fix ratio potential issue

lib/basedriver/commands/find.js

@@ -363,19 +363,50 @@ helpers.getScreenshotForImageFind = async function (screenWidth, screenHeight) {
   // of coordinates returned by the image match algorithm, since we match based
   // on the screenshot coordinates not the device coordinates themselves. There
   // are two potential types of mismatch: aspect ratio mismatch and scale
-  // mismatch.
+  // mismatch. we need to detect and fix both
+
+  let scale = {xScale: 1.0, yScale: 1.0};
+
+  const screenAR = screenWidth / screenHeight;
+  const shotAR = shotWidth / shotHeight;
+  if (screenAR === shotAR) {
+    log.info('Screenshot aspect ratio matched screen aspect ratio');
+  } else {
+    log.warn(`When trying to find an element, determined that the screen ` +
+             `aspect ratio and screenshot aspect ratio are different. Screen ` +
+             `is ${screenWidth}x${screenHeight} whereas screenshot is ` +
+             `${shotWidth}x${shotHeight}.`);
+
+    // Select smaller ratio
+    // this.getScreenshot is 540x397, this.getDeviceSize is 1080x1920.
+    // The ratio is {xScale: 2, yScale: 4.83}.
+    // In this case, we must choose `xScale: 2` as scaleFactor.
+    // Because if Appium selects the both ratio, the screenshot will be distorted.
+    // If Appium selects the yScale, width will be bigger than real screenshot.
+    const _xScale = (1.0 * shotWidth) / screenWidth;
+    const _yScale = (1.0 * shotHeight) / screenHeight;
+    const scaleFactor = _xScale >= _yScale ? _yScale : _xScale;
+
+    log.warn(`Resizing screenshot to ${shotWidth * scaleFactor}x${shotHeight * scaleFactor} to match ` +
+             `screen aspect ratio so that image element coordinates have a ` +
+             `greater chance of being correct.`);
+    imgObj = imgObj.resize(shotWidth * scaleFactor, shotHeight * scaleFactor);
+
+    scale.xScale *= scaleFactor;
+    scale.yScale *= scaleFactor;
+  }
 
   // Resize based on the screen dimensions only if both width and height are mismatched
   // since except for that, it might be a situation which is different window rect and
   // screenshot size like `@driver.window_rect #=>x=0, y=0, width=1080, height=1794` and
   // `"deviceScreenSize"=>"1080x1920"`
-  let scale;
   if (screenWidth !== shotWidth && screenHeight !== shotHeight) {
     log.info(`Scaling screenshot from ${shotWidth}x${shotHeight} to match ` +
              `screen at ${screenWidth}x${screenHeight}`);
     imgObj = imgObj.resize(screenWidth, screenHeight);
 
-    scale = {xScale: (1.0 * screenWidth) / shotWidth, yScale: (1.0 * screenHeight) / shotHeight};
+    scale.xScale *= (1.0 * screenWidth) / shotWidth;
+    scale.yScale *= (1.0 * screenHeight) / shotHeight;
   }
 
   b64Screenshot = (await imgObj.getBuffer(imageUtil.MIME_PNG)).toString('base64');

test/basedriver/commands/find-specs.js

@@ -281,21 +281,27 @@ describe('finding elements by image', function () {
 
       // try first with portrait screen
       let screen = [TINY_PNG_DIMS[0] * 2, TINY_PNG_DIMS[1] * 3];
+      let expectedScale = { xScale: 0.67, yScale: 1 };
+
       const {b64Screenshot, scale} = await d.getScreenshotForImageFind(...screen);
       b64Screenshot.should.not.eql(TINY_PNG);
       let screenshotObj = await imageUtil.getJimpImage(b64Screenshot);
       screenshotObj.bitmap.width.should.eql(screen[0]);
       screenshotObj.bitmap.height.should.eql(screen[1]);
-      scale.should.eql({ xScale: 2, yScale: 3 });
+      scale.xScale.toFixed(2).should.eql(expectedScale.xScale.toString());
+      scale.yScale.should.eql(expectedScale.yScale);
 
       // then with landscape screen
       screen = [TINY_PNG_DIMS[0] * 3, TINY_PNG_DIMS[1] * 2];
+      expectedScale = { xScale: 1, yScale: 0.67 };
+
       const {b64Screenshot: newScreen, scale: newScale} = await d.getScreenshotForImageFind(...screen);
       newScreen.should.not.eql(TINY_PNG);
       screenshotObj = await imageUtil.getJimpImage(newScreen);
       screenshotObj.bitmap.width.should.eql(screen[0]);
       screenshotObj.bitmap.height.should.eql(screen[1]);
-      newScale.should.eql({ xScale: 3, yScale: 2 });
+      newScale.xScale.should.eql(expectedScale.xScale);
+      newScale.yScale.toFixed(2).should.eql(expectedScale.yScale.toString());
     });
   });
 });