[ReneG]

If you're an avid sa-mp scripter, you may have seen this piece of code before

pawn Code:

x += (Distance * floatsin(-r, degrees));
y += (Distance * floatcos(-r, degrees));

Up until now, I really had no idea what this code even did, but seeing it applied in mathematics and then seeing applied in sa-mp gives rise to one question.

Look at the diagram below.

(Source: http://en.wikipedia.org/wiki/File:Unit_circle.svg)

t would represent a player's facing angle relative to the x-axis, and the point on the circle would be the point we are trying to solve for.

I know for a fact that the x coordinate is equal to the cos t, and the y coordinate is equal to sin t.

The player's position will not always be at 0, 0 so it's evident that we need to append these values to the player's current position, giving us this

x + cos t
y + sin t

but that produces an error in game and spawns the object to the right of the player (excuse the image sizes)


if we switch the code to be

x + sin t
y + cos t

we get the correct output


Why is that? By the definition of the unit circle, the first example should be correct.

I haven't found any reliable information as to why the initial code (at the top of the post) works, so if you have any knowledge as to why it does, please contribute.

[Gamer_Z]

the GTA degrees go clockwise from -180 to 180, the maths unit circle goes with the clock from 0 to 360 (or reverse, dunno if I said it good in English :P)

At least I know it has to do with the directions (clockwise/counter-clockwise) and the domain ([-180,180] / [0, 360]) of the degrees.

[ReneG]

I have no idea what you mean, lol.

However, I think I've just figured out why.

A player's angle is relative to the y axis, not the x. For example, look at the diagram, t is the value returned from GetPlayerFacingAngle

Now here is the same diagram just flipped 90 degrees clockwise.


In case it was hard to read, I just constructed a congruent triangle in red.

Just looking at it, makes sense to me now.

x + sin t
y + cos t

I guess I just answered my own question

[thefatshizms]

I would love to know what this is. But as even the images with sin t cos t etc confuses me I doubt I will know any time soon. Until now i never heard of cos t and sin t.

[Gamer_Z]

Quote:

Originally Posted by thefatshizms I would love to know what this is. But as even the images with sin t cos t etc confuses me I doubt I will know any time soon. Until now i never heard of cos t and sin t.

don't worry, you will get it soon, dunno how old you 're.. but it isn't that hard.

[thefatshizms]

I'm 15 years old. The most with have done with circles in maths is circumference of a circle and the other basic things.

[MP2]

Quote:

Originally Posted by Gamer_Z the GTA degrees go clockwise from -180 to 180, the maths unit circle goes with the clock from 0 to 360 (or reverse, dunno if I said it good in English :P) At least I know it has to do with the directions (clockwise/counter-clockwise) and the domain ([-180,180] / [0, 360]) of the degrees.

Are you 100% sure? I'm fairly confident that they go from 0-360, just anti-clockwise (east is 270, but is 90 in real life). I've never seen negative angles in SA:MP..

[Gamer_Z]

Quote:

Originally Posted by MP2 Are you 100% sure? I'm fairly confident that they go from 0-360, just anti-clockwise (east is 270, but is 90 in real life). I've never seen negative angles in SA:MP..

try GetVehicleZAngle and you will see :P

[MP2]

Quote:

Originally Posted by Gamer_Z Quote: Originally Posted by MP2 Quote: Originally Posted by Gamer_Z the GTA degrees go clockwise from -180 to 180, the maths unit circle goes with the clock from 0 to 360 (or reverse, dunno if I said it good in English :P) At least I know it has to do with the directions (clockwise/counter-clockwise) and the domain ([-180,180] / [0, 360]) of the degrees. Are you 100% sure? I'm fairly confident that they go from 0-360, just anti-clockwise (east is 270, but is 90 in real life). I've never seen negative angles in SA:MP.. try GetVehicleZAngle and you will see :P

I had to test this just to be sure, as I was very confident I was right, and I was.. (sorry to correct you :P)

[ame]http://www.youtube.com/watch?v=f9vm8VWRdMs[/ame]

pawn Code:

public OnPlayerUpdate(playerid)
{
    new Float:a, szString[32];
    if(!IsPlayerInAnyVehicle(playerid))
    {
        GetPlayerFacingAngle(playerid, a);
        format(szString, sizeof(szString), "Player Angle: %.0f", a);
    }
    else
    {
        GetVehicleZAngle(GetPlayerVehicleID(playerid), a);
        format(szString, sizeof(szString), "Veh Angle: %.0f", a);
    }
    GameTextForPlayer(playerid, szString, 3000, 3);
    return 1;
}

Are you referring to something else?

[Gamer_Z]

Quote:

Originally Posted by MP2 I had to test this just to be sure, as I was very confident I was right, and I was.. (sorry to correct you :P) http://www.youtube.com/watch?v=f9vm8VWRdMs pawn Code: public OnPlayerUpdate(playerid) {     new Float:a, szString[32];     if(!IsPlayerInAnyVehicle(playerid))     {         GetPlayerFacingAngle(playerid, a);         format(szString, sizeof(szString), "Player Angle: %.0f", a);     }     else     {         GetVehicleZAngle(GetPlayerVehicleID(playerid), a);         format(szString, sizeof(szString), "Veh Angle: %.0f", a);     }     GameTextForPlayer(playerid, szString, 3000, 3);     return 1; } Are you referring to something else?

Whathe.. ;o When I was creating the AutoPilot i had difficulty with it just because the car angles returned between -180 and 180, and I doubt sa-mp changed anything.. probbly some code I didn't notice was changing my angle >_>

at least, where it happend to me was north-east in LV, but I highly doubt location change will matter.

So well I was wrong ;p