## Transform perspective mode BR offset Y

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donkeyhead

Posts: 3
Joined: 08 Dec 2019, 15:23

### Transform perspective mode BR offset Y

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 (22.73 KiB) Viewed 13932 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 (35.62 KiB) Viewed 13932 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 (41.68 KiB) Viewed 13932 times

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

u2bleank

Posts: 1179
Joined: 11 Jun 2012, 10:41

### Re: Transform perspective mode BR offset Y

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.

donkeyhead

Posts: 3
Joined: 08 Dec 2019, 15:23

### Re: Transform perspective mode BR offset Y

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.

u2bleank

Posts: 1179
Joined: 11 Jun 2012, 10:41

### Re: Transform perspective mode BR offset Y

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 )

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