From 6fde17649f7404e79a17d4d8f96662d03011aca1 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Thu, 30 Oct 2025 20:08:53 -0700
Subject: Move animation module outside of scene/

---
 src/animation_impl.h | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 src/animation_impl.h

(limited to 'src/animation_impl.h')

diff --git a/src/animation_impl.h b/src/animation_impl.h
new file mode 100644
index 0000000..4929b97
--- /dev/null
+++ b/src/animation_impl.h
@@ -0,0 +1,96 @@
+#pragma once
+
+#include <gfx/animation.h>
+#include <gfx/sizes.h>
+
+#include "types.h"
+
+#include <cstring.h>
+#include <math/defs.h>
+#include <math/mat4.h>
+#include <math/quat.h>
+#include <math/vec3.h>
+
+#include <stddef.h>
+
+typedef struct Buffer Buffer;
+
+// Currently ignoring scale in skinning and animation.
+//
+// TODO: Simultaneous animation of disjoint animations.
+
+/// Skeleton joint.
+/// Joints are mutable and store the transform and joint matrices that result
+/// from animation, aside from the inverse bind matrix.
+typedef struct Joint {
+  joint_idx child;       // First child Joint; index into Anima's joints.
+  joint_idx next;        // Next sibling Joint; index into Anima's joints.
+  mat4      transform;   // Local transform relative to parent.
+  mat4  inv_bind_matrix; // Transforms the mesh into the joint's local space.
+  mat4  joint_matrix;    // inv(global) * global joint transform * inv(bind).
+  aabb3 box;             // Bounding box of vertices affected by joint.
+} Joint;
+
+/// Animation skeleton.
+typedef struct Skeleton {
+  skeleton_idx next;
+  size_t       num_joints;
+  joint_idx    joints[GFX_MAX_NUM_JOINTS]; // Indices into Anima's joints array.
+} Skeleton;
+
+/// A keyframe of animation.
+typedef struct Keyframe {
+  R time; // Start time in [0, end animation time]
+  union {
+    vec3 translation;
+    quat rotation;
+  };
+} Keyframe;
+
+/// Animation channel.
+typedef struct Channel {
+  joint_idx              target; // Index into Anima's joints array.
+  ChannelType            type;
+  AnimationInterpolation interpolation;
+  size_t                 num_keyframes;
+  Keyframe               keyframes[GFX_MAX_NUM_KEYFRAMES];
+} Channel;
+
+/// A skeletal animation.
+typedef struct Animation {
+  animation_idx next;
+  sstring       name;
+  R             duration;
+  size_t        num_channels;
+  Channel       channels[GFX_MAX_NUM_CHANNELS];
+} Animation;
+
+/// Animation state.
+///
+/// This represents the current state of an animation.
+typedef struct AnimationState {
+  R start_time; // Time when the current animation started playing. -1 means the
+                // animation playback has not yet been initialized.
+  animation_idx animation; // Current animation. 0 = no animation.
+  bool          loop;
+} AnimationState;
+
+/// Animation object.
+///
+/// This is the top-level animation object that encapsulates everything
+/// necessary for animation.
+///
+/// For lack of a better name, this is called an Anima. It is short and the
+/// Latin root of animation.
+///
+/// The last joint of the joints array at index 'num_joints - 1' is the root of
+/// all skeletons; specifically, the root of all joints that otherwise would
+/// have no parent (a skeleton need not have its own root and can be a set of
+/// disjoint node hierarchies).
+typedef struct Anima {
+  skeleton_idx   skeleton;   // Index of first skeleton.
+  animation_idx  animation;  // Index of first animation.
+  AnimationState state;      // Current animation state.
+  size_t         num_joints; // Number of actual joints in the array.
+  Joint          joints[GFX_MAX_NUM_JOINTS]; // Shared by all skeletons.
+} Anima;
-- 
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