Method Plot

plotter/field.go:88–161

Plot implements the Plot method of the plot.Plotter interface.

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

// Plot implements the Plot method of the plot.Plotter interface.
func (f *Field) Plot(c draw.Canvas, plt *plot.Plot) {
	c.Push()
	defer c.Pop()
	c.SetLineStyle(f.LineStyle)

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

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

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

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

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

			c.Push()
			c.Translate(vg.Point{X: (x + dx) / 2, Y: (y + dy) / 2})

			v := f.FieldXY.Vector(i, j)
			s := math.Hypot(v.X, v.Y) / (2 * f.max)
			// Do not scale when the vector is zero, otherwise the
			// user cannot render special-case glyphs for that case.