# Spec: tileset

Tilesets are files that are used to draw a map by copying individual cells from
an image into the screen by repeating those. A unique tileset can be reused by
several maps to avoid recreating every collision and animations each time a new
map is created.

They can be used directly as C code but can be written and read from files as
well.

Tilesets consists of:

- An image to use as a sprite,
- Dimensions of individual cells in that image,
- Set of animations for specific tiles,
- Set of collision masks for specific tiles.

Tilesets have an extension of `.tileset`.

## File format

The file format is a simple plain text where each each line consist of a
directive.

!!! caution
    Order is important. You must make sure that every directives are listed in
    the same order.

The file format must be defined as following where each ``<>`` must be replaced
by the appropriate C type name.

    tilewidth|<unsigned int>
    tileheight|<unsigned int>
    image|<const char *>
    tiledefs
    <unsigned short>|<int>|<int>|<unsigned int>|<unsigned int>
    ...
    animations
    <unsigned short>|<const char *>|<unsigned int>

Description of directives:

tilewidth
:   Cell width in the image.

tileheight
:   Cell height in the image.

image
:   Path to image to use (must be relative).

tiledefs
:   Start a list of tile definitions to describe a collision mask for a given
    tile. Each line after this directive describe a unique rectangle for one
    tile by specifying `tile id`, `x`, `y`, `width`, `height` in order.

    This section is optional and can be omitted entirely.

animations
:   Start a list of tile animations that should be used instead of drawing from
    the image sprite itself. Each line after this directive describe an animation
    for a given tile by specifying ``tile id``, ``animation file``, ``delay`` in
    order.

## Examples

The following file is a tileset using the image *world.png* that has 64x64
dimensions for each cell.

    tilewidth|64
    tileheight|64
    image|world.png

The following file adds some collision rectangles on tiles *3* and *5*. The
rectangle collision for the tile id *3* has dimensions of W=30, H=30, X=5, Y=5
and the rectangle for the tile id *5* has dimensions of W=10, H=15, X=10, Y=10.

    tilewidth|64
    tileheight|64
    image|world.png
    tiledefs
    3|30|30|5|5
    5|10|15|10|10

The following file adds an animation for the tile id *3* using the file
*animation-water.png* with a delay of *500* ms per tile.

    tilewidth|64
    tileheight|64
    image|world.png
    animations
    3|animation-water.png|500