Procedural Walking Animation in Minecraft — Transcript

Full transcript

1. 0:02Hi. Today's project is a spider with a procedural walking animation.
2. 0:07Its movements are generated in real time to adapt to its surroundings,
3. 0:11which would be infeasible to implement with traditional key-framed animations.
4. 0:18Let's start by creating a kinematic chain for a leg.
5. 0:21A chain is composed of a root node, and any number of rigid segments,
6. 0:25which we can render using the new Block Display entities.
7. 0:30To move the chain, we will first move the last segment to the target position.
8. 0:35Then, we will recursively move each parent segment to the base of its child.
9. 0:41Now the chain is no longer attached to its root.
10. 0:44We can move it back using the same principles.
11. 0:47We will repeat this procedure until we find a solution within some acceptable margin of error.
12. 0:54I specified a maximum of 10 iterations in case a solution is never found.
13. 0:55This a commonly used algorithm called FABRIK.
14. 1:01Currently, the joints can rotate with 360 degrees of freedom.
15. 1:06This is fine for flexible appendages,
16. 1:08but for leg joins, we typically want to restrict them to only rotate on one axis.
17. 1:14To apply this constraint,
18. 1:15I straightened the chain towards the target before applying the algorithm.
19. 1:21Here, I created a spider with 4 chains for legs.
20. 1:26Let's accelerate the body forward.
21. 1:33If each leg gets too far away from its rest-position, let's tell it to return to the rest-position.
22. 1:50Let's also make sure that the adjacent legs are grounded before we start moving each leg.
23. 2:12Right now, the spider will stand in awkward poses after coming to a rest.
24. 2:17Let's decrease the trigger-distance while the spider is standing still.
25. 2:34One other issue, is that the legs will phase through each other
26. 2:37if the rotation changes too rapidly.
27. 2:40We can interpolate the rotation gradually across multiple frames.
28. 2:49Next, we could tell the spider to stop moving if its legs get too far away from their rest-position.
29. 3:03Right now, the spider can only walk on a flat plane.
30. 3:08To fix this, we will scan a column of blocks to find the ground height
31. 3:12and use that as our new rest-position.
32. 3:19We need to move the body as well.
33. 3:22So I averaged the position of all the legs, added a small offset, and used the result
34. 3:28for the body position.
35. 3:57Next, I would like the spider to respond to gravity.
36. 4:03To add this, we will accelerate the body downwards.
37. 4:07If the spider has at least one pair of opposite legs on the ground,
38. 4:11we can apply an upwards force to counteract gravity.
39. 4:28For the final challenge, I want the spider to be able to walk on these discontiguous pillars.
40. 4:34This is impossible with our current strategy, as the spider's leg won't be able to locate the ground
41. 4:38while passing between gaps in the terrain.
42. 4:43To fix this, we could try scanning the 8 neighbouring columns as well and picking the one closest
43. 4:48to the rest-position.
44. 4:49However, this created a new problem, since the legs would now prefer moving half a block
45. 4:55to the adjacent columns instead of stepping up one full block.
46. 4:59To address this, I set the comparison point half a block above the rest-position
47. 5:03if the path is obstructed.
48. 5:31Lastly, I want to mention a bit about the block display entities I used to render the spider.
49. 5:38In Minecraft, all entities can rotate on 2 axes.
50. 5:42They have a pitch,
51. 5:44a yaw,
52. 5:46but no tilt.
53. 5:49This is a problem for the leg joints, since every time they crossed over the y-axis,
54. 5:54they would rotate 180 degrees in order to re-orient themselves upwards.
55. 5:59Here's what that looks like in context.
56. 6:09Thankfully, the block display entities allow us to specify a custom transformation matrix.
57. 6:15This means can rotate them using a matrix with an arbitrary up-vector
58. 6:19instead of the usual rotation component.
59. 6:23I used the cross-product between the y-axis and the end-effector,
60. 6:27since that always faces the same direction.
61. 6:30Here are some variations I was able to create by changing a few parameters.