Improve takeScreenshot performance in ie driver.

IsSameColor method could take a lot of time, especially for pages with solid background (like login or search forms, where only several elements exists on the page). This becomes even worse if IEDriverServer runs several sessions in parallel. This happens beacause of GetPixel method calls winapi each time it is called. So we get rid of it and use already captured bytes to check screenshot.

Signed-off-by: Jim Evans <james.h.evans.jr@gmail.com>

cpp/iedriver/CommandHandlers/ScreenshotCommandHandler.cpp

@@ -1,4 +1,4 @@
-// Licensed to the Software Freedom Conservancy (SFC) under one
+// Licensed to the Software Freedom Conservancy (SFC) under one
 // or more contributor license agreements. See the NOTICE file
 // distributed with this work for additional information
 // regarding copyright ownership. The SFC licenses this file
@@ -126,12 +126,34 @@ void ScreenshotCommandHandler::CaptureWindow(HWND window_handle,
 }
 
 bool ScreenshotCommandHandler::IsSameColour() {
-  COLORREF firstPixelColour = this->image_->GetPixel(0, 0);
-
-  for (int i = 0; i < this->image_->GetWidth(); i++) {
-    for (int j = 0; j < this->image_->GetHeight(); j++) {
-      if (firstPixelColour != this->image_->GetPixel(i, j)) {
-        return false;
+  int bytes_per_pixel = this->image_->GetBPP() / 8;
+  if (bytes_per_pixel >= 3) {
+    BYTE* root_pixel_pointer = reinterpret_cast<BYTE*>(this->image_->GetBits());
+    int pitch = this->image_->GetPitch();
+    int first_pixel_red = *(root_pixel_pointer);
+    int first_pixel_green = *(root_pixel_pointer + 1);
+    int first_pixel_blue = *(root_pixel_pointer + 2);
+
+    for (int i = 0; i < this->image_->GetWidth(); ++i) {
+      for (int j = 0; j < this->image_->GetHeight(); ++j) {
+        int current_pixel_offset = (pitch * j) + (bytes_per_pixel * i);
+        int current_pixel_red = *(root_pixel_pointer + current_pixel_offset);
+        int current_pixel_green = *(root_pixel_pointer + current_pixel_offset + 1);
+        int current_pixel_blue = *(root_pixel_pointer + current_pixel_offset + 2);
+        if (first_pixel_red != current_pixel_red ||
+            first_pixel_green != current_pixel_green ||
+            first_pixel_blue != current_pixel_blue) {
+          return false;
+        }
+      }
+    }
+  } else {
+    COLORREF firstPixelColour = this->image_->GetPixel(0, 0);
+    for (int i = 0; i < this->image_->GetWidth(); ++i) {
+      for (int j = 0; j < this->image_->GetHeight(); ++j) {
+        if (this->image_->GetPixel(i, j)) {
+          return false;
+        }
       }
     }
   }