Kaijuengine Game Dev

Kaiju Engine — Game Development

Kaiju Engine is a 2D/3D game engine in Go (kaijuengine.com, Go 1.25.0+) backed by Vulkan, with a custom math library, a hierarchical entity system, and a web-inspired UI. Cross-platform: Windows, Linux, macOS, Android.

A game is a type implementing bootstrap.GameInterface (ContentDatabase, PluginRegistry, Launch). The engine creates a *engine.Host — the central runtime mediator — and calls Launch(host). Your code creates entities, attaches drawings, and registers per-frame update functions on the host.

Source of truth: this skill is distilled from the engine's AGENTS.md. When it disagrees with the current source, trust the source — and verify a symbol exists before relying on it, since some details here describe internals conceptually and may drift from the live API.

Critical rules (do not violate)

1. Use kaijuengine.com/matrix for ALL math. Never import gonum, mathgl, or any external math library. Use matrix.Float (configurable, default float32) instead of bare float32/float64 in engine-facing code.
2. Attach the entity transform to the drawing: Transform: &entity.Transform. This is the link that makes a drawing follow its entity. Without it the drawing won't track the entity.
3. Create entities with the work group: engine.NewEntity(host.WorkGroup()) — enables concurrent transform updates.
4. Clean up in OnDestroy: destroy ShaderData and remove updaters (host.Updater.RemoveUpdate(&id)) to avoid leaks. RemoveUpdate takes a pointer to the id.
5. UI markup has NO JavaScript. .go.html files are Go templates; an onclick="fn" maps to a SINGLE Go function in the funcMap. Chained JS-style calls (a(); b()) are invalid. CSS is custom-parsed; manage active states with CSS classes via document.SetElementClasses(elm, ...).
6. Content paths are relative to the working directory at runtime. Games load content via assets.NewFileDatabase("game_content"); the editor places content in database/content by UUID.
7. deltaTime is in seconds. host.Runtime() is seconds since start; host.Frame() is the current frame number.

Engine Go conventions

Follow the repo's Go style guide (also in the user's global instructions): builder-is-implementation pattern, public API surface is interfaces/methods only (no exported structs), locks are a last resort (prefer channels or github.com/puzpuzpuz/xsync/v4), and platform build-tag files (_darwin.go/_linux.go/_windows.go) hold ONLY what differs — shared structs and constructors live in a single untagged file.

Quick start — minimal game

package main

import (
    "reflect"
    "kaijuengine.com/bootstrap"
    "kaijuengine.com/engine"
    "kaijuengine.com/engine/assets"
)

type Game struct{ host *engine.Host }

func (Game) PluginRegistry() []reflect.Type        { return nil }
func (Game) ContentDatabase() (assets.Database, error) {
    return assets.NewFileDatabase("game_content")
}
func (g *Game) Launch(host *engine.Host) {
    g.host = host
    // create entities, add drawings, register updates here
    id := host.Updater.AddUpdate(g.update)
    _ = id
}
func (g *Game) update(deltaTime float64) { /* game logic; deltaTime in seconds */ }

func getGame() bootstrap.GameInterface { return &Game{} }

See reference/making-a-game.md for the full entity+drawing example.

Frame / update order

Each frame the host runs, in order:

1. FrameRunner — functions scheduled via RunAfterFrames / RunNextFrame (run after window poll, before the UI)
2. UIUpdater — UI update logic
3. UILateUpdater — late UI updates
4. Update — main game logic (host.Updater)
5. LateUpdate — physics, collision (host.LateUpdater)
6. EndUpdate — internal frame preparation (input state transitions)

Reference index (read on demand)

• reference/making-a-game.md — GameInterface, Launch steps, the complete entity-with-drawing example, and common patterns (update registration, frame-safe ops). Read when scaffolding a game or wiring entities to drawings.
• reference/host-entities-transform.md — Host responsibilities and methods, the Entity type (hierarchy, named data, activation), and the matrix Transform (local vs world, direction vectors, dirty-flag system). Read for entity hierarchy, positioning, or host caches.
• reference/rendering.md — Vulkan architecture, the caches, building Drawings, pre-built meshes, and terrain texture painting / splat-map contract. Read for rendering, meshes, materials, shaders, or terrain.
• reference/ui.md — the UI system: Manager, element types, events, layout, panel/label/input ops, dirty flags, and the HTML/CSS markup system. Read for any UI work in a game or the editor.
• reference/matrix.md — the custom math library: vector/matrix/quaternion types and common operations. Read before doing any math.
• reference/building-and-testing.md — build prerequisites, build tags, build commands, content layout, and the integration-testing framework (screenshots + video). Read to build, run, or visually test.

Verifying visually

• For automated visual checks, use the integration testing framework (screenshots / video) — see reference/building-and-testing.md.
• To drive a running game interactively (screenshot + inject input), build with -tags ai_driver and use the kaiju-aidriver skill.