noa-engine/src/components/position.js

Experimental voxel game engine

/** 
 * @module 
 * @internal 
 */

import vec3 from 'gl-vec3'



// definition for this component's state object
export class PositionState {
    constructor() {
        /** Position in global coords (may be low precision) 
         * @type {null | number[]} */
        this.position = null
        this.width = 0.8
        this.height = 0.8

        /** Precise position in local coords
         * @type {null | number[]} */
        this._localPosition = null

        /** [x,y,z] in LOCAL COORDS
         * @type {null | number[]} */
        this._renderPosition = null

        /** [lo,lo,lo, hi,hi,hi] in LOCAL COORDS
         * @type {null | number[]} */
        this._extents = null
    }
}




/**
 * 	Component holding entity's position, width, and height.
 *  By convention, entity's "position" is the bottom center of its AABB
 * 
 *  Of the various properties, _localPosition is the "real", 
 *  single-source-of-truth position. Others are derived.
 *  Local coords are relative to `noa.worldOriginOffset`.
 * @param {import('..').Engine} noa
*/

export default function (noa) {

    return {

        name: 'position',

        order: 60,

        state: new PositionState,

        onAdd: function (eid, state) {
            // copy position into a plain array
            var pos = [0, 0, 0]
            if (state.position) vec3.copy(pos, state.position)
            state.position = pos

            state._localPosition = vec3.create()
            state._renderPosition = vec3.create()
            state._extents = new Float32Array(6)

            // on init only, set local from global
            noa.globalToLocal(state.position, null, state._localPosition)
            vec3.copy(state._renderPosition, state._localPosition)
            updatePositionExtents(state)
        },

        onRemove: null,



        system: function (dt, states) {
            var off = noa.worldOriginOffset
            for (var i = 0; i < states.length; i++) {
                var state = states[i]
                vec3.add(state.position, state._localPosition, off)
                updatePositionExtents(state)
            }
        },


    }
}



// update an entity's position state `_extents` 
export function updatePositionExtents(state) {
    var hw = state.width / 2
    var lpos = state._localPosition
    var ext = state._extents
    ext[0] = lpos[0] - hw
    ext[1] = lpos[1]
    ext[2] = lpos[2] - hw
    ext[3] = lpos[0] + hw
    ext[4] = lpos[1] + state.height
    ext[5] = lpos[2] + hw
}