From cf23267a9e40f8f5601b087ee9fda84c9a7d86e8 Mon Sep 17 00:00:00 2001
From: Benjamin Kraft <benjamin.kraft@online.de>
Date: Sun, 6 Oct 2024 15:42:40 +0200
Subject: [PATCH] grab ignores back faces, properly selects closest face

---
 shaders/grab.comp | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/shaders/grab.comp b/shaders/grab.comp
index acc6d99..1d3e401 100644
--- a/shaders/grab.comp
+++ b/shaders/grab.comp
@@ -40,7 +40,7 @@ layout (set = 1, binding = 0) uniform CameraUniform {
 layout (std430, set = 2, binding = 1) buffer GrabInformation {
 	float originalInverseMass;
 	uint vID;
-	float distanceToFace;
+	uint distanceToFace; // bits are float format
 	bool foundHit;
 };
 
@@ -88,7 +88,6 @@ void rayForward(out vec3 origin, out vec3 direction){
 }
 
 void testFace(uint fID){
-	// test this face, if hit, set grabinformation if distance is new minimum
 	vec3 origin;
 	vec3 direction;
 	rayForward(origin, direction);
@@ -102,7 +101,14 @@ void testFace(uint fID){
 	vec3 ac = c - a;
 
 	vec3 n = cross(ab, ac);
+	if (dot(direction, n) < 0){
+		return;
+	}
+
 	float r = dot(a - origin, n) / dot(direction, n);
+	if (r < 0){
+		return;
+	}
 	vec3 q = origin + r * direction;
 
 	vec3 qa = a - q;
@@ -117,14 +123,17 @@ void testFace(uint fID){
 	bool isOne = abs(alpha + beta + gamma - 1) < 0.001;
 
 	if (alpha >= 0 && alpha <= 1 && beta >= 0 && beta <= 1 && gamma >= 0 && gamma <= 1 && isOne){
-		if (r < distanceToFace){
+		uint newDistance;
+		uint expectedOriginalDistance;
+		do {
+			expectedOriginalDistance = distanceToFace;
+			newDistance = floatBitsToUint(min(r, uintBitsToFloat(expectedOriginalDistance)));
+		} while (atomicCompSwap(distanceToFace, expectedOriginalDistance, newDistance) != expectedOriginalDistance);
+		if (newDistance == floatBitsToUint(r)){
 			foundHit = true;
 			vID = face.a;
-			distanceToFace = r;
 		}
 	}
-
-	
 }
 
 void move(){
@@ -146,7 +155,7 @@ void move(){
 
 void release(){
 	vertices[vID].inverseMass = originalInverseMass;
-	distanceToFace = 1e20;
+	distanceToFace = floatBitsToUint(1.0e20);
 	foundHit = false;
 }