From 6280256f0c2ae61521183c08584a9a4664451af4 Mon Sep 17 00:00:00 2001
From: Jim Page <jim.page@redmatter.com>
Date: Sun, 30 Jun 2024 10:34:53 +0200
Subject: [PATCH] Revert "Skinning Shaders: Remove need skinning texture size
 uniform by using textureSize function (#27117)"

This reverts commit 3e0f80faa748a52ec469c838053fe8a748eba27b.
---
 src/objects/Skeleton.js                       |  2 ++
 src/renderers/WebGLRenderer.js                |  1 +
 .../ShaderChunk/skinning_pars_vertex.glsl.js  | 26 ++++++++++++-------
 3 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/src/objects/Skeleton.js b/src/objects/Skeleton.js
index 23abe42b09be41..d256e98bb458c4 100644
--- a/src/objects/Skeleton.js
+++ b/src/objects/Skeleton.js
@@ -21,6 +21,7 @@ class Skeleton {
 		this.boneMatrices = null;
 
 		this.boneTexture = null;
+		this.boneTextureSize = 0;
 
 		this.init();
 
@@ -179,6 +180,7 @@ class Skeleton {
 
 		this.boneMatrices = boneMatrices;
 		this.boneTexture = boneTexture;
+		this.boneTextureSize = size;
 
 		return this;
 
diff --git a/src/renderers/WebGLRenderer.js b/src/renderers/WebGLRenderer.js
index aae548d8df6e46..44571ffc9b9ddd 100644
--- a/src/renderers/WebGLRenderer.js
+++ b/src/renderers/WebGLRenderer.js
@@ -1988,6 +1988,7 @@ class WebGLRenderer {
 						if ( skeleton.boneTexture === null ) skeleton.computeBoneTexture();
 
 						p_uniforms.setValue( _gl, 'boneTexture', skeleton.boneTexture, textures );
+						p_uniforms.setValue( _gl, 'boneTextureSize', skeleton.boneTextureSize );
 
 					} else {
 
diff --git a/src/renderers/shaders/ShaderChunk/skinning_pars_vertex.glsl.js b/src/renderers/shaders/ShaderChunk/skinning_pars_vertex.glsl.js
index 10b4dc5222ff53..a17c93391afa8a 100644
--- a/src/renderers/shaders/ShaderChunk/skinning_pars_vertex.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/skinning_pars_vertex.glsl.js
@@ -5,19 +5,27 @@ export default /* glsl */`
 	uniform mat4 bindMatrixInverse;
 
 	uniform highp sampler2D boneTexture;
+	uniform int boneTextureSize;
 
 	mat4 getBoneMatrix( const in float i ) {
 
-		int size = textureSize( boneTexture, 0 ).x;
-		int j = int( i ) * 4;
-		int x = j % size;
-		int y = j / size;
-		vec4 v1 = texelFetch( boneTexture, ivec2( x, y ), 0 );
-		vec4 v2 = texelFetch( boneTexture, ivec2( x + 1, y ), 0 );
-		vec4 v3 = texelFetch( boneTexture, ivec2( x + 2, y ), 0 );
-		vec4 v4 = texelFetch( boneTexture, ivec2( x + 3, y ), 0 );
+		float j = i * 4.0;
+		float x = mod( j, float( boneTextureSize ) );
+		float y = floor( j / float( boneTextureSize ) );
 
-		return mat4( v1, v2, v3, v4 );
+		float dx = 1.0 / float( boneTextureSize );
+		float dy = 1.0 / float( boneTextureSize );
+
+		y = dy * ( y + 0.5 );
+
+		vec4 v1 = texture2D( boneTexture, vec2( dx * ( x + 0.5 ), y ) );
+		vec4 v2 = texture2D( boneTexture, vec2( dx * ( x + 1.5 ), y ) );
+		vec4 v3 = texture2D( boneTexture, vec2( dx * ( x + 2.5 ), y ) );
+		vec4 v4 = texture2D( boneTexture, vec2( dx * ( x + 3.5 ), y ) );
+
+		mat4 bone = mat4( v1, v2, v3, v4 );
+
+		return bone;
 
 	}