Pull getCoords into a Mouse util module

This is part of the work to prepare for the upcoing selection changes

Related #207

src/utils/Mouse.ts

@@ -0,0 +1,49 @@
+/**
+ * @license MIT
+ */
+
+import { CharMeasure } from './CharMeasure';
+
+export function getCoords(event: MouseEvent, rowContainer: HTMLElement, charMeasure: CharMeasure): [number, number] {
+  // ignore browsers without pageX for now
+  if (event.pageX == null) {
+    return null;
+  }
+
+  let x = event.pageX;
+  let y = event.pageY;
+  let el = rowContainer;
+
+  // should probably check offsetParent
+  // but this is more portable
+  while (el && el !== self.document.documentElement) {
+    x -= el.offsetLeft;
+    y -= el.offsetTop;
+    el = 'offsetParent' in el ? <HTMLElement>el.offsetParent : <HTMLElement>el.parentElement;
+  }
+
+  // convert to cols/rows
+  x = Math.ceil(x / charMeasure.width);
+  y = Math.ceil(y / charMeasure.height);
+
+  return [x, y];
+}
+
+export function getRawByteCoords(event: MouseEvent, rowContainer: HTMLElement, charMeasure: CharMeasure, colCount: number, rowCount: number): { x: number, y: number } {
+  const coords = getCoords(event, rowContainer, charMeasure);
+  let x = coords[0];
+  let y = coords[1];
+
+  // be sure to avoid sending bad positions to the program
+  if (x < 0) x = 0;
+  if (x > colCount) x = colCount;
+  if (y < 0) y = 0;
+  if (y > rowCount) y = rowCount;
+
+  // xterm sends raw bytes and
+  // starts at 32 (SP) for each.
+  x += 32;
+  y += 32;
+
+  return { x, y };
+}