Screen VS Viewport What is the difference

Screen and Viewport represent same area - on screen, but they have different coordinate systems (IIRC):

• Screen: from [0,0] to [Screen.width, Screen.height]

• Viewport: from [0,0] to [1,1]

World point is a point in world space.

edit(Bunny83)
I just fixed the Viewport coordinates. It's [0,0] to [1,1] and not [-1,-1] to [1,1]. The latter are homogeneous device coordinates. T$$anonymous$$s is the space where the GPU actually clips the geometry against the frustum. The result of the projection matrix outputs homogeneous coordinates.

A simplified version of the pipeline is:

 local space   [-inf, -inf] to [+inf, +inf]
     \/                                     -- localToWorld (Model)
 world space   [-inf, -inf] to [+inf, +inf]
     \/                                     -- worldToCamera (View)
 camera space  [-inf, -inf] to [+inf, +inf]
     \/                                     -- projectionMatrix (Projection)
 clip space    [  -1,   -1] to [   1,    1]
     \/                                     
 view space    [   0,    0] to [   1,    1] \
     \/                                      -- handled by GPU / driver
 screen space  [   0,    0] to [   W,    H] /

In all cases [0,0] is the bottom left. T$$anonymous$$s only handles normal geometry. The GUI space is a special case where the camera space has to invert the y axis, hence it starts at the top left.

Screen point is defined in pixels. The bottom-left of the screen is (0,0); bottom-right of the screen is (Screen.width,0), left-top is (0, Screen.height) and the right-top is (Screen.width,Screen.height).

A viewport space point is normalized and relative to the Camera. The points on the screen range between 0 and 1. You can determine the the x-coordinate by dividing the screenPoint.x by Screen.width and the y-coordinate by dividing the screenPoint.y by Screen.height.

For more information, check out the link http://codesaying.com/understanding-screen-point-world-point-and-viewport-point-in-unity3d/