// Approximate a circular arc using multiple
// cubic Bézier curves, one for each π/2 segment.
//
// This is from:
// http://hansmuller-flex.blogspot.com/2011/04/approximating-circular-arc-with-cubic.html
func arc(p *pdf.Path, comp vg.PathComp) {
x0 := comp.X + comp.Radius*vg.Length(math.Cos(comp.Start))
y0 := comp.Y + comp.Radius*vg.Length(math.Sin(comp.Start))
p.Line(pdfPoint(x0, y0))
a1 := comp.Start
end := a1 + comp.Angle
sign := 1.0
if end < a1 {
sign = -1.0
}
left := math.Abs(comp.Angle)
// Square root of the machine epsilon for IEEE 64-bit floating
// point values. This is the equality threshold recommended
// in Numerical Recipes, if I recall correctly—it's small enough.
const epsilon = 1.4901161193847656e-08
for left > epsilon {
a2 := a1 + sign*math.Min(math.Pi/2, left)
partialArc(p, comp.X, comp.Y, comp.Radius, a1, a2)
left -= math.Abs(a2 - a1)
a1 = a2
}
}
func main() {
doc := pdf.New()
canvas := doc.NewPage(pdf.USLetterWidth, pdf.USLetterHeight)
canvas.Translate(500, 500)
// canvas.SetColor(230, 100, 30)
canvas.SetStrokeColor(20, 40, 60)
path := new(pdf.Path)
path.Move(pdf.Point{0, 0})
path.Line(pdf.Point{0, 50})
canvas.Stroke(path)
text := new(pdf.Text)
text.SetFont(pdf.Helvetica, 14)
text.Text("Hello, World!")
canvas.DrawText(text)
canvas.Close()
err := doc.Encode(os.Stdout)
if err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(1)
}
}
func EngraveStaff(origin pdf.Point, width, height, lineWidth pdf.Unit, canvas *pdf.Canvas) {
path := new(pdf.Path)
noteHeight := pdf.Unit(height / 4)
for i := 0; i < 5; i++ {
path.Move(origin)
path.Line(pdf.Point{origin.X + width, origin.Y})
origin.Y = origin.Y + noteHeight
}
canvas.Push()
canvas.SetLineWidth(lineWidth)
canvas.Stroke(path)
canvas.Pop()
}
// pdfPath returns a pdf.Path from a vg.Path.
func pdfPath(c *Canvas, path vg.Path) *pdf.Path {
p := new(pdf.Path)
for _, comp := range path {
switch comp.Type {
case vg.MoveComp:
p.Move(pdfPoint(comp.X, comp.Y))
case vg.LineComp:
p.Line(pdfPoint(comp.X, comp.Y))
case vg.ArcComp:
arc(p, comp)
case vg.CloseComp:
p.Close()
default:
panic(fmt.Sprintf("Unknown path component type: %d\n", comp.Type))
}
}
return p
}
// Approximate a circular arc using multiple
// cubic Bézier curves, one for each π/2 segment.
//
// This is from:
// http://hansmuller-flex.blogspot.com/2011/04/approximating-circular-arc-with-cubic.html
func arc(p *pdf.Path, comp vg.PathComp) {
x0 := comp.X + comp.Radius*vg.Length(math.Cos(comp.Start))
y0 := comp.Y + comp.Radius*vg.Length(math.Sin(comp.Start))
p.Line(pdfPoint(x0, y0))
a1 := comp.Start
end := a1 + comp.Angle
sign := 1.0
if end < a1 {
sign = -1.0
}
left := math.Abs(comp.Angle)
for left > 0 {
a2 := a1 + sign*math.Min(math.Pi/2, left)
partialArc(p, comp.X, comp.Y, comp.Radius, a1, a2)
left -= math.Abs(a2 - a1)
a1 = a2
}
}
func EngraveSurrogateNoteHead(origin pdf.Point, size pdf.Unit, canvas *pdf.Canvas) {
outline := new(pdf.Path)
topRight := pdf.Point{origin.X + size, origin.Y + size}
outline.Rectangle(pdf.Rectangle{origin, topRight})
mid := pdf.Point{origin.X + pdf.Unit(size/2), origin.Y + pdf.Unit(size/2)}
midPoints := new(pdf.Path)
midPoints.Move(pdf.Point{mid.X, origin.Y})
midPoints.Line(pdf.Point{mid.X, origin.Y + size})
midPoints.Move(pdf.Point{origin.X, mid.Y})
midPoints.Line(pdf.Point{origin.X + size, mid.Y})
canvas.Push()
canvas.SetColor(0.6, 0.6, 0.6)
canvas.Fill(outline)
canvas.SetLineWidth(pdf.Unit(0.1))
canvas.Stroke(midPoints)
canvas.Pop()
}
