From 99df7cda423c0257144eeb907a34db3b4512e3ec Mon Sep 17 00:00:00 2001
From: Duncan Murdoch <murdoch.duncan@gmail.com>
Date: Sun, 18 Feb 2024 08:30:12 -0500
Subject: [PATCH] Use luminance, not red, for compatibility with older shader.

---
 inst/htmlwidgets/lib/rglClass/shaders/rgl_fragment.glsl | 6 ++++--
 man/material.Rd                                         | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/inst/htmlwidgets/lib/rglClass/shaders/rgl_fragment.glsl b/inst/htmlwidgets/lib/rglClass/shaders/rgl_fragment.glsl
index 7d4a03752..8c5ffb5c1 100644
--- a/inst/htmlwidgets/lib/rglClass/shaders/rgl_fragment.glsl
+++ b/inst/htmlwidgets/lib/rglClass/shaders/rgl_fragment.glsl
@@ -203,12 +203,14 @@ void main(void) {
 #endif //TEXTURE_rgba
     
 #ifdef TEXTURE_alpha
+    float luminance = dot(vec3(1.,1.,1.),textureColor.rgb)/3.;
+
 #if defined(TEXMODE_replace) || defined(TEXMODE_decal)
-    textureColor = vec4(lighteffect.rgb, textureColor.r);
+    textureColor = vec4(lighteffect.rgb, luminance);
 #endif 
 
 #if defined(TEXMODE_modulate) || defined(TEXMODE_blend) || defined(TEXMODE_add)
-    textureColor = vec4(lighteffect.rgb, lighteffect.a*textureColor.r);
+    textureColor = vec4(lighteffect.rgb, lighteffect.a*luminance);
 #endif
  
 #endif // TEXTURE_alpha
diff --git a/man/material.Rd b/man/material.Rd
index 22ffcf8af..5ddaa3f6a 100644
--- a/man/material.Rd
+++ b/man/material.Rd
@@ -117,7 +117,8 @@ of objects in an \pkg{rgl} scene.
 in the display within R versus the WebGL display using
 \code{rglwidget()}.  In particular, in WebGL 
 \code{textype = "alpha"} will always take the alpha value from
-the red channel of the texture, whereas the R display bases
+the luminance (i.e. the average of the R, G and B channels) 
+of the texture, whereas the R display bases
 the choice on the internal format of the texture file.
   }
   \item{texmode}{