Deproject Screen To World Coordinates (Unreal Engine 4.15)

Question

I am working on a small game in Unreal Engine 4.15 using blueprints only and encountered a behaviour I don't understand.

The game is based on the Top Down Example. As I'd like to teleport an actor to a world location corresponding to a screen location (i.e. left edge of the viewport). I use "Deproject Screen To World". Giving screen X = 0 and screen Y = 0 as input to this node, outputs world coordinates close to the bottom center of the viewport. In order to get a test actor to move to outputted world coordinates close to the left edge of the viewport, input screen coordinates need to unexpectedly high (around -20000.00 for both x and y). This occurs strange to me, as the viewport is much smaller (around 1400x740 in editor preview).

I was hoping to use something like -(viewport width/2) for x screen coord (in case the x origin is centered.

Where is the origin for screen coordinates?
What unit are they measured in?

Note: The location on screen is not set from mouse position, so i can not use "Get Hit Result Under Cursor".

Answer 1

Origin screen coord in Unreal 4.21 are x=0.5, y=0.5. The coords you are giving (0,0) are the bottom left of the screen. The scale is based on a 1:1 scale, so that all screens regardless of number of pixels, shape, or size can display the crosshair (or other output) in the same "relative" location. So if you wanted a health bar at the bottom left of the screen you could code something like this "x=0.025, y=0.025" and it would be in the same relative bottom left corner of every screen (i.e. iPhone, PC, tablet, landscape mode, portrait mode, etc...