Add ability to create an undecorated window

backend.go

@@ -11,12 +11,19 @@ import "git.tebibyte.media/tomo/tomo/canvas"
 type Backend interface {
 	// These methods create new objects. The backend must reject any object
 	// that was not made by it.
-	NewWindow       (image.Rectangle) (MainWindow, error)
 	NewBox          () Box
 	NewTextBox      () TextBox
 	NewCanvasBox    () CanvasBox
 	NewContainerBox () ContainerBox
 
+	// NewWindow creates a normal MainWindow and returns it.
+	NewWindow (image.Rectangle) (MainWindow, error)
+
+	// NewPlainWindow creates an undecorated window that does not appear in
+	// window lists and returns it. This is intended for making things like
+	// panels, docks, etc.
+	NewPlainWindow (image.Rectangle) (MainWindow, error)
+
 	// NewTexture creates a new texture from an image. The backend must
 	// reject any texture that was not made by it.
 	NewTexture (image.Image) canvas.TextureCloser

tomo.go

@@ -57,6 +57,14 @@ func NewWindow (bounds image.Rectangle) (MainWindow, error) {
 	return backend.NewWindow(bounds)
 }
 
+// NewPlainWindow is like NewWindow, but it creates an undecorated window that
+// does not appear in window lists. It is intended for creating things like
+// docks, panels, etc.
+func NewPlainWindow (bounds image.Rectangle) (MainWindow, error) {
+	assertBackend()
+	return backend.NewPlainWindow(bounds)
+}
+
 // NewBox creates and returns a basic Box.
 func NewBox () Box {
 	assertBackend()