attempt to reject invalid pointerType

fix for wonderunit/storyboarder#927
#19

doesn't work reliably though, because `pointerType` is not reliable!

example/app.js

@@ -117,6 +117,7 @@ window.fetch('./example/brushes/brushes.json')
         })
 
         window.addEventListener('pointermove', function (e) {
+          console.log('pointermove', e.pointerType, e.timeStamp)
           if (gui.domElement.contains(e.target)) return // ignore GUI pointer movement
 
           // if (e.target.parentNode !== document.body) return

src/ts/sketch-pane/sketch-pane.ts

@@ -29,7 +29,10 @@ interface IStrokeState {
   lastStaticIndex?: number
   lastSpacing?: number | undefined
   grainOffset?: { x: number, y: number }
-// snapshot brush configuration
+
+  pointerType: string, // 'mouse' | 'pen' | 'touch'
+
+  // snapshot brush configuration
   size?: number
   color?: number
   opacity?: number
@@ -460,6 +463,16 @@ export default class SketchPane {
     strokeContainer.addChild(sprite)
   }
 
+  acceptsEvent (e: PointerEvent) {
+    // console.log('down?', this.pointerDown, 'type:', e.pointerType)
+    // reject if pointer is already down and event pointerType doesn't match initial pointerType
+    if (this.pointerDown && e.pointerType != this.strokeState.pointerType) {
+      return false
+    } else {
+      return true
+    }
+  }
+
   pointerDown = false
 
   down (e: PointerEvent, options = {}) {
@@ -471,6 +484,8 @@ export default class SketchPane {
   }
 
   move (e: PointerEvent) {
+    if (!this.acceptsEvent(e)) return
+
     if (this.pointerDown) {
       this.strokeContinue(e)
     }
@@ -480,6 +495,8 @@ export default class SketchPane {
   }
 
   up (e: PointerEvent) {
+    if (!this.acceptsEvent(e)) return
+
     if (this.pointerDown) {
       this.strokeEnd(e)
     }
@@ -509,6 +526,9 @@ export default class SketchPane {
         ? {x: Math.floor(Math.random() * 100), y: Math.floor(Math.random() * 100)}
         : {x: 0, y: 0},
 
+      // initial pointer type
+      pointerType: e.pointerType,
+
       // snapshot brush configuration
       size: this.brushSize,
       color: this.brushColor,