cf_toi¶
Category: collision
GitHub: cute_math.h
Computes the time of impact of two shapes.
CF_ToiResult cf_toi(const void* A, CF_ShapeType typeA, const CF_Transform* ax_ptr, CF_V2 vA, const void* B, CF_ShapeType typeB, const CF_Transform* bx_ptr, CF_V2 vB, int use_radius);
| Parameters | Description |
|---|---|
| A | The first shape. |
| typeA | The CF_ShapeType of the first shape A. |
| ax_ptr | Can be NULL to represent an identity transform. An optional pointer to a CF_Transform to transform A. |
| vA | The velocity of A. |
| B | The second shape. |
| typeA | The CF_ShapeType of the second shape B. |
| bx_ptr | Can be NULL to represent an identity transform. An optional pointer to a CF_Transform to transform B. |
| vB | The velocity of B. |
| use_radius | True if you want to use the radius of any CF_Circle or CF_Capsule inputs, false to treat them as a point/line segment respectively (a radius of zero). |
Return Value¶
Returns a CF_ToiResult containing information about the time of impact.
Remarks¶
This is an advanced function, intended to be used by people who know what they're doing.
Computes the time of impact from shape A and shape B. The velocity of each shape is provided by vA and vB respectively. The shapes are
not allowed to rotate over time. The velocity is assumed to represent the change in motion from time 0 to time 1, and so the return value
will be a number from 0 to 1. To move each shape to the colliding configuration, multiply vA and vB each by the return value.
IMPORTANT NOTE
The cf_toi function can be used to implement a "swept character controller", but it can be difficult to do so. Say we compute a time of impact with cf_toi and move the shapes to the time of impact, and adjust the velocity by zeroing out the velocity along the surface normal. If we then call cf_toi again, it will fail since the shapes will be considered to start in a colliding configuration. There are many styles of tricks to get around this problem, and all of them involve giving the next call to cf_toi some breathing room. It is recommended to use some variation of the following algorithm:
- Call cf_toi.
- Move the shapes to the TOI.
- Slightly inflate the size of one, or both, of the shapes so they will be intersecting. The purpose is to make the shapes numerically intersecting, but not visually intersecting. Another option is to call cf_toi with slightly deflated shapes. See the function cf_inflate for some more details.
- Compute the collision manifold between the inflated shapes (for example, use cf_poly_to_poly_manifold).
- Gently push the shapes apart. This will give the next call to cf_toi some breathing room.