Transform perspective mode BR offset Y

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donkeyhead
 
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Joined: 08 Dec 2019, 15:23

Transform perspective mode BR offset Y

Postby donkeyhead » 23 Feb 2021, 16:06

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 2911 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 2911 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 2911 times


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

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u2bleank
 
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Joined: 11 Jun 2012, 10:41

Re: Transform perspective mode BR offset Y

Postby u2bleank » 23 Feb 2021, 16:36

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

Postby donkeyhead » 23 Feb 2021, 17:47

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.

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u2bleank
 
Posts: 1179
Joined: 11 Jun 2012, 10:41

Re: Transform perspective mode BR offset Y

Postby u2bleank » 23 Feb 2021, 18:57

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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