Method naivePlot

plotter/contour.go:193–257

naivePlot implements a naive rendering approach for contours. It is here as a debugging mode since it simply draws line segments generated by conrec without further computation.

(c draw.Canvas, plt *plot.Plot)

// It is here as a debugging mode since it simply draws line segments
// generated by conrec without further computation.
func (h *Contour) naivePlot(c draw.Canvas, plt *plot.Plot) {
	var pal []color.Color
	if h.Palette != nil {
		pal = h.Palette.Colors()
	}

	trX, trY := plt.Transforms(&c)

	// Sort levels prior to palette scaling since we can't depend on
	// sorting as a side effect from calling contourPaths.
	sort.Float64s(h.Levels)
	// ps is a palette scaling factor to scale the palette uniformly
	// across the given levels. This enables a discordance between the
	// number of colours and the number of levels.
	ps := float64(len(pal)-1) / (h.Levels[len(h.Levels)-1] - h.Levels[0])
	if len(h.Levels) == 1 {
		ps = 0
	}

	levelMap := make(map[float64]int)
	for i, z := range h.Levels {
		levelMap[z] = i
	}

	// Draw each line segment as conrec generates it.
	var pa vg.Path
	conrec(h.GridXYZ, h.Levels, func(_, _ int, l line, z float64) {
		if math.IsNaN(z) {
			return
		}

		pa = pa[:0]

		x1, y1 := trX(l.p1.X), trY(l.p1.Y)
		x2, y2 := trX(l.p2.X), trY(l.p2.Y)

		pt1 := vg.Point{X: x1, Y: y1}
		pt2 := vg.Point{X: x2, Y: y2}
		if !c.Contains(pt1) || !c.Contains(pt2) {
			return
		}

		pa.Move(pt1)
		pa.Line(pt2)
		pa.Close()

		style := h.LineStyles[levelMap[z]%len(h.LineStyles)]
		var col color.Color
		switch {
		case z < h.Min:
			col = h.Underflow
		case z > h.Max:
			col = h.Overflow
		case len(pal) == 0:
			col = style.Color
		default:
			col = pal[int((z-h.Levels[0])*ps+0.5)] // Apply palette scaling.
		}