Use red channel to retrieve value for textype="alpha"; all textures…

… are converted to RGBA.

NEWS.md

@@ -1,4 +1,4 @@
-# rgl 1.2.13
+# rgl 1.2.14
 
 ## Major changes
 
@@ -28,6 +28,7 @@ run in a Shiny session.
 * Fixed issue with `warning()` call reported by CRAN.
 * Smooth shapes were not rendered correctly by `rglwidget()`.
   This was especially noticeable for spheres with `fov = 0`, but was present in other cases as well (issue #401).
+* `textype = "alpha"` was not rendered correctly by `rglwidget()` (issue #408).
 
 # rgl 1.2.1
 

inst/htmlwidgets/lib/rglClass/shaders/rgl_fragment.glsl

@@ -204,14 +204,14 @@ void main(void) {
 
 #ifdef TEXTURE_alpha
 #if defined(TEXMODE_replace) || defined(TEXMODE_decal)
-    textureColor = vec4(lighteffect.rgb, textureColor.a);
+    textureColor = vec4(lighteffect.rgb, textureColor.r);
 #endif 
 
 #if defined(TEXMODE_modulate) || defined(TEXMODE_blend) || defined(TEXMODE_add)
-    textureColor = vec4(lighteffect.rgb, lighteffect.a*textureColor.a);
+    textureColor = vec4(lighteffect.rgb, lighteffect.a*textureColor.r);
 #endif
 
-#endif
+#endif // TEXTURE_alpha
 
 // The TEXTURE_luminance values are not from that reference    
 #ifdef TEXTURE_luminance

man/material.Rd

@@ -113,6 +113,12 @@ of objects in an \pkg{rgl} scene.
       \item{"rgb"}{color}
       \item{"rgba"}{color and alpha texture}
     }
+    Note that support for these modes is slightly different
+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 choice on the internal format of the texture file.
   }
   \item{texmode}{
     specifies how the texture interacts with the existing