Page 1 of 1

Transform perspective mode BR offset Y

PostPosted: 23 Feb 2021, 16:06
by donkeyhead
I don't quite understand what the BR offset Y does when perspective mode is used on transform.

I have a square and I want to apply a perspective transform to it.
square_not_transformed.png
square_not_transformed.png (22.73 KiB) Viewed 5916 times


Using BR offset X gives me the expected result: increasing the X gives the effect that the front edge of the square moves closer.
square_perspective_mode_br_offset_x_increased.png
square_perspective_mode_br_offset_x_increased.png (35.62 KiB) Viewed 5916 times


However, using BR offset Y similarly applies some kind of squish or an rotation to the square?
(Kind of like the two opposite corners are moved up?)
square_perspective_mode_br_offset_y_increased.png
square_perspective_mode_br_offset_y_increased.png (41.68 KiB) Viewed 5916 times


What does the BR offset Y do with the perspective mode applied?

Re: Transform perspective mode BR offset Y

PostPosted: 23 Feb 2021, 16:36
by u2bleank
hi donkeyhead,

the "BR" parameter mean "Bottom Right offset". This parameter add an offset to the Bottom Right corner of the transform Box. which is useful when you want to do a "free" quad transformation.

Re: Transform perspective mode BR offset Y

PostPosted: 23 Feb 2021, 17:47
by donkeyhead
That I understand, but why does it behave differently from BR offset X when perspective mode is on?

When using BR offset X with perspective mode on horizontal lines stay as horizontal lines.
Using BR offset Y with perspective mode I would expect similar behaviour with vertical lines staying vertical lines.
However, the vertical lines in the middle of the square are angled.

Re: Transform perspective mode BR offset Y

PostPosted: 23 Feb 2021, 18:57
by u2bleank
The algorithm try to "guess" the right perspective to match given points.
If you change some orientation or "order" it can generate slightly different results ( which points are closer and wich one are farther is a unknow for example )