In your example, are there two connected displays or one display? If two, is the one at -2560,-400 the primary or secondary?

To answer comment #2, there are 2 displays. The primary is the PixelBook built in display with origin of (0, 0) and dimension of 1200x800. The secondary has origin of (-2560, -400) and dimension of 2560x1600.

That is my test setup. The secondary display is physically on the left side of the PixelBook so I changed the settings to make it on the left of the PixelBook as well.

Tim, when you were calling SetBoundsInScreen() with bounds_in_screen (0,0), what display ID were you passing?

I'm asking because |bounds_in_screen| is in "virtual screen coordinates", a coordinate system across all known displays. I would expect bounds_in_screen (0,0) to be the top-left corner of the primary monitor, regardless of display configuration. So a window in the top-left of the primary display should be at (0,0) in the coordinates of the primary display. (2560,400) sounds like the same position, but in the coordinates of the secondary (on the left) display. It would also be odd for the |display| to be the secondary display and the bounds_in_screen to be (0,0), since that would imply the window is offscreen.

Is it possible you were expecting |bounds_in_screen| to mean the position in the coordinate system of the |display|?

I get pretty reasonable results for |new_bounds| when I drag a window from display 1 to display 2 -- it's in the coordinates of display 2.

(I have no idea why we pass both parameters to that function, since you should be able to use display::Screen::GetDisplayNearestPoint to figure out the display.)

James, you're right that I was expecting |bounds_in_screen| to mean the position in the coordinate system of the |display|. So It might be my misunderstanding of SetBoundsInScreen().

So what does SetBoundsInScreen() actually do? I am using it to re-parent a window from a display to another display. The window is in the primary display at the top left corner, so the origin is (0,0). I want to move it to the second display at the same top left corner, which has the coordinate of (-2560, -400). So I call SetBoundsInScreen((0,0) ..., second_display_id). After the call the window is re-parent to the second display but the origin becomes (2560, 400), out of screen.

Please not that the second screen has x axis range from -2560 to 0 and the y axis range from -400 to 1200.

https://cs.chromium.org/chromium/src/ui/aura/window.h?rcl=f8e6447dcc8d0d35455592c4b259de42d1009030&l=223

The name of the first parameter of SetBoundsInScreen() is 'new_bounds_in_screen_coords'. I understand the screen as the same as display. So do you think the name is misleading here?

Never mind. I should read more carefully. So screen is the "virtual screen". Okay, I think it's my misunderstanding. Thanks for the help.

Right, Screen is composed of some number of Displays:
  https://cs.chromium.org/chromium/src/ui/display/screen.h?l=29

Yeah, the names aren't great. We don't have a good name for "bounds in current display" vs. "bounds across all displays". (We also have problems with dips vs pixels.) For better or worse, |in_screen| in variables and method names means virtual screen coordinates.