Improve rendering pipeline

[danielfdsilva]

Summary

This replaces the old single vertex color extension with an explicit fragment pipeline built from small luma.gl shader modules. Filtering, rescaling, and coloring are separate stages with clear ordering.
The public API gains colorMode, filterMin / filterMax, rescaleMin / rescaleMax, optional shaderModules, and multi-texel value packing so cells can have more than four values.

Two GLSL hooks were added: HEALPIX_SELECT_VALUES and HEALPIX_RESCALE_VALUES, so callers can inject GLSL without forking the layer - useful for band math.

Api Changes

The user defines how many values sit behind each HEALPix cell using dimensions. Then through setting a colorMode the GPU knows whether the user wants:

• a scalar value pulled through filter, rescale, and a color ramp;
• the former plus a separate alpha channel;
• or straight RGB or RGBA with no ramp.

By default the layer will consider the data to have one dimension and will be rendered as a scalar with a color ramp (default to gray unless provided). If there are more than 4 dimensions the user can provide custom glsl (passed to the layer as a shader module) to select the values they want.

const ndviSelector = {
  name: 'ndviSelector',
  inject: {
    'fs:HEALPIX_SELECT_VALUES': `\

// healpixValueAt is a utility function to select a value at a given index.

float nir = healpixValueAt(7);
float red = healpixValueAt(3);
float ndvi = (nir - red) / max(nir + red, 1e-6);
selectedValues = vec4(ndvi, 0.0, 0.0, 0.0);
`
  }
};

Whenever the color mode is set to scalar, the pipeline goes through a rescale function based on the rescaleMin / rescaleMax props, but the user can provide their own custom rescaling through the HEALPIX_RESCALE_VALUES hook.

flowchart LR
  subgraph GPU_fragment["Fragment shader — ordered stages"]
    V[Default selected values\n0-3]
    S[HEALPIX_SELECT_VALUES\ncustom selection hook]
    F[Filter\non scalar modes]
    R[Rescale\non scalar modes]
    H[HEALPIX_RESCALE_VALUES\ncustom rescale hook]
    C[Color\nLUT when scalar / RGB / RGBA]
    D[DECKGL_FILTER_COLOR\nnormal deckgl pipeline]
  end
  V --> S --> F --> R --> H --> C --> D

Loading

Demos

A demo site is now available at https://deck.gl-healpix.ds.io/examples/sandbox/

[kylebarron]

ooo I like the idea of having shared components for your examples

[kylebarron]

I made developmentseed/deck.gl-raster#519 to do the same