svg

Documentation

Overview

Package svg parses a document from an SVG subset and rasterises it to a straight-alpha RGBA bitmap, built on the sibling github.com/go-gfx/gfx/vector and github.com/go-gfx/gfx/raster packages.

It is not a general-purpose SVG renderer: it understands a practical subset — a root <svg> with a viewBox (or width/height), nested <g> groups carrying transforms and fills, <path> outlines (commands M/L/H/V/C/S/Q/T/Z, absolute and relative; arcs are unsupported and cause the path to be skipped), <rect>, <circle>, nested <svg> islands with their own viewBox, and embedded raster <image> data URIs.

Fills and STROKES resolve black/white/currentColor/none, #rgb and #rrggbb literals, and url(#id) references to a <linearGradient> or <radialGradient> — in objectBoundingBox units (the SVG default, placed across the filled shape's own box) or userSpaceOnUse. A stroke honours stroke-width, carried through the transform as the length it is; caps and joins are round. <rect> honours rx/ry. An ink recolour and a transparent-or-opaque paper background are available.

A value this subset does not implement leaves the shape UNPAINTED rather than inheriting: silently flooding it with the ancestor's colour is what rendered every gradient-filled document as a flat square. Malformed shapes are skipped rather than failing the page.

Text is NOT rendered: <text> needs a font, which this package deliberately does not depend on.

Every <g> element is reported in Result.Groups together with the device-pixel bounding box of everything it drew. That is the generic seam a consumer uses to map a group attribute back to a screen region: filter Result.Groups by whatever attribute you care about — id, class, aria-*, a custom data-* marker — and read its Group.Bounds. The package itself assigns no meaning to any particular attribute.

Index

• type Group
• type Options
• type Result
  • func Rasterize(doc string, opt Options) (*Result, error)

Types

type Group

type Group struct {
	Attrs  map[string]string
	Bounds image.Rectangle
}

Group records one <g> element: its attributes (namespace-insensitive local names) and the device-pixel bounding box of everything drawn within it, including nested descendants. A group that drew nothing has an empty Bounds (see image.Rectangle.Empty). Groups are reported in document order.

type Options

type Options struct {
	Scale float64    // device pixels per SVG user-unit (pt). <=0 defaults to 2.0
	Ink   color.RGBA // colour used for the default black / currentColor fills
	Paper color.RGBA // page background fill (the document's fill="white" rect). If Paper.A==0, no background is painted (transparent).
}

Options controls rasterization.

type Result

type Result struct {
	Image  *raster.Image // straight-alpha RGBA surface, W*H pixels
	Groups []Group       // one entry per <g> element, in document order
}

Result is a rasterized SVG document.

func Rasterize

func Rasterize(doc string, opt Options) (*Result, error)

Rasterize parses ONE SVG document and renders it to a Result. It returns an error only for a document with no parseable <svg> root.