Investigated terminal line deletion and scrollback
Public
Investigated terminal line deletion and scrollback
Agent
Pi
Model
Claude Opus 4.5 (latest)
Started
Jan 30, 4:05 PM
Messages173
Downloads0
Reviewed TUI source and terminal escape sequences.
UnderstandAnalyzed editor and autocomplete line handling.
UnderstandExplained scroll region versus scrollback buffer.
UnderstandClarified limitations of Delete Line on scrollback.
Understand
buffer += "\r\n\x1b[2K"; // move down + clear line (EL)if (this.previousLines.length > newLines.length) { const extraLines = this.previousLines.length - newLines.length; for (let i = newLines.length; i < this.previousLines.length; i++) { buffer += "\r\n\x1b[2K"; // <-- EL clears but keeps the line } buffer += `\x1b[${extraLines}A`;}Before autocomplete: After autocomplete: After close (with EL): After close (with DL):┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐│ │ │ top border │ │ top border │ │ ││ │ │ input │ │ input │ │ ││ top border │ │ bottom border │ │ bottom border │ │ top border ││ input │ │ completion 1 │ │ (blank) │ │ input ││ bottom border │ │ completion 2 │ │ (blank) │ │ bottom border │└─────────────────┘ └─────────────────┘ └─────────────────┘ └─────────────────┘ ^ editor shifted up ^ editor stays putprivate maxLinesRendered = 0; // Track terminal's working area (max lines ever rendered)const viewportTop = Math.max(0, this.maxLinesRendered - height);const workingHeight = Math.max(this.maxLinesRendered, minLinesNeeded);while (result.length < workingHeight) { result.push(""); // Pad with empty lines}if (this.previousLines.length > newLines.length) { const extraLines = this.previousLines.length - newLines.length; // Move to first line to delete, then delete N lines buffer += `\x1b[${extraLines}M`; // DL - delete N lines this.maxLinesRendered -= extraLines; // Shrink working area // No need to move cursor back - DL doesn't move it}// Before: loop with EL and cursor danceif (extraLines > 0) { buffer += "\x1b[1B";}for (let i = 0; i < extraLines; i++) { buffer += "\r\x1b[2K"; if (i < extraLines - 1) buffer += "\x1b[1B";}if (extraLines > 0) { buffer += `\x1b[${extraLines}A`;}
// After: single DL commandif (extraLines > 0) { buffer += "\x1b[1B"; // Move to first line to delete buffer += `\x1b[${extraLines}M`; // Delete N lines buffer += "\x1b[1A"; // Move back up this.maxLinesRendered = Math.max(newLines.length, this.maxLinesRendered - extraLines);}// Before: loop with ELfor (let i = newLines.length; i < this.previousLines.length; i++) { buffer += "\r\n\x1b[2K";}buffer += `\x1b[${extraLines}A`;
// After: single DL commandbuffer += "\r\n"; // Move to first line to deletebuffer += `\x1b[${extraLines}M`; // Delete N linesbuffer += "\x1b[1A"; // Move back upthis.maxLinesRendered = Math.max(newLines.length, this.maxLinesRendered - extraLines);