Question

How can i calulate a valid range (RED) for my object’s (BLACK) traveling direction (GREEN). The green is a Vector2 where x and y range is -1 to 1.

What I’m trying to do here is to create rocket fuel burn effekt. So what i got is

• rocket speed (float)
• rocket direction (Vector2 x = [-1, 1], y = [-1, 1])

I may think that rocket speed does not matter as fuel burn effect (particle) is created on position with its own speed.

Answer 1

A cheap and cheerful trick with 2D vectors is to transpose the x and y, then flip the sign on one of them to get the perpendicular vector (pseudo code):

Vector2 perpendicular ( -original.y, original.x ) // Or original.y, -original.x

Then you could do something like:

direction + perpendicular * rand(-0.3 , 0.3)

Update: having realised the question asks for the opposite vector (too busy looking at the picture!) I figure I had better answer that too. Multiply ‘direction’ by -1 to get the opposite vector. So this:

perpendicular * rand(-0.3 , 0.3) - direction

should give you a random direction vector somewhere in your range (not normalised, but close enough for these purposes). Then you can multiply that result by a random number depending on how long you want the tail.