Added more efficient damage buffer method

backends/x/draw.go

@@ -46,9 +46,8 @@ func (backend *Backend) drawCells (forceRedraw bool) (areas []image.Rectangle) {
 	for y := 0; y < height; y ++ {
 	for x := 0; x < width;  x ++ {
 		if !forceRedraw && backend.application.Clean(x, y) { continue }
-		backend.application.MarkClean(x, y)
 
-		cell := backend.application.Cell(x, y)
+		cell := backend.application.GetForRendering(x, y)
 		content := cell.Rune()
 
 		if forceRedraw && content < 32 { continue }
@@ -93,13 +92,24 @@ func (backend *Backend) drawRune (
 	if character < 32 { return }
 	
 	origin := backend.originOfCell(x, y + 1)
-	destinationRectangle, mask, maskPoint, _, _ := backend.font.face.Glyph (
+	destinationRectangle, mask, maskPoint, _, ok := backend.font.face.Glyph (
 		fixed.Point26_6 {
 			X: fixed.I(origin.X),
 			Y: fixed.I(origin.Y - backend.metrics.descent),
 		},
 		character)
 
+	if !ok {
+		println("warning")
+		strokeRectangle (
+			&image.Uniform {
+				C: backend.config.Color(stone.ColorForeground),
+			},
+			backend.canvas,
+			backend.boundsOfCell(x, y))
+		return
+	}
+
 	if backend.drawCellBounds {	
 		strokeRectangle (
 			&image.Uniform {