Document>Clip Canvas issue

[NotMyFault]

Hi,

Clip Canvas shifts a perfectly pixel-aligned document by a fraction and causes mis-aligned of all objects (regarding pixel-exact positions).

To reproduce:

• open the attached document,
• have a look at transform panel (all curves etc. perfectly aligned)
• and Click Document>Clip Canvas
• activate move-tool again to see transform panel (all curves mis-aligned regarding position)

This was observed while creating a wheel hub-design (with much larger size).

Before

 

After:

clip canvas bug.afphoto

[Chris B]

😮 Thanks—I will get this logged! 

[NotMyFault]

Hi @Chris B,

 

I think i found an explanation for what is going on 😉

The issue is not caused by "Clip Canvas", but by rendering issues of the curves regarding (at least) the alpha channel. It is very hard to spot, but when cropping to a larger area (e.g. 10x10), you can spot some slightly darker pixels. To make this easy to detect, using my preferred Sherlock Holmes method to peek into pixel values by procedural texture filters, i found that the rotated curves lead to alpha > 0 in the extension of their axes. You get more asymmetrically higher alpha values to the lower right side (135 degree), which i explain in a second.

This asymmetry misleads clip canvas - which i assume works just right and falls victim to the asymmetric curves. This might be caused by even canvas sizes: The center of the shapes cannot be places exactly into the center, it will be by 1/e down and right to the real center. 1/e is the smallest position larger than 0, based on the maximum possible coordinates in Affinty.

The issue cannot be reproduced with uneven document size, as then the center gets an pixel-exact position.

You can set the input parameter "a" to values of -1 to -10. The PT filter transforms the alpha channel values into pure white, giving proof that alpha is about 1 to 5 at places where it should be 0. I assume small rounding issues as root cause.

The real and new issue: the info panel does not show the correct information! It continues to show "0" even if the pixel is pure white. This happens when really zooming in and trying to get the info for one dedicated pixel. Look at the values shown by info panel for the white pixel where i placed the cross-hairs.