24bit color -> 6bit color dithering library for Pebble. Tested on Aplite, Basalt and Chalk. Should be forward compatible with Diorite, Emery and future watches.

Draws a filled rectangle to the screen which is dithered from 24bit (3 channels of 8bit colors: red, green and blue) color down to Pebble's native 6bit color.

Also can replace screen colors with the dithered color, allowing you to use native pebble API calls (e.g. graphics_draw_line, graphics_fill_circle, gpath_draw_filled, etc.) with dithered colors. To do this, draw with the Pebble function using a placeholder color that doesn't occur anywhere else on the screen, then call replace_color_with_dithered (see: below) to replace that placeholder color with the dithered color. Or use replace_color_in_rect_with_dithered to only replace colors within a screen region.

Currently it does not work on antialiased shapes, unless you specifically replace each color. For instance, if you draw an antialiased red (GColorRed=0b11110000) line on a black background, you'd have to run the replacement funciton 3 times: once for red, once for darker red (GColorDarkCandyAppleRed=0b111000) and once for darkest red (GColorBulgarianRose=0b11010000). Each will be replaced with the full dithered color, so the input 24bit RGB must be darkened to reproduce the antialiased look.

##Screenshots
Aplite:

Basalt:

Chalk:

##Function calls
#####fill_rect_dithered(ctx, rect, r, g, b)
Given a graphics context, a rect (absolute screen coordinates), and a 24bit RGB color, draws a rectangle filled with a dithered (patterned) 6-bit color. Note that rect uses absolute screen coordinates, unlike graphics_fill_rect() which draws relative to its layer.

#####replace_color_with_dithered(ctx, replacement_color, r, g, b)
Given a graphcs context, a color to look for, and a 24bit RGB dithered color to replace it with, searches the ENTIRE SCREEN for replacement_color and replaces it with a 6bit color dithered from the 24bit RGB given. Note that it currently doesn't ignore the alpha channel, though screen pixels are nearly always alpha = 3.

#####replace_color_in_rect_with_dithered(ctx, rect, replacement_color, r, g, b)
Same as replace_color_with_dithered() but only searches within the rect for replacement_color. Note that rect uses absolute screen coordinates, unlike normal Pebble API functions (e.g. graphics_fill_rect()) which draw relative to their layer.