draw2d/draw2d.go
2017-12-24 13:45:56 +01:00

255 lines
7.7 KiB
Go

// Copyright 2010 The draw2d Authors. All rights reserved.
// created: 13/12/2010 by Laurent Le Goff
// Package draw2d is a pure go 2D vector graphics library with support
// for multiple output devices such as images (draw2d), pdf documents
// (draw2dpdf) and opengl (draw2dgl), which can also be used on the
// google app engine. It can be used as a pure go Cairo alternative.
// draw2d is released under the BSD license.
//
// Features
//
// Operations in draw2d include stroking and filling polygons, arcs,
// Bézier curves, drawing images and text rendering with truetype fonts.
// All drawing operations can be transformed by affine transformations
// (scale, rotation, translation).
//
// Package draw2d follows the conventions of http://www.w3.org/TR/2dcontext for coordinate system, angles, etc...
//
// Installation
//
// To install or update the package draw2d on your system, run:
// go get -u github.com/llgcode/draw2d
//
// Quick Start
//
// Package draw2d itself provides a graphic context that can draw vector
// graphics and text on an image canvas. The following Go code
// generates a simple drawing and saves it to an image file:
// package main
//
// import (
// "github.com/llgcode/draw2d/draw2dimg"
// "image"
// "image/color"
// )
//
// func main() {
// // Initialize the graphic context on an RGBA image
// dest := image.NewRGBA(image.Rect(0, 0, 297, 210.0))
// gc := draw2dimg.NewGraphicContext(dest)
//
// // Set some properties
// gc.SetFillColor(color.RGBA{0x44, 0xff, 0x44, 0xff})
// gc.SetStrokeColor(color.RGBA{0x44, 0x44, 0x44, 0xff})
// gc.SetLineWidth(5)
//
// // Draw a closed shape
// gc.MoveTo(10, 10) // should always be called first for a new path
// gc.LineTo(100, 50)
// gc.QuadCurveTo(100, 10, 10, 10)
// gc.Close()
// gc.FillStroke()
//
// // Save to file
// draw2dimg.SaveToPngFile("hello.png", dest)
// }
//
//
// There are more examples here:
// https://github.com/llgcode/draw2d/tree/master/samples
//
// Drawing on pdf documents is provided by the draw2dpdf package.
// Drawing on opengl is provided by the draw2dgl package.
// See subdirectories at the bottom of this page.
//
// Testing
//
// The samples are run as tests from the root package folder `draw2d` by:
// go test ./...
//
// Or if you want to run with test coverage:
// go test -cover ./... | grep -v "no test"
//
// This will generate output by the different backends in the output folder.
//
// Acknowledgments
//
// Laurent Le Goff wrote this library, inspired by Postscript and
// HTML5 canvas. He implemented the image and opengl backend with the
// freetype-go package. Also he created a pure go Postscript
// interpreter, which can read postscript images and draw to a draw2d
// graphic context (https://github.com/llgcode/ps). Stani Michiels
// implemented the pdf backend with the gofpdf package.
//
// Packages using draw2d
//
// - https://github.com/llgcode/ps: Postscript interpreter written in Go
//
// - https://github.com/gonum/plot: drawing plots in Go
//
// - https://github.com/muesli/smartcrop: content aware image cropping
//
// - https://github.com/peterhellberg/karta: drawing Voronoi diagrams
//
// - https://github.com/vdobler/chart: basic charts in Go
package draw2d
import "image/color"
// FillRule defines the type for fill rules
type FillRule int
const (
// FillRuleEvenOdd determines the "insideness" of a point in the shape
// by drawing a ray from that point to infinity in any direction
// and counting the number of path segments from the given shape that the ray crosses.
// If this number is odd, the point is inside; if even, the point is outside.
FillRuleEvenOdd FillRule = iota
// FillRuleWinding determines the "insideness" of a point in the shape
// by drawing a ray from that point to infinity in any direction
// and then examining the places where a segment of the shape crosses the ray.
// Starting with a count of zero, add one each time a path segment crosses
// the ray from left to right and subtract one each time
// a path segment crosses the ray from right to left. After counting the crossings,
// if the result is zero then the point is outside the path. Otherwise, it is inside.
FillRuleWinding
)
// LineCap is the style of line extremities
type LineCap int
const (
// RoundCap defines a rounded shape at the end of the line
RoundCap LineCap = iota
// ButtCap defines a squared shape exactly at the end of the line
ButtCap
// SquareCap defines a squared shape at the end of the line
SquareCap
)
func (cap LineCap) String() string {
return map[LineCap]string{
RoundCap: "round",
ButtCap: "cap",
SquareCap: "square",
}[cap]
}
// LineJoin is the style of segments joint
type LineJoin int
const (
// BevelJoin represents cut segments joint
BevelJoin LineJoin = iota
// RoundJoin represents rounded segments joint
RoundJoin
// MiterJoin represents peaker segments joint
MiterJoin
)
func (join LineJoin) String() string {
return map[LineJoin]string{
RoundJoin: "round",
BevelJoin: "bevel",
MiterJoin: "miter",
}[join]
}
// StrokeStyle keeps stroke style attributes
// that is used by the Stroke method of a Drawer
type StrokeStyle struct {
// Color defines the color of stroke
Color color.Color
// Line width
Width float64
// Line cap style rounded, butt or square
LineCap LineCap
// Line join style bevel, round or miter
LineJoin LineJoin
// offset of the first dash
DashOffset float64
// array represented dash length pair values are plain dash and impair are space between dash
// if empty display plain line
Dash []float64
}
// SolidFillStyle define style attributes for a solid fill style
type SolidFillStyle struct {
// Color defines the line color
Color color.Color
// FillRule defines the file rule to used
FillRule FillRule
}
// Valign Vertical Alignment of the text
type Valign int
const (
// ValignTop top align text
ValignTop Valign = iota
// ValignCenter centered text
ValignCenter
// ValignBottom bottom aligned text
ValignBottom
// ValignBaseline align text with the baseline of the font
ValignBaseline
)
// Halign Horizontal Alignment of the text
type Halign int
const (
// HalignLeft Horizontally align to left
HalignLeft = iota
// HalignCenter Horizontally align to center
HalignCenter
// HalignRight Horizontally align to right
HalignRight
)
// TextStyle describe text property
type TextStyle struct {
// Color defines the color of text
Color color.Color
// Size font size
Size float64
// The font to use
Font FontData
// Horizontal Alignment of the text
Halign Halign
// Vertical Alignment of the text
Valign Valign
}
// ScalingPolicy is a constant to define how to scale an image
type ScalingPolicy int
const (
// ScalingNone no scaling applied
ScalingNone ScalingPolicy = iota
// ScalingStretch the image is stretched so that its width and height are exactly the given width and height
ScalingStretch
// ScalingWidth the image is scaled so that its width is exactly the given width
ScalingWidth
// ScalingHeight the image is scaled so that its height is exactly the given height
ScalingHeight
// ScalingFit the image is scaled to the largest scale that allow the image to fit within a rectangle width x height
ScalingFit
// ScalingSameArea the image is scaled so that its area is exactly the area of the given rectangle width x height
ScalingSameArea
// ScalingFill the image is scaled to the smallest scale that allow the image to fully cover a rectangle width x height
ScalingFill
)
// ImageScaling style attributes used to display the image
type ImageScaling struct {
// Horizontal Alignment of the image
Halign Halign
// Vertical Alignment of the image
Valign Valign
// Width Height used by scaling policy
Width, Height float64
// ScalingPolicy defines the scaling policy to applied to the image
ScalingPolicy ScalingPolicy
}