Add padleft and padright options for buffer padding

internal/config/settings.go

@@ -31,6 +31,8 @@ var optionValidators = map[string]optionValidator{
 	"helpsplit":       validateChoice,
 	"matchbracestyle": validateChoice,
 	"multiopen":       validateChoice,
+	"padleft":         validateNonNegativeValue,
+	"padright":        validateNonNegativeValue,
 	"pageoverlap":     validateNonNegativeValue,
 	"reload":          validateChoice,
 	"scrollmargin":    validateNonNegativeValue,
@@ -78,6 +80,8 @@ var defaultCommonSettings = map[string]any{
 	"matchbraceleft":  true,
 	"matchbracestyle": "underline",
 	"mkparents":       false,
+	"padleft":         float64(0),
+	"padright":        float64(0),
 	"pageoverlap":     float64(2),
 	"permbackup":      false,
 	"readonly":        false,

internal/display/bufwindow.go

@@ -26,6 +26,7 @@ type BufWindow struct {
 	bufWidth         int
 	bufHeight        int
 	gutterOffset     int
+	padLeftOffset    int
 	hasMessage       bool
 	maxLineNumLength int
 	drawDivider      bool
@@ -64,7 +65,7 @@ func (w *BufWindow) SetBuffer(b *buffer.Buffer) {
 		}
 
 		if option == "diffgutter" || option == "ruler" || option == "scrollbar" ||
-			option == "statusline" {
+			option == "statusline" || option == "padleft" || option == "padright" {
 			w.updateDisplayInfo()
 			w.Relocate()
 		}
@@ -107,7 +108,7 @@ func (w *BufWindow) IsActive() bool {
 // ruler, scrollbar and statusline.
 func (w *BufWindow) BufView() View {
 	return View{
-		X:         w.X + w.gutterOffset,
+		X:         w.X + w.gutterOffset + w.padLeftOffset,
 		Y:         w.Y,
 		Width:     w.bufWidth,
 		Height:    w.bufHeight,
@@ -158,12 +159,22 @@ func (w *BufWindow) updateDisplayInfo() {
 		w.gutterOffset += w.maxLineNumLength + 1
 	}
 
-	if w.gutterOffset > w.Width-scrollbarWidth {
+	padLeft := util.IntOpt(b.Settings["padleft"])
+	padRight := util.IntOpt(b.Settings["padright"])
+	w.padLeftOffset = padLeft
+
+	if w.gutterOffset+padLeft > w.Width-scrollbarWidth {
+		w.gutterOffset = w.Width - scrollbarWidth
+		w.padLeftOffset = 0
+	} else if w.gutterOffset > w.Width-scrollbarWidth {
 		w.gutterOffset = w.Width - scrollbarWidth
 	}
 
 	prevBufWidth := w.bufWidth
-	w.bufWidth = w.Width - w.gutterOffset - scrollbarWidth
+	w.bufWidth = w.Width - w.gutterOffset - padLeft - scrollbarWidth - padRight
+	if w.bufWidth < 0 {
+		w.bufWidth = 0
+	}
 
 	if w.bufWidth != prevBufWidth && w.Buf.Settings["softwrap"].(bool) {
 		for _, c := range w.Buf.GetCursors() {
@@ -268,7 +279,7 @@ func (w *BufWindow) Relocate() bool {
 // If the requested position does not correspond to a buffer location it returns
 // the nearest position
 func (w *BufWindow) LocFromVisual(svloc buffer.Loc) buffer.Loc {
-	vx := svloc.X - w.X - w.gutterOffset
+	vx := svloc.X - w.X - w.gutterOffset - w.padLeftOffset
 	if vx < 0 {
 		vx = 0
 	}
@@ -387,7 +398,7 @@ func (w *BufWindow) displayBuffer() {
 		return
 	}
 
-	maxWidth := w.gutterOffset + w.bufWidth
+	maxWidth := w.gutterOffset + w.padLeftOffset + w.bufWidth
 
 	if b.ModifiedThisFrame {
 		if b.Settings["diffgutter"].(bool) {
@@ -503,8 +514,14 @@ func (w *BufWindow) displayBuffer() {
 			if b.Settings["ruler"].(bool) {
 				w.drawLineNum(s, false, &vloc, &bloc)
 			}
+
+			// draw left padding cells
+			for vloc.X < w.gutterOffset+w.padLeftOffset {
+				screen.SetContent(w.X+vloc.X, w.Y+vloc.Y, ' ', nil, config.DefStyle)
+				vloc.X++
+			}
 		} else {
-			vloc.X = w.gutterOffset
+			vloc.X = w.gutterOffset + w.padLeftOffset
 		}
 
 		bline := b.LineBytes(bloc.Y)
@@ -668,7 +685,7 @@ func (w *BufWindow) displayBuffer() {
 				}
 
 				if s, ok := config.Colorscheme["color-column"]; ok {
-					if colorcolumn != 0 && vloc.X-w.gutterOffset+w.StartCol == colorcolumn && !preservebg {
+					if colorcolumn != 0 && vloc.X-w.gutterOffset-w.padLeftOffset+w.StartCol == colorcolumn && !preservebg {
 						fg, _, _ := s.Decompose()
 						style = style.Background(fg)
 					}
@@ -701,8 +718,14 @@ func (w *BufWindow) displayBuffer() {
 				if b.Settings["ruler"].(bool) {
 					w.drawLineNum(lineNumStyle, true, &vloc, &bloc)
 				}
+
+				// draw left padding cells on wrapped lines
+				for vloc.X < w.gutterOffset+w.padLeftOffset {
+					screen.SetContent(w.X+vloc.X, w.Y+vloc.Y, ' ', nil, config.DefStyle)
+					vloc.X++
+				}
 			} else {
-				vloc.X = w.gutterOffset
+				vloc.X = w.gutterOffset + w.padLeftOffset
 			}
 		}
 
@@ -754,7 +777,7 @@ func (w *BufWindow) displayBuffer() {
 			}
 
 			// If a word (or just a wide rune) does not fit in the window
-			if vloc.X+wordwidth > maxWidth && vloc.X > w.gutterOffset {
+			if vloc.X+wordwidth > maxWidth && vloc.X > w.gutterOffset+w.padLeftOffset {
 				for vloc.X < maxWidth {
 					draw(' ', nil, config.DefStyle, false, false, true)
 				}
@@ -817,7 +840,7 @@ func (w *BufWindow) displayBuffer() {
 		for i := vloc.X; i < maxWidth; i++ {
 			curStyle := style
 			if s, ok := config.Colorscheme["color-column"]; ok {
-				if colorcolumn != 0 && i-w.gutterOffset+w.StartCol == colorcolumn {
+				if colorcolumn != 0 && i-w.gutterOffset-w.padLeftOffset+w.StartCol == colorcolumn {
 					fg, _, _ := s.Decompose()
 					curStyle = style.Background(fg)
 				}

runtime/help/options.md

@@ -283,6 +283,13 @@ Here are the available options:
 
     default value: `tab`
 
+* `padleft`: the number of columns of whitespace to add to the left of the
+    text buffer. Useful for centering text on wide screens.
+    default value: `0`
+* `padright`: the number of columns of whitespace to add to the right of the
+    text buffer. Useful for centering text on wide screens.
+    default value: `0`
+
 * `pageoverlap`: the number of lines from the current view to keep in view
    when paging up or down. If this is set to 2, for instance, and you page
    down, the last two lines of the previous page will be the first two lines