Is rendering to RenderTexture changing output of Camera.ScreenToWorldPoint()?

Question

Hello there!

What am I doing?

I'm attempting to draw a worldspace Canvas on a RenderTexture and have the mouse events function properly.

What happens?

The moment I make the UI camera draw on a RenderTexture it seems to confuzzle the transformation from screen to world point. That apparently causes a wrong world position within the uGUI event system and my buttons won't receive mouse-over or mouse-out events. Kind of like this: alt text I'm debugging that by fetching a world position from the camera and drawing a way from there in the forward direction like so:

 var pos = uiCanvas.worldCamera.ScreenToWorldPoint(Input.mousePosition);
 Ray r = new Ray(ev.position, Vector3.forward);
 Debug.DrawLine(r.origin, r.GetPoint(1000), Color.blue);

While the mouse, on the screen, is above a button the raycast comes out at a completely shifted-away position. The moment I make the camera render to screen, things start to work normally again.

I confirmed that the uGUI event system has the same off-set position by moving stuff around until the wrong mouse position was above the buttons and the events worked.

I also tried to convert screen to viewport point first and from there to world. But to no avail. Still wonky.

So my question is, what needs to be done to account for that offset? It seems to vary from resolution to resolution and I can't find the correct values for the life of it.

Answer 1

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Answer by Alsio · Aug 28, 2016 at 06:50 PM

It's a bit hard to tell without seeing the whole hierarchy and scene, but this may help

RectTransformUtility.ScreenPointToLocalPointInRectangle https://docs.unity3d.com/ScriptReference/RectTransformUtility.ScreenPointToLocalPointInRectangle.html

I have used this to convert a screen point > render texture rect > its camera > ray cast > button thing Once you're in the rect you should convert to a [0,1] viewport space instead of pixels. Good luck!

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damagefilter · Aug 29, 2016 at 05:14 AM 0

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Hey, thanks for answering :D

Lets see if I got this right.

So I'll put a UI Canvas (which has the RectTransform on it ofc) on the RT plane, then do a screen-to-local-point conversion of mouse pointer => RT rect.

Then I'll transform that into a viewport point ... and raycast through the other camera that's actually capturing the UI, does that sound about right?

I'll try that out now myself, just making sure I get it right.

damagefilter · Aug 29, 2016 at 11:16 AM 0

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So, as additional info: That did help and it is working now, thank you very much.

The big deal here was (and is also very important) the viewport point MUST be generated by the camera that is rendering to screen, otherwise it won't work.

Damjan-Mozetic damagefilter · Aug 25, 2017 at 11:04 AM 0

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Hi, I know it's an old topic, but would you mind explaining a bit more on the process behind this? I am having the same issue.

Is rendering to RenderTexture changing output of Camera.ScreenToWorldPoint()?

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