gistfile1.js

var behaviours = {
	select: {
		onstart: function(p) {
			this.from = alignPos(this, p);
			this.workspace.viewer.unselect();
		},
		onresume: function(p) {
			if (this.from) {
				this.mousemoved = true;
				updateSelection(this, p);
			}
		},
		onfinish: function(p) {
			if (this.from) {
				if (this.mousemoved) {
					updateSelection(this, p);
				} else {
					this.workspace.unselect();
				}
				delete this.mousemoved;
				delete this.from;
			}
		}
	}
};

function alignPos(ctx, p) {
	var gridSize = ctx.workspace.viewer.gridSize;
	return {
		x: p.x - (p.x % gridSize),
		y: p.y - (p.y % gridSize)
	};
}

function updateSelection(ctx, p) {
	var viewer = ctx.workspace.viewer;
	var gridSize = viewer.gridSize;
	var compo = viewer.compo;
	var to = alignPos(ctx, p);
	if (from.x <= to.x) {
		to.x += gridSize;
	}
	if (to.x < 0) {
		to.x = 0;
	} else if (compo.width < to.x) {
		to.x = compo.width - compo.width % gridSize;
	}
	if (from.y <= to.y) {
		to.y += gridSize;
	}
	if (to.y < 0) {
		to.y = 0;
	} else if (compo.height < to.y) {
		to.y = compo.height - compo.height % gridSize;
	}
	viewer.select(from.x, from.y, to.x, to.y);
}