🌀 RunePulse Engine

A Genre-Agnostic 2D Engine Template for Odin + SDL3.

RunePulse is designed for developers who want a "Scenario-Proof" foundation. It handles the complex math of polygon collisions and input buffering, leaving you free to define the rules of your world.

🧠 The Mental Model

To master RunePulse, you must understand how data flows through the engine. You don't "create" objects; you activate data slots.

1. The "Parking Lot" (Entity Management)

The engine pre-allocates 1,024 slots for entities.

Inactive Slots: The engine ignores these. They cost zero processing power.
Active Slots: When you set active = true, the engine pulls that slot into the Physics and Render systems.

2. The "Assembly Line" (Game Loop)

Every frame (calculated via Delta Time dt) follows this order:

Input: The engine captures what keys are being pressed or tapped.
Your Logic: This is the ONLY part you edit. You change the velocity of entities based on input.
Physics (SAT): The engine moves entities and resolves collisions.
Render: The engine draws the final positions to the screen.

🛠️ Data Reference

Entity Properties

Property	Type	Description
`active`	`bool`	Must be `true` to exist in the world.
`pos`	`[2]f32`	The center/anchor point of the entity.
`vel`	`[2]f32`	Speed in pixels per second. Always multiply by `dt`!
`vertices`	`[dynamic]`	The points that form the shape (must be convex).
`type`	`Enum`	Set to `.Solid` to make it a physical wall.

⚡ The Physics: SAT Collision

RunePulse uses Separating Axis Theorem (SAT). Imagine shining a flashlight on two shapes from different angles. If there is ever a gap in their shadows, they are not touching. If no gap exists on any axis, the engine pushes them apart.

The Rule: Your polygons must be convex (no "dents" or "caves" in the shape).

⌨️ Input System

Function	Use Case
`is_key_down()`	Continuous movement (e.g., walking, thrusting).
`is_key_pressed()`	Single actions (e.g., jumping, shooting, menus).

🚀 Creating Your First Entity

Add this to your "Initialize" section in main.odin:

// 1. Grab a slot
p := &state.entities[0]
p.active = true
p.pos = {400, 300}
p.color = {0.2, 0.8, 0.3, 1.0}

// 2. Define the shape (a simple square)
append(&p.vertices, [2]f32{-25, -25}, [2]f32{25, -25}, [2]f32{25, 25}, [2]f32{-25, 25})

// 3. Move it (Inside the loop)
if is_key_down(.D) do p.vel.x = 500