From cef016d393959e989df259aeacd055fc702a55ca Mon Sep 17 00:00:00 2001
From: x2048 <codeforsmile@gmail.com>
Date: Sun, 31 Oct 2021 19:18:30 +0100
Subject: [PATCH] Apply shadow only to the naturally lit part of the fragment
 color (#11722)

Fragment color for nodes is now calculated from:

 * Texture color, highlighted by artificial light if present (light color conveyed via vertex color).
 * Texture color highlighted by natural light (conveyed via vertex color) filtered by shadow.
 * Reflected day/moonlight filtered by shadow (color and intensity), assuming some portion of the light is directly reflected from the materials.
---
 .../shaders/nodes_shader/opengl_fragment.glsl | 27 ++++++++++++++-----
 .../shadow_shaders/pass1_trans_fragment.glsl  |  5 ++--
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/client/shaders/nodes_shader/opengl_fragment.glsl b/client/shaders/nodes_shader/opengl_fragment.glsl
index e21890710..b4a605b28 100644
--- a/client/shaders/nodes_shader/opengl_fragment.glsl
+++ b/client/shaders/nodes_shader/opengl_fragment.glsl
@@ -1,5 +1,6 @@
 uniform sampler2D baseTexture;
 
+uniform vec3 dayLight;
 uniform vec4 skyBgColor;
 uniform float fogDistance;
 uniform vec3 eyePosition;
@@ -497,23 +498,35 @@ void main(void)
 		shadow_int = visibility.r;
 		shadow_color = visibility.gba;
 #else
-		shadow_int = getShadow(ShadowMapSampler, posLightSpace.xy, posLightSpace.z);
+		if (cosLight > 0.0)
+			shadow_int = getShadow(ShadowMapSampler, posLightSpace.xy, posLightSpace.z);
+		else
+			shadow_int = 1.0;
 #endif
 		shadow_int *= distance_rate;
-		shadow_int *= 1.0 - nightRatio;
-
+		shadow_int = clamp(shadow_int, 0.0, 1.0);
 
 	}
 
+	// turns out that nightRatio falls off much faster than
+	// actual brightness of artificial light in relation to natual light.
+	// Power ratio was measured on torches in MTG (brightness = 14).
+	float adjusted_night_ratio = pow(nightRatio, 0.6);
+
 	if (f_normal_length != 0 && cosLight < 0.035) {
-		shadow_int = max(shadow_int, min(clamp(1.0-nightRatio, 0.0, 1.0), 1 - clamp(cosLight, 0.0, 0.035)/0.035));
+		shadow_int = max(shadow_int, 1 - clamp(cosLight, 0.0, 0.035)/0.035);
 	}
 
-	shadow_int = 1.0 - (shadow_int * f_adj_shadow_strength);
+	shadow_int *= f_adj_shadow_strength;
 	
-	// apply shadow (+color) as a factor to the material color
-	col.rgb = col.rgb * (1.0 - (1.0 - shadow_color) * (1.0 - pow(shadow_int, 2.0)));
+	// calculate fragment color from components:
+	col.rgb =
+			adjusted_night_ratio * col.rgb + // artificial light
+			(1.0 - adjusted_night_ratio) * ( // natural light
+					col.rgb * (1.0 - shadow_int * (1.0 - shadow_color)) +  // filtered texture color
+					dayLight * shadow_color * shadow_int);                 // reflected filtered sunlight/moonlight
 	// col.r = 0.5 * clamp(getPenumbraRadius(ShadowMapSampler, posLightSpace.xy, posLightSpace.z, 1.0) / SOFTSHADOWRADIUS, 0.0, 1.0) + 0.5 * col.r;
+	// col.r = adjusted_night_ratio; // debug night ratio adjustment
 #endif
 
 #if ENABLE_TONE_MAPPING
diff --git a/client/shaders/shadow_shaders/pass1_trans_fragment.glsl b/client/shaders/shadow_shaders/pass1_trans_fragment.glsl
index 032cd9379..b267c2214 100644
--- a/client/shaders/shadow_shaders/pass1_trans_fragment.glsl
+++ b/client/shaders/shadow_shaders/pass1_trans_fragment.glsl
@@ -33,9 +33,8 @@ void main()
 	//col.rgb = col.a == 1.0 ? vec3(1.0) : col.rgb;
 #ifdef COLORED_SHADOWS
 	col.rgb *= varColor.rgb;
-	// alpha 0.0 results in all-white, 0.5 means full color, 1.0 means all black
-	// resulting color is used as a factor in the final shader
-	float packedColor = packColor(mix(mix(vec3(1.0), col.rgb, 2.0 * clamp(col.a, 0.0, 0.5)), black, 2.0 * clamp(col.a - 0.5, 0.0, 0.5)));
+	// premultiply color alpha (see-through side)
+	float packedColor = packColor(col.rgb * (1.0 - col.a));
 	gl_FragColor = vec4(depth, packedColor, 0.0,1.0);
 #else
 	gl_FragColor = vec4(depth, 0.0, 0.0, 1.0);