# Glossary

> Short definitions of anti-aliasing, MSAA, SSAA, FXAA, signed distance fields, coverage, device pixel ratio, squircles, OKLab, banding and dithering.

Source: https://pixi-silk.schmooky.dev/docs/glossary/

This page defines the terms used across these docs. Each entry starts with a one-sentence definition.

- **Aliasing** (jaggies, staircase artifacts): The jagged or crawling edges that appear when you sample a continuous shape at only one point per pixel. Each pixel is then either fully in or fully out.
- **Analytic anti-aliasing**: Anti-aliasing computed exactly per pixel from the shape's geometry, not from extra samples. pixi-silk derives coverage from the signed distance to the shape and the size of one device pixel.
- **Anti-aliasing** (antialiasing, AA): Techniques that remove the jagged "staircase" look of edges on a pixel grid. Each edge pixel gets a partial colour proportional to how much of it the shape covers.
- **Coverage**: The fraction of a pixel's area covered by a shape, from 0 to 1. Anti-aliasing uses coverage as the pixel's opacity along edges.
- **Device pixel**: One physical pixel of the display. A canvas is sharp only when each of its pixels maps to exactly one device pixel.
- **Device pixel ratio** (DPR, devicePixelRatio): The number of physical screen pixels per CSS pixel: 1 on standard displays, 2 or 3 on retina or HiDPI screens. Many laptops and phones have fractional ratios such as 1.25 or 1.5.
- **Dithering**: Adding a little structured noise (here ±½ of an 8-bit step) before quantising. It hides banding and leaves exact colours unchanged.
- **Draw call**: One command from the CPU telling the GPU to draw. Fewer draw calls usually mean better performance. Each SilkGraphics is one draw call.
- **FXAA** (fast approximate anti-aliasing): A cheap post-processing filter that detects and blurs high-contrast edges in the finished image. It softens detail and text and cannot recover geometry lost between pixels.
- **Gradient banding** (colour banding): Visible steps in a smooth gradient caused by 8-bit colour precision, most obvious in dark, wide gradients.
- **Hairline**: A line thinner than one device pixel. pixi-silk keeps hairlines one pixel wide and scales their opacity with their width, so they fade instead of breaking up.
- **Instanced rendering** (instancing): Drawing many copies of one mesh in a single draw call, each with its own data. pixi-silk draws every primitive of a SilkGraphics as one instance of a quad.
- **Monotone interpolation**: A curve through data points that never overshoots them. Peaks stay on the data and flat runs stay flat. pixi-silk uses Steffen's method (like d3's curveMonotoneX) for charts.
- **MSAA** (multisample anti-aliasing): A GPU technique that stores several coverage samples per pixel (typically 4) and averages them. In PixiJS, you enable it with antialias: true. By default it covers only the main canvas. Filters and render textures must opt in one by one.
- **OKLab**: A perceptual colour space by Björn Ottosson, where equal steps look equally different. Gradients interpolated in OKLab stay bright and even, without muddy midpoints.
- **Premultiplied alpha**: Storing colour already multiplied by opacity. Interpolating premultiplied colours prevents dark fringes when a gradient fades to transparent.
- **Signed distance field** (SDF): A function that returns the distance from any point to the nearest edge of a shape: negative inside, positive outside. Rendering a shape from its SDF gives exact edges at any scale.
- **Squircle** (superellipse corner, continuous corner): A rounded rectangle whose corners are superellipse arcs, so curvature grows gradually from the straight edge instead of jumping. iOS app icons and cards use it.
- **SSAA** (supersampling): Anti-aliasing by rendering at a higher resolution and downscaling. It is simple and high quality. Memory and fill-rate costs grow with the scale factor squared.
- **Tessellation**: Converting curves and shapes into triangles for the GPU. PixiJS Graphics tessellates when you draw, so curves become polygons with a fixed number of segments.