Method plotVectorized

plotter/heat.go:149–231

plotVectorized plots the heatmap using vector-based drawing.

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

// plotVectorized plots the heatmap using vector-based drawing.
func (h *HeatMap) plotVectorized(c draw.Canvas, plt *plot.Plot) {
	if h.Min > h.Max {
		panic("contour: invalid Z range: min greater than max")
	}
	pal := h.Palette.Colors()
	if len(pal) == 0 {
		panic("heatmap: empty palette")
	}
	// ps scales the palette uniformly across the data range.
	ps := float64(len(pal)-1) / (h.Max - h.Min)

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

	var pa vg.Path
	cols, rows := h.GridXYZ.Dims()
	for i := range cols {
		var right, left float64
		switch i {
		case 0:
			if cols == 1 {
				right = 0.5
			} else {
				right = (h.GridXYZ.X(1) - h.GridXYZ.X(0)) / 2
			}
			left = -right
		case cols - 1:
			right = (h.GridXYZ.X(cols-1) - h.GridXYZ.X(cols-2)) / 2
			left = -right
		default:
			right = (h.GridXYZ.X(i+1) - h.GridXYZ.X(i)) / 2
			left = -(h.GridXYZ.X(i) - h.GridXYZ.X(i-1)) / 2
		}

		for j := range rows {
			var up, down float64
			switch j {
			case 0:
				if rows == 1 {
					up = 0.5
				} else {
					up = (h.GridXYZ.Y(1) - h.GridXYZ.Y(0)) / 2
				}
				down = -up
			case rows - 1:
				up = (h.GridXYZ.Y(rows-1) - h.GridXYZ.Y(rows-2)) / 2
				down = -up
			default:
				up = (h.GridXYZ.Y(j+1) - h.GridXYZ.Y(j)) / 2
				down = -(h.GridXYZ.Y(j) - h.GridXYZ.Y(j-1)) / 2
			}

			x, y := trX(h.GridXYZ.X(i)+left), trY(h.GridXYZ.Y(j)+down)
			dx, dy := trX(h.GridXYZ.X(i)+right), trY(h.GridXYZ.Y(j)+up)

			if !c.Contains(vg.Point{X: x, Y: y}) || !c.Contains(vg.Point{X: dx, Y: dy}) {
				continue
			}