bitbash

Come let us arrange
These lovely flowers in the bowl
Since there is no rice
- Basho

Create BMP files from scratch using pure bash. No external dependencies.

Currently used in BitBar plugins like mtop to draw small graphs to display on the Mac OS menubar.

Usage

bitbash supports two versions of BMP files.

• Version 1 corresponds to BITMAPINFOHEADER as described on Wikipedia. This is the most compatible version of BMP, but most viewers don't honour the alpha channel.
• Version 5 corresponds to BITMAPV5HEADER, which officially supports alpha.

Note that file doesn't recognize the v5 files we make, or that ImageMagick makes, but Preview et al do.

Drawing primitives set the current color. No alpha blending is done.

pixels=()             # set pixels to empty or with background of same size
                      # as will be declared in init_bmp
curcol=(bb 66 44 aa)  # set current color, BGRA, hex (%02x)
init_bmp 1 25 16      # initialize BMP, version 1 width 25 height 16
                      # if pixels not valid, initialize to $curcol
curcol=(00 00 00 ff)  # set current color to fully opaque black
point $x $y           # set ($x, $y) to $curcol. (0, 0) is bottom left
line $x1 $y1 $x2 $y2  # draw horizontal or vertical line
rect $x $y $w $h      # draw rectangle. ($x, $y) is bottom left
fill $x $y $w $h      # draw filled rectangle. ($x, $y) is bottom left
output_bmp            # output BMP to stdout

Examples

Swiss flag

pixels=()                   # clear pixels
curcol=(00 00 ff ff)        # set color to red
init_bmp 1 32 32            # declare 32x32 BMP, version 1
fill 0 0 $width $height     # fill the whole thing with red (current color)
curcol=(ff ff ff ff)        # set color to white
fill 13 6 6 20              # vertical stripe
fill 6 13 20 6              # horizontal strip
output_bmp >/tmp/flag.bmp   # write BMP to file

produces this 32x32 BMP:

Bar graph

pixels=()                                               # clear pixels
curcol=(00 00 00 00)                                    # transparent back
init_bmp 5 25 16                                        # 25x16, v5
curcol=(00 00 00 ff)                                    # opaque black
fill 0 0 $width 2                                       # 2px bottom border
line 0 $((height - 1)) $((width - 1)) $((height - 1))   # 1px top border
heights=(0 1 2 3 4 5 6 7 8 9 10 11 12 13 12 11 8 4 0 0) # height of bars
for ((i = 0; i < ${#heights[@]}; i++)); do
    line $i 1 $i $((1 + ${heights[$i]}))                # draw 1px bars
done
output_bmp >/tmp/graph.bmp                              # write BMP to file

produces the following 25x16 BMP: