fix materials for wind and add new snow system

core/daynight/weather_overlay.gdshader

@@ -8,6 +8,12 @@ global uniform float global_snow_melt_time         = -1.0;
 global uniform float global_snow_melt_speed        = 0.1;
 global uniform float global_snow_threshold         = 0.5;
 global uniform vec4  global_snow_color             = vec4(0.92, 0.96, 1.0, 1.0);
+global uniform float global_snow_max_accumulation  = 0.72;
+global uniform float global_snow_cap_height        = 0.06;
+global uniform float global_snow_cap_flatness_start = 0.72;
+global uniform float global_snow_cap_flatness_end  = 0.96;
+global uniform float global_snow_cap_noise_scale   = 0.22;
+global uniform float global_snow_cap_noise_strength = 0.18;
 uniform float snow_noise_scale : hint_range(0.01, 1.0) = 0.15;
 uniform float snow_edge_softness : hint_range(0.01, 0.5) = 0.2;
 uniform float snow_roughness_variation : hint_range(0.0, 0.3) = 0.15;
@@ -29,6 +35,52 @@ uniform float puddle_threshold : hint_range(0.0, 0.8) = 0.45;
 
 uniform sampler2D noise_texture : filter_linear_mipmap, repeat_enable;
 
+varying float v_snow_amount;
+varying float v_snow_cap_mask;
+
+float hash(vec2 p) {
+    return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453123);
+}
+
+float value_noise(vec2 p) {
+    vec2 i = floor(p);
+    vec2 f = fract(p);
+    vec2 u = f * f * (3.0 - 2.0 * f);
+
+    float a = hash(i);
+    float b = hash(i + vec2(1.0, 0.0));
+    float c = hash(i + vec2(0.0, 1.0));
+    float d = hash(i + vec2(1.0, 1.0));
+
+    return mix(mix(a, b, u.x), mix(c, d, u.x), u.y);
+}
+
+float fbm(vec2 p) {
+    float value = 0.0;
+    float amplitude = 0.5;
+    float frequency = 1.0;
+
+    for (int i = 0; i < 3; i++) {
+        value += value_noise(p * frequency) * amplitude;
+        frequency *= 2.0;
+        amplitude *= 0.5;
+    }
+
+    return clamp(value, 0.0, 1.0);
+}
+
+float get_snow_amount() {
+    float snow_amount = 0.0;
+    if (global_snow_start_time >= 0.0) {
+        snow_amount = clamp((TIME - global_snow_start_time) * global_snow_accumulation_speed, 0.0, 1.0);
+    }
+    if (global_snow_melt_time >= 0.0) {
+        float melt = clamp((TIME - global_snow_melt_time) * global_snow_melt_speed, 0.0, 1.0);
+        snow_amount *= (1.0 - melt);
+    }
+    return snow_amount * global_snow_max_accumulation;
+}
+
 float ripple_ring(vec2 uv, float time_offset) {
     float d = length(uv);
     float ring = sin(d * 30.0 - TIME * ripple_speed + time_offset) * 0.5 + 0.5;
@@ -36,6 +88,26 @@ float ripple_ring(vec2 uv, float time_offset) {
     return ring * fade;
 }
 
+void vertex() {
+    float snow_amount = get_snow_amount();
+    vec3 world_pos = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz;
+    vec3 world_normal = normalize((MODEL_MATRIX * vec4(NORMAL, 0.0)).xyz);
+
+    float flat_surface = smoothstep(
+        max(global_snow_threshold, global_snow_cap_flatness_start),
+        global_snow_cap_flatness_end,
+        world_normal.y
+    );
+    float accumulation_growth = smoothstep(0.08, 0.65, snow_amount);
+    float cap_noise = fbm(world_pos.xz * global_snow_cap_noise_scale + vec2(11.3, 4.7));
+    float cap_variation = mix(1.0 - global_snow_cap_noise_strength, 1.0 + global_snow_cap_noise_strength, cap_noise);
+
+    v_snow_amount = snow_amount;
+    v_snow_cap_mask = flat_surface * accumulation_growth * cap_variation;
+
+    VERTEX += NORMAL * (global_snow_cap_height * snow_amount * v_snow_cap_mask);
+}
+
 void fragment() {
     vec3 world_pos = (INV_VIEW_MATRIX * vec4(VERTEX, 1.0)).xyz;
     vec3 world_normal = normalize((INV_VIEW_MATRIX * vec4(NORMAL, 0.0)).xyz);
@@ -43,25 +115,22 @@ void fragment() {
     float noise_val = texture(noise_texture, world_pos.xz * snow_noise_scale).r;
 
     //Snow
-    float snow_amount = 0.0;
-    if (global_snow_start_time >= 0.0) {
-        snow_amount = clamp((TIME - global_snow_start_time) * global_snow_accumulation_speed, 0.0, 1.0);
-    }
-    if (global_snow_melt_time >= 0.0) {
-        float melt = clamp((TIME - global_snow_melt_time) * global_snow_melt_speed, 0.0, 1.0);
-        snow_amount *= (1.0 - melt);
-    }
+    float snow_amount = v_snow_amount;
 
     float snow_edge = smoothstep(
         global_snow_threshold - snow_edge_softness,
         global_snow_threshold + snow_edge_softness,
         facing_up + (noise_val - 0.5) * 0.4
     );
-    float snow_coverage = smoothstep(0.0, 0.6, noise_val + snow_amount - 0.4);
-    float snow_factor = snow_edge * snow_coverage * snow_amount;
+    float flat_accumulation = smoothstep(0.0, 0.35, v_snow_cap_mask) * snow_amount;
+    float snow_coverage = smoothstep(0.0, 0.6, noise_val + snow_amount - 0.4 + flat_accumulation * 0.25);
+    float snow_factor = max(snow_edge * snow_coverage * snow_amount, flat_accumulation);
+    float snow_opacity = smoothstep(0.04, 0.28, snow_factor);
+    snow_opacity = max(snow_opacity, flat_accumulation * 0.9);
 
     float shade = mix(-snow_color_variation, snow_color_variation, noise_val);
     vec3 snow_albedo = clamp(global_snow_color.rgb + vec3(shade), 0.0, 1.0);
+    snow_albedo = mix(snow_albedo, vec3(1.0), 0.18 + snow_opacity * 0.12);
     float snow_rough = mix(0.15 - snow_roughness_variation, 0.15 + snow_roughness_variation, noise_val);
 
     //Rain
@@ -173,7 +242,7 @@ void fragment() {
         ALBEDO    = snow_albedo;
         ROUGHNESS = snow_rough;
         METALLIC  = 0.0;
-        ALPHA     = snow_factor;
+        ALPHA     = snow_opacity;
     } else {
         ALBEDO    = rain_albedo;
         ROUGHNESS = rain_rough;