ImpactJS Mixin That Adds Tile-Based Grid Movement to Entities

mixin-grid-movement.js

ig.module('plugins.mixin-grid-movement')
.requires()
.defines(function() {

    MixinGridMovement = {

        src_tile: null,
        dst_tile: null,

        grid_move: function(direction, seconds) {

            var valid_directions = ['UP', 'DOWN', 'LEFT', 'RIGHT', 'NONE'];
            if(valid_directions.indexOf(direction) === -1) {
                throw 'An invalid direction was provided.';
            }

            if(typeof seconds !== 'number') {
                throw 'The seconds argument must be a number.';
            }

            var tilesize = ig.game.collisionMap.tilesize;
            if(!tilesize) {
                throw 'The collision map must have a valid tilesize.';
            }

            var speed = this.speed || 64;

            // Start moving towards a tile
            if(this.src_tile === null && this.dst_tile === null) {

                if(direction === 'NONE') {
                    return;
                }

                var new_src_tile = {
                    x: this.pos.x / tilesize,
                    y: this.pos.y / tilesize
                };

                var new_dst_tile = ig.copy(new_src_tile);
                if(direction === 'LEFT') {
                    new_dst_tile.x -= 1;
                } else if(direction === 'RIGHT') {
                    new_dst_tile.x += 1;
                } else if(direction === 'UP') {
                    new_dst_tile.y -= 1;
                } else if(direction === 'DOWN') {
                    new_dst_tile.y += 1;
                }

                // Prevent travel if destination tile is a wall
                var data = ig.game.collisionMap.data;
                if(data[new_dst_tile.y][new_dst_tile.x] !== 0) {
                    return;
                }

                this.src_tile = new_src_tile;
                this.dst_tile = new_dst_tile;
            }

            // Move toward destination
            var mx = 0;
            var my = 0;
            if(this.pos.x < this.dst_tile.x * tilesize) {
                mx = seconds * speed;
            } else if(this.pos.x > this.dst_tile.x * tilesize) {
                mx = seconds * -speed;
            } else if(this.pos.y < this.dst_tile.y * tilesize) {
                my = seconds * speed;
            } else if(this.pos.y > this.dst_tile.y * tilesize) {
                my = seconds * -speed;
            }
            var res = ig.game.collisionMap.trace(
                this.pos.x, this.pos.y, mx, my, this.size.x, this.size.y
            );
            this.handleMovementTrace( res );

            if(typeof this.pos.x !== 'number' || typeof this.pos.y !== 'number') {
                throw 'The entity position was set to a non-number.';
            }

            var reached_destination = (
                (
                    // Right
                    this.src_tile.x < this.dst_tile.x &&
                    this.pos.x >= this.dst_tile.x * tilesize
                ) || (
                    // Left
                    this.src_tile.x > this.dst_tile.x &&
                    this.pos.x <= this.dst_tile.x * tilesize
                ) || (
                    // Down
                    this.src_tile.y < this.dst_tile.y &&
                    this.pos.y >= this.dst_tile.y * tilesize
                ) || (
                    // Up
                    this.src_tile.y > this.dst_tile.y &&
                    this.pos.y <= this.dst_tile.y * tilesize
                )
            );

            if(reached_destination) {
                
                // Calculate distance travelled beyond destination
                var distance_over = 0;
                if(this.src_tile.x !== this.dst_tile.x) {
                    distance_over = Math.abs(this.pos.x - (this.dst_tile.x * tilesize));
                } else if(this.src_tile.y !== this.dst_tile.y) {
                    distance_over = Math.abs(this.pos.y - (this.dst_tile.y * tilesize));
                }

                // Snap to destination tile
                this.pos.x = this.dst_tile.x * tilesize;
                this.pos.y = this.dst_tile.y * tilesize;

                if(typeof this.pos.x !== 'number' || typeof this.pos.y !== 'number') {
                    throw 'The entity position was set to a non-number.';
                }

                this.src_tile = null;
                this.dst_tile = null;

                var time_over = distance_over / speed;
                if(time_over > 0) {
                    this.grid_move(direction, time_over);
                }
            }
        }
    };
});