GLCapabilities Native Aquisition: Set alpha bits at last - due to it's auto setting by setSampleBuffers(true) and setBackgroundOpaque(false)

This bug lead to X11 GLCapabilities rgba: 8/8/8/1 - which ofc is invalid. Sideeffect was a bad selected GLXFB configuration
and the GLContext couldn't be made current.

Patch sets alpha bits reflecting reality carefully after opaque/samples. Added API doc note.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/jogl/classes/jogamp/opengl/GLGraphicsConfigurationUtil.java b/src/jogl/classes/jogamp/opengl/GLGraphicsConfigurationUtil.java
index 900d6a2a0..3f38f33bc 100644
--- a/src/jogl/classes/jogamp/opengl/GLGraphicsConfigurationUtil.java
+++ b/src/jogl/classes/jogamp/opengl/GLGraphicsConfigurationUtil.java
@@ -177,14 +177,16 @@ public class GLGraphicsConfigurationUtil {
         return capsRequested;
     }
 
+    /** Fix opaque setting while preserve alpha bits */
     public static GLCapabilitiesImmutable fixOpaqueGLCapabilities(GLCapabilitiesImmutable capsRequested, boolean isOpaque)
     {
         GLCapabilities caps2 = null;
         
         if( capsRequested.isBackgroundOpaque() != isOpaque) {
-            // fix caps ..
+            final int alphaBits = capsRequested.getAlphaBits();
             caps2 = (GLCapabilities) capsRequested.cloneMutable();
             caps2.setBackgroundOpaque(isOpaque);
+            caps2.setAlphaBits(alphaBits);
             return caps2;
         }
         return capsRequested;