# Pressure Brush Stroke Renderer

> Render textured pressure strokes as SVG and editable Flipline drawings. Turn normalized points and pressure samples into graphite, ink, marker, pigment-wash or airbrush strokes. Download a deterministic SVG, reusable brush recipe and editable Flipline project.

Part of usefulweb.app (https://usefulweb.app/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://fliplinebrushstroke.usefulweb.app/ (interactive tool at https://fliplinebrushstroke.usefulweb.app/tool)
- JSON API: POST https://fliplinebrushstroke.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://fliplinebrushstroke.usefulweb.app/api/v1/tool)
- OpenAPI: https://fliplinebrushstroke.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://fliplinebrushstroke.usefulweb.app/mcp - tool `flipline_brush_stroke`

## Inputs
- points (textarea): Stroke points: x y pressure (0–1, one point per line)
- width (integer): Canvas width (px)
- height (integer): Canvas height (px)
- size (number): Brush width (px)
- kind (select): Brush style
- color (text): Ink HEX color
- background (text): Paper HEX color
- opacity (number): Pigment opacity (%)
- flow (number): Pigment flow (%)
- texture (number): Brush texture (%)
- pressure (boolean): Use pressure samples
- seed (integer): Texture seed

## Method
- Accept 1–256 points with normalized x/y and optional pressure in 0–1. Missing pressure is 1. Canvas dimensions are 32–1600 px and at most 2 MP.
- Resample by pixel arc length using brush spacing, at most 1024 centers per stroke. Linear interpolation carries pressure between samples. Brush width and pigment respond to pressure when enabled.
- Five authored stamp styles use a seeded linear-congruential generator for texture. At most four ellipse dabs per center. Opacity and flow multiply per dab; overlap accumulates pigment.
- The SVG and browser use the same ellipse geometry. Pigment wash is a layered stamp approximation, not wet-paint physics. sRGB canvas compositing can vary slightly across renderers.