From a5d29fa1d4bc6849d7a6529edc522accac8219d2 Mon Sep 17 00:00:00 2001
From: x2048 <codeforsmile@gmail.com>
Date: Thu, 14 Apr 2022 22:49:30 +0200
Subject: Implement shadow offsets for the new SM distortion function (#12191)

* Move shadow position calculation to vertex shaders
* Animate entire scene before rendering shadows to prevent lagging of shadows
* Remove unnecessary use of PolygonOffsetFactor
* Apply normal offset to both nodes and objects
* Rename getPerspectiveFactor -> applyPerspectiveDistortion
* Remove perspective distortion from fragment shaders
---
 client/shaders/object_shader/opengl_vertex.glsl | 72 +++++++++++++++++++------
 1 file changed, 56 insertions(+), 16 deletions(-)

(limited to 'client/shaders/object_shader/opengl_vertex.glsl')

diff --git a/client/shaders/object_shader/opengl_vertex.glsl b/client/shaders/object_shader/opengl_vertex.glsl
index 55861b0e9..6dc25f854 100644
--- a/client/shaders/object_shader/opengl_vertex.glsl
+++ b/client/shaders/object_shader/opengl_vertex.glsl
@@ -24,10 +24,12 @@ centroid varying vec2 varTexCoord;
 	uniform float f_shadowfar;
 	uniform float f_shadow_strength;
 	uniform float f_timeofday;
+	uniform vec4 CameraPos;
+
 	varying float cosLight;
-	varying float normalOffsetScale;
 	varying float adj_shadow_strength;
 	varying float f_normal_length;
+	varying vec3 shadow_position;
 #endif
 
 varying vec3 eyeVec;
@@ -39,8 +41,36 @@ const float e = 2.718281828459;
 const float BS = 10.0;
 uniform float xyPerspectiveBias0;
 uniform float xyPerspectiveBias1;
+uniform float zPerspectiveBias;
 
 #ifdef ENABLE_DYNAMIC_SHADOWS
+
+vec4 getRelativePosition(in vec4 position)
+{
+	vec2 l = position.xy - CameraPos.xy;
+	vec2 s = l / abs(l);
+	s = (1.0 - s * CameraPos.xy);
+	l /= s;
+	return vec4(l, s);
+}
+
+float getPerspectiveFactor(in vec4 relativePosition)
+{
+	float pDistance = length(relativePosition.xy);
+	float pFactor = pDistance * xyPerspectiveBias0 + xyPerspectiveBias1;
+	return pFactor;
+}
+
+vec4 applyPerspectiveDistortion(in vec4 position)
+{
+	vec4 l = getRelativePosition(position);
+	float pFactor = getPerspectiveFactor(l);
+	l.xy /= pFactor;
+	position.xy = l.xy * l.zw + CameraPos.xy;
+	position.z *= zPerspectiveBias;
+	return position;
+}
+
 // custom smoothstep implementation because it's not defined in glsl1.2
 // https://docs.gl/sl4/smoothstep
 float mtsmoothstep(in float edge0, in float edge1, in float x)
@@ -107,20 +137,31 @@ void main(void)
 #ifdef ENABLE_DYNAMIC_SHADOWS
 	if (f_shadow_strength > 0.0) {
 		vec3 nNormal = normalize(vNormal);
-		cosLight = dot(nNormal, -v_LightDirection);
-
-		// Calculate normal offset scale based on the texel size adjusted for 
-		// curvature of the SM texture. This code must be change together with
-		// getPerspectiveFactor or any light-space transformation.
-		vec3 eyeToVertex = worldPosition - eyePosition + cameraOffset;
-		// Distance from the vertex to the player
-		float distanceToPlayer = length(eyeToVertex - v_LightDirection * dot(eyeToVertex, v_LightDirection)) / f_shadowfar;
-		// perspective factor estimation according to the
-		float perspectiveFactor = distanceToPlayer * xyPerspectiveBias0 + xyPerspectiveBias1;
-		float texelSize = f_shadowfar * perspectiveFactor * perspectiveFactor /
-				(f_textureresolution * xyPerspectiveBias1  - perspectiveFactor * xyPerspectiveBias0);
-		float slopeScale = clamp(pow(1.0 - cosLight*cosLight, 0.5), 0.0, 1.0);
-		normalOffsetScale = texelSize * slopeScale;
+		f_normal_length = length(vNormal);
+
+		/* normalOffsetScale is in world coordinates (1/10th of a meter)
+		   z_bias is in light space coordinates */
+		float normalOffsetScale, z_bias;
+		float pFactor = getPerspectiveFactor(getRelativePosition(m_ShadowViewProj * mWorld * inVertexPosition));
+		if (f_normal_length > 0.0) {
+			nNormal = normalize(vNormal);
+			cosLight = dot(nNormal, -v_LightDirection);
+			float sinLight = pow(1 - pow(cosLight, 2.0), 0.5);
+			normalOffsetScale = 0.1 * pFactor * pFactor * sinLight * min(f_shadowfar, 500.0) / 
+					xyPerspectiveBias1 / f_textureresolution;
+			z_bias = 1e3 * sinLight / cosLight * (0.5 + f_textureresolution / 1024.0);
+		}
+		else {
+			nNormal = vec3(0.0);
+			cosLight = clamp(dot(v_LightDirection, normalize(vec3(v_LightDirection.x, 0.0, v_LightDirection.z))), 1e-2, 1.0);
+			float sinLight = pow(1 - pow(cosLight, 2.0), 0.5);
+			normalOffsetScale = 0.0;
+			z_bias = 3.6e3 * sinLight / cosLight;
+		}
+		z_bias *= pFactor * pFactor / f_textureresolution / f_shadowfar;
+
+		shadow_position = applyPerspectiveDistortion(m_ShadowViewProj * mWorld * (inVertexPosition + vec4(normalOffsetScale * nNormal, 0.0))).xyz;
+		shadow_position.z -= z_bias;
 
 		if (f_timeofday < 0.2) {
 			adj_shadow_strength = f_shadow_strength * 0.5 *
@@ -133,7 +174,6 @@ void main(void)
 				mtsmoothstep(0.20, 0.25, f_timeofday) *
 				(1.0 - mtsmoothstep(0.7, 0.8, f_timeofday));
 		}
-		f_normal_length = length(vNormal);
 	}
 #endif
 }
-- 
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