Handle rendering tabs

editor/draw.go

@@ -20,7 +20,7 @@ func (e *editor) RefreshScreen() {
 	ab.append(terminal.ResetCursor)
 
 	e.drawRows(ab)
-	ab.append(terminal.MoveCursor(e.cursor.x - e.offset.x, e.cursor.y - e.offset.y))
+	ab.append(terminal.MoveCursor(e.renderX - e.offset.x, e.cursor.y - e.offset.y))
 
 	ab.append(terminal.ShowCursor)
 
@@ -28,6 +28,12 @@ func (e *editor) RefreshScreen() {
 }
 
 func (e *editor) scroll() {
+	e.renderX = 0
+
+	if e.cursor.y < e.rowCount() {
+		e.renderX = e.rows[e.cursor.y].cursorXToRenderX(e.cursor.x)
+	}
+
 	if e.cursor.y < e.offset.y {
 		e.offset.y = e.cursor.y
 	}
@@ -36,12 +42,12 @@ func (e *editor) scroll() {
 		e.offset.y = e.cursor.y - e.screen.Rows + 1
 	}
 
-	if e.cursor.x < e.offset.x {
-		e.offset.x = e.cursor.x
+	if e.renderX < e.offset.x {
+		e.offset.x = e.renderX
 	}
 
-	if e.cursor.x >= e.offset.x + e.screen.Cols {
-		e.offset.x = e.cursor.x - e.screen.Cols
+	if e.renderX >= e.offset.x + e.screen.Cols {
+		e.offset.x = e.renderX - e.screen.Cols
 	}
 }
 
@@ -49,7 +55,7 @@ func (e *editor) drawRows(ab *buffer) {
 	for y :=0; y < e.screen.Rows; y++ {
 		fileRow := y + e.offset.y
 
-		if fileRow >= len(e.rows) {
+		if fileRow >= e.rowCount() {
 			e.drawPlaceholderRow(y, ab)
 		} else {
 			rawRow := e.rows[fileRow]
@@ -76,7 +82,7 @@ func (e *editor) drawRows(ab *buffer) {
 }
 
 func (e *editor) drawPlaceholderRow(y int, ab *buffer) {
-	if len(e.rows) == 0 && y == e.screen.Rows / 3 {
+	if e.rowCount() == 0 && y == e.screen.Rows / 3 {
 		welcome := fmt.Sprintf("Gilo editor -- version %s", KiloVersion)
 		if len(welcome) > e.screen.Cols {
 			welcome = truncateString(welcome, e.screen.Cols)

editor/editor.go

@@ -20,6 +20,7 @@ type editor struct {
 	screen *terminal.Screen
 	cursor *point
 	offset *point
+	renderX int
 	rows []*row
 }
 
@@ -33,6 +34,7 @@ func New() *editor {
 		screen,
 		cursor,
 		offset,
+		0,
 		rows,
 	}
 }
@@ -162,6 +164,10 @@ func (e *editor) appendRow(s string) {
 	e.rows = append(e.rows, newRow)
 }
 
+func (e *editor) rowCount() int {
+	return len(e.rows)
+}
+
 // Convert the raw ANSI escape sequences to the type of key input
 func parseEscapeSequence () string {
 	var runes []rune

editor/row.go

@@ -37,3 +37,17 @@ func (r *row) update() {
 	}
 }
 
+func (r *row) cursorXToRenderX (cursorX int) int {
+	renderX := 0
+	i := 0
+
+	for ; i < cursorX; i++ {
+		if r.chars[i] == '\t' {
+			renderX += (KiloTabStop - 1) - (renderX % KiloTabStop)
+		}
+
+		renderX += 1
+	}
+
+	return renderX
+}