Enable limited scrollback support

escape.go

@@ -28,6 +28,7 @@ var escapes = map[rune]func(*Terminal, string){
 	'P': escapeDeleteChars,
 	'r': escapeSetScrollArea,
 	's': escapeSaveCursor,
+	'S': escapeScrollUp,
 	'u': escapeRestoreCursor,
 	'i': escapePrinterMode,
 }
@@ -363,6 +364,37 @@ func escapeSetScrollArea(t *Terminal, msg string) {
 	t.scrollBottom = end
 }
 
+func escapeScrollUp(t *Terminal, msg string) {
+	lines, _ := strconv.Atoi(msg)
+	if lines == 0 {
+		lines = 1
+	}
+
+	// Ensure we are within the scrollable area
+	if t.cursorRow < t.scrollTop || t.cursorRow > t.scrollBottom {
+		return
+	}
+
+	// Calculate new cursor position after scrolling
+	newCursorRow := t.cursorRow - lines
+
+	// Make sure we don't scroll above the scroll top
+	if newCursorRow < t.scrollTop {
+		newCursorRow = t.scrollTop
+	}
+
+	// Move cursor to the new position
+	t.moveCursor(newCursorRow, t.cursorCol)
+
+	// Perform the actual scrolling action
+	for i := t.scrollTop; i <= t.scrollBottom-lines; i++ {
+		t.content.SetRow(i, t.content.Row(i+lines))
+	}
+	for i := t.scrollBottom - lines + 1; i <= t.scrollBottom; i++ {
+		t.content.SetRow(i, widget.TextGridRow{}) // Clear the last lines
+	}
+}
+
 func trimLeftZeros(s string) string {
 	if s == "" {
 		return s

escape_test.go

@@ -1,6 +1,7 @@
 package terminal
 
 import (
+	"strconv"
 	"testing"
 
 	"fyne.io/fyne/v2"
@@ -18,6 +19,48 @@ func TestClearScreen(t *testing.T) {
 	assert.Equal(t, "", term.content.Text())
 }
 
+// test clearing the screen by using "scrollback"
+// this is a method tmux uses to "clear the screen"
+func TestScrollBack(t *testing.T) {
+	// Step 1: Setup a new terminal instance
+	term := New()
+	term.debug = true
+	term.config.Columns = 80 // 80 columns (standard terminal width)
+	term.config.Rows = 5     // Doesn't matter
+
+	// Step 2: Populate the entire screen with lines using cursor movement
+	for i := 1; i <= 40; i++ {
+		lineText := "Line " + strconv.Itoa(i)
+		// Move the cursor to the beginning of each line using the escape sequence \x1b[{row};{col}H
+		escapeMoveCursor := "\x1b[" + strconv.Itoa(i) + ";1H"
+		term.handleOutput([]byte(escapeMoveCursor + lineText))
+	}
+
+	// Step 3: Set up the scroll region and scroll content away
+	term.handleOutput([]byte("\x1b[1;47r")) // Set scroll region from lines 1 to 47
+	term.handleOutput([]byte("\x1b[2;47r")) // Set scroll region again (redundant in most cases)
+	term.handleOutput([]byte("\x1b[46S"))   // Scroll up by 46 lines (this should move almost all content out of view)
+
+	// Step 4: Additional escape sequences to clear the screen
+	term.handleOutput([]byte("\x1b[1;1H"))  // Move cursor to the top-left corner
+	term.handleOutput([]byte("\x1b[K"))     // Clear the current line
+	term.handleOutput([]byte("\x1b[1;48r")) // Restore scroll region to the full screen
+	term.handleOutput([]byte("\x1b[1;1H"))  // Move cursor to top-left again
+	term.handleOutput([]byte("\x1b(B"))     // Reset character set
+	term.handleOutput([]byte("\x1b[m"))     // Reset all attributes
+
+	// Step 5: Check the final content of the terminal
+	expectedContent := "" // After scrolling and clearing, the visible area should be empty
+	for i := 0; i < 46; i++ {
+		expectedContent += "\n" // Each row should be an empty line
+	}
+
+	assert.Equal(t, 0, term.cursorRow)
+	assert.Equal(t, 0, term.cursorCol)
+
+	assert.Equal(t, expectedContent, term.content.Text())
+}
+
 func TestInsertDeleteChars(t *testing.T) {
 	term := New()
 	term.config.Columns = 5