| 118 | } |
| 119 | |
| 120 | func ExampleField_gophers() { |
| 121 | file, err := os.Open("testdata/gopher_running.png") |
| 122 | if err != nil { |
| 123 | log.Panic(err) |
| 124 | } |
| 125 | defer file.Close() |
| 126 | gopher, err := png.Decode(file) |
| 127 | if err != nil { |
| 128 | log.Panic(err) |
| 129 | } |
| 130 | |
| 131 | f := plotter.NewField(field{ |
| 132 | r: 5, c: 9, |
| 133 | fn: func(x, y float64) plotter.XY { |
| 134 | return plotter.XY{ |
| 135 | X: -0.75*x + y, |
| 136 | Y: -0.75*y - x, |
| 137 | } |
| 138 | }, |
| 139 | }) |
| 140 | |
| 141 | // Provide a DrawGlyph function to render a custom |
| 142 | // vector glyph instead of the default arrow. |
| 143 | f.DrawGlyph = func(c vg.Canvas, _ draw.LineStyle, v plotter.XY) { |
| 144 | // The canvas is unscaled if the vector has a zero |
| 145 | // magnitude, so return in that case. |
| 146 | if math.Hypot(v.X, v.Y) == 0 { |
| 147 | return |
| 148 | } |
| 149 | // Vector glyphs are scaled to half unit length by the |
| 150 | // plotter, so scale the gopher to twice unit size so |
| 151 | // it fits the cell, and center on the cell. |
| 152 | c.Translate(vg.Point{X: -1, Y: -1}) |
| 153 | c.DrawImage(vg.Rectangle{Max: vg.Point{X: 2, Y: 2}}, gopher) |
| 154 | } |
| 155 | |
| 156 | p := plot.New() |
| 157 | p.Title.Text = "Gopher vortex" |
| 158 | p.X.Tick.Marker = integerTicks{} |
| 159 | p.Y.Tick.Marker = integerTicks{} |
| 160 | |
| 161 | p.Add(f) |
| 162 | |
| 163 | img := vgimg.New(250, 175) |
| 164 | dc := draw.New(img) |
| 165 | |
| 166 | p.Draw(dc) |
| 167 | w, err := os.Create("testdata/gopher_field.png") |
| 168 | if err != nil { |
| 169 | log.Panic(err) |
| 170 | } |
| 171 | png := vgimg.PngCanvas{Canvas: img} |
| 172 | if _, err = png.WriteTo(w); err != nil { |
| 173 | log.Panic(err) |
| 174 | } |
| 175 | } |