How can I create a custom physics data for my game?

An exporter consists of 2 files:

exporter.xml - the description of the exporter itself
template.txt - a template file containing the file layout

The exporters shipped with PhysicsEditor are located inside the application's folder in a folder called exporters.

To add your own exporter you can simply point PhysicsEditor's preferences to a location where you want to keep your custom exporters.

exporter.xml

Let's first have a look at the exporter.xml. This file describes the basic information about the exporter itself.

PhysicsEditor scans the exporter directories with each start. If you change the directory location in the preferences or make some changes in the exporter.xml you need to restart PhysicsEditor. If you change the contents template file there is no need for restarting - it is read with each export.

The exporter.xml is - as the name already says - an xml file.

It has 4 main blocks:

Global exporter settings - settings for the exporter itself
Global parameters - settings for all bodies - e.g. gravity
Body parameters - settings for one body - e.g. body name, type, ...
Fixture parameters - settings for a single fixture - e.g. bounce rate of the head

Global exporter parameters

Element	Type	Info
`<name>`	string	Identifier for the exporter, must be unique. Otherwise the lastest exporter found for that name will overwrite the others.
`<displayName>`	string	This is how the exporter's name is displayed in the combo box in the GUI
`<description>`	string	Some information about the exporter
`<version>`	string	Exporter version - should be build from digits separated with dots - e.g. 1.0 or 1.0.1
`<yAxisDirection>`	`up` / `down`	Direction of the yAxis
`<physicsEngine>`	`box2d` / `chipmunk` / `generic`	Name of the physics engine used. This currently set the polygon orientation.
`<template>`	string	Name of the template file - relative to the exporter.xml
`<fileExtension>`	string	File extension used when exporting the data file

Anchor Points

PhysicsEditor with AnchorPoint in cocos2d exporter

AnchorPoints can be used as the center of a sprite - e.g. for rotation or move operations. When setting the origin to anchorPoint it is also possible to center.

Additional global parameters are anchor points:

Element	Type	Info
`<enabled>`	`yes` / `no`	Display and use anchor points for this exporter
`<relX>`	float	Relative position of the anchor points x position
`<relY>`	float	Relative position of the anchor points y position

Origin

Origin - the 0/0 location of the sprite. This might be set to a fixed position or to the anchor point.

Element	Type	Info
`<type>`	`fixed` / `anchorPoint`	Fixed sets a fixed relative position to the sprite's size, anchorPoint uses the AnchorPoint as sprite's center
`<relX>`	float	Relative position of the origin x position
`<relY>`	float	Relative position of the origin y position

Parameter blocks

There are 3 parameter blocks which can be used to define properties and values on file base, per body and per fixture.

Element	Type	Info
`<global>`	list of `<parameter>`	The global parameters used for the complete file - e.g. gravity
`<body>`	list of `<parameter>`	Parameters used for an individual body
`<fixture>`	list of `<parameter>`	Parameters used on an individual fixture. Might be multiple sub-fixtures in case the fixture is decomposed into convex parts.

Parameter definitions

In each of the elements <global>, <body> and <fixture> 0 or more parameters can be defined.

Values for all parameters

These elements must be present for all parameters and define their appearance in the GUI.

Element	Type	Info
`<name>`	string	Name of the value (used in the template)
`<displayName>`	string	Human readable name of the value (used in the user interface)
`<description>`	string	Description of the element used in the tooltip when hovering over the element for some time
`<shortDescription>`	string	Short description of the element used in the status bar when hovering over the element
`<type>`	`bool`, `string`,`float`, `int`, `uint16`, `bitfield`	Type of the parameter - which adds additional fields
`<bitfield>`	`yes`, `no`	Connects a value to an existing bit field

bool

Element	Type	Info
`<type>`	`bool`	Defines a bool input field / Checkbox
`<default>`	`false` / `true`	The default value

<parameter>
    <name>isSensor</name>
    <displayName>Is Sensor</displayName>
    <description>The object only detects collisions without colliding</description>
    <shortDescription>Turns the fixture into a sensor</shortDescription>
    <type>bool</type>
    <default>false</default>
</parameter>

string

Element	Type	Info
`<type>`	string	Defines a string input field
`<default>`	string	The default value which is used if nothing else is entered

<parameter>
    <name>fixture_id</name>
    <displayName>Identifier</displayName>
    <description>Identify a fixture during collision detection</description>
    <shortDescription>Identifier for the fixture</shortDescription>
    <type><code>string</code></type>
    <default>fixture123</default>
</parameter>

float

Element	Type	Info
`<type>`	float	Defines a float input field
`<default>`	float	The default value
`<min>`	float	Minimum value
`<max>`	float	Maximum value

<parameter>
    <name>density</name>
    <displayName>Density</displayName>
    <description>
        Density of the fixture, results in the mass if multiplied with the fixture's area
    </description>
    <shortDescription>Density of the fixture</shortDescription>
    <type>float</type>
    <min>-1000</min>
    <max>1000</max>
    <default>2.0</default>
</parameter>

int / uint16

Element	Type	Info
`<type>`	`int`	Defines a int input field
`<default>`	int	The default value

<parameter>
    <name>filter_groupIndex</name>
    <displayName>Group</displayName>
    <description>
        Collision group - objects which have collision enabled need to be in the same collision group
    </description>
    <shortDescription>The collision group</shortDescription>
    <type>int</type>
    <default>0</default>
</parameter>

BitField

The bit field is a more complicated structure and might get a better XML representation some day.

