A guide to making 2D sprite animations in FlatRedBall, a game-development framework. It covers animation sequences, image files, playback, timing, and per-frame collision shapes.

Use it when adding or changing character and object animations, loading Aseprite or sprite-sheet artwork, setting loops and frame timing, or attaching hitboxes and hurtboxes to frames.

It removes the need to work out how FlatRedBall's animation files and runtime types fit together. It also helps avoid broken image paths and incorrectly configured animation playback.

animation — Skill for Claude Code and Codex by vchelaru/FlatRedBall2

Install

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.

Any agent

npx skills add vchelaru/FlatRedBall2 --skill animation

Clone the repo

git clone --depth 1 https://github.com/vchelaru/FlatRedBall2

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/vchelaru/flatredball2/animation/github.svg)](https://agentmods.dev/skills/vchelaru/flatredball2/animation)

Your own site

<a href="https://agentmods.dev/skills/vchelaru/flatredball2/animation"><img src="https://agentmods.dev/badge/skills/vchelaru/flatredball2/animation/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/vchelaru/flatredball2/animation"><img src="https://agentmods.dev/badge/skills/vchelaru/flatredball2/animation.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 90 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,439 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00090	$0.02439
Opus 5.5	$0.00036	$0.00976
Sonnet 5.5	$0.00018	$0.00488
Haiku 4.5	$0.00009	$0.00244

Measured 4d ago against content hash f30f439df2f3, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

animation 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 4d 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.

frb-skills/animation/SKILL.md · 94 lines

How it starts

The opening of the file, as written. The whole thing — 94 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Sprite Animation in FlatRedBall2

Sprites animate via AnimationChain / AnimationChainList, driven automatically by Screen.Update — no per-frame call needed in game code.

Quick setup: adding animation content

Create a folder in your *.Common project's Content directory (for example Content/Animations).
Copy your source spritesheet PNG into that folder.
Open AnimationEditor and save a new .achx in the same folder as the PNG.
Ensure your project copies these files to output (for example Content/Animations/** in .csproj; see references/platformer-template.md).

FileRelativeTextures in .achx expects relative texture paths, so keeping .achx and texture content together avoids broken lookups.

Runtime Types

AnimationFrame — texture + source rectangle (pixel coords) + flip flags + FrameLength (TimeSpan) + per-frame RelativeX/Y offsets + optional Shapes collection + optional Events (AnimationFrameEvent: Name, free-form Data)
AnimationChain : List<AnimationFrame> — named sequence; TotalLength = sum of FrameLengths
AnimationChainList : List<AnimationChain> — string indexer for lookup by name; the unit of "ownership" for per-frame shapes (see Topics)

Standalone AnimationChain.MonoGame/.Common Package

The types above live in FlatRedBall2.Animation and back Sprite.PlayAnimation. A separate generic package (namespaces FlatRedBall.AnimationChain / FlatRedBall2.AnimationEditorCommon) — AnimationChainList<TFrame>, AnimationPlayer<TFrame>, AchxLoader (src/AnimationChain.MonoGame/AchxLoader.cs) — is for raw MonoGame projects with no FRB2 Screen/Sprite. Same names, different (generic) shape — don't conflate the two; see samples/AnimationChainSample.

Sprite Playback API

Member	Default	Notes
`AnimationChains`	`null`	Assign before `PlayAnimation`; without a parent entity, `RelativeX/Y` and per-frame shapes don't behave usefully
`PlayAnimation(string name)`	—	Looks up by name; no-op if not found
`PlayAnimation(AnimationChain chain)`	—	Play a specific chain directly
`Animate`	`false`	Auto-managed. Do not write to express idle state — see Gotchas
`IsLooping`	seeded from `AnimationChain.Loop` on `PlayAnimation`	overridable per-instance after `PlayAnimation` — set it before that and it gets reseeded
`AnimationSpeed`	`1f`	Multiplier
`CurrentAnimation`	—	Read-only; returns the active chain
`AnimationFinished`	—	Fires when a non-looping animation ends
`AnimationLooped`	—	Fires when a looping chain wraps. Never fires for non-looping chains or from `PlayAnimation`
`FrameChanged`	—	Fires when the displayed frame changes, including `PlayAnimation` to a different chain (not re-playing the same one). `CurrentFrame` is already the new frame
`FrameEventRaised`	—	Fires per `AnimationFrameEvent` when its frame is entered. Branch on `e.Name`, never on a frame index, so reordering frames in the AnimationEditor can't break it. Skipped frames still fire; the XML doc has the loop/frame-0 rules
`FrameControlledProperties`	`SpriteFrameProperties.All`	`[Flags]` of `Flip`, `Offset`, `Color`: the groups frames write on each frame change. Clear a flag to own that group in game code
`AddColor`	`Vector3.Zero`	Public, -1..1 per channel. Frames assign it (non-Add frames reset it to zero) while the `Color` group is on. The shader adds it first, then `Color` and `Alpha` multiply the sum

Read the full file on GitHub · 94 lines

Files

What ships with it

5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

4d ago Changed f30f439df2f3
5d ago Changed · +1 lines 7a9b7b23bed1
7d ago Changed · +6 lines · +7 tokens per session 5c1296887bb1
13d ago Changed · +2 lines 97f33fea59bb
21d ago Changed · +1 lines · +7 tokens per session 1a92f23d6ab5
1mo ago Changed 2c1ef8b7b850
1mo ago First seen · 84 lines · 76 tokens per session scan A 7784a4606121

Subscribe to this mod's changes

animation is a skill published in the GitHub repository vchelaru/FlatRedBall2 (15 stars, last pushed yesterday), licensed MIT. It adds 90 tokens to every session and 2,439 once invoked, about $0.0004 per session on Opus 5.5. 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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