Degrees with SDL coordinate system

[Sanshin77]

Hey, we started trigonometry in math this year. I sat down a few days ago and created a function calculating the angle, in degrees(0-360), from one point to another. I have tested my function thoroughly(in all "4 main directions"), and it seems to work. I started thinking about using this for direction of objects in games and I wondered what is the best way to go about doing this with SDL's coordinate system.

I made a simple drawing to kinda illustrate my question:


It's natural for me to think that 90 degrees is straight up, 0 is straight to the right, 135 is diagonally up to the left, 270 is straight down and so on. Should I translate the angle(in degrees) in my function so that 90 is in fact straight up( on-screen ) or should I keep it as it is, 90 = straight down, higher y value?

[xiphirx]

I would suggest that you make it so it seems natural to you...

So, going up would mean an angle of 90.

[Falco Girgis]

I, personally, would be consistent with the unit circle.

[Arce]

I, personally, would be consistent with the unit circle.

Agree.

So, just treat it the same as a Cartesian coordinate system, with the exception of an inverted y-axis.

So, if you want a projectile to fly NorthEast in SDL, I'd make my calls something like this:

Code: Select all

bullet.y+= sin( (-1)*(45) ) * bull.speed;
bullet.x+= cos( 0 ) * bullet.speed;

or for a generic direction something like

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bullet.y+= sin( (-1)*(bullet.direction) ) * bull.speed;
bullet.x+= cos( bullet.direction ) * bullet.speed;

Note how I just multiplied bullet.direction in the call to sin by negative one to account for the inverted axis.

[short]

when doing this just remember how computationally expensive sin and cos really are..

[Ginto8]

Why use angles when you can use vectors? Yes, it could be an option to generate a vector at a certain angle, but other than that, there is little to no advantage (and plenty of disadvantages - mainly that trig is so expensive to calculate) that comes from using angles over vectors. I mean, it's cool and all, but it's not really a good idea in the long run.

[Sanshin77]

Sorry for not replying, my comp. was at repair for like a month (stupid ash-cloud preventing part transport) and now I had exams, so I haven't been around or devved a lot.

Why use angles when you can use vectors? Yes, it could be an option to generate a vector at a certain angle, but other than that, there is little to no advantage (and plenty of disadvantages - mainly that trig is so expensive to calculate) that comes from using angles over vectors. I mean, it's cool and all, but it's not really a good idea in the long run.

Yeah, I actually have a good system working with vectors now, I saw your reply and changed my mind. This will be featured in my next youtube video, the 4th episode of my Amateur Game Dev series, along with some simple collision/physics... :D