live plot example and screenToPlot helper

lib/WallPlotter.js

@@ -320,6 +320,38 @@ class WallPlotter {
     this.timingMultiplier = Math.max(0.1, Number(mult) || 1);
   }
 
+  /**
+   * Convert canvas pixel coordinates to plot coordinates in mm.
+   * By default this uses machine bounds so live-click targeting stays stable.
+   * @param {number} px
+   * @param {number} py
+   * @param {{clamp?: boolean, useDisplayBounds?: boolean}} [options]
+   */
+  screenToPlot(px, py, options = {}) {
+    const layout = this._getPlotLayout();
+    const bounds =
+      options.useDisplayBounds === true
+        ? this._getDisplayBounds()
+        : {
+            xMin: this.machineXMin,
+            xMax: this.machineXMax,
+            yMin: this.machineYMin,
+            yMax: this.machineYMax,
+          };
+
+    const scale = Math.max(layout.scale || 0, 1e-9);
+    const worldX = (px - layout.cx) / scale + layout.worldCx;
+    const worldY = -(py - layout.cy) / scale + layout.worldCy;
+    const clamp = options.clamp !== false;
+
+    if (!clamp) return { x: worldX, y: worldY };
+
+    return {
+      x: Math.min(bounds.xMax, Math.max(bounds.xMin, worldX)),
+      y: Math.min(bounds.yMax, Math.max(bounds.yMin, worldY)),
+    };
+  }
+
   // ===========================================================================
   // Public API — path buffer (queue only; nothing is sent until runPath)
   // ===========================================================================
@@ -929,19 +961,42 @@ class WallPlotter {
   /** Pen up and travel to (x, y) mm immediately. Requires home. */
   async moveTo(x, y) {
     if (!this._requireHome()) return;
+    const startX = this.x;
+    const startY = this.y;
     await this.penUp();
     await this.send(`G1 X${this._fmt(x)} Y${this._fmt(y)} F${this.feedRateTravel}`);
     this.x = x;
     this.y = y;
+    await this._waitForMotionComplete(
+      Math.hypot((x ?? 0) - (startX ?? 0), (y ?? 0) - (startY ?? 0)),
+      this.feedRateTravel
+    );
   }
 
   /** Pen down and draw to (x, y) mm immediately. Requires home. */
   async drawTo(x, y) {
     if (!this._requireHome()) return;
+    const startX = this.x;
+    const startY = this.y;
     await this.penDown();
     await this.send(`G1 X${this._fmt(x)} Y${this._fmt(y)} F${this.feedRateDraw}`);
     this.x = x;
     this.y = y;
+    await this._waitForMotionComplete(
+      Math.hypot((x ?? 0) - (startX ?? 0), (y ?? 0) - (startY ?? 0)),
+      this.feedRateDraw
+    );
+  }
+
+  async _waitForMotionComplete(distanceMm, feedRateMmPerMin) {
+    const distance = Number.isFinite(distanceMm) ? Math.max(0, distanceMm) : 0;
+    const speedMmPerS = Math.max(1, Number(feedRateMmPerMin) || 1) / 60;
+    const etaMs = Math.round((distance / speedMmPerS) * 1000);
+    await this.send('M400', {
+      timeoutMs: Math.max(WallPlotter.OK_TIMEOUT_MS, etaMs + 15000),
+      // M400 legitimately blocks until mechanics are done moving.
+      waitLogAfterMs: Math.max(WallPlotter.OK_WAIT_LOG_MS, etaMs + 1500),
+    });
   }
 
   /** Travel to (0, 0). */

lib/doc.md

@@ -184,13 +184,21 @@ Write one G-code line and wait for Marlin `ok`.
 
 Send pen G-code and wait the pen delay. By default, no-op if already in that state. Pass `true` to always send (used by `P` and on connect) so you can test the configured angles.
 
+### `screenToPlot(px, py, options?)`
+
+Convert canvas pixel coordinates to plot coordinates in mm.
+
+- `px`, `py` (number): screen/canvas pixel coordinates.
+- `options.clamp` (boolean, default `true`): clamp result to bounds.
+- `options.useDisplayBounds` (boolean, default `false`): use current display bounds (preview when disconnected) instead of machine bounds.
+
 ### `moveTo(x, y)`
 
-Pen up, travel to `(x, y)` mm immediately (not queued). Requires home.
+Pen up, travel to `(x, y)` mm immediately (not queued), then wait for motion completion (`M400`). Requires home.
 
 ### `drawTo(x, y)`
 
-Pen down, draw to `(x, y)` mm immediately. Requires home.
+Pen down, draw to `(x, y)` mm immediately, then wait for motion completion (`M400`). Requires home.
 
 ### `goToZero()`