217 lines
4.8 KiB
Markdown
217 lines
4.8 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 -u github.com/fogleman/gg
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Alternatively, you may use gopkg.in to grab a specific major-version:
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go get -u gopkg.in/fogleman/gg.v1
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## Documentation
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https://godoc.org/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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## Examples
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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.
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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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DrawPoint(x, y, r float64)
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DrawLine(x1, y1, x2, y2 float64)
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DrawRectangle(x, y, w, h float64)
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DrawRoundedRectangle(x, y, w, h, r 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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DrawRegularPolygon(n int, x, y, r, rotation float64)
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DrawImage(im image.Image, x, y int)
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DrawImageAnchored(im image.Image, x, y int, ax, ay float64)
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SetPixel(x, y int)
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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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CubicTo(x1, y1, x2, y2, x3, y3 float64)
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ClosePath()
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ClearPath()
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NewSubPath()
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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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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.
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## Text Functions
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It will even do word wrap for you!
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```go
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DrawString(s string, x, y float64)
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DrawStringAnchored(s string, x, y, ax, ay float64)
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DrawStringWrapped(s string, x, y, ax, ay, width, lineSpacing float64, align Align)
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MeasureString(s string) (w, h float64)
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WordWrap(s string, w float64) []string
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SetFontFace(fontFace font.Face)
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LoadFontFace(path string, points float64) error
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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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SetDash(dashes ...float64)
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SetFillRule(fillRule FillRule)
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```
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## Gradients & Patterns
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`gg` supports linear and radial gradients and surface patterns. You can also implement your own patterns.
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```go
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SetFillStyle(pattern Pattern)
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SetStrokeStyle(pattern Pattern)
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NewSolidPattern(color color.Color)
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NewLinearGradient(x0, y0, x1, y1 float64)
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NewRadialGradient(x0, y0, r0, x1, y1, r1 float64)
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NewSurfacePattern(im image.Image, op RepeatOp)
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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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Shear(x, y float64)
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ScaleAbout(sx, sy, x, y float64)
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RotateAbout(angle, x, y float64)
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ShearAbout(sx, sy, x, y float64)
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TransformPoint(x, y float64) (tx, ty float64)
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InvertY()
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```
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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.
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`InvertY` is provided in case Y should increase from bottom to top vs. the default top to bottom.
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## Stack Functions
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Save and restore the state of the context. These can be nested.
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```go
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Push()
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Pop()
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```
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## Clipping Functions
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Use clipping regions to restrict drawing operations to an area that you
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defined using paths.
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```go
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Clip()
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ClipPreserve()
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ResetClip()
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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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LoadImage(path string) (image.Image, error)
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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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## 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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