Merge pull request #174 from emanuel-skrenkovic/limit-right-scroll

Limit right paging to text

m/pager.go

@@ -99,6 +99,9 @@ type Pager struct {
 	// ChromaStyle and ChromaFormatter. Used for coloring unstyled text lines
 	// based on the Chroma style.
 	linePrefix string
+
+	// Length of the longest line displayed. This is used for limiting scrolling to the right.
+	longestLineLength int
 }
 
 type _PreHelpState struct {
@@ -243,6 +246,12 @@ func (p *Pager) moveRight(delta int) {
 	} else {
 		p.leftColumnZeroBased = result
 	}
+
+	// If we try to move past the characters when moving right, stop scrolling to
+	// avoid moving infinitely into the void.
+	if p.leftColumnZeroBased > p.longestLineLength {
+		p.leftColumnZeroBased = p.longestLineLength
+	}
 }
 
 func (p *Pager) handleScrolledUp() {

m/screenLines.go

@@ -33,6 +33,7 @@ type renderedLine struct {
 // the bottom
 func (p *Pager) redraw(spinner string) overflowState {
 	p.screen.Clear()
+	p.longestLineLength = 0
 
 	lastUpdatedScreenLineNumber := -1
 	var renderedScreenLines [][]twin.Cell
@@ -147,6 +148,7 @@ func (p *Pager) renderLines() ([]renderedLine, string, overflowState) {
 
 	allLines := make([]renderedLine, 0)
 	for lineIndex, line := range inputLines.lines {
+
 		lineNumber := inputLines.firstLineOneBased + lineIndex
 
 		rendering, lineOverflow := p.renderLine(line, lineNumber, p.scrollPosition.internalDontTouch)
@@ -154,6 +156,26 @@ func (p *Pager) renderLines() ([]renderedLine, string, overflowState) {
 			// Everything did not fit
 			screenOverflow = didOverflow
 		}
+
+		var onScreenLength int
+		for i := 0; i < len(rendering); i++ {
+			trimmedLen := len(twin.TrimSpaceRight(rendering[i].cells))
+			if trimmedLen > onScreenLength {
+				onScreenLength = trimmedLen
+			}
+		}
+
+		// We're trying to find the max length of readable characters to limit
+		// the scrolling to right, so we don't go over into the vast emptiness for no reason.
+		//
+		// The -1 fixed an issue that seemed like an off-by-one where sometimes, when first
+		// scrolling completely to the right, the first left scroll did not show the text again.
+		displayLength := p.leftColumnZeroBased + onScreenLength - 1
+
+		if displayLength >= p.longestLineLength {
+			p.longestLineLength = displayLength
+		}
+
 		allLines = append(allLines, rendering...)
 	}
 
@@ -260,6 +282,7 @@ func (p *Pager) decorateLine(lineNumberToShow *int, contents []twin.Cell, scroll
 		if endColumn > len(contents) {
 			endColumn = len(contents)
 		}
+
 		newLine = append(newLine, contents[startColumn:endColumn]...)
 	}