Color-Map Overhaul

[chr5tphr]

• added ColorMap, which are objects created from a color-map specification language (cmsl), which specifies linearly interpolated colormaps
• added LazyColorMapCache, which stores, compiles and caches color maps on demand
• implement existing built-in color maps with cmsl
• implement CMAPS (dictionary of built-in color maps) with a LazyColorMapCache object
• implement get_cmap, which is a convenience function used everywhere where color maps are required and returns a ColorMap object either by looking up its name in the built-in color maps, creates a new one if it is valid cmsl code, or returns the passed ColorMap if it already receives an instance
• added 4 new built-in color maps based on #19

cmsl are comma-separated hexa-decimal values, with an arbitrary index before each value. If no index is specified, the indices of the colors are evenly spaced from 0 to 255, or between their neighbors with indices.

A color-map from blue to white to red may be specified equivalently as

• 00f,000,f00
• 00f,80:000,f00
• 0000ff,000,ff:f00
• 00:f00,80:000000,ff:ff0000.

If the first and last indices are not zero, they are assumed to not change until the respective boundaries, ie. a color map which only shows the sign as either blue or red may be specified as

• 79:00f,80:f00

If indices are supplied, they must be in ascending order from left to right.

Built-in color-maps are implemented as

sources = {
    # black to white
    'gray': '000,fff',
    # white to red
    'wred': 'fff,f00',
    # white to blue
    'wblue': 'fff,00f',
    # black to red to yellow to white
    'hot': '000,f00,ff0,fff',
    # black to blue to cyan
    'cold': '000,00f,0ff',
    # combination of cold (reversed) and hot, centered around black
    'coldnhot': '0ff,00f,80:000,f00,ff0,fff',
    # combination of wblue (reversed) and wred, centered around white
    'bwr': '00f,80:fff,f00',
    # red to white to blue as in the french flag
    'france': '0055a4,80:fff,ef4135',
    # red to white to blue with brightness 0xd0
    'seismic': 'd00000,80:d0d0d0,0000d0',
    # cyan to white to magenta with brightness 0xd0
    'coolio': '00d0d0,80:d0d0d0,d000d0',
    # green to white to magenta with brightness 0xd0
    'coleus': '00d000,80:d0d0d0,d000d0',
}

Here is an example of all built-in color-maps visualized:

In order: - `gray` - `wred` - `wblue` - `hot` - `cold` - `coldnhot` - `bwr` - `france` - `seismic` - `coolio` - `coleus`