Gltf animations (bevyengine#3751)

# Objective

- Load informations for animations from GLTF
- Make experimenting on animations easier

# Non Objective

- Implement a solutions for all animations in Bevy. This would need a discussion / RFC. The goal here is only to have the information available to try different APIs

## Solution

- Load animations with a representation close to the GLTF spec
- Add an example to display animations. There is an animation driver in the example, not in Bevy code, to show how it can be used. The example is cycling between examples from the official gltf sample ([AnimatedTriangle](https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/AnimatedTriangle), [BoxAnimated](https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/BoxAnimated)), and one from me with some cases not present in the official examples.


https://user-images.githubusercontent.com/8672791/150696656-073403f0-d921-43b6-beaf-099c7aee16ed.mp4




Co-authored-by: Carter Anderson <[email protected]>

CREDITS.md

@@ -21,3 +21,5 @@
 * Ground tile from [Kenney's Tower Defense Kit](https://www.kenney.nl/assets/tower-defense-kit) (CC0 1.0 Universal)
 * Game icons from [Kenney's Game Icons](https://www.kenney.nl/assets/game-icons) (CC0 1.0 Universal)
 * Space ships from [Kenny's Simple Space Kit](https://www.kenney.nl/assets/simple-space) (CC0 1.0 Universal)
+* glTF animated triangle from [glTF Sample Models](https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/AnimatedTriangle) (CC0 1.0 Universal)
+* glTF box animated from [glTF Sample Models](https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/BoxAnimated) ([CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) - by [Cesium](https://cesium.com))

Cargo.toml

@@ -183,6 +183,10 @@ path = "examples/3d/lighting.rs"
 name = "load_gltf"
 path = "examples/3d/load_gltf.rs"
 
+[[example]]
+name = "manual_gltf_animation_player"
+path = "examples/3d/manual_gltf_animation_player.rs"
+
 [[example]]
 name = "many_cubes"
 path = "examples/3d/many_cubes.rs"

assets/models/animated/AnimatedTriangle.gltf

@@ -0,0 +1,118 @@
+{
+  "scene" : 0,
+  "scenes" : [
+    {
+      "nodes" : [ 0 ]
+    }
+  ],
+
+  "nodes" : [
+    {
+      "mesh" : 0,
+      "rotation" : [ 0.0, 0.0, 0.0, 1.0 ]
+    }
+  ],
+
+  "meshes" : [
+    {
+      "primitives" : [ {
+        "attributes" : {
+          "POSITION" : 1
+        },
+        "indices" : 0
+      } ]
+    }
+  ],
+
+  "animations": [
+    {
+      "samplers" : [
+        {
+          "input" : 2,
+          "interpolation" : "LINEAR",
+          "output" : 3
+        }
+      ],
+      "channels" : [ {
+        "sampler" : 0,
+        "target" : {
+          "node" : 0,
+          "path" : "rotation"
+        }
+      } ]
+    }
+  ],
+
+  "buffers" : [
+    {
+      "uri" : "data:application/octet-stream;base64,AAABAAIAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAACAPwAAAAA=",
+      "byteLength" : 44
+    },
+    {
+      "uri" : "data:application/octet-stream;base64,AAAAAAAAgD4AAAA/AABAPwAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAD0/TQ/9P00PwAAAAAAAAAAAACAPwAAAAAAAAAAAAAAAPT9ND/0/TS/AAAAAAAAAAAAAAAAAACAPw==",
+      "byteLength" : 100
+    }
+  ],
+  "bufferViews" : [
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+      "byteOffset" : 0,
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+      "target" : 34963
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+      "target" : 34962
+    },
+    {
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+      "byteLength" : 100
+    }
+  ],
+  "accessors" : [
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+      "count" : 3,
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+      "min" : [ 0.0, 0.0, 0.0, -0.707 ]
+    }
+  ],
+
+  "asset" : {
+    "version" : "2.0"
+  }
+
+}