Create a "pie element" with RasterX package using AddArc

Issue

I’m working on a chart widget for Fyne, I use rasterx package (https://github.com/srwiley/rasterx) and it works well. But I spent hours to try to make a circle arc (to create a pie chart elements) without success.

Let’s take this starting point:

cx, cy := float64(w/2.0), float64(h/2.0)
r := float64(w / 3.0)
angle := 45.0
rot := angle * math.Pi / 180.0

I take the AddArc function at https://github.com/srwiley/rasterx/blob/master/shapes.go#L99 to understand the principle and do:

points := []float64{r, r, angle, 1, 0, px, py}

stroker.Start(rasterx.ToFixedP(px, py))
rasterx.AddArc(points, cx, cy, px, py, stroker)
stroker.Stop(false)
stroker.Draw()

The result is a circle, not an arc.

As the rasterx package is based on SVG 2.0 spec, maybe I miss something. Can you please give me a hand to show me how to create a "pie chart element" for a given angle?

Thanks a lot.

PS: I should not use other package than rasterx, please do not tell me to use another one.

Solution

The px, py in points needs to be different to the ones passed to AddArc. This works for me:

        angle := 45.0
        rot1 := angle * math.Pi / 180.0
        rot2 := (angle - 90) * math.Pi / 180.0

        p1x := cx + r*math.Cos(rot1)
        p1y := cy + r*math.Sin(rot1)
        p2x := cx + r*math.Cos(rot2)
        p2y := cy + r*math.Sin(rot2)

        points := []float64{r, r, angle, 1, 0, p2x, p2y}

...

        stroker.Start(rasterx.ToFixedP(p1x, p1y))
        rasterx.AddArc(points, cx, cy, p1x, p1y, stroker)

Answered By – andy.xyz

Answer Checked By – Cary Denson (GoLangFix Admin)