// Render on existing image buffer. Resize it if needed
func On(img *image.RGBA, f *data.Slice, fmin, fmax string, arrowSize int, colormap ...color.RGBA) {
dim := f.NComp()
switch dim {
default:
log.Fatalf("unsupported number of components: %v", dim)
case 3:
drawVectors(img, f.Vectors(), arrowSize)
case 1:
min, max := extrema(f.Host()[0])
if fmin != "auto" {
m, err := strconv.ParseFloat(fmin, 32)
if err != nil {
util.Fatal("draw: scale:", err)
}
min = float32(m)
}
if fmax != "auto" {
m, err := strconv.ParseFloat(fmax, 32)
if err != nil {
util.Fatal("draw: scale:", err)
}
max = float32(m)
}
if min == max {
min -= 1
max += 1 // make it gray instead of black
}
drawFloats(img, f.Scalars(), min, max, colormap...)
}
}