Add LineFeed method

elements/grid.go

@@ -96,6 +96,23 @@ func (element *Grid) Set (point image.Point, cell Cell) {
 	element.cells[element.index(point)].clean = false
 }
 
+// LineFeed pushes all cells up by one line.
+func (element *Grid) LineFeed () {
+	if element.cells == nil { return }
+	element.cells = element.cells[element.stride:]
+
+	var index int
+	for index = 0; index < len(element.cells) - element.stride; index ++ {
+		element.cells[index] = element.cells[index + element.stride]
+		element.cells[index].clean = false
+	}
+	
+	for ; index < len(element.cells); index ++ {
+		element.cells[index] = gridCell { }
+		element.cells[index].initColor()
+	}
+}
+
 // Push pushes whatever changes were made to the grid to the screen.
 func (element *Grid) Push () {
 	if !element.ignorePush {
@@ -263,6 +280,7 @@ func (element *Grid) draw (force bool) (updatedRegion image.Rectangle) {
 
 	for index, cell := range element.cells {
 	if force || !cell.clean {
+		element.cells[index].clean = true
 		cellBounds := element.bound(index)
 		updatedRegion = updatedRegion.Union(cellBounds)
 		shapes.FillColorRectangle (