Ubasic - Canon Camera Hackers Manual

as soon as you load another script, the new script will run at start-up, so it
is necessary to reload flashoff.lua before switching off.
Many scripts can be configured with parameters. These parameters are
defined in the header section of the script. After the script has been loaded,
they are listed in the bottom section of the CHDK Script menu. The param-
eter values shown there can be modified with the LEFT,
SET keys. If a script has many parameters, it can be tedious to set up all the
parameters before running the script. The CHDK therefore offers the pos-
sibility to store frequently used parameter combinations in parameter sets.
Ten of those sets exist (0–9). By modifying the value of the menu entry
Parameters set, you can easily switch among different parameter combina-
tions.
5.2

uBasic

The original uBasic interpreter was written by the Swedish programmer
Adam Dunkels. He said, "I've always wanted to write a really small BASIC
interpreter. So I sat down for an hour or two and did it." It's probably true.
uBasic is tiny, and there are only a few commands to learn. The original
uBasic interpreter didn't even understand labels—instead you specified
line numbers as GOTO targets, just like in the days of the legendary C64.
Labels were later added by Pablo d'Angelo who is also the main contributor
for the Hugin panorama stitcher.
So, let's jump right into another small script and see how uBasic looks
these days. (A more systematic introduction into uBasic is given in the fol-
lowing sections.) The following script implements an electronic magnify-
ing glass by switching the camera into the Digital Macro mode and setting
a predefined magnification level. Also, most of the info texts are hidden
from the display.
@title Digital Magnifier
@param m Initial Magnification
@default m 3
This is the header section of the script. The title will appear at the bottom
of the display after the script is loaded. You should avoid using more than
24 characters; otherwise, the title would override the <ALT> indicator.
The title declaration is followed by the declaration of the parameters
providing input to the script. With the @param instruction, you specify a
variable name and a parameter description. Variable names for parameters
always consist of a single lower case letter. In newer CHDK versions, you
can have variable names from a–z, in older versions only a–j. The parame-
ter description is shown in the script menu
RIGHT, and FUNC/
(ALT > FUNC/SET) below the
5.2 uBasic
Figure 5-1
The CHDK Script menu. The upper half
is used for general script configuration,
such as script loading, delaying the
execution of the script for a specified
number of 1/10 secs, resetting to the
default parameter values, and
switching and saving parameter sets.
The lower half is reserved for the script
parameters. Here are some of the
parameters from the motion detection
script discussed in section 5.7.3
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