Calculate mouse coordinates using correct char dimensions

Previously the Mouse class was using raw CSS pixels, we need CSS pixels based
on the amount of space the cells take up on the canvas

See Microsoft/vscode#35114

src/utils/MouseHelper.test.ts

@@ -0,0 +1,70 @@
+/**
+ * Copyright (c) 2017 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import jsdom = require('jsdom');
+import { assert } from 'chai';
+import { MouseHelper } from './MouseHelper';
+import { MockCharMeasure, MockRenderer } from './TestUtils.test';
+
+const CHAR_WIDTH = 10;
+const CHAR_HEIGHT = 20;
+
+describe('MouseHelper.getCoords', () => {
+  let dom: jsdom.JSDOM;
+  let window: Window;
+  let document: Document;
+  let mouseHelper: MouseHelper;
+
+  let charMeasure: MockCharMeasure;
+
+  beforeEach(() => {
+    dom = new jsdom.JSDOM('');
+    window = dom.window;
+    document = window.document;
+    charMeasure = new MockCharMeasure();
+    charMeasure.width = CHAR_WIDTH;
+    charMeasure.height = CHAR_HEIGHT;
+    const renderer = new MockRenderer();
+    renderer.dimensions = <any>{
+      actualCellWidth: CHAR_WIDTH,
+      actualCellHeight: CHAR_HEIGHT
+    };
+    mouseHelper = new MouseHelper(renderer);
+  });
+
+  describe('when charMeasure is not initialized', () => {
+    it('should return null', () => {
+      charMeasure = new MockCharMeasure();
+      assert.equal(mouseHelper.getCoords({ pageX: 0, pageY: 0 }, document.createElement('div'), charMeasure, 1, 10, 10), null);
+    });
+  });
+
+  describe('when pageX/pageY are not supported', () => {
+    it('should return null', () => {
+      assert.equal(mouseHelper.getCoords({ pageX: undefined, pageY: undefined }, document.createElement('div'), charMeasure, 1, 10, 10), null);
+    });
+  });
+
+  it('should return the cell that was clicked', () => {
+    let coords: [number, number];
+    coords = mouseHelper.getCoords({ pageX: CHAR_WIDTH / 2, pageY: CHAR_HEIGHT / 2 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 1]);
+    coords = mouseHelper.getCoords({ pageX: CHAR_WIDTH, pageY: CHAR_HEIGHT }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 1]);
+    coords = mouseHelper.getCoords({ pageX: CHAR_WIDTH, pageY: CHAR_HEIGHT + 1 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 2]);
+    coords = mouseHelper.getCoords({ pageX: CHAR_WIDTH + 1, pageY: CHAR_HEIGHT }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [2, 1]);
+  });
+
+  it('should ensure the coordinates are returned within the terminal bounds', () => {
+    let coords: [number, number];
+    coords = mouseHelper.getCoords({ pageX: -1, pageY: -1 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 1]);
+    // Event are double the cols/rows
+    coords = mouseHelper.getCoords({ pageX: CHAR_WIDTH * 20, pageY: CHAR_HEIGHT * 20 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [10, 10], 'coordinates should never come back as larger than the terminal');
+  });
+});