magiclysm: replace spell_effect_line

[OrenAudeles]

Summary

SUMMARY: Bugfixes "Fix holes in spell_effect::spell_effect_line"

Purpose of change

Previous implementation occasionally misses tiles that should be hit in some orientations.

Describe the solution

Currently does not work outside of 2D space. Allowing 3D line spells is work for the future.

1. Get 2D delta vector
2. Calculate square distance, if zero we can quit early. We are targeting self.
3. Calculate clockwise perpendicular vector from delta vector
4. Find primary axis (north, east, south, west) of delta vector, and from that its clockwise perpendicular axis
5. Calculate clockwise and counter/anti-clockwise axis leg lengths, modify further if distance metric is non-circular
6. Get orientation of delta vector relative to primary axis. This signifies which leg is behind or in front of the clockwise perpendicular axis
7. Get a canonical tile path along delta vector, pop off the endpoint and insert the origin at the beginning. This is done so that we can walk along the path easily.
8. Fill tile path between the source and target points using the line walker
9. Dependant on the orientation found in (6), fill paths for clockwise and counter clockwise legs.

Testing

Tossed around some Megablast spells in a group of zombies, did not see holes where there shouldn't be holes.

Additional context

All targeting a tile diagonally away from the Player to most easily demonstrate holes in current implementation

• Current Implementation: Without Circular Distance metric
  
• Current Implementation: With Circular Distance Metric
  
• PR Implementation: Without Circular Distance Metric
  
• PR Implementation: With Circular Distance Metric
  

[OrenAudeles]

@KorGgenT I think the blah & name stuff was the result of astyle being weird with lambda. Issue disappeared when I converted the lambda into functions.

[KorGgenT]

Suggested change

	int cross = ( ( b.x - a.x ) * ( c.y - a.y ) - ( b.y - a.y ) * ( c.x - a.x ) );
	const int cross = ( ( b.x - a.x ) * ( c.y - a.y ) - ( b.y - a.y ) * ( c.x - a.x ) );