Fix center of light halo for non-square LightWidgets.

src/app/LightWidget.cpp

@@ -69,15 +69,16 @@ void LightWidget::drawHalo(const DrawArgs& args) {
 	if (color.r == 0.f && color.g == 0.f && color.b == 0.f)
 		return;
 
+	math::Vec c = box.size.div(2);
 	float radius = std::min(box.size.x, box.size.y) / 2.0;
 	float oradius = radius + std::min(radius * 4.f, 15.f);
 
 	nvgBeginPath(args.vg);
-	nvgRect(args.vg, radius - oradius, radius - oradius, 2 * oradius, 2 * oradius);
+	nvgRect(args.vg, c.x - oradius, c.y - oradius, 2 * oradius, 2 * oradius);
 
 	NVGcolor icol = color::mult(color, halo);
 	NVGcolor ocol = nvgRGBA(0, 0, 0, 0);
-	NVGpaint paint = nvgRadialGradient(args.vg, radius, radius, radius, oradius, icol, ocol);
+	NVGpaint paint = nvgRadialGradient(args.vg, c.x, c.y, radius, oradius, icol, ocol);
 	nvgFillPaint(args.vg, paint);
 	nvgFill(args.vg);
 }