Documentation Index
Fetch the complete documentation index at: https://mintlify.com/AmyangXYZ/reze-studio/llms.txt
Use this file to discover all available pages before exploring further.
Linear interpolation between two keyframes gives motion that starts and stops at the same speed — correct, but mechanical. Real movement accelerates into a pose and decelerates out of it, overshoots, settles. Reze Studio’s per-channel Bézier editor lets you sculpt that timing independently for each of the six bone channels (three rotation axes, three translation axes), which means a wrist can snap into a frame fast while the shoulder eases in gently, all on the same keyframe pair.
The Six Channels
Each BoneKeyframe carries four independent Bézier curves stored as two control points in 0–127 space: one curve shared across all rotation axes (the VMD convention is to use a single rotation slerp-t curve), and three separate curves for the X, Y, and Z translation axes.
The timeline curve editor and the Properties Inspector use colour coding to distinguish channels at a glance:
| Key | Label | Color | Group |
|---|
rx | Rot.X | #e25555 | Rotation |
ry | Rot.Y | #44bb55 | Rotation |
rz | Rot.Z | #4477dd | Rotation |
tx | Trans.X | #e2a055 | Translation |
ty | Trans.Y | #55bba0 | Translation |
tz | Trans.Z | #7755dd | Translation |
Switching to the Curve Editor Tab
The timeline panel at the bottom of the screen has a tab bar above the canvas. Click any of the curve tabs to switch from the dopesheet diamond view to the per-channel curve view:
| Tab | Shows |
|---|
| All Rot | All three rotation curves overlaid |
| X / Y / Z (rot section) | A single rotation axis curve |
| All Trans | All three translation curves overlaid |
| X / Y / Z (tra section) | A single translation axis curve |
| Morph | The morph weight curve for the selected morph |
rx.
Reading the Curve
In the curve editor view:
- The horizontal axis is time in frames, scrolling and zooming with the rest of the timeline.
- The vertical axis is the channel value (degrees for rotation, MMD units for translation, 0–1 for morphs).
- Each keyframe has a dot on the curve at the exact stored value.
- The smooth line between dots is the interpolated result evaluated at every integer frame using the stored Bézier handles.
Zoom the value (Y) axis with Shift + scroll to spread out the vertical range and make small handle adjustments easier to see.
Dragging Bézier Handles
The interpolation curves for the currently-active keyframe are also editable in the Interpolation section at the bottom of the Properties Inspector (visible when a bone is selected and the playhead is on or past a keyframe).
The miniature curve editor widget shows a 160×160 canvas in VMD 127×127 space:
- cp0 (red square) — the ease-out handle of the current keyframe (controls how the motion leaves this key). It is anchored to the bottom-left corner
(0, 0) and its control arm points toward p1.
- cp1 (green square) — the ease-in handle of the next keyframe (controls how the motion arrives at that key). It is anchored to the top-right corner
(127, 127) and its control arm points toward p2.
Drag either square to adjust the curve. The canvas redraws imperatively on every pointer-move for a smooth feel, and a commit() fires on pointer-up so each drag is one undo step.
The channel being edited is selected via the four tabs directly above the curve editor widget:
- Rotation — the shared rotation slerp-t curve
- Trans X, Trans Y, Trans Z — per-axis translation curves
The bezierY Algorithm
Reze Studio uses a standard VMD-compatible cubic Bézier evaluator. Given a parameter t ∈ [0, 1] representing fractional progress through the frame span, it finds the Bézier curve’s y output by:
- Normalising the control-point coordinates from 0–127 space to 0–1:
x1 = cp0.x / 127, etc.
- Running a 15-iteration binary search to find the parameter
mid where the cubic’s x-component equals t.
- Evaluating the cubic’s y-component at that
mid.
function bezierY(
cp0: { x: number; y: number },
cp1: { x: number; y: number },
t: number
): number {
const x1 = cp0.x / 127, y1 = cp0.y / 127
const x2 = cp1.x / 127, y2 = cp1.y / 127
let lo = 0, hi = 1, mid = 0.5
for (let i = 0; i < 15; i++) {
const x = 3 * (1 - mid) ** 2 * mid * x1
+ 3 * (1 - mid) * mid ** 2 * x2
+ mid ** 3
if (Math.abs(x - t) < 0.0001) break
if (x < t) lo = mid
else hi = mid
mid = (lo + hi) / 2
}
return 3 * (1 - mid) ** 2 * mid * y1
+ 3 * (1 - mid) * mid ** 2 * y2
+ mid ** 3
}
Common Easing Patterns
Reze Studio ships a set of one-click presets in the Properties Inspector panel beside the curve editor widget:
| Preset | cp0 (p1) | cp1 (p2) | Description |
|---|
| Linear | (20, 20) | (107, 107) | Constant speed — diagonal line from corner to corner |
| In | (64, 0) | (107, 107) | Starts slow, accelerates — ease-in from bottom-left |
| Out | (20, 20) | (64, 127) | Starts fast, decelerates — ease-out into top-right |
| InOut | (64, 0) | (64, 127) | Slow start and end, fast middle — S-curve |
| Slow In | (100, 0) | (107, 107) | Very gradual ramp-up, then full speed |
| Slow Out | (20, 20) | (27, 127) | Full speed into the key, then a long deceleration |
| Slow IO | (100, 0) | (27, 127) | Extreme S-curve — maximum hang time at both ends |
| Over | (0, 127) | (127, 0) | Overshoot — value exceeds target then settles back |
Example: Bounce Effect
A bounce effect requires the value to accelerate down, decelerate briefly at the floor (impact), then ease back up. Using two keyframes — one at the top, one at the bottom of the bounce — set the Trans.Y channel handles like this:
Before (Linear):
cp0 = (20, 20) — leaves the top key at constant speed
cp1 = (107, 107) — arrives at the floor at constant speed
cp0 = (20, 20) — leave the top at moderate speed (gravity builds)
cp1 = (27, 127) — arrive at the floor fast then slow abruptly (Slow Out)
cp0 = (100, 0) — leave the floor slowly (compression rebound)
cp1 = (107, 107) — arrive at the top at full speed
Edit rotation and translation channels independently for more natural motion. A character’s arm during a swing might use an ease-in-out on Rot.X but a faster ease-out on Trans.Y so the hand rises quickly at the end even as the rotation is still decelerating. Per-channel Bézier control — not a single curve over everything — is what enables that nuance.
Y-Axis Zoom
When many keyframes are clustered close together in value, handles stack up and become hard to grab. Hold Shift and scroll the mouse wheel to zoom the vertical (value) axis. The centre of the view stays fixed while the range expands or contracts. The Y-zoom range is 0.5× to 8× (Y_ZOOM_MIN to Y_ZOOM_MAX).