zntg/ui/draw.go

package ui

import (
	"image"
	"image/color"
	"math"

	"github.com/llgcode/draw2d/draw2dimg"
	"opslag.de/schobers/zntg/allg5"
)

func drawBitmap(w, h int, draw func(*draw2dimg.GraphicContext)) *allg5.Bitmap {
	dest := image.NewRGBA(image.Rect(0, 0, w, h))
	gc := draw2dimg.NewGraphicContext(dest)
	gc.SetFillColor(color.Transparent)
	gc.Clear()
	draw(gc)
	bmp, err := allg5.NewBitmapFromImage(dest, false)
	if nil != err {
		return nil
	}
	return bmp
}

func drawCircle(r, w int, startAngle, a float64, c color.Color) *allg5.Bitmap {
	var width = 2*r + w
	return drawBitmap(width, width, func(gc *draw2dimg.GraphicContext) {
		gc.SetFillColor(c)
		gc.SetStrokeColor(c)
		gc.SetLineWidth(float64(w))
		var rad = float64(r)
		var cnt = float64(width) * .5
		var dx1, dy1 = cnt + math.Cos(startAngle)*rad, cnt + math.Sin(startAngle)*rad
		gc.MoveTo(dx1, dy1)
		gc.ArcTo(cnt, cnt, rad, rad, startAngle, a)
		gc.Stroke()
	})
}