Crate flo_canvas

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flo_canvas

flo_canvas provides an abstraction of a 2D vector canvas, and supporting methods to stream updates to implementations.

The main features that this library supports are the set of primitives in the Draw enum, the Canvas type for streaming drawing instructions elsewhere, and the encoding and decoding functions that can be used to send canvas instructions over a byte stream. Encoding uses MIME64 characters, so it’s easy to embed encoded canvases in other protocols.

By itself, flo_canvas is an excellent way to describe how a 2D scene should be rendered without needing to depend on a system-specific library.

FlowBetween comes with several implementations of the canvas for generating the final rendered results. Most notably, flo_render_canvas will convert between a stream of Draw instructions and a stream of instructions suitable for rendering with most graphics APIs. The accompanying flo_render can render these instructions to OpenGL or Metal and flo_render_gl_offscreen is available to generate bitmap images on a variety of systems.

canvas.js provides a Javascript implementation that can render the instructions to a HTML canvas, and there are also Quartz and Cairo implementations of the canvas provided in FlowBetween’s user interface layers.

Features

Some features of flo_canvas are optional due to the extra dependencies they can bring in. They can be enabled if the extra functionality is required or left out to get a more compact library.

  • outline-fonts - provides a function that will convert a stream of Draw instructions into another stream of Draw instructions, except all the font commands will be removed and replaced with an outline rendering of the font (useful for rendering back-ends that don’t have native font support or for generating vector files that don’t require particular fonts to be installed)

Re-exports

Structs

  • A canvas is an abstract interface for drawing graphics. It doesn’t actually provide a means to render anything, but rather a way to describe how things should be drawn and pass those on to a renderer elsewhere.
  • Represents a (stateful) canvas decoder
  • Representation of a font face
  • Graphics context for a Canvas
  • Represents a 2D point
  • A draw stream relays Draw instructions from a source such as a Canvas or a DrawContext as a stream
  • A drawing target sends drawing instructions to a DrawStream
  • Identifier for a font
  • Describes where to position a line relative to some text
  • Metrics for a font
  • The properties to use when selecting a font face
  • ID for a glyph within a font
  • Describes how a glyph is positioned on the canvas
  • Identifies a gradient
  • Identifier of a canvas layer
  • Identifier of a canvas ‘sprite’
  • The layout metrics for a piece of text
  • Identifier for a texture
  • Represents a 2D affine transformation matrix

Enums

Traits

  • Trait implemented by objects that can be encoded into a canvas
  • Represents a coordinate with a 2D position
  • A graphics context provides the basic set of graphics actions that can be performed
  • GraphicsPrimitives adds new primitives that can be built directly from a graphics context

Functions

  • Decodes a canvas drawing represented as an iterator of characters. If there’s an error in the stream, it will be the last item decoded.
  • Decodes a canvas drawing represented as a stream of characters.
  • Returns the drawing commands for a circle
  • Returns the drawing commands for a rectangle
  • Converts a stream of drawing instructions into a stream of bezier paths with attributes that specify how they’re rendered.
  • Converts a stream of drawing instructions into a stream of bezier paths (stripping any other attributes from the stream)
  • Converts dashed line stroke operations into separate lines
  • Creates a gradient scale, as 8-bit RGBA quads from a set of gradient operations
  • Converts a bezier path to a set of paths by a dash patter