// 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...)
}
}
func checkNaN(s *data.Slice, name string) {
h := s.Host()
for _, h := range h {
for _, v := range h {
if math.IsNaN(float64(v)) || math.IsInf(float64(v), 0) {
util.Fatal("NaN or Inf in", name)
}
}
}
}
// Extract real parts, copy them from src to dst.
// In the meanwhile, check if imaginary parts are nearly zero
// and scale the kernel to compensate for unnormalized FFTs.
// scale = 1/N, with N the FFT logical size.
func scaleRealParts(dst, src *data.Slice, scale float32) {
util.Argument(2*dst.Len() == src.Len())
util.Argument(dst.NComp() == 1 && src.NComp() == 1)
srcList := src.Host()[0]
dstList := dst.Host()[0]
// Normally, the FFT'ed kernel is purely real because of symmetry,
// so we only store the real parts...
maximg := float32(0.)
for i := 0; i < src.Len()/2; i++ {
dstList[i] = srcList[2*i] * scale
if fabs(srcList[2*i+1]) > maximg {
maximg = fabs(srcList[2*i+1])
}
}
maximg *= float32(math.Sqrt(float64(scale))) // after 1 FFT, normalization is sqrt(N)
// ...however, we check that the imaginary parts are nearly zero,
// just to be sure we did not make a mistake during kernel creation.
if maximg > FFT_IMAG_TOLERANCE {
log.Fatalf("FFT kernel imaginary part: %v\n", maximg)
}
}