What are some of the common challenges and pitfalls of 3D collision detection and how do you debug them?

1 Collision types

There are two main types of collision detection in 3D games: discrete and continuous. Discrete collision detection checks for collisions at fixed intervals, such as every frame or every physics update. Continuous collision detection tracks the movement of objects and detects collisions at any point along their trajectories. Discrete collision detection is simpler and faster, but it can miss collisions that occur between intervals, resulting in tunneling or clipping. Continuous collision detection is more accurate and realistic, but it can be more computationally expensive and complex to implement.

2 Collision shapes

Another challenge of 3D collision detection is choosing the appropriate collision shapes for your objects. Collision shapes are simplified representations of the geometry of your objects, such as spheres, boxes, capsules, or convex hulls. They are used to perform collision tests more efficiently and robustly than using the actual meshes of your objects. However, collision shapes also introduce some trade-offs between accuracy and performance. If your collision shapes are too simple or too large, they can cause false positives or unwanted overlaps. If your collision shapes are too complex or too small, they can cause false negatives or gaps.

4 Collision debugging

Debugging 3D collision detection can be a tedious and time-consuming process. To identify and fix the causes of your collision problems, you can utilize various tools and techniques, such as visualizing your collision shapes and points in wireframes, colors, or markers to see if they match your objects and when collisions occur. Logging or printing your collision data, like flags, normals, distances, or impulses, can verify if your algorithms are functioning correctly. Step-by-step execution or slow motion can be used to pause or slow down your game to inspect collisions in detail. Additionally, test cases, unit tests, or automated tests can check your collision detection and resolution against expected outcomes to guarantee the consistency and reliability of your code.

5 Collision optimization

Finally, 3D collision detection can be a performance bottleneck for your game, as it can consume a lot of CPU or GPU resources. Therefore, you need to optimize your collision detection by reducing the number and complexity of your collision tests. Common methods for this include using spatial partitioning techniques such as grids, trees, or hashing to divide the game world into smaller regions and only check collisions within or across those regions. Additionally, broad-phase and narrow-phase algorithms can be employed to filter out potential collisions using simple and fast tests like bounding volumes or distance checks, and then performing more accurate and detailed tests like shape intersections or ray casts on the remaining candidates. Caching, pooling, or pre-computing techniques can also be used to store or reuse collision data or results that do not change frequently or significantly, such as static objects, collision shapes, or collision responses. This can help prevent redundant or repetitive calculations.