Go draw2d
last modified April 11, 2024
In this article we show how to work with graphics in Go with draw2d.
The draw2d package is a pure go 2D vector graphics library. It supports multiple output devices including images (draw2d), pdf documents (draw2dpdf) and opengl (draw2dgl).
In our examples we draw on the image output device.
Drawing a rectangle
In the first example, we draw a rectangle.
package main
import (
"image"
"github.com/llgcode/draw2d"
"github.com/llgcode/draw2d/draw2dimg"
"github.com/llgcode/draw2d/draw2dkit"
)
func main() {
dest := image.NewRGBA(image.Rect(0, 0, 300, 300))
gc := draw2dimg.NewGraphicContext(dest)
gc.SetStrokeColor(image.White)
draw2dkit.Rectangle(gc, 50, 50, 200, 200)
gc.Stroke()
draw2dimg.SaveToPngFile("srect.png", dest)
}
The example draws a white rectangle on a transparent background.
dest := image.NewRGBA(image.Rect(0, 0, 300, 300))
A drawing destination is created.
gc := draw2dimg.NewGraphicContext(dest)
From the destination, we create a drawing context. It is an interface for drawing.
gc.SetStrokeColor(image.White)
We set the stroke color to white using SetStrokeColor.
draw2dkit.Rectangle(gc, 50, 50, 200, 200)
We draw a rectangle with Rectangle. The parameters are the graphics
context and the x, y coordinates of the top-left and bottom-right points of
the rectangle.
gc.Stroke()
The rectangle path is stroked with Stroke.
draw2dimg.SaveToPngFile("srect.png", dest)
We save the drawing to a PND file with SaveToPngFile.
Drawing a line
In the next example we draw a line.
package main
import (
"image"
"github.com/llgcode/draw2d"
"github.com/llgcode/draw2d/draw2dimg"
"github.com/llgcode/draw2d/draw2dkit"
)
func main() {
dest := image.NewRGBA(image.Rect(0, 0, 300, 300))
gc := draw2dimg.NewGraphicContext(dest)
gc.SetFillColor(image.White)
draw2dkit.Rectangle(gc, 0, 0, 300, 300)
gc.Fill()
DrawLine(gc, 0, 0, 300, 300)
draw2dimg.SaveToPngFile("line.png", dest)
}
func DrawLine(gc draw2d.GraphicContext, x0, y0, x1, y1 float64) {
gc.MoveTo(x0, y0)
gc.LineTo(x1, y1)
gc.Stroke()
}
A diagonal black line is drawn on a white background.
gc.SetFillColor(image.White) draw2dkit.Rectangle(gc, 0, 0, 300, 300) gc.Fill()
We fill the background of the surface in white colour.
func DrawLine(gc draw2d.GraphicContext, x0, y0, x1, y1 float64) {
gc.MoveTo(x0, y0)
gc.LineTo(x1, y1)
gc.Stroke()
}
We build the path with MoveTo and LineTo and then
stroke it with Stroke.
Drawing a circle
A circle is drawn with Ellipse.
package main
import (
"image"
"image/color"
"github.com/llgcode/draw2d"
"github.com/llgcode/draw2d/draw2dimg"
"github.com/llgcode/draw2d/draw2dkit"
)
func main() {
dest := image.NewRGBA(image.Rect(0, 0, 300, 300))
gc := draw2dimg.NewGraphicContext(dest)
gc.SetFillColor(image.White)
draw2dkit.Rectangle(gc, 0, 0, 300, 300)
gc.Fill()
DrawCircle(gc, 0, 0, 300, 300)
draw2dimg.SaveToPngFile("circle.png", dest)
}
func DrawCircle(gc draw2d.GraphicContext) {
draw2dkit.Ellipse(gc, 150, 150, 80, 80)
gc.SetFillColor(color.RGBA{0x44, 0x44, 0x44, 0xff})
gc.SetStrokeColor(color.RGBA{0x44, 0x44, 0x44, 0xff})
gc.FillStroke()
}
A gray circle is drawn in the middle of the surface.
func DrawCircle(gc draw2d.GraphicContext) {
draw2dkit.Ellipse(gc, 150, 150, 80, 80)
gc.SetFillColor(color.RGBA{0x44, 0x44, 0x44, 0xff})
gc.SetStrokeColor(color.RGBA{0x44, 0x44, 0x44, 0xff})
gc.FillStroke()
}
We draw the circle with Ellipse. We set the fill and stroke color
using SetFillColor and SetStrokeColor. The
FillStroke fills the path and then strokes the path.
Drawing a cubic line
A cubic line is drawn with CubicCurveTo.
package main
import (
"image"
"github.com/llgcode/draw2d"
"github.com/llgcode/draw2d/draw2dimg"
"github.com/llgcode/draw2d/draw2dkit"
)
func main() {
dest := image.NewRGBA(image.Rect(0, 0, 300, 300))
gc := draw2dimg.NewGraphicContext(dest)
gc.SetFillColor(image.White)
draw2dkit.Rectangle(gc, 0, 0, 300, 300)
gc.Fill()
DrawCurvedLine(gc)
draw2dimg.SaveToPngFile("curved.png", dest)
}
func DrawCurvedLine(gc draw2d.GraphicContext) {
gc.MoveTo(30, 30)
gc.CubicCurveTo(200, 150, 250, 100, 280, 30)
gc.Stroke()
}
The example draws a cubic line.
func DrawCurvedLine(gc draw2d.GraphicContext) {
gc.MoveTo(30, 30)
gc.CubicCurveTo(200, 150, 250, 100, 280, 30)
gc.Stroke()
}
We go to the starting point with MoveTo. With
CubicCurveTo, we draw the cubic line. The first two parameters are
the x, y coordinates of the two control points. The last two values are the
coordinates of the ending point.
Source
In this article we have worked with graphics in Golang using draw2d package.
Author
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