150 lines
2.8 KiB
Markdown
150 lines
2.8 KiB
Markdown
# Go Graphics
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`gg` is a library for rendering 2D graphics in pure Go.
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## Installation
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go get github.com/fogleman/gg
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## Hello, Circle!
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Look how easy!
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```go
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package main
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import "github.com/fogleman/gg"
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func main() {
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dc := gg.NewContext(1000, 1000)
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dc.DrawCircle(500, 500, 400)
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dc.SetRGB(0, 0, 0)
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dc.Fill()
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dc.SavePNG("out.png")
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}
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```
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## Creating Contexts
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There are a few ways of creating a context.
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```go
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NewContext(width, height int) *Context
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NewContextForImage(im image.Image) *Context
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NewContextForRGBA(im *image.RGBA) *Context
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```
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## Drawing Functions
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Ever used a graphics library that didn't have functions for drawing rectangles
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or circles? What a pain!
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```go
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DrawLine(x1, y1, x2, y2 float64)
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DrawRectangle(x, y, w, h float64)
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DrawCircle(x, y, r float64)
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DrawArc(x, y, r, angle1, angle2 float64)
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DrawEllipse(x, y, rx, ry float64)
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DrawEllipticalArc(x, y, rx, ry, angle1, angle2 float64)
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DrawImage(im image.Image, x, y int)
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DrawString(x, y float64, s string)
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MoveTo(x, y float64)
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LineTo(x, y float64)
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QuadraticTo(x1, y1, x2, y2 float64)
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ClosePath()
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ClearPath()
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Clear()
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Stroke()
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Fill()
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StrokePreserve()
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FillPreserve()
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```
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## Color Functions
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Colors can be set in several different ways for your convenience.
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```go
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SetRGB(r, g, b float64)
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SetRGBA(r, g, b, a float64)
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SetRGB255(r, g, b int)
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SetRGBA255(r, g, b, a int)
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SetColor(c color.Color)
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SetHexColor(x string)
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```
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## Stroke & Fill Options
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```go
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SetLineWidth(lineWidth float64)
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SetLineCap(lineCap LineCap)
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SetLineJoin(lineJoin LineJoin)
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SetFillRule(fillRule FillRule)
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```
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## Transformation Functions
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```go
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Identity()
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Translate(x, y float64)
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Scale(x, y float64)
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Rotate(angle float64)
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RotateAbout(angle, x, y float64)
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Shear(x, y float64)
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TransformPoint(x, y float64) (tx, ty float64)
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Push()
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Pop()
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```
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## Helper Functions
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Sometimes you just don't want to write these yourself.
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```go
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Radians(degrees float64) float64
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Degrees(radians float64) float64
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LoadPNG(path string) (image.Image, error)
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SavePNG(path string, im image.Image) error
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```
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## What's Missing?
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If you need any of the features below, I recommend using `cairo` instead. Or even better, implement it and submit a pull request!
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- Clipping Regions
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- Gradients / Patterns
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- Cubic Beziers
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- Dashed Lines
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## How Do it Do?
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`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.
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## Another Example
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See the output of this example below.
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```go
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package main
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import "github.com/fogleman/gg"
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func main() {
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const S = 1024
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dc := gg.NewContext(S, S)
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dc.SetRGBA(0, 0, 0, 0.1)
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for i := 0; i < 360; i += 15 {
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dc.Push()
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dc.RotateAbout(gg.Radians(float64(i)), S/2, S/2)
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dc.DrawEllipse(S/2, S/2, S*7/16, S/8)
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dc.Fill()
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dc.Pop()
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}
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dc.SavePNG("out.png")
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}
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```
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