Sin And Cos Help

Sin And Cos Help

dakatt

Member #10,695

February 2009

Can someone with a bit more knowledge tell me where I'm going wrong. I've tried different combinations of fixed and floats but the results seem weird. The rotation is off after a full rotation.

<code ="1">
class CPlayer{
public:
CPlayer(CKeyboard*,CMouse*);
~CPlayer(){}

void Update();
void Move();

void Draw();

CShip* my_ship;

CKeyboard* keyboard;
CMouse* mouse;

al_fixed xpos,ypos,xvel,yvel;
al_fixed angle_rad,angle_deg;
al_fixed speed_acc,speed_current;
};

CPlayer::CPlayer(CKeyboard* k,CMouse* m){
keyboard = k;
mouse = m;

my_ship = new CShip();

angle_rad = al_ftofix(0.0);
angle_deg = al_ftofix(0.0);

speed_acc = al_ftofix(0.5);
speed_current = al_itofix(0);

xpos = al_itofix(0);
ypos = al_itofix(0);

xvel = al_itofix