Allow transparency without a Mask via pixelValuesToColorFn

[jfoclpf]

First of all PROPS for you guys for developing this GREAT AND FREE tool, thanks a lot

Is your feature request related to a problem? I have this elevation map with lots of zeros mapped to white, it would be nice to have transparency for values under zero, for example

Describe the solution you'd like

Allowing transparency without the need for an external GeoJSON mask via pixelValuesToColorFn

      var layer = new GeoRasterLayer({
          georaster: georaster,
          opacity: 0.7,
          pixelValuesToColorFn: values => values[0] < 0 ? 'transparent' : '#ffffff',
          resolution: 64 // optional parameter for adjusting display resolution
      });

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Use an external GeoJSON file for the mask

Additional context Working example I just made using your tool: https://stackoverflow.com/a/78298578/1243247

Again, thanks a lot for the great tool

[jfoclpf]

Found it :) null was the trick, perhaps docs should be more clear

      const layer = new GeoRasterLayer({
        georaster: georaster,
        opacity: 0.7,
        pixelValuesToColorFn: vals => Math.round(vals[0]) < 1 ? null : '#ffffff',
        resolution: 512 // optional parameter for adjusting display resolution
      }).addTo(map)

again, congrats for the great work @DanielJDufour

[DanielJDufour]

@jfoclpf , would you be open to submitting a PR, adding this example to https://github.com/GeoTIFF/georaster-layer-for-leaflet-example

?

[jfoclpf]

@jfoclpf , would you be open to submitting a PR, adding this example to https://github.com/GeoTIFF/georaster-layer-for-leaflet-example

?

sure, I will do it ASAP

[jfoclpf]

@DanielJDufour I already submitted 3 PRs as you requested, tell me what you think