https://bugs.kde.org/show_bug.cgi?id=418557
Bug ID: 418557
Summary: Rotation transforms around the 'x' or 'y' axis have a
fixed construction viewpoint distance
Product: krita
Version: 4.2.8
Platform: Debian stable
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: Tools/Transform
Assignee: krita-bugs-n...@kde.org
Reporter: ahab.greybe...@hotmail.co.uk
Target Milestone: ---
Created attachment 126637
--> https://bugs.kde.org/attachment.cgi?id=126637&action=edit
Examples of 'y' axis transform rotation at different canvas sizes
SUMMARY
This happens on all versions.
When you do a rotation transform about the 'x' or 'y' axis, the edges of the
object being rotated appear to 'come out' and 'go in' to the plane of the
image, as would be expected. The amount by which this happens would depend on
the distance of the 'viewpoint' that is used to construct the projection of the
transformed object.
This viewpoint seems to be approximately 1000 pixels above the plane of the
image and it is fixed.
It does not change with image size.
There is a general rule that a 'natural' viewpoint distance is about 1.5 to 2.0
times the image diagonal distance. (This is subject to personal opinion and the
optimal distance probably depends on the shape and type of image.)
The fixed viewpoint distance in krita gives an unrealistic effect with large
(2000 + ) image sizes.
STEPS TO REPRODUCE
Perform rotation transforms about the 'y' or 'x' axis for a variety of canvas
sizes in the range 500 px to 3000 px.
OBSERVED RESULT
I attach four images that illustrate this with a simple square shape. For
apparently identical images, the effect varies depending on the canvas size.
For each image, the 'y' axis rotation was adjusted to give maximum shift of the
left side of the orange square to the left side of the image. The green square
is a fixed square for reference.
EXPECTED RESULT
The construction viewpoint distance should vary as a multiple of the image
diagonal size, or whatever formula is determined to be suitable, so that the
apparent visual effect does not vary with canvas size.
Ideally, the distance could be adjusted by the user, possibly as a multiple
within a ceratin range, of the canvas diagonal.
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