OpenLIME

Class: ShaderMultispectral

ShaderMultispectral

ShaderMultispectral - WebGL2 shader implementation for multispectral visualization

This shader handles the real-time rendering of multispectral imagery with various visualization modes and Color Twist Weight (CTW) transformations. It leverages WebGL2 features such as Uniform Buffer Objects (UBO) for efficient handling of CTW coefficients and texture() for consistent texture sampling.

Features:

  • Multiple rendering modes (RGB, single band)
  • UBO-based Color Twist Weights for spectral transformations
  • Optimized memory access by skipping zero-weight bands
  • Support for up to 33 spectral bands (11 RGB textures)
  • Compatible with both single images and tile-based formats (DeepZoom, etc.)

Technical implementation:

  • Efficient std140 UBO layout for CTW coefficients
  • Loop unrolling for faster rendering
  • Optimized band access with constant indices

new ShaderMultispectral( [options])

Creates a new multispectral shader

Parameters:
Name Type Argument Description
options ShaderMultispectralOptions <optional>

Configuration options
Source:

Extends

Methods

addFilter(filter)

Adds a filter to the shader pipeline.

Parameters:
Name Type Description
filter Object

Filter to add
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allUniforms()

Returns all uniform variables associated with the shader and its filters. Combines uniforms from both the base shader and all active filters into a single object.

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Combined uniform variables

Type
Object.<string, Object>

clearFilters()

Clears all filters from the shader pipeline.

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fragShaderSrc()

Generate fragment shader source code

Creates optimized GLSL code for multispectral visualization. Uses texture() with normalized coordinates instead of texelFetch.

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GLSL fragment shader source code

Type
string

getUniform(name)

Gets a uniform variable by name. Searches both shader uniforms and filter uniforms.

Parameters:
Name Type Description
name string

Uniform variable name
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Returns:

Uniform object if found

Type
Object | undefined

init(info)

Initializes shader with multispectral configuration

Sets up wavelength information, calculates the number of required textures, and configures samplers for each texture.

Parameters:
Name Type Description
info Object

Multispectral configuration object from info.json
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removeFilter(name)

Removes a filter from the pipeline by name.

Parameters:
Name Type Description
name string

Name of filter to remove
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setMode(mode)

Sets the rendering mode

Changes how multispectral data is visualized:

  • 'rgb': Uses CTW coefficients to create RGB visualization
  • 'single_band': Shows a single spectral band
Parameters:
Name Type Description
mode string

Visualization mode ('rgb', 'single_band')
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Throws:

If mode is not recognized

Type
Error

setSingleBand(bandIndex, outputChannel)

Sets single band visualization

Configures the shader to display a specific spectral band on a chosen output channel.

Parameters:
Name Type Default Description
bandIndex number

Index of band to view
outputChannel number 0

Output channel (0=all/gray, 1=R, 2=G, 3=B)
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Throws:

If band index is out of range

Type
Error

setTextureSize()

Sets texture dimensions for calculations

No longer needed since we're using normalized coordinates

Deprecated:
  • Use normalized texture coordinates instead
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setTileSize(size)

Sets tile dimensions for shader calculations.

Parameters:
Name Type Description
size Array.<number>

[width, height] of tile
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setUniform(name, value)

Sets a uniform variable value.

Parameters:
Name Type Description
name string

Uniform variable name
value number | boolean | Array

Value to set
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If uniform doesn't exist

Type
Error

setupCTW(gl, redCTW, greenCTW, blueCTW)

Sets up Uniform Buffer Object for Color Twist Weights

Creates and configures a UBO for efficient handling of CTW coefficients. Uses WebGL2's std140 layout for optimal performance.

Parameters:
Name Type Description
gl WebGL2RenderingContext

WebGL2 context
redCTW Float32Array

Red channel CTW coefficients
greenCTW Float32Array

Green channel CTW coefficients
blueCTW Float32Array

Blue channel CTW coefficients
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vertShaderSrc(gl)

Gets vertex shader source code. Default implementation provides basic vertex transformation and texture coordinate passing.

Parameters:
Name Type Description
gl WebGL2RenderingContext

WebGL2 context
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Returns:

Vertex shader source code

Type
string

Events

update

Fired when shader state changes (uniforms, filters, etc).

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