Fix cursor position bug

ansi.test.ts

@@ -17,7 +17,19 @@ describe(AnsiTerminalDisplay, () => {
       { r: 0.5, g: 0.1, b: 1.0 },
     ]);
     await display.setChar({ x: 0, y: 0 }, { ch: "$", fg: 1, bg: 0 });
-    checkSequence(stdout, "![38;2;128;26;255m![48;2;0;0;0m![0;0H$");
+    checkSequence(stdout, "![38;2;128;26;255m![48;2;0;0;0m![1;1H$");
+  });
+
+  it("moves the cursor only when needed", async () => {
+    const stdout = new Buffer();
+    const display = new AnsiTerminalDisplay(stdout);
+    display.forceSize({ w: 4, h: 3 });
+    await display.setChar({ x: 0, y: 0 }, { ch: "a", fg: 0, bg: 0 });
+    await display.setChar({ x: 1, y: 0 }, { ch: "b", fg: 0, bg: 0 });
+    await display.setChar({ x: 3, y: 0 }, { ch: "c", fg: 0, bg: 0 });
+    await display.setChar({ x: 0, y: 1 }, { ch: "d", fg: 0, bg: 0 });
+    await display.setChar({ x: 0, y: 2 }, { ch: "e", fg: 0, bg: 0 });
+    checkSequence(stdout, "![1;1Hab![1;4Hcd![3;1He");
   });
 });
 

ansi.ts

@@ -46,29 +46,42 @@ export class AnsiTerminalDisplay implements Display {
 
     if (f != char.fg) {
       f = char.fg;
-      await this.writer.write(this.palette_fg[f]);
+      const col = this.palette_fg[f];
+      if (col) {
+        await this.writer.write(col);
+      }
     }
 
     if (b != char.bg) {
       b = char.bg;
-      await this.writer.write(this.palette_bg[b]);
+      const col = this.palette_bg[b];
+      if (col) {
+        await this.writer.write(col);
+      }
     }
 
     if (x != at.x || y != at.y) {
       x = at.x;
       y = at.y;
-      await this.writer.write(escape(`[${at.y};${at.x}H`));
+      await this.writer.write(escape(`[${y + 1};${x + 1}H`));
     }
 
     await this.writer.write(new TextEncoder().encode(char.ch));
 
     x += 1;
-    if (x > this.width) {
+    if (x >= this.width) {
       x = 0;
       y += 1;
     }
     this.state = { x, y, f, b };
   }
+
+  /**
+   * Force the display size for subsequent prints
+   */
+  forceSize(size: BufferSize) {
+    this.width = size.w;
+  }
 }
 
 function escape(sequence: string): Uint8Array {

demo.ts

@@ -11,5 +11,6 @@ await ui.init([
   { r: 0, g: 1, b: 1 },
 ]);
 ui.drawing.color(2, 0).text("hello", { x: 10, y: 3 });
+ui.drawing.color(0, 1).text("world", { x: 10, y: 5 });
 await ui.flush();
 await new Promise((resolve) => setTimeout(resolve, 3000));