glsl-gradient-palette
Module for creating gradient palettes for usage in glsl.
Last updated 5 years ago by erkaman .
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glsl-gradient-palette

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This module can be used to create gradient color palettes. These can be used to colorize noise functions and procedurally generate textures in shaders. Below is an example of such a procedural texture.

More examples can be found in the provided demo

Usage

To create a gradient palette, you basically give the API a sequential list of colors. The API will then create a palette, by linearly interpolating between these colors. It is very easy to create a palette:

    var simple =  [
        [0.0, [1.0,0.0,0.0]],
        [0.5, [0.0,0.0,0.0]],
        [1.0, [0.0,0.0,1.0]],
    ];

    var opts =  {size:1024};

    simplePaletteTexture = createGradientPalette(gl,simple);

above, we create a palette where we first interpolate from red to black, and then from black to red. To be more specific, From 0.0 to 0.5 we interpolate between the RGB colors [1.0,0.0,0.0] and [0.0,0.0,0.0], and from 0.5 to 1.0 we interpolate from [0.0,0.0,0.0] to [0.0,0.0,1.0]. The palette we just have created will look like this:

in the upper parts of the image, we can see the palette, and below, we see what happens if we use the palette to colorize a noise function.

It is easy to use the created palette in a shader. createGradientPalette will return the created palette as a texture(as a gl-texture2d), and this texture can be sent to a shader by doing

   sphereShader.uniforms.uPalette = simplePaletteTexture.bind()

now we can use it to colorize a noise function by sampling from it, based on the noise value:

   float t = noise(vPosition);
   vec3 tex =   texture2D(uPalette, vec2(t, 0.0) ).xyz;

and that results in the textured sphere seen above.

By specifying more colors, we can create more advanced textures. For instance, the palette


    var fireball =  [
        [0.0, [0.4,0.4,0.4]],
        [0.55, [0.0,0.0,0.0]],
        [0.60, [1.0,0.0, 0.0]],
        [0.70, [1.0,1.0, 0.0]],
        [1.0, [0.4,0.4, 0.0]]
    ];

results in

API

function createGradientPalette(gl, gradientList[, opts])

Creates a gradient palette, and returns the created palette stored as a gl-texture2d, with a default size of 1024x1.

  • gl your WebGL context.
  • gradientList the list of colors to use when creating the palette. See the previous section for more details.
  • opts optional arguments objects. Can currently only contains the property opts.size, which specifies the width of the created palette texture. Defaults to 1024.

paletteDrawer = new PaletteDrawer(gl, position, size )

Creates a palette drawer, that can be used for drawing a palette texture on the screen. Useful for visualising a palette.

  • gl your WebGL context.
  • position the pixel position where your palette drawer will be drawn. Stored as an array [x,y].
  • size the pixel size of your palette drawer. Stored as an array[x_size,y_size].

paletteDrawer.draw(paletteTexture, canvasWidth, canvasHeight)

Draws a palette texture as a simple quad.

  • paletteTexture the palette texture to draw.
  • canvasWidth the width of the canvas.
  • canvasHeight the height of the canvas.

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