Treat the rain as a range between 0.0 and 1.0, fixes #40

NEWS.md

@@ -5,6 +5,8 @@
 * Reworked the water completely. Now it has much more convincing waves
   and specular highlights.
 * Clouds now have highlights and shade.
+* Shadows no longer disappear all of a sudden when it starts raining
+  (#40).
 
 ## 1.4.0 -- 2019-01-14
 

src/shaders/glsl/natural-mystic-hacks.h

@@ -55,7 +55,15 @@ bool isTheEndFog(vec4 fogColor) {
  * also be the bad weather fog.
  */
 bool isRenderDistanceFog(vec2 fogControl) {
-    return fogControl.x > 0.5;
+    return fogControl.x > 0.6;
+}
+
+/* When it's raining on the Overworld, the game gradually reduces the
+ * fog far to < 1.0. We exploit this fact to detect rain. This
+ * function returns 0.0 when it's raining, and 1.0 otherwise.
+ */
+float isClearWeather(vec2 fogControl) {
+    return smoothstep(0.8, 1.0, fogControl.y);
 }
 
 #endif /* NATURAL_MYSTIC_HACKS_H_INCLUDED */

src/shaders/glsl/renderchunk.fragment

@@ -116,6 +116,11 @@ vec4 inColor = color;
 #else
 	const bool isUnderwater = false;
 #endif /* defined(UNDERWATER) */
+#if defined(FOG)
+	float clearWeather = isClearWeather(FOG_CONTROL);
+#else
+	const float clearWeather = 1.0;
+#endif /* defined(FOG) */
 
 	vec3 ambientColor;
 #if defined(FOG)
@@ -125,13 +130,21 @@ vec4 inColor = color;
 		ambientColor = ambientLightColor(uv1.y, daylight);
 	}
 	else {
-		ambientColor = ambientLightColor(fogColor);
-
 		/* The existence of bad weather fog (and also underwater fog)
 		 * should increase the intensity of ambient light (#32). But
 		 * at night it should work the other way.
 		 */
-		ambientBrightness *= mix(0.9, 1.4, daylight);
+		if (isUnderwater) {
+			ambientColor = ambientLightColor(fogColor);
+			ambientBrightness *= mix(0.9, 1.4, daylight);
+		}
+		else {
+			ambientColor = mix(
+				ambientLightColor(fogColor),
+				ambientLightColor(uv1.y, daylight),
+				clearWeather);
+			ambientBrightness *= mix(mix(0.9, 1.4, daylight), 1.0, clearWeather);
+		}
 	}
 #else
 	ambientColor = ambientLightColor(uv1.y, daylight);
@@ -148,13 +161,17 @@ vec4 inColor = color;
 	light += ambientLight(ambientColor, ambientBrightness);
 #if defined(FOG)
 	/* When it's raining the sunlight shouldn't affect the scene
-	 * (#24), but this has a side effect. Shadows appear and disappear
-	 * all of sudden (#33).
+	 * (#24), but we cannot treat the rain as a boolean switch as that
+	 * would cause #40.
 	 */
-	if (isUnderwater || isRenderDistanceFog(FOG_CONTROL)) {
+	if (isUnderwater) {
 		light += sunlight(uv1.y, daylight);
 		light += moonlight(uv1.y, daylight);
 	}
+	else {
+		light += sunlight(uv1.y, daylight) * clearWeather;
+		light += moonlight(uv1.y, daylight) * clearWeather;
+	}
 #else
 	light += sunlight(uv1.y, daylight);
 	light += moonlight(uv1.y, daylight);