gg/README.md

# Go Graphics

`gg` is a library for rendering 2D graphics in pure Go.

![Stars](http://i.imgur.com/CylQIJt.png)

## Installation

    go get github.com/fogleman/gg

## GoDoc

https://godoc.org/github.com/fogleman/gg

## Hello, Circle!

Look how easy!

```go
package main

import "github.com/fogleman/gg"

func main() {
    dc := gg.NewContext(1000, 1000)
    dc.DrawCircle(500, 500, 400)
    dc.SetRGB(0, 0, 0)
    dc.Fill()
    dc.SavePNG("out.png")
}
```

## Examples

There are [lots of examples](https://github.com/fogleman/gg/tree/master/examples) included. They're mostly for testing the code, but they're good for learning, too.

![Examples](http://i.imgur.com/tMFoyzu.png)

## Creating Contexts

There are a few ways of creating a context.

```go
NewContext(width, height int) *Context
NewContextForImage(im image.Image) *Context
NewContextForRGBA(im *image.RGBA) *Context
```

## Drawing Functions

Ever used a graphics library that didn't have functions for drawing rectangles
or circles? What a pain!

```go
DrawLine(x1, y1, x2, y2 float64)
DrawRectangle(x, y, w, h float64)
DrawRoundedRectangle(x, y, w, h, r float64)
DrawCircle(x, y, r float64)
DrawArc(x, y, r, angle1, angle2 float64)
DrawEllipse(x, y, rx, ry float64)
DrawEllipticalArc(x, y, rx, ry, angle1, angle2 float64)
DrawRegularPolygon(n int, x, y, r, rotation float64)
DrawImage(im image.Image, x, y int)
DrawImageAnchored(im image.Image, x, y int, ax, ay float64)

MoveTo(x, y float64)
LineTo(x, y float64)
QuadraticTo(x1, y1, x2, y2 float64)
CubicTo(x1, y1, x2, y2, x3, y3 float64)
ClosePath()
ClearPath()
NewSubPath()

Clear()
Stroke()
Fill()
StrokePreserve()
FillPreserve()
```

It is often desired to center an image at a point. Use `DrawImageAnchored` with `ax` and `ay` set to 0.5 to do this. Use 0 to left or top align. Use 1 to right or bottom align. `DrawStringAnchored` does the same for text, so you don't need to call `MeasureString` yourself.

## Text Functions

It will even do word wrap for you!

```go
DrawString(s string, x, y float64)
DrawStringAnchored(s string, x, y, ax, ay float64)
DrawStringWrapped(s string, x, y, ax, ay, width, lineSpacing float64, align Align)
MeasureString(s string) (w, h float64)
WordWrap(s string, w float64) []string
SetFontFace(fontFace font.Face)
LoadFontFace(path string, points float64) error
```

## Color Functions

Colors can be set in several different ways for your convenience.

```go
SetRGB(r, g, b float64)
SetRGBA(r, g, b, a float64)
SetRGB255(r, g, b int)
SetRGBA255(r, g, b, a int)
SetColor(c color.Color)
SetHexColor(x string)
```

## Stroke & Fill Options

```go
SetLineWidth(lineWidth float64)
SetLineCap(lineCap LineCap)
SetLineJoin(lineJoin LineJoin)
SetDash(dashes ...float64)
SetFillRule(fillRule FillRule)
```

## Transformation Functions

```go
Identity()
Translate(x, y float64)
Scale(x, y float64)
Rotate(angle float64)
Shear(x, y float64)
ScaleAbout(sx, sy, x, y float64)
RotateAbout(angle, x, y float64)
ShearAbout(sx, sy, x, y float64)
TransformPoint(x, y float64) (tx, ty float64)
InvertY()
```

It is often desired to rotate or scale about a point that is not the origin. The functions `RotateAbout`, `ScaleAbout`, `ShearAbout` are provided as a convenience.

`InvertY` is provided in case Y should increase from bottom to top vs. the default top to bottom.

Note: transforms do not currently affect `DrawImage` or `DrawString`.

## Stack Functions

Save and restore the state of the context. These can be nested.

```go
Push()
Pop()
```

## Clipping Functions

Use clipping regions to restrict drawing operations to an area that you
defined using paths.

```go
Clip()
ClipPreserve()
ResetClip()
```

Note: As currently implemented, clipping isn't very fast, but it works.

## Helper Functions

Sometimes you just don't want to write these yourself.

```go
Radians(degrees float64) float64
Degrees(radians float64) float64
LoadImage(path string) (image.Image, error)
LoadPNG(path string) (image.Image, error)
SavePNG(path string, im image.Image) error
```

![Separator](http://i.imgur.com/fsUvnPB.png)

## What's Missing?

If you need any of the features below, I recommend using `cairo` instead. Or
even better, implement it and submit a pull request!

- Gradients / Patterns

## How Do it Do?

`gg` is mostly a wrapper around `github.com/golang/freetype/raster`. The goal
is to provide some more functionality and a nicer API that will suffice for
most use cases.

## Another Example

See the output of this example below.

```go
package main

import "github.com/fogleman/gg"

func main() {
	const S = 1024
	dc := gg.NewContext(S, S)
	dc.SetRGBA(0, 0, 0, 0.1)
	for i := 0; i < 360; i += 15 {
		dc.Push()
		dc.RotateAbout(gg.Radians(float64(i)), S/2, S/2)
		dc.DrawEllipse(S/2, S/2, S*7/16, S/8)
		dc.Fill()
		dc.Pop()
	}
	dc.SavePNG("out.png")
}
```

![Ellipses](http://i.imgur.com/J9CBZef.png)