Introducing Vertigo Vortex! Coming to you courtesy of "little" help from @JonB.
This demonstrates both visual warping and a vortex field effect.
You can read more about warping in Apple docs. Here I included a custom spiral warping effect, which resembles some of the shader effects except it is much nicer to code in Python than in the shader quasi-C.
Applying the effect:
spritenode.warp = WarpGrid(21,21).set_spiral(-math.pi*2)
Parameter of set_spiral tells how much the points on the outer circle move counter-clockwise; in the example case, full 360 degrees clockwise. Spiral effect then happens when points closer to the center are rotated less.
Sequences of warps can be animated, e.g. like this:
warps = [
WarpGrid(21,21).set_spiral(-math.pi/1.25/10*i) for i in range(11)
]
spritenode.run_action(Action.warps(warps, duration=3.0))
About the magic numbers 21,21 in the grid initialization - I do not know how detailed the grid must be, but I expect some detail is needed for most effects, as different grid sizes produce very different results. You can see the difference below, where all the images except the origonal apply the same 90-degree counter-clockwise effect, only with different level of granularity:
With the vortex physics field effect, I had to cheat, since I could not get the SpriteKit vortex field to work.
With field strength 0.003, the field was still throwing the ship around much too hard, yet with strength 0.002 the field turned off completely.
So instead of fighting this, I opted to manually apply a tangential force in the update. Works fine here, but could be a performance topic if you need more complex things.
