// Plot implements the Plot method of the plot.Plotter interface.
func (h *Contour) Plot(c draw.Canvas, plt *plot.Plot) {
if naive {
h.naivePlot(c, plt)
return
}
var pal []color.Color
if h.Palette != nil {
pal = h.Palette.Colors()
}
trX, trY := plt.Transforms(&c)
// Collate contour paths and draw them.
//
// The alternative naive approach is to draw each line segment as
// conrec returns it. The integrated path approach allows graphical
// optimisations and is necessary for contour fill shading.
cp := contourPaths(h.GridXYZ, h.Levels, trX, trY)
// 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. Sorting is not
// necessary since contourPaths sorts the levels as a side effect.
ps := float64(len(pal)-1) / (h.Levels[len(h.Levels)-1] - h.Levels[0])
if len(h.Levels) == 1 {
ps = 0
}
for i, z := range h.Levels {
if math.IsNaN(z) {
continue
}
for _, pa := range cp[z] {
if isLoop(pa) {
pa.Close()
}
style := h.LineStyles[i%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.
}
if col != nil && style.Width != 0 {
c.SetLineStyle(style)
c.SetColor(col)
c.Stroke(pa)
}
}
}
}
// naivePlot implements the 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.
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)
if !c.Contains(draw.Point{x1, y1}) || !c.Contains(draw.Point{x2, y2}) {
return
}
pa.Move(x1, y1)
pa.Line(x2, y2)
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.
}
if col != nil && style.Width != 0 {
c.SetLineStyle(style)
c.SetColor(col)
c.Stroke(pa)
}
})
}