# Weird Shadow effects with a moving directional light (sun)

Hi everyone

I was implementing a TimeSystem into my game which internally increases a counter every 1/60 second. At the moment one in-game-hour has 3600 ticks, which is a minute in real-time. Therefore, the maximum tick count is 86400 (24 In-Game-Hours/In-GameDay * 3600 Ticks/In-Game-Hour). The count 0 means an in-game-time of 6 am. The TimeSystem notifies all listeners if the ticks changed, one of the listeners being the LightingState. This one calculates the new light direction like so:

``````float timeOfDay = FastMath.PI / (2f * 21600) * ticks;
float x = FastMath.cos(timeOfDay) * HORIZONTAL_AMPLITUDE;
float y = FastMath.sin(timeOfDay) * VERTICAL_AMPLITUDE;
float z = FastMath.sin(timeOfDay) * HORIZONTAL_AMPLITUDE;
direction.set(x, y, z);
directionalLight.setDirection(direction.negate());
``````

The tick count of 21600 corresponds to 12 am (where sun is at the highest point). I am using a DirectionalLightShadowFilter for shadows, and it works fine if the directional light doesnĀ“t change its direction. But when changing the direction with the above code I get weird shadows.

I have tried changin the shadow map resolution and using a DirectionalLightShadowRenderer instead of a Filter. Nothing worked, but I canĀ“t see the problem. The light is changing like is supposed it (at least I canĀ“t see any mistakes in the calculation, PLS correct me if I am wrong).

So any ideas what might be the problem?

I suggest to use a range limit for the shadows, as else you will get all kinds of interesting/strange effects.

May you shortly explain what it does? And what is a good value?

Also:
directionalLight.setDirection(direction.negate().normalizeLocal());

Though the way you calculate the lighting direction is going to create really strange arcs, I thinkā¦ since they are all calculated independently. Would be better to use quaternion and multiply a fixed vector to get direction.

Similar to your SimFx Lighting State? Already looked there, but thought this sin and cos would do their job
Well then, IĀ“ll try to use quaternions for that and post again if I get stuck.

They could but not the way you have them. Presumably you want a straight arc overhead but tilted at some angle off of directly vertical. In that case, youād have to first calculate the regular arc:
x = cos(angle)
y = sin(angle)
z = 0
ā¦and then rotate that position again north/southā¦ which is more complicated than I want to write here since Iād just use a quaternion for it.

Keep an angle for time of day and an angle for āplanet tiltā or āseasonā or whatever. Assuming you want the sun to rise and set in +x/-x then I think you can even do it with one fromAngles() call.

timeAngle = 0 to 2 * PI = midnight to midnight.
seasonAngle = -QUARTER_PI to +QUARTERPI = winter to summer or summer to winterā¦ not sure.

rot = new Quaternion().fromAngles(seasonAngle, 0, timeAngle);
dir = rot.mult(Vector3f.UNIT_X);

I think.

it fades the shades to invisible, and increases the resolution in the now smaller range / together with limit)

I found 50-100meter for larger ground terrains to be a nice value. this makes the shadows vanish slowly enough to not be that noticeable, but still saves quite a lot of distance and inaccuracy, especially for larger frustrums.