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// uses shadowcasting to calculate lighting at specified position
function LightSource(position, radius) {
this.tiles = [];
this.position = position;
this.radius = radius;
// multipliers for transforming coordinates into other octants.
this.mult = [
[1, 0, 0, -1, -1, 0, 0, 1],
[0, 1, -1, 0, 0, -1, 1, 0],
[0, 1, 1, 0, 0, -1, -1, 0],
[1, 0, 0, 1, -1, 0, 0, -1]
];
// calculates an octant. Called by the this.calculate when calculating lighting
this.calculateOctant = function(cx, cy, row, start, end, radius, xx, xy, yx, yy, id) {
map.data[cx][cy].lit = true;
map.data[cx][cy].unseen = false;
map.data[cx][cy].draw(this.position, radius);
this.tiles.push(map.data[cx][cy]);
var new_start = 0;
if(start < end) return;
var radius_squared = radius * radius;
for(var i = row; i<radius+1; i++) {
var dx = -i-1;
var dy = -i;
var blocked = false;
while(dx <= 0) {
dx += 1;
var X = cx + dx * xx + dy * xy;
var Y = cy + dx * yx + dy * yy;
if(X < map.size.x && X >= 0 && Y < map.size.y && Y >=0) {
var l_slope = (dx-0.5)/(dy+0.5);
var r_slope = (dx+0.5)/(dy-0.5);
if(start < r_slope) {
continue;
} else if( end > l_slope) {
break;
} else {
if(dx*dx + dy*dy < radius_squared) {
map.data[X][Y].lit = true;
map.data[X][Y].unseen = false;
map.data[X][Y].draw(this.position, radius);
this.tiles.push(map.data[X][Y]);
}
if(blocked) {
if(map.data[X][Y].blocksSight) {
new_start = r_slope;
continue;
} else {
blocked = false;
start = new_start;
}
} else {
if(map.data[X][Y].blocksSight && i < radius) {
blocked = true;
this.calculateOctant(cx, cy, i+1, start, l_slope, radius, xx, xy, yx, yy, id+1);
new_start = r_slope;
}
}
}
}
}
if(blocked) break;
}
}
// sets flag lit to false on all tiles within radius of position specified
this.clear = function () {
for(var i = 0; i<this.tiles.length; i++) {
this.tiles[i].lit = false;
this.tiles[i].draw();
}
this.tiles = [];
}
// sets flag lit to true on all tiles within radius of position specified
this.calculate = function () {
this.clear();
for(var i = 0; i<8; i++) {
this.calculateOctant(this.position.x, this.position.y, 1, 1.0, 0.0, this.radius,
this.mult[0][i], this.mult[1][i], this.mult[2][i], this.mult[3][i], 0);
}
map.tile(this.position).lit = true;
map.tile(this.position).unseen = false;
map.tile(this.position).draw();
this.tiles.push(map.tile(this.position));
}
// update the position of the light source
this.update = function(position) {
this.position = position;
this.clear();
this.calculate();
}
}
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