func Draw(img *image.RGBA, col color.RGBA, box shp.Box, shape shp.Shape) error {
poly, ok := shape.(*shp.Polygon)
if !ok {
return fmt.Errorf("cannot draw non-polygon shape")
}
gc := draw2dimg.NewGraphicContext(img)
gc.SetStrokeColor(col)
gc.SetLineWidth(1)
rect := img.Bounds()
dx := float64(rect.Max.X-rect.Min.X) / (box.MaxX - box.MinX)
dy := float64(rect.Max.Y-rect.Min.Y) / (box.MaxY - box.MinY)
for i, start := range poly.Parts {
end := len(poly.Points)
if i+1 < len(poly.Parts) {
end = int(poly.Parts[i+1])
}
part := poly.Points[start:end]
path := draw2d.Path{}
for j, p := range part {
x := ((p.X - box.MinX) * dx)
y := ((box.MaxY - p.Y) * dy)
if j == 0 {
path.MoveTo(x, y)
} else {
path.LineTo(x, y)
}
}
path.Close()
gc.Stroke(&path)
}
return nil
}
