M1c: weather, snap building, shelter, beds and regrowth

- Seeded weather (clear/cloudy/rain/storm, snow and blizzards on cold days
  and above the snowline), lightning, synthesised rain/wind/thunder sound
- Rain/snow particles stopped by roofs; wet ground, settled snow and wind
  via global shader uniforms
- Snap-together wood floor, wall, door, roof and gable with structural
  support, collapse and X to dismantle
- Shelter detection: dry under a roof, warmer and Rested inside with a fire;
  rain burns an uncovered campfire faster
- Bed sets the spawn point and lets you sleep through the night
- Trees, boulders and ground pickups regrow; timers saved
- Grass cleared under floors; shorter HUD hint
- New test_weather_building suite (62 checks) and tests/run_all.sh, which
  also fails on script errors

shaders/common.gdshaderinc

@@ -5,6 +5,22 @@
 
 uniform sampler2D noise_tex : filter_linear_mipmap, repeat_enable;
 
+// Set every frame by weather_fx.gd (declared in project.godot [shader_globals]).
+global uniform float weather_wet;    // 0..1 rain-soaked ground
+global uniform float weather_snow;   // 0..1 settled snow
+global uniform float weather_wind;   // wind multiplier, ~1 on a calm day
+
+// Wet surfaces: darker and glossier.
+vec3 wet_albedo(vec3 c, float wet) {
+	return c * (1.0 - 0.35 * wet);
+}
+
+// Settled snow on upward-facing surfaces, patchy where it's thin.
+float snow_mask(float up, float patch) {
+	float s = weather_snow * 1.25 - (1.0 - patch) * 0.45;
+	return clamp(s, 0.0, 1.0) * smoothstep(0.55, 0.85, up);
+}
+
 float nz(vec2 p) {
 	return texture(noise_tex, p).r;
 }

shaders/foliage.gdshader

@@ -18,8 +18,9 @@ void vertex() {
 	float phase = dot(inst_pos.xz, vec2(0.13, 0.17));
 	float gust = nz(inst_pos.xz * 0.012 + vec2(TIME * 0.02, TIME * 0.013));
 	vec3 sway = vec3(sin(TIME * 0.9 + phase), 0.0, cos(TIME * 0.7 + phase * 1.3) * 0.6);
-	sway *= wind_strength * h * (0.4 + gust);
-	sway += vec3(sin(TIME * 3.7 + dot(VERTEX, vec3(3.1, 1.7, 2.3)) + phase)) * flutter * clamp(VERTEX.y, 0.0, 1.0);
+	float wk = min(weather_wind, 2.2);   // storms bend crowns, but not into the ground
+	sway *= wind_strength * wk * h * (0.4 + gust);
+	sway += vec3(sin(TIME * 3.7 * (0.7 + 0.3 * wk) + dot(VERTEX, vec3(3.1, 1.7, 2.3)) + phase)) * flutter * wk * clamp(VERTEX.y, 0.0, 1.0);
 	VERTEX += (inverse(MODEL_MATRIX) * vec4(sway, 0.0)).xyz;
 }
 
@@ -27,6 +28,10 @@ void fragment() {
 	float v = nz(inst_pos.xz * 0.045);
 	vec3 tint = mix(vec3(0.88, 1.0, 0.85), vec3(1.12, 1.04, 0.78), v);
 	vec3 col = to_linear(COLOR.rgb) * tint;
+	// Snow on the upper faces of the crowns.
+	float up = (INV_VIEW_MATRIX * vec4(NORMAL, 0.0)).y;
+	col = mix(col, vec3(0.86, 0.89, 0.93), snow_mask(up, v) * 0.9);
+	col = wet_albedo(col, weather_wet * 0.5);
 	ALBEDO = col;
 	ROUGHNESS = 0.85;
 	SPECULAR = 0.3;

shaders/grass.gdshader

@@ -23,7 +23,7 @@ void vertex() {
 	vec2 wd = normalize(wind_dir);
 	float gust = nz(wp.xz * 0.015 - TIME * 0.05 * wd);
 	float sway = sin(TIME * 1.8 + wp.x * 0.35 + wp.z * 0.25) * 0.35 + gust * 1.3 - 0.4;
-	float k = wind_strength * hfac * hfac;
+	float k = wind_strength * weather_wind * hfac * hfac;
 	vec3 off = vec3(wd.x * sway * k, -abs(sway) * k * 0.3, wd.y * sway * k);
 	VERTEX += (inverse(MODEL_MATRIX) * vec4(off, 0.0)).xyz;
 }
@@ -35,6 +35,10 @@ void fragment() {
 	base *= 0.82 + 0.36 * nz(inst_pos.xz * 0.17);
 	vec3 col = base * mix(0.55, 1.0, hfac);              // darker at the root
 	col = mix(col, col * tip_tint * 1.3, smoothstep(0.6, 1.0, hfac) * 0.3);
+	// Snow weighs down on the blades from the root up; rain darkens them.
+	float snowy = clamp(weather_snow * 1.3 - hfac * 0.5 + (nz(inst_pos.xz * 0.17) - 0.5) * 0.4, 0.0, 0.85);
+	col = mix(col, vec3(0.62, 0.65, 0.7), snowy);   // greyer than ground snow: blades are lit as if flat
+	col = wet_albedo(col, weather_wet * 0.6 * (1.0 - snowy));
 	ALBEDO = col;
 	ROUGHNESS = 0.9;
 	SPECULAR = 0.2;

shaders/rock.gdshader

@@ -33,8 +33,13 @@ void fragment() {
 	float snow = smoothstep(snow_height - 3.0, snow_height + 3.0, w_pos.y + (a - 0.5) * 10.0);
 	snow *= smoothstep(0.35, 0.7, w_nrm.y);
 	col = mix(col, snow_col, snow);
+	float wsnow = snow_mask(w_nrm.y, a);
+	col = mix(col, snow_col, wsnow);
+	snow = max(snow, wsnow);
+	float wet = weather_wet * (1.0 - snow);
+	col = wet_albedo(col, wet);
 
 	ALBEDO = col;
-	ROUGHNESS = mix(mix(0.8, 0.95, moss), 0.6, snow);
+	ROUGHNESS = mix(mix(mix(0.8, 0.95, moss), 0.6, snow), 0.3, wet * 0.8);
 	SPECULAR = 0.35;
 }

shaders/terrain.gdshader

@@ -66,8 +66,16 @@ void fragment() {
 	snow_m *= 1.0 - smoothstep(0.5, 0.7, slope);
 	col = mix(col, snow_col * (0.92 + 0.08 * fine), snow_m);
 
+	// Weather: fresh snow settles on flat ground above the waterline; rain
+	// darkens and glosses everything else.
+	float wsnow = snow_mask(w_nrm.y, fine * 0.6 + mid * 0.4) * step(water_level + 0.1, w_pos.y);
+	col = mix(col, snow_col * (0.9 + 0.1 * fine), wsnow);
+	snow_m = max(snow_m, wsnow);
+	float wet = weather_wet * (1.0 - snow_m);
+	col = wet_albedo(col, wet);
+
 	ALBEDO = col;
-	ROUGHNESS = mix(mix(0.95, 0.82, rock_m), 0.6, snow_m);
+	ROUGHNESS = mix(mix(mix(0.95, 0.82, rock_m), 0.6, snow_m), 0.4, wet * 0.8);
 	SPECULAR = 0.3;
 	NORMAL_MAP = texture(normal_tex, w_pos.xz * 0.35).rgb;
 	NORMAL_MAP_DEPTH = mix(0.5, 1.4, rock_m) * (1.0 - snow_m * 0.7);