Get bone rotation in pose mode using Python

Question

I want to get angles of joints in armature in pose mode, see the picture below. I tried to get local rotation of bones, but I can't find a way to do this.

I tried:

bone.rotation_euler()   # everytime returns [0, 0, 0] 
bone.matrix.to_euler()  # everytime returns some constant value e.g. [2, 0, 0]

I can rotate bone, but values don't change. How can I get actual rotations of the bone?

Also I find out a strange thing:

1. If bone has Rotation Constrait I can rotate it to constraint and it stops, but in Transform panel I see that angle is stil growing
2. If I use IK and move bone, location and translation in Transform window doesn't change.

Maybe this is relating to my problem. What is actually displays the Transform panel?

Answer 1

First note that bones have two representations within blender, the EditBone data represents it's static rest position within the armature while the PoseBone is the animated bone data that you would be moving around. The edit bones are stored in obj.data.edit_bones while the pose bones are in obj.pose.bones.

The rotation_mode value of a pose bone is used to switch between using rotation_euler, rotation_axis_angle or rotation_quaternion. These three rotation values can be seen in the bones properties and will show values without any constraints being applied. Note that euler values are stored as radians so you may want to use math.degrees() for the display value. Also the W in axis angle is radians.

The pose bones matrix value should give you the world position of the bone after constraints and drivers have been applied. You can get the bones euler rotation with bone.matrix.to_euler(). If using bpy.context to get the bone, you will find that bpy.context.active_bone.matrix will give you a matrix of zeros and ones while bpy.context.active_pose_bone.matrix will give you the matrix that you are after.

You can use a panel to watch the rotation of a bone -

import bpy
from math import degrees

class SimpleBoneAnglesPanel(bpy.types.Panel):
    bl_label = "Bone Angles"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'

    def draw(self, context):
        arm = context.scene.objects['Armature']
        bone = arm.pose.bones['Bone']

        mat = bone.matrix.to_euler()
        row = self.layout.row()
        row.label(text='X: {:.3}'.format(degrees(mat.x)))
        row.label(text='Y: {:.3}'.format(degrees(mat.y)))
        row.label(text='Z: {:.3}'.format(degrees(mat.z)))

bpy.utils.register_class(SimpleBoneAnglesPanel)