From f666c76a9cd19b1e9b8d45d6c069e65d6fd6ec3f Mon Sep 17 00:00:00 2001
From: Rudolph Bester <Rudolph.f.Bester@gmail.com>
Date: Tue, 28 May 2024 14:09:08 +0200
Subject: [PATCH] Fixed collided 3D GPU particles sometimes jittering

---
 drivers/gles3/shaders/particles.glsl               | 14 ++++++++------
 .../rendering/renderer_rd/shaders/particles.glsl   | 12 +++++++-----
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/gles3/shaders/particles.glsl b/drivers/gles3/shaders/particles.glsl
index 096f0a57ae6..2591937a1da 100644
--- a/drivers/gles3/shaders/particles.glsl
+++ b/drivers/gles3/shaders/particles.glsl
@@ -372,10 +372,10 @@ void main() {
 
 				float d = vec4_to_float(texture(height_field_texture, uv_pos)) * SDF_MAX_LENGTH;
 
+				// Allowing for a small epsilon to allow particle just touching colliders to count as collided
+				const float EPSILON = 0.001;
 				d -= sdf_particle_size;
-
-				if (d < 0.0) {
-					const float EPSILON = 0.001;
+				if (d < EPSILON) {
 					vec2 n = normalize(vec2(
 							vec4_to_float(texture(height_field_texture, uv_pos + vec2(EPSILON, 0.0))) - vec4_to_float(texture(height_field_texture, uv_pos - vec2(EPSILON, 0.0))),
 							vec4_to_float(texture(height_field_texture, uv_pos + vec2(0.0, EPSILON))) - vec4_to_float(texture(height_field_texture, uv_pos - vec2(0.0, EPSILON)))));
@@ -400,10 +400,12 @@ void main() {
 				vec3 rel_vec = xform[3].xyz - colliders[i].transform[3].xyz;
 				vec3 local_pos = rel_vec * mat3(colliders[i].transform);
 
+				// Allowing for a small epsilon to allow particle just touching colliders to count as collided
+				const float EPSILON = 0.001;
 				if (colliders[i].type == COLLIDER_TYPE_SPHERE) {
 					float d = length(rel_vec) - (particle_size + colliders[i].extents.x);
 
-					if (d < 0.0) {
+					if (d < EPSILON) {
 						col = true;
 						depth = -d;
 						normal = normalize(rel_vec);
@@ -418,7 +420,7 @@ void main() {
 						vec3 closest = min(abs_pos, colliders[i].extents.xyz);
 						vec3 rel = abs_pos - closest;
 						depth = length(rel) - particle_size;
-						if (depth < 0.0) {
+						if (depth < EPSILON) {
 							col = true;
 							normal = mat3(colliders[i].transform) * (normalize(rel) * sgn_pos);
 							depth = -depth;
@@ -453,7 +455,7 @@ void main() {
 
 					float y = 1.0 - texture(height_field_texture, uvw_pos.xz).r;
 
-					if (y > uvw_pos.y) {
+					if (y + EPSILON > uvw_pos.y) {
 						//inside heightfield
 
 						vec3 pos1 = (vec3(uvw_pos.x, y, uvw_pos.z) * 2.0 - 1.0) * colliders[i].extents.xyz;
diff --git a/servers/rendering/renderer_rd/shaders/particles.glsl b/servers/rendering/renderer_rd/shaders/particles.glsl
index efdf1c2278f..60c49bacaed 100644
--- a/servers/rendering/renderer_rd/shaders/particles.glsl
+++ b/servers/rendering/renderer_rd/shaders/particles.glsl
@@ -528,11 +528,13 @@ void main() {
 				vec3 rel_vec = PARTICLE.xform[3].xyz - FRAME.colliders[i].transform[3].xyz;
 				vec3 local_pos = rel_vec * mat3(FRAME.colliders[i].transform);
 
+				// Allowing for a small epsilon to allow particle just touching colliders to count as collided
+				const float EPSILON = 0.001;
 				switch (FRAME.colliders[i].type) {
 					case COLLIDER_TYPE_SPHERE: {
 						float d = length(rel_vec) - (particle_size + FRAME.colliders[i].extents.x);
 
-						if (d < 0.0) {
+						if (d <= EPSILON) {
 							col = true;
 							depth = -d;
 							normal = normalize(rel_vec);
@@ -549,7 +551,7 @@ void main() {
 							vec3 closest = min(abs_pos, FRAME.colliders[i].extents);
 							vec3 rel = abs_pos - closest;
 							depth = length(rel) - particle_size;
-							if (depth < 0.0) {
+							if (depth <= EPSILON) {
 								col = true;
 								normal = mat3(FRAME.colliders[i].transform) * (normalize(rel) * sgn_pos);
 								depth = -depth;
@@ -588,10 +590,10 @@ void main() {
 						float s = texture(sampler3D(sdf_vec_textures[FRAME.colliders[i].texture_index], SAMPLER_LINEAR_CLAMP), uvw_pos).r;
 						s *= FRAME.colliders[i].scale;
 						s += extra_dist;
-						if (s < particle_size) {
+						if (s <= particle_size + EPSILON) {
 							col = true;
 							depth = particle_size - s;
-							const float EPSILON = 0.001;
+
 							normal = mat3(FRAME.colliders[i].transform) *
 									normalize(
 											vec3(
@@ -614,7 +616,7 @@ void main() {
 
 						float y = texture(sampler2D(height_field_texture, SAMPLER_LINEAR_CLAMP), uvw_pos.xz).r;
 
-						if (y > uvw_pos.y) {
+						if (y + EPSILON >= uvw_pos.y) {
 							//inside heightfield
 
 							vec3 pos1 = (vec3(uvw_pos.x, y, uvw_pos.z) * 2.0 - 1.0) * FRAME.colliders[i].extents;