It works quite simple for now. First you need to define a bitfield parameter which holds the other values. The values themselves get an additional field <bitfield>yes</bitfield> which connects them to the bit field.

Make sure to match the size of the values to the <size> value in the bitfield definition.

Element	Type	Info
`<type>`	`bitfield`	Defines a bitfield input
`<size>`	int	The number of bits usually 16 or 32

<parameter>
    <name>filter_bitfield</name>
    <type>bitfield</type>
    <size>16</size>
</parameter>
<parameter>
    <name>filter_categoryBits</name>
    <displayName>Cat.</displayName>
    <description>Collision category</description>
    <shortDescription>Collision category</shortDescription>
    <type>uint16</type>
    <default>1</default>
    <bitfield>yes</bitfield>
</parameter>
<parameter>
    <name>filter_maskBits</name>
    <displayName>Mask</displayName>
    <description>Collision mask</description>
    <shortDescription>Collision mask</shortDescription>
    <type>uint16</type>
    <default>65535</default>
    <bitfield>yes</bitfield>
</parameter>

Data structure

Top level objects

Value	Description
`global`	Contains all generic parameters defined in `<global>`
`bodies`	Contains all bodies as `body` objects

Body

A body object holds all the bodies defined in PhysicsEditor. Here's a table of the built in values. Values defined in the <body> section of the exporter.xml are added to the object.

Value	Description
`anchorPointRel.x`	Anchorpoint's `x` coordinate relative to the sprite's size.
`anchorPointRel.y`	Anchorpoint's `y` coordinate relative to the sprite's size.
`anchorPointAbs.x`	Anchorpoint's `x` coordinate in pixels.
`anchorPointAbs.y`	Anchorpoint's `y` coordinate in pixels.
`body.size.width`	The body's width in pixels. Same as sprite width.
`body.size.height`	The body's height in pixels. Same as sprite width.
`body.fixtures`	List of body's `fixture` objects.

Fixture

A fixture object holds all the fixtures defined in a body. Here's a table of the built in values. Values defined in the <fixture> section of the exporter.xml are added to the object.

Value	Description
`type`	Type of the fixture `POLYGON` or `CIRCLE`
`isCircle`	Convenience function to check if the fixture is a circle

Circle-Fixture

These additional values are available inside circle fixtures.

Value	Description
`fixture.radius`	The radius of the shape in pixels
`fixture.center.x`	Circle's center coordinate, x value
`fixture.center.y`	Circle's center coordinate, y value

Polygon-Fixture

These additional values are available inside polygon fixtures.

Value	Description
`fixture.hull`	All points as a single `polygon` object - may be concave. Order of the points depends on the physics engine set in the exporter.xml
`fixture.polygons`	List of convex `polygon` objects after convex decomposition.

Polygon

A polygon is a list of point objects:

Value	Description
`x`	x coordinate of a vertex in pixels
`y`	y coordinate of a vertex in pixels

The Template

I am using the GrantLee template system, which is close to Django templates. The basics are available from the GrantLee documentation.

A good starting point is the plain text exporter which is part of PhysicsEditor's distribution - since it contains all variables and features.

Referencing values

You can access 2 types of values

Build in values
Values that are added through parameters in exporter.xml

Values are surrounded by {{ and }}

Sub values are separated by ..

You might use | after the value itself to use filters for changing the value itself. Please have a look a the GrantLee documentation for more details about that.

Template	Output	Remark
`gravity={{global.gravity}};`	`gravity=9.800000;`	This uses the `gravity` property from the `global` object and insers it into the template. (Gravity is a custom property.)
`gravity={{global.gravity\|floatformat:3}};`	`gravity=9.800;`	Same as above with shortening the float value to 3 digits.

Control structures

Control-Structure: if

{% if condition %} ... {% else %} ... {% endif %}

Control-Structure: for

{% for object in objectList %} ... {% endfor %}

Mixed example

This example prints a list of coordinates, separating each block with a , but not adding a comma before the first element of the list:

{% for point in fixture.hull %}
{% if not forloop.first %}, {% endif %}({{point.x}}, {{point.y}})
{% endfor %}