Support signed types

[oeway]

In some of the images, we have data type in <i2 and that generated an error in vizarr:

Error: Dtype not supported, must be u1, u2, u4, or f4

@manzt mentioned that it was possible to do data casting with geotiff (see here), and it will be great if we can have this generally available for vizarr as well.

[manzt]

Thanks for opening the issue! Yes, this should be feasible (we do cast int -> uint for geotiff). There are two approaches I see.

• Duplicate the logic from TiffPixelSource to ZarrPixelSource and have the pixel-sources be responsible for adapting data for Viv layers.
• Have the Viv layers cast data that isn't compatible, rather than the pixel sources.

I think the the latter is my preferred solution. The conversion logic would then be shared regardless of the pixel source. This way the sources shouldn't get out of sync. I'll take a look into adding this.

[ilan-gold]

Just seeing this but I think we can just update the shaders' handling without casting anything? Is there something blocking this that I'm missing (very possible)?

viv/src/layers/XRLayer/XRLayer.js

Line 30 in 855d29b

dtype === 'Float32' || isWebGL1 ? 'sampler2D' : 'usampler2D',

We just need to add isampler2D as an option to the above, I think, and then add the GL constants here (or we could refactor to move that line into the DTYPE_VALUES object):

viv/src/constants.ts

Lines 12 to 38 in a21b080

	export const DTYPE_VALUES = {
	Uint8: {
	format: GL.R8UI,
	dataFormat: GL.RED_INTEGER,
	type: GL.UNSIGNED_BYTE,
	max: 2 ** 8 - 1
	},
	Uint16: {
	format: GL.R16UI,
	dataFormat: GL.RED_INTEGER,
	type: GL.UNSIGNED_SHORT,
	max: 2 ** 16 - 1
	},
	Uint32: {
	format: GL.R32UI,
	dataFormat: GL.RED_INTEGER,
	type: GL.UNSIGNED_INT,
	max: 2 ** 32 - 1
	},
	Float32: {
	format: GL.R32F,
	dataFormat: GL.RED,
	type: GL.FLOAT,
	// Not sure what to do about this one - a good use case for channel stats, I suppose:
	// https://en.wikipedia.org/wiki/Single-precision_floating-point_format.
	max: 3.4 * 10 ** 38
	}

[manzt]

Nope, sounds totally reasonable! I just assumed we needed to cast because that is what the tiff source did.