Two bugs I found in Flex

[lyd405121]

AABB Initialize problem

• /core/aabbtree.h, line86
• origin: Bounds() : m_min(0.0f), m_max(0.0f)
• I think it should be: Bounds() : m_min(INFINITY), m_max(-INFINITY)
• The reason is when you do function "Union", we will merge another aabb with this initialized box
• For example, the initialized box is min[0.0,0.0,0.0] max[0.0,0.0,0.0], Union a box like min[1.0,1.0,1.0], max[2.0,2.0,2.0]
• The answer will be min[0.0,0.0,0.0] max[2.0,2.0,2.0], though it won't change the accuracy of bvh，but the efficiency will not be good as expected for the sah algrithm

Deform probelm for rigidbody

• I have talked with one of the author of this repo， Prof. Dr. Jan Bender
• The difference between Flex and this work InteractiveComputerGraphics/PositionBasedDynamics#107
• I found a deform probelm for rigidbody as I drag too fast with it

• Prof. Dr. Jan think it is wrong for rigidbody to deform
• I read the PBD paper， And I think maybe the Flex don't do shape match for every frame，so when I drag too fast, the rigidbody will deform.Is it right?