Blend Tree is a technical term that is extremely important in rendering and optimizing game graphics (technical art). An explanation of a visual tool in Animator Controller that dynamically blends and synthesizes multiple animations (walking, running, leaning, etc.) in a smooth ratio according to parameter values such as the character's movement speed and orientation.
Real world example: Stepless adjustment valve that creates lukewarm water at the perfect temperature (intermediate animation) by steplessly changing the twist of the hot and cold faucets
Rather than abruptly switching between "cold water (walking)" and "hot water (running)," the bone positions of each frame of the two movements are mixed in a perfect ratio according to the sliding degree of the parameter (faucet), achieving a smooth change in movement where the joints completely disappear.
Figure: Infographic that clearly illustrates the basic processing flow and mechanism of Blend Tree in Japanese notation
Detailed mechanism and operating principle
Create a "Blend Tree" in Animator, and output intermediate poses such as 40% walking and 60% running, smoothly mixing each frame based on parameters such as "Speed".