fix: flickering eyebleed

cli/TerminalLayout.ts

@@ -111,6 +111,8 @@ export class TerminalBlock {
   private renderHeight: number = 0;
   private lastRenderRow = 1;
 
+  private lastRendered: string[] = [];
+
   private preserveHistory = false;
 
   constructor(private prepend: string = "") {}
@@ -193,27 +195,37 @@ export class TerminalBlock {
   }
 
   renderInternal(startRow?: number) {
-    this.lastRenderRow = startRow ?? this.lastRenderRow;
-    this.clear(); // uses old renderedLineCount
+    const outputLines: string[] = [];
 
-    const outputLines = this.renderLines.map((line) =>
-      `${this.prepend}${line}\x1b[K`
-    );
-    const output = outputLines.join("\n");
-    if (startRow !== undefined) {
-      const moveCursor = `\x1b[${startRow};1H`;
-      Deno.stdout.writeSync(new TextEncoder().encode(moveCursor + output));
-    } else {
-      Deno.stdout.writeSync(new TextEncoder().encode(output));
+    for (let i = 0; i < this.renderLines.length; i++) {
+      const line = `${this.prepend}${this.renderLines[i]}`;
+      const previous = this.lastRendered[i];
+      if (line !== previous) {
+        const moveToLine = `\x1b[${(startRow ?? this.lastRenderRow) + i};1H`;
+        outputLines.push(moveToLine + line + "\x1b[K");
+      }
     }
 
-    // update rendered line count *after* rendering
-    this.renderedLineCount = outputLines.reduce(
-      (count, line) =>
-        count +
-        Math.ceil((line.length) / (Deno.consoleSize().columns || 80)),
-      0,
-    );
+    if (this.lastRendered.length > this.renderLines.length) {
+      const baseRow = startRow ?? this.lastRenderRow;
+      for (let i = this.renderLines.length; i < this.lastRendered.length; i++) {
+        const moveToLine = `\x1b[${baseRow + i};1H\x1b[2K`;
+        Deno.stdout.writeSync(new TextEncoder().encode(moveToLine));
+      }
+    }
+
+    const baseRow = startRow ?? this.lastRenderRow;
+    const excessLines = this.renderHeight - this.renderLines.length;
+    for (let i = 0; i < excessLines; i++) {
+      const moveToLine = `[${baseRow + this.renderLines.length + i};1H`;
+      Deno.stdout.writeSync(new TextEncoder().encode(moveToLine));
+    }
+
+    this.lastRendered = [...this.renderLines];
+    this.renderedLineCount = this.renderHeight;
+    this.lastRenderRow = baseRow;
+    const output = outputLines.join("\n");
+    Deno.stdout.writeSync(new TextEncoder().encode(output));
   }
 
   clear() {