Impact Line of Sight

Information

This plugin for the Impact Game Engine adds line of sight to the collition map, which also can take entities in his calculations! I was trying to check the line of sight with the collision map trace function, but it is not working very well. Thats why I created this plugin.

Usage

Check the example/lib/game/entities/player.js and example/lib/game/entities/enemy.js!

The function

traceLos(x, y, vx, vy, objectWidth, objectHeight, entityTypesArray, ignoreEntityArray)

• x, y, vx, vy, objectWidth and objectHeight are the same as the trace function in collision map.
• entityTypesArray are the names of the entity types which should marked in the pixel collision map (Example: ['EntitySoldier', 'EntityEnemy', ...]).
• ignoreEntityArray are references of the entities which should be ignored (Example: [currentSodier, currentEnemy, ...]). For example if you try to get the line of sight from the middle of one entity to middle of another entity, this two must be ignorered!

Live demo

Check out: http://www.andreasgiemza.de/programmieren/javascript/impact-line-of-sight

Example

To change the level or work with the code, add in the example folder the missing libary files and folders:

lib/weltmeister/
lib/impact/
tools/
index.htmlw
weltmeister.html

Example image

How it works

init

• When a collision map is loaded, the plugin creates an pixel based collision map and adds the walls to it.

traceLos

• When you call the traceLos function it adds the entitiy types you want to the pixel based collision map.
• Then it uses the bresenham's line algorithm to check if the "lines" from the corners of the trace boxes are free in the pixel based collision map.
• After that it erases all the added entities from the pixel based collision map.
• And retuns true when there was an collision and when not false.

Example image for the line of sight checks

Color explanation

• Green are soldiers (EntitySoldiers)
• Red are enemies (EntityEnemies)
• Black is a wall
• The different blue lines are tested in the pixel based collison map, when a pixel is a wall or an entity their is no line of sight!

Code example

• The upper green soldier is currentSodier (This a reference on this soldier).
• The lower red enemy is the currentEnemy (This a reference on this enemy).

	var dx = currentEnemy.pos.x - currentSodier.pos.x;
	var dy = currentEnemy.pos.y - currentSodier.pos.y;

	var los = ig.game.collisionMap.traceLos(currentSodier.pos.x + currentSodier.size.x / 2 - 2, currentSodier.pos.y + currentSodier.size.y / 2 - 2, dx, dy, 4, 4, ['EntitySoldier', 'EntityEnemy'], [currentSodier, currentEnemy]);

The pixel based collision map

That is how the pixel based collision map look like for the example.

TODO

• Improve the line of sight check, because when objectWidth, objectHeight are very big and their are very small entities, they can slip through
• Collision layer changes are ignored (The collison map is loaded on the init!), this is NOT affecting entities
• Make a debug view
• Slopes support
• Make it faster

Changelog

v0.4.1

• added vars in traceLosDetailed()

v0.4.0

• Added traceLosDetailed, check the example how to use it (player.js)

v0.3.1

• Very little speedup (When there was an collision it doesn't check the other lines of sight!)

v0.3.0

• Adding and eraising of entities is now in a seperatet function
• _traceLosStep renamed to _traceLosLine
• _traceLosLine returns now the distance (Returns 0 when their was no collision and the distance when their was one, starting with 1!)
• Example added

v0.2.3

• Fixed the error when the check was outside the map

v0.2.2

• Fixed bug with objectWidth and objectHeight

v0.2.1

• objectWidth and objectHeight can be null now, without error
• Readme improved

v0.2.0

• Doesn't copy the pixel collision map anymore, adds the entities and after the check it erases them

v0.1.0

• First commit