So, I have a plane sprite with 24 angles. The planeRot value can thus be an integer in the range 0..23, inclusive.

I managed to translate the crank degrees to this 24-angle coordinate system: crankRot.

Now, I can easily check whether the plane should rotate to point in the same direction as the crank:

if planeRot == crankRot then
-- nothing to do
else
-- rotate plane left or right??
end

Given that the plane is allowed to rotate one step per frame, How to calculate whether the the plane should rotate counter-clockwise or clockwise?
To rephrase the question: how do I create an algorithm that would output -1 if crankRot can be reached from planeRot in fewer steps by rotating counter-clockwise that rotating clockwise?

I guess @matt might have solved this problem ages ago for Daily Driver
(or perhaps he doess not have that one-step-per-frame limitation and can simply call planeRot = crankRot)

Excellent. Thanks for the Google-fu, these kind of problems are doable but hard to wrap your head around at the end of the day. Let alone feel confident that you have the most efficient solution. I do unittest, so I can feel confident that the implementation is correct, at least. I also tend to forget that the gamedev stackoverflow exists. So thanks!

for those interested, here is my little testing framework:

--- calculate the shortest distance to reach destRotation from startRotation
--- assumes a circle with 24 angles, so that angle 0 == angle 24 and the maximum angle is 23
--- example: smallestPlaneRotation(23, 1) => -2
function smallestPlaneRotation(destRotation, startRotation)
return ((destRotation - startRotation) + 12) % 24 - 12
end
local function test(expected, actual, description)
if expected ~= actual then
print(description)
error(string.format("Expected %s, got %s", expected, actual))
end
end
local smallestPlaneRotation <const> = smallestPlaneRotation
local function smallestRotationTest(destRotation, startRotation, expected)
test(expected, smallestPlaneRotation(destRotation,startRotation), table.concat({ "smallestRotation", destRotation, startRotation }, ", " ))
end
smallestRotationTest(6,5, 1)
smallestRotationTest(5,6, -1)
smallestRotationTest(23, 0 , -1)
smallestRotationTest(0,23, 1)
smallestRotationTest(1, 23, 2)
smallestRotationTest(23, 1, -2)
smallestRotationTest(0, 12, -12) -- equal distance, result sign doesn't matter