[no bug] matrix4.getScale() just after matrix4.setScale()

[greenya]

Hi!

Bug #1: I've noticed that setting rotation via setRotationDegrees() causes scale to be changed too.
Bug #2: Also the order of what you do fist: set rotation or set scale - does matter.

Next test case shows this problem:

Code: Select all

	core::matrix4 m;
	m.setTranslation(core::vector3df(-5210, -582, -9738));
	m.setRotationDegrees(core::vector3df(124, 352, 8));
	m.setScale(1.1f);
	// NOW: m[0] == m[5] == m[10] == 1.1f
	core::vector3df v = m.getScale();
	// NOW: v == X=1.1173017 Y=1.3730689 Z=1.3796232

Now, all the same, we've only interchanged order of rotation and scale calls:

Code: Select all

	core::matrix4 m;
	m.setTranslation(core::vector3df(-5210, -582, -9738));
	m.setScale(1.1f);
	// NOW: m[0] == m[5] == m[10] == 1.1f
	m.setRotationDegrees(core::vector3df(124, 352, 8));
	// NOW: m[0] == 0.98063082, m[5] == -0.56980854, m[10] == -0.55375081
	core::vector3df v = m.getScale();
	// NOW: v == X=0.99999994 Y=0.99999994 Z=0.99999994 // this is 1.0 (but not 1.1)

P.S.: if i don't set rotation at all, i get back correct scale.

[Radikalizm]

To me this is pretty much expected behavior, those matrix operations are not commutative so the order of executed operations matters

[greenya]

To me it seems incorrect at all. To me all 3 attributes of the object (scene node) are completly independent, so if i set position and rotation - scale must not be changed. I do not do projection using projective camera matrix or somthing like that, i just translate, rotate and scale - a simple operations on the object. So to me - matrix is a container for translation, rotation and scale vectors only.

[hybrid]

This is (almost) not possible, at least not efficient. You need to multiply matrices which define rotation and scale. These operations (only in this combination) are commutative, so no problem which order you do. Otherwise we'd need to check for each call, whether rotation or scale is set, and decompose the matrix in case it is. This takes a few hundred cycles each, and would kill all update performance. But it should be documented in the API.

[CuteAlien]

Actually it's correctly done for SceneNodes. As SceneNodes keep internally a vector for scale - so it works for those as you expect. It's just a problem when working with matrices.

[greenya]

Ah, now i see. If SceneNode keeps dedicated vector for scale then everything is OK. Then this is not a bug ofcause.
Thank you for explanation!