Modulate DTI V1 (AFNI)

import NiiVue from '@niivue/niivue'

const nv1 = new NiiVue({
  backgroundColor: [0.0, 0.0, 0.2, 1],
  is3DCrosshairVisible: true,
  crosshairWidth: 1,
  isSnapToVoxelCenters: true,
})
nv1.addEventListener('locationChange', (e) => {
  document.getElementById('location').innerHTML =
    `  ${e.detail.string}`
})
await nv1.attachTo('gl1')
// V1 lines benefit from nearest neighbor interpolation
nv1.volumeIsNearestInterpolation = true
// AFNI detached images: header (.HEAD) and image data (.BRIK.gz) are separate
// files. Given only the .HEAD URL, NiiVue finds the .BRIK (or .BRIK.gz) beside it.
await nv1.loadVolumes([
  {
    url: '/volumes/afni/DT_FA+orig.HEAD',
    opacity: 1,
  },
  {
    url: '/volumes/afni/DT_V1+orig.HEAD',
    opacity: 1,
  },
])
// AFNI lacks NIfTI intent codes, so explicitly convert V1 vector data to RGBA
await nv1.loadImgV1(1, false, true)
// Set initial crosshair position in voxel coordinates
nv1.crosshairPos = nv1.vox2frac([64, 60, 45])

function minMax() {
  const mn = 0.01 * slide.value
  const mx = 0.01 * slideX.value
  nv1.volumes[0].calMin = Math.min(mn, mx)
  nv1.volumes[0].calMax = Math.max(mn, mx)
  nv1.updateGLVolume()
}
slide.oninput = minMax
slideX.oninput = minMax

check.onchange = function () {
  nv1.volumeIsAlphaClipDark = this.checked
  nv1.updateGLVolume()
}
webgpuCheck.onclick = function () {
  nv1.reinitializeView({ backend: this.checked ? 'webgpu' : 'webgl2' })
}
mode.onchange = async () => {
  const idx = mode.selectedIndex
  if (idx === 0) {
    // FA only
    await nv1.setVolume(0, { opacity: 1.0 })
    await nv1.setVolume(1, { opacity: 0.0 })
  } else if (idx <= 2) {
    // V1 (with or without modulation)
    await nv1.setVolume(0, { opacity: 0.0 })
    await nv1.setVolume(1, { opacity: 1.0 })
  } else {
    // V1 + FA (isV1SliceShader modes)
    await nv1.setVolume(0, { opacity: 1.0 })
    await nv1.setVolume(1, { opacity: 1.0 })
  }
  // Apply or clear modulation
  if (idx === 2 || idx === 4) {
    await nv1.setModulationImage(nv1.volumes[1].id, nv1.volumes[0].id)
  } else {
    await nv1.setModulationImage(nv1.volumes[1].id, '')
  }
  nv1.volumeIsV1SliceShader = idx > 2
}
mode.onchange()
check.onchange()