Slow Glass Directives

Directives are instructions that affect the operation of Slow Glass as a whole, or help structure the script into parts that can be re-used.

The following directives are supported:

display width / height

display width {integer}

dipslay height {integer}

display fullscreen (*)

Sets the width and height of the HTML Canvas object that the animation will be drawn on.

The current display size can be accessed through the variables $WIDTH and $HEIGHT

(*) Not implemented yet

script width / height

script width {integer}

script height {integer}

script scale (fit | stretch | none) (*)

This is optional, but if your script has assumed a particular size for the drawing area you can specify this here. You can also choose how the script coordinates are mapped on to the actual drawing area. The options are:

• stretch - the x and y coordinates are indenpendently scaled so the script fills the drawing area
• fit - the coordinates are uniformly scaled so that the script fits into the drawing area, possibly leaving unused areas at the side or bottom depending on the aspect ratio
• none - (the default) just use the script coordinates unchanged (i.e. if the script assumes a smaller area, it will just be drawn in the top left)

(*) “fit” not yet implemented, other options may be added also

Global Options

There are some options which can be set that apply throughout the whole of the script. These options are:

option lat {number}

option lon {number}

These options allow you to set the latitude and longitude that Slow Glass should use in its calculation of hemisphere, season and sun angle. It defaults to the lat and lon of London, England.

option evaluator (basic | advanced)

This switches the evaluation function between a https://bugwheels94.github.io/math-expression-evaluator/ to a https://github.com/toggledbits/lexpjs.

Given that simplicity was the intention of Slow Glass the basic evaluator should hopefully be sufficient for most things, however it does not support comparisons, string operatios or complex logical expressions. The advanced option does these things but you need to be very careful with syntax and, for example, ensure that strings are enclosed in quotes.

end file

end file

This is just a convenience directive that causes Slow Glass to ignore everything in the file beyond this point, even if it is valid script.

You can use this feature to include free text content after your script, although there are more flexible commenting systems available (see below).

scene / end scene

scene {name}

end scene

These directives are used to split your script into smaller, reusable parts. A scene is introduced with the “scene” directive, which must be followed by a single word which is used as the name of the scene. You can end a scene with the “end scene” directive, or (since scenes cannot be nested) you can just start a new scene.

Scenes are NOT started automatically, they must be started using the “start” action.

Note that any triggers and actions that are NOT in a named scene are considered to be in the “top level” scene, which is given the name “_MAIN_”. There must be at least one trigger and one action in the top level scene otherwise nothing will happen! Typically you will have several named scenes which are started and stopped by actions in the top level scene.

Documentation

Documentation is always a good thing! Slow Glass gives you a lot of flexibility in documenting your code. In addition to the different commenting styles discussed below you can include a longer section of descriptive text anywhere in your script file, introduced by the directive:

description

All content lines after this directive will be completely ignored by the command processor, until it finds the corresponding directive:

end description

You can have as many description sections as you like, of any length, although putting one at the top of each file might be useful!

Comments

Comments aren’t really directives as such but discussion of them seems to fit best here as they are also a means of structuring your scripts

Ignored lines

Lines begining with ‘#’ (hash, or octothorpe) are completely ignored. You can have whitespace in front the hash but no other content, hence in the action:

text greeting colour #00ff00

The hash does NOT introduce a comment and will be treated as normal text.

Blank lines are ignored.

Finally, lines that do not contain any alphabetic characters are also ignored. This means that you can break up your file with lines such as:

======================================

Without having to explicitly put them into comments.

Programmer’s style comments

To add documentation to your code you can use two variations of programmer style comments.

Any content on a line after two slash characters will be ignored:

start my-scene // this is ignored

Also, anything enclosed between /* and */ will be ignored, even if it spans over multiple lines.

/*******
This content will be ignored
********/