Issue with WorldToScreenPoint

Questions & Answers
1

Hi, i am trying to show some GUI item with a 3D object, let me first explain the scenario. There is a table with 3D items on it, and a camera from top down on the table so everything on the table can be seen from above, now what i do is

screenPos = tblCam.camera.WorldToScreenPoint (selItemHandle.transform.position);

to convert the position from world to screen and then i draw the gui according to it

leftButtonRect = new Rect(screenPos.x, Screen.height - screenPos.y, 48,48);
GUI.Button (leftButtonRect, icnRotateLeft, myStyle)

It works fine but as i move the item from left or right, the GUI item get a bit off, if i move the item toward left the GUI item goes off toward right a bit, and the GUI item goes off toward left if i move the item toward right…

Can someone tell me how to fix this?

Thanks

2

I finally figured it out… i was having a simiar problem…

Quick Description of my problem:
I was using the Canvas to display a sprite ( a healthbar) which floats over all the characters. The problem however, was when i tried to obtain the WorldToScreenPoint it kept giving a result that was slightly off… for example: the healthbar looked a little okay when the character was immediately in front of the camera… but as the character walks to the edge of the camera’s fulstrum, the screens x,y placement becomes more and more incorrect.

Days and days of research and trying different combinations finally showed me that maybe there is a scaling issue which pointed me to look at Canvas / Canvas Scaler / scaling mode: scale with screen

Originally, this worked wonderfully when i had only 1 character and his healthbar stayed stuck to the top of the screen like old classic double dragon games. BUT when i made the decision to have many characters and they all need “floating healthbars”, i didnt come back to re-evaluate whether this option needed to change.

Setting the canvas Scaler to: keep constant pixel size
, fixes the problem and i now have the correct WORLDtoSCREENpoint that i needed! And now the healthbar floats beautifully above the characters…

BUT WAIT, ANOTHER PROBLEM! Now, if the screen resolution is small… the Ui sprite is obsurdly large… and if the screen resolution is high definition then Ui sprite is way too small!

QUESTION: So how do i use the “scale with screen size” mode, but yet also still get back a correct WorldToScreenPoint?

ANSWER: you must take into consideration the overal scaling of the canvas when it is stretched to fit (whatever current resolution that you are using)

INSTEAD OF:

RectTransform myRect = GetComponent<RectTransform>();
Vector2 myPositionOnScreen = Camera.main.WorldToScreenPoint (myOwner);
myRect.anchoredPosition = myPositionOnScreen;

YOU CALCULATE THE OVERALL SCALE FACTOR LIKE THIS:

RectTransform myRect = GetComponent<RectTransform>();
    Vector2 myPositionOnScreen = Camera.main.WorldToScreenPoint (myOwner);

Canvas copyOfMainCanvas = GameObject.Find ("Canvas").GetComponent <Canvas>();
float scaleFactor = copyOfMainCanvas.scaleFactor

Vector2 finalPosition = new Vector2 (myPositionOnScreen.x / scaleFactor , myPositionOnScreen.y / scaleFactor);
myRect.anchoredPosition = finalPosition;

If this helped anyone please log in to give me a thumbs up…

3

This is a little old topic but for future clarity here are some points I noticed while investigating WorldToScreenPoint in 2019.11.f1.

The point you are given from WorldToScreenPoint is not scaled according to the scale of the canvas.
So if your Canvas is scaled in any way including the below - the vector you receive will not be scaled to fit the canvas.

  • Screen Space - Camera
  • World Space
  • Scale Factor

Since I was using Screen Space - Camera - the Canvas was scaled by the camera.
I got a relatively precise vector by scaling the WorldToScreenPoint by the scale of the canvas.

I was able to get a precise WorldToScreenPoint by using Screen Space - Overlay.