unable to rotate image?

[teras]

Hello!

I am trying to do a test rotation on an image.
I am using this code

var test = newImage(50,50,4)
discard test.rotate(2)

but it fails with the following error message:

/Users/teras/Works/Development/Nim/emailform/emailform.nim(7) emailform
/Users/teras/.nimble/pkgs/flippy-0.4.1/flippy.nim(684) rotate
/Users/teras/.nimble/pkgs/flippy-0.4.1/flippy.nim(578) getSubImage
/Users/teras/.nimble/pkgs/flippy-0.4.1/flippy.nim(159) getRgba
/Users/teras/.choosenim/toolchains/nim-1.0.6/lib/system/assertions.nim(27) failedAssertImpl
/Users/teras/.choosenim/toolchains/nim-1.0.6/lib/system/assertions.nim(20) raiseAssert
/Users/teras/.choosenim/toolchains/nim-1.0.6/lib/system/fatal.nim(39) sysFatal
Error: unhandled exception: /Users/teras/.nimble/pkgs/flippy-0.4.1/flippy.nim(159, 10) `y >= 0 and y < image.height`  [AssertionError]

Am I using it wrong?

[teras]

I added before line 684 in flippy.nim the following code to debug it:

  echo $result & " -- " , 1+int((result.width - newWidth)/2) , " " , 1+int((result.height - newHeight)/2) , " " , newWidth , "/" , newHeight

I found that the problem is indeed with out of bounds numbers and the result is
<Image 50x51:4> -- 1 1 51/51
different values, I even have negative numbers, like for

var image = newImage(500,50,4)
echo image.rotate(20)

I get negative results
<Image 547x223:4> -- 166 -130 217/486

Should this happen?

[treeform]

There seems to be a bug with the rotate method. @benjif could you take a look?

[treeform]

Oh I have figured it out. It was trimming the image incorrectly. I created a better trim function and will now use that.

0c1a9f9

Also added a test case for your error.

Thank you for reporting the bug!

[teras]

Please excuse my comment.
I think the trim function is wrong.
It is good as a generic method, but not in this case.
What if an image is mostly "transparent", but only the center is painted?
Then rotation will minimize the image instead, not just rotate it.

IMHO the four edges of the rotated box should be calculated and crop the image accordingly.
Do you think we should discuss it more?

[treeform]

Yeah you are probably right. I did not think about this case.

…

On Fri, Apr 10, 2020, 7:38 AM Panayotis ***@***.***> wrote: Please excuse my comment. I think the trim function is wrong. It is good as a generic method, but not in this case. What if an image is mostly "transparent", but only the center is painted? Then rotation will minimize the image instead, not just rotate it. IMHO the four edges of the rotated box should be calculated and crop the image accordingly. Do you think we should discuss it more? — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#12 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAA6X7AMK6XZFG3PFZFVMLDRL4VNRANCNFSM4L7U7R3A> .

[teras]

Maybe take into account something like this
https://gamedev.stackexchange.com/questions/86755/how-to-calculate-corner-positions-marks-of-a-rotated-tilted-rectangle

Find the location of the four points

• (x,y)
• (x+width, y)
• (x+width,y+height)
• (x,y+height)

and keep the min/max X and min/max Y as bounding box of the clipped area

[treeform]

Yes you are right. I will take a look.

[treeform]

I thing it was fixed by @guzba #16