Function ExampleField_colors

plotter/field_example_test.go:55–118

()

}

func ExampleField_colors() {
	f := plotter.NewField(field{
		r: 5, c: 9,
		fn: func(x, y float64) plotter.XY {
			return plotter.XY{
				X: -0.75*x + y,
				Y: -0.75*y - x,
			}
		},
	})

	pal := moreland.ExtendedBlackBody()
	pal.SetMin(0)
	pal.SetMax(1.1) // Use 1.1 to make highest magnitude vectors visible on white.

	// Provide a DrawGlyph function to render a custom
	// vector instead of the default monochrome arrow.
	f.DrawGlyph = func(c vg.Canvas, sty draw.LineStyle, v plotter.XY) {
		c.Push()
		defer c.Pop()
		mag := math.Hypot(v.X, v.Y)
		var pa vg.Path
		if mag == 0 {
			// Draw a black dot for zero vectors.
			c.SetColor(color.Black)
			pa.Move(vg.Point{X: sty.Width})
			pa.Arc(vg.Point{}, sty.Width, 0, 2*math.Pi)
			pa.Close()
			c.Fill(pa)
			return
		}
		// Choose a color from the palette for the magnitude.
		col, err := pal.At(mag)
		if err != nil {
			panic(err)
		}
		c.SetColor(col)
		pa.Move(vg.Point{})
		pa.Line(vg.Point{X: 1, Y: 0})
		pa.Close()
		c.Stroke(pa)
	}

	p := plot.New()
	p.Title.Text = "Vortex"
	p.X.Tick.Marker = integerTicks{}
	p.Y.Tick.Marker = integerTicks{}

	p.Add(f)

	img := vgimg.New(250, 175)
	dc := draw.New(img)

	p.Draw(dc)
	w, err := os.Create("testdata/color_field.png")
	if err != nil {
		log.Panic(err)
	}