GTKD - Get the size of the context

[TheDGuy via Digitalmars-d-learn]

Thank you very much for your answer! I really appreciate it 
because it is kind of hard to find explanations for GTKD.

But know i face a strange problem:

	this(Vector3D camera, Context cr, Widget widget){
		this.camera = camera;
		this.cr = cr;
		this.widget = widget;

		GtkAllocation size;
		widget.getAllocation(size);
		this.width = size.width;
		this.height = size.height;
	}
	void restartProgressiveRendering(){
		int[this.width*this.height*3+1] space;
		this.accumulator = space;
	}

I get the error "value of 'this' is not known at compile time" 
which refers to the line where i create the int-array "space"
Why is it not possible to use it there?