Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add vchelaru/FlatRedBall2 --skill collision-relationshipsgit clone --depth 1 https://github.com/vchelaru/FlatRedBall2Wrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/vchelaru/flatredball2/collision-relationships)<a href="https://agentmods.dev/skills/vchelaru/flatredball2/collision-relationships"><img src="https://agentmods.dev/badge/skills/vchelaru/flatredball2/collision-relationships.svg" alt="Measured on agentmods" height="20"></a>- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00119 | $0.04543 |
| Opus 5 | $0.00060 | $0.02271 |
| Sonnet 5 | $0.00024 | $0.00909 |
| Haiku 4.5 | $0.00012 | $0.00454 |
Grade A, and why
collision-relationships scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 339 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Collision Relationships in FlatRedBall2
Screen.AddCollisionRelationship<A,B> registers a pair of collidable groups. Each frame, after physics runs, every entity in group A is tested against every entity in group B. If they overlap, the configured response fires.
Basic Setup
Call AddCollisionRelationship inside Screen.CustomInitialize after creating your factories:
AddCollisionRelationship<Player, Wall>(_playerFactory, _wallFactory)
.MoveFirstOnCollision();
Self-Collision (Same List)
To collide entities within the same list (e.g., enemies pushing each other apart):
AddSelfCollisionRelationship<Enemy>(_enemyFactory)
.MoveBothOnCollision(firstMass: 1f, secondMass: 1f);
Iterates unique unordered pairs only — no duplicate checks, and never an entity against itself.
Set AllowDuplicatePairs = true if CollisionOccurred should also fire in the (b, a) ordering
(physics still runs once per pair).
Fluent Modifiers
| Method | Effect |
|---|---|
.MoveFirstOnCollision() |
A gets pushed out, B stays fixed. Use for player vs. solid walls. |
.MoveSecondOnCollision() |
B gets pushed out, A stays fixed. |
.MoveBothOnCollision(firstMass, secondMass) |
Both objects share the separation weighted by mass. |
.BounceFirstOnCollision(elasticity) |
A bounces off B; B stays fixed. Use for a ball vs. immovable walls. |
.BounceSecondOnCollision(elasticity) |
B bounces off A; A stays fixed. Mirror of the above when the static side is A. |
.BounceBothOnCollision(firstMass, secondMass, elasticity) |
Both sides bounce; separation splits by mass ratio (equal masses share equally). |
.BounceOnCollision(firstMass, secondMass, elasticity) |
Escape hatch for the asymmetric raw-mass case. Prefer the three above. |
Responding to Collision Events
CollisionOccurred fires once per overlapping pair per frame, after position separation and velocity adjustment have been applied.
Entity logic
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 3d ago First seen · 339 lines · 119 tokens per session scan A b844ebd1ec2c
collision-relationships is a skill published in the GitHub repository vchelaru/FlatRedBall2 (14 stars, last pushed today), licensed MIT. It adds 119 tokens to every session and 4,543 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-04.
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