Module: RGame::Engine::Culling

Included in:

RGame::Engine::Components::AnimatedSprite, RGame::Engine::Components::Sprite

Defined in:

lib/rgame/engine/culling.rb

Overview

Skipping a drawable that the viewport cannot show.

Mixed into the components that draw a node's own footprint, which are the ones that know both where they put it and how big it is.

Why it is worth doing at all

It was not, while the world was drawn once: a handful of skipped draws against a frame's worth of work. Split-screen changes the arithmetic — the world is walked once per viewport, and an actor at one player's end of the map is off the other player's view every frame. What used to be a small saving becomes a saving multiplied by the number of people playing.

Conservative on purpose

Culling one frame too eagerly is a sprite popping in at the edge of the screen, which is worse than the draw it saved. So two rules:

• No size means no culling. node.width/height are what a drawable's footprint is measured from, and a node that never set them (nothing requires it — examples/14_asteroids does not) reads as 0×0, which would otherwise cull everything instantly. Unknown means draw.
• A rotated node is measured generously. Node2D#draw rotates about the node's absolute origin, so a rotated footprint can reach further than its box in any direction. The margin is width + height, which is always at least the diagonal hypot(width, height) and costs no square root on a path that runs once per drawable per viewport.