ASCII field

A grid of characters that never quite sits still. On every update a small share of the cells swap to a new glyph, and anything the pointer crosses lights up in a gradient before fading back to rest. It started life as the texture behind this site's share image.

Controls

• Speed sets how many times a second the field updates.
• Churn is the share of cells that swap glyphs on each update.
• Trail is how long a lit cell takes to fade back to rest.
• Brush is the block of cells the pointer lights at once.
• Resting is the opacity of the top row when nothing is lit; it falls away to nothing at the bottom.
• Size is the glyph size, which also sets how many cells fit.
• Palette and Characters swap the lit colors (spread left to right) and the glyphs drawn from.

How it works

The field is a single canvas. Each cell keeps a glyph and the moment it was last touched, so a lit cell's opacity is worked out from how long ago that was. The trail needs no animation state of its own.

Frames where nothing would change are skipped, so between updates the field costs almost nothing. It also stops drawing while it's scrolled out of view. Changing a control applies on the next frame without restarting the field.