = if snowline_height == 0 {
                 true
             } else if snowline_height == u8::MAX {
                 false
             } else {
-                (height_value * 255.0).round() > snowline_height as f32
+                u8_height > snowline_height
             };
             let is_rock = slope_angle >= slope_threshold_radians;
 
             grass_mask_image.put_pixel(x as u32, y as u32, Luma([255]));
+            water_mask_image.put_pixel(x as u32, y as u32, Luma([if is_water { 255 } else { 0 }]));
             rock_mask_image.put_pixel(x as u32, y as u32, Luma([if is_rock { 255 } else { 0 }]));
             snow_mask_image.put_pixel(x as u32, y as u32, Luma([if is_snow { 255 } else { 0 }]));
 
-            let mut color = grass_color;
-            if is_rock {
-                color = rock_color;
-            }
-            if is_snow {
-                color = snow_color;
-            }
+            let color = if is_water {
+                water_color
+            } else if is_snow {
+                snow_color
+            } else if is_rock {
+                rock_color
+            } else {
+                base_color
+            };
 
             terrain_color_image.put_pixel(x as u32, y as u32, color);
         }
@@ -514,18 +565,30 @@ fn build_terrain_layers(
     TerrainLayers {
         terrain_color_image,
         grass_mask_image,
+        water_mask_image,
         rock_mask_image,
         snow_mask_image,
     }
 }
 
-fn build_soft_light_composite(color_image: &RgbaImage, bumpmap_image: &GrayImage) -> RgbaImage {
+fn build_soft_light_composite(
+    color_image: &RgbaImage,
+    bumpmap_image: &GrayImage,
+    heightmap_image: &GrayImage,
+    water_mask_image: &GrayImage,
+) -> RgbaImage {
     let mut composite = RgbaImage::new(color_image.width(), color_image.height());
 
     for y in 0..color_image.height() {
         for x in 0..color_image.width() {
             let base = color_image.get_pixel(x, y).0;
-            let blend = bumpmap_image.get_pixel(x, y).0[0] as f32 / 255.0;
+            let is_water = water_mask_image.get_pixel(x, y).0[0] > 0;
+
+            let blend = if is_water {
+                heightmap_image.get_pixel(x, y).0[0] as f32 / 255.0
+            } else {
+                bumpmap_image.get_pixel(x, y).0[0] as f32 / 255.0
+            };
 
             let r = soft_light_channel(base[0] as f32 / 255.0, blend);
             let g = soft_light_channel(base[1] as f32 / 255.0, blend);