Mobile input issues

[riotcam]

Hi there, thanks for the nice Unreal ImGui integration plugin!

I have noticed that on mobile there are some input issues that mean ImGui isn't really usable.

It seems like the touch position is not correctly passed to ImGui on Mobile, so a couple of things happen:

• The input doesn't go to the correct place
• It seems like it gets stuck in a touch down state, where each new touch will move the ImGui Demo window to the touched position

I've made a small 5.5 project hat just shows the ImGui demo window that makes it easy to reproduce.

1. git clone clone https://github.com/riotcam/ImGuiTest.git
2. cd ImGuiTest
3. git submodule init
4. git submodule update
5. Open the ImGuiTest.uproject in UE >= 5.5
6. If you Play In Editor the ImGui.ToggleDemo console command should toggle the ImGui Demo, in the PIE window this should work as expected
7. Started a "Standalone Game Mobile" from the PIE menu
8. Alt Enter to full screen the "Standalone Mobile Game" window (not strictly necessary but is closer to the real mobile experience)
9. Show the demo with the ImGui.ToggleDemo console command
10. Try interact with the ImGui window and the game window, note that it does not behave the same as the (not mobile) "Standalone Game"

The Standalone Mobile Game window seems to behave the same as running on an Android or iOS device for this issue.

Do you have any idea what the difference in input handling might be that causes this to behave differently between PC and Mobile?

[VesCodes]

Looks like this PR might resolve this, if you'd like to try it out before I set up to validate it #37