From 62639996448f2188f82cf1e4ef4a60618a81fa4e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emmanuel=20Beno=C3=AEt?= <tseeker@nocternity.net>
Date: Tue, 3 Oct 2017 09:12:21 +0200
Subject: [PATCH] "Enhanced sphere tracing" by Mercury /et al./

---
 shaders/raymarcher.glsl | 45 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/shaders/raymarcher.glsl b/shaders/raymarcher.glsl
index 3b0d922..d28a147 100644
--- a/shaders/raymarcher.glsl
+++ b/shaders/raymarcher.glsl
@@ -9,7 +9,7 @@ vec3 getNormal( vec3 pos )
 
 // -----------------------------------------------------------------------------
 
-vec3 march( vec3 o , vec3 d , int steps , float factor )
+vec3 RM_Basic( vec3 o , vec3 d , int steps , float factor )
 {
 	int i = 0;
 	float dist = .01 , mat = -1;
@@ -26,6 +26,47 @@ vec3 march( vec3 o , vec3 d , int steps , float factor )
 	return vec3( dist , dist >= u_Render.w ? -1 : mat , i );
 }
 
+vec3 RM_Advanced( vec3 o , vec3 d , int steps , float factor )
+{
+	const float dMin = .1 , dMax = u_Render.w , pixel = u_Render.z;
+
+	int i = 0;
+	float dist = dMin , mat = -1;
+	float omega = factor;
+	float cError = 1 / 0. , cDist = dMin;
+	float pRad = 0 , sLen = 0;
+
+	for ( ; i < steps ; ++ i ) {
+		vec2 res = map( o + d * dist );
+		float rad = abs( res.x );
+
+		bool sorFail = omega > 1 && ( rad + pRad ) < sLen;
+		if ( sorFail ) {
+			sLen -= omega * sLen;
+			omega = 1;
+		} else {
+			sLen = res.x * omega;
+		}
+		pRad = rad;
+
+		float error = rad / dist;
+		if ( !sorFail && error < cError ) {
+			cError = error;
+			cDist = dist;
+		}
+
+		if ( !sorFail && error < pixel || dist > dMax ) {
+			break;
+		}
+
+		dist += sLen;
+	}
+	if ( dist <= dMax && cError <= pixel ) {
+		return vec3( cDist , map( o + d * cDist ).y , i );
+	}
+	return vec3( cDist , -1 , steps );
+}
+
 // -----------------------------------------------------------------------------
 
 void main( )
@@ -40,7 +81,7 @@ void main( )
 			+ uv.x * side * u_Resolution.x / u_Resolution.y
 			+ uv.y * up );
 
-	vec3 r = march( camPos , rayDir , int( u_Render.x ) , u_Render.y );
+	vec3 r = RM_Advanced( camPos , rayDir , int( u_Render.x ) , u_Render.y );
 	vec3 hitPos = camPos + rayDir * r.x;
 
 	vec3 bc = vec3( 0 );