Fix a screen capture issue on retina macOS devices.

webrtc/modules/desktop_capture/screen_capturer_mac.mm

Index: webrtc/modules/desktop_capture/screen_capturer_mac.mm
diff --git a/webrtc/modules/desktop_capture/screen_capturer_mac.mm b/webrtc/modules/desktop_capture/screen_capturer_mac.mm
index f11b36d2d2001d6fd0079d8d9464a1dcfd7c89fb..09220b798450d3b695c91f0e667167c730868a4e 100644
--- a/webrtc/modules/desktop_capture/screen_capturer_mac.mm
+++ b/webrtc/modules/desktop_capture/screen_capturer_mac.mm
@@ -304,6 +304,10 @@ class ScreenCapturerMac : public DesktopCapturer {
   bool RegisterRefreshAndMoveHandlers();
   void UnregisterRefreshAndMoveHandlers();
 
+  void ScreenUpdateMove(CGFloat delta_x,
+                        CGFloat delta_y,
+                        CGRectCount count,
+                        const CGRect* rect_array);
   void ScreenRefresh(CGRectCount count, const CGRect *rect_array);
   void ReleaseBuffers();
 
@@ -955,10 +959,18 @@ bool ScreenCapturerMac::RegisterRefreshAndMoveHandlers() {
 
           size_t count = 0;
           const CGRect* rects = CGDisplayStreamUpdateGetRects(
-              updateRef, kCGDisplayStreamUpdateDirtyRects, &count);
+              updateRef, kCGDisplayStreamUpdateMovedRects, &count);

[Sergey Ulanov, 2016/12/20 18:56:51]

I would still prefer to use kCGDisplayStreamUpdateDirtyRects if it works
properly with the rect scaling fixed. Using MovedRects/RefreshedRects here makes
this code more complicated with no clear benefits. 
MovedRects/RefreshedRects may give more precise update region, but it's not
clear if that would always provide any performance benefits. Having too detailed
updated region may be costly as well: each rect results in GlBlit*() call, and
capturing whole screen at once may be faster than every simple change
individually. We currently don't have any benchmarks to show potential
performance wins one way or the other and without them I'd prefer to keep this
simpler code.

+          if (count != 0) {
+            CGFloat dx = 0;
+            CGFloat dy = 0;
+            CGDisplayStreamUpdateGetMovedRectsDelta(updateRef, &dx, &dy);
+            ScreenUpdateMove(dx, dy, count, rects);
+          }
+
+          count = 0;
+          rects = CGDisplayStreamUpdateGetRects(
+              updateRef, kCGDisplayStreamUpdateRefreshedRects, &count);
           if (count != 0) {
-            // According to CGDisplayStream.h, it's safe to call
-            // CGDisplayStreamStop() from within the callback.
             ScreenRefresh(count, rects);
           }
         };
@@ -984,6 +996,20 @@ void ScreenCapturerMac::UnregisterRefreshAndMoveHandlers() {
   display_stream_manager_->UnregisterActiveStreams();
 }
 
+void ScreenCapturerMac::ScreenUpdateMove(CGFloat delta_x,
+                                         CGFloat delta_y,
+                                         CGRectCount count,
+                                         const CGRect* rect_array) {
+  // Refresh the source rects.
+  ScreenRefresh(count, rect_array);
+
+  // Refresh the destination rects.
+  CGRect refresh_rects[count];
+  for (CGRectCount i = 0; i < count; ++i)
+    refresh_rects[i] = CGRectOffset(rect_array[i], delta_x, delta_y);
+  ScreenRefresh(count, refresh_rects);
+}
+
 void ScreenCapturerMac::ScreenRefresh(CGRectCount count,
                                       const CGRect* rect_array) {
   if (screen_pixel_bounds_.is_empty())
@@ -991,8 +1017,8 @@ void ScreenCapturerMac::ScreenRefresh(CGRectCount count,
 
   DesktopRegion region;
   for (CGRectCount i = 0; i < count; ++i) {
-    // Convert from Density-Independent Pixel to physical pixel coordinates.
-    DesktopRect rect = ScaleAndRoundCGRect(rect_array[i], dip_to_pixel_scale_);
+    // All rects are already in physical pixel coordinates.
+    DesktopRect rect = ScaleAndRoundCGRect(rect_array[i], 1.0);

[Sergey Ulanov, 2016/12/20 18:56:51]

It would be cleaner to write this as 
DesktopRect::MakeXYWH(rect.origin.x, rect.origin.y, rect.size.width,
bounds.size.height) . As you don't really need the rect scaled here, just
converting one rect type to another.

     region.AddRect(rect);
   }