fix T83880: Added check for valid context object to avoid null pointer exception when no object in scene

refactor vec_roll_to_mat3_normalized() for clarity

the function vec_roll_to_mat3_normalized() has a bug as described in T82455. This Differential is only for refactoring the code such that it becomes more clear what the function does and how the bug can be fixed. This differential is supposed to not introduce any functional changes.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D9410

Allow vertex tools to operate on weight groups when armature is in object mode

Since a few versions (even before 2.79) we have an option that allows to restrict the vertex tools to operate only on deform groups. This was originally implemented for working with vertex groups for skeletal animation. In that case it is fortunate to have weight tools operate only on deforming vertext groups (vgroups assigned to bones)

In previous versions of Blender (up to 2.79) we have been able to use this option in Mesh Edit mode regardless of the armature mode. The current implementation (since 2.80 as far as i know) enables this option only when the associated armature is in pose mode. this has a bad consequence:

It is not at all intuitive that you have to put the armature into Pose mode before you can make use of the option in mesh edit mode.
Besides this it is not even necessary in the case when the user wants to restrict the tool only to all pose bones. In that case the armature can safely be kept in Object mode. However, when the tool shall apply only to selected pose bones, then it actually makes sense to have the armature in pose mode (as it is implemented right now)

I do not know why this feature has been restricted as described above. It must have got lost somewhere on the way to Blender 2.90

This patch fixes the issue as it allows to select the "restrict to pose bones" option when the armature is in any mode. I see no downsides of this change, actually this is a fix for a feature that once worked and apparently got forgotten in newer releases.

Reviewed By: sybren, campbellbarton

Differential Revision: https://developer.blender.org/D9658

refactor vec_roll_to_mat3_normalized() for clarity

the function vec_roll_to_mat3_normalized() has a bug as described in T82455. This Differential is only for refactoring the code such that it becomes more clear what the function does and how the bug can be fixed. This differential is supposed to not introduce any functional changes.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D9410

fix: added missing float declarations

Test cases for vec_roll_to_mat3_normalized

The function vec_roll_to_mat3_normalized() basically has to handle 3 scenarios:

- When a bone is oriented along the negative Y axis
- When a bone is very close to the negative Y axis
- All other cases

The tests in the Differential make sure that all 3 situations are covered.

Reviewed By: sybren, mont29

Differential Revision: https://developer.blender.org/D9525

Fix T69090: Collada Exporter now exports the base color if Nodes are disabled

I also changed the Collada importer scuh that the diffuse Alpha is now set
for the generated PBSDF Shader AND for the base color.

Note: we can not export the base color AND the color
from the PBSDF Shaders at the same time. And when importing
we do not know if the color was originally coming from a base
material or from a shader. Setting them both in import seems
to give the most consistent results.

cleanup: Collada exporter: Removed misleading comments

cleanup: do no longer use deprecated Alpha channel from Shader diffuse color (use Shader's Alpha value instead)

fix T69772 Collada importer creates wrong fcurves for skeletal animation