Support SDL_VIDEO_X11_NODIRECTCOLOR for OpenGL visuals

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401061

src/video/x11/SDL_x11gl.c

@@ -145,15 +145,17 @@ XVisualInfo *X11_GL_GetVisual(_THIS)
 	}
 
 #ifdef GLX_DIRECT_COLOR /* Try for a DirectColor visual for gamma support */
-	attribs[i++] = GLX_X_VISUAL_TYPE;
-	attribs[i++] = GLX_DIRECT_COLOR;
+	if ( !getenv("SDL_VIDEO_X11_NODIRECTCOLOR") ) {
+		attribs[i++] = GLX_X_VISUAL_TYPE;
+		attribs[i++] = GLX_DIRECT_COLOR;
+	}
 #endif
 	attribs[i++] = None;
 
  	glx_visualinfo = this->gl_data->glXChooseVisual(GFX_Display, 
 						  SDL_Screen, attribs);
 #ifdef GLX_DIRECT_COLOR
-	if( !glx_visualinfo ) { /* No DirectColor visual?  Try again.. */
+	if( !glx_visualinfo && !getenv("SDL_VIDEO_X11_NODIRECTCOLOR") ) { /* No DirectColor visual?  Try again.. */
 		attribs[i-3] = None;
  		glx_visualinfo = this->gl_data->glXChooseVisual(GFX_Display, 
 						  SDL_Screen, attribs);