xgb-render: add some comments

Some containing code to list out potentially interesting information
from the X server.

prototypes/xgb-xrender.go

@@ -73,11 +73,34 @@ func main() {
 
 	_ = xproto.MapWindow(X, wid)
 
+	/*
+		rfilters, err := render.QueryFilters(X, xproto.Drawable(wid)).Reply()
+		if err != nil {
+			log.Fatalln(err)
+		}
+
+		filters := []string{}
+		for _, f := range rfilters.Filters {
+			filters = append(filters, f.Name)
+		}
+
+		log.Printf("filters: %v\n", filters)
+	*/
+
 	pformats, err := render.QueryPictFormats(X).Reply()
 	if err != nil {
 		log.Fatalln(err)
 	}
 
+	/*
+		for _, pf := range pformats.Formats {
+			log.Printf("format %2d: depth %2d, RGBA %3x %3x %3x %3x\n",
+				pf.Id, pf.Depth,
+				pf.Direct.RedMask, pf.Direct.GreenMask, pf.Direct.BlueMask,
+				pf.Direct.AlphaMask)
+		}
+	*/
+
 	// Similar to XRenderFindVisualFormat.
 	// The DefaultScreen is almost certain to be zero.
 	var pformat render.Pictformat
@@ -100,6 +123,8 @@ func main() {
 	if err != nil {
 		log.Fatalln(err)
 	}
+
+	// Dithering is not supported. :(
 	render.CreatePicture(X, pid, xproto.Drawable(wid), pformat, 0, []uint32{})
 
 	// Reserve an ID for the gradient.
@@ -133,6 +158,7 @@ func main() {
 			return
 		}
 
+		// We could also use a transformation matrix for changes in size.
 		_ = render.CreateLinearGradient(X, gid,
 			render.Pointfix{F64ToFixed(0), F64ToFixed(0)},
 			render.Pointfix{F64ToFixed(0), F64ToFixed(float64(h) - 100)},
@@ -172,5 +198,4 @@ func main() {
 			gradient()
 		}
 	}
-
 }