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fix(sprite): 修复 BillboardY 垂直视角下左右甩动 (fix #504) #503

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fix(sprite): 修复 BillboardY 垂直视角下左右甩动 (fix #504) #503

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16 changes: 15 additions & 1 deletion src/components/BillboardComponent.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -54,10 +54,24 @@ export class BillboardComponent extends ComponentBase {
if (this.type == BillboardType.BillboardXYZ) {
} else if (this.type == BillboardType.BillboardY) {
this._cameraPosition.y = 0;

// A cylindrical billboard has no defined yaw when the camera is
// looking straight up or down. Normalizing that near-zero XZ
// projection amplifies floating-point noise and makes the sprite
// swing between opposite directions as the camera rotates.
// Keep the last valid orientation until a horizontal camera
// direction is available again.
const horizontalLengthSquared =
this._cameraPosition.x * this._cameraPosition.x +
this._cameraPosition.z * this._cameraPosition.z;
if (horizontalLengthSquared <= Vector3.EPSILON * Vector3.EPSILON) return;
}
this._cameraPosition.normalize();
Vector3.add(this._cameraPosition, this.object3D.localPosition, this._cameraPosition);
this.transform.lookAt(this.object3D.localPosition, this._cameraPosition, camera.transform.up);
// BillboardY must stay locked to the world Y axis. Using the camera's
// up vector introduces roll and becomes unstable at a vertical view.
const up = this.type == BillboardType.BillboardY ? Vector3.Y_AXIS : camera.transform.up;
this.transform.lookAt(this.object3D.localPosition, this._cameraPosition, up);
}

/**
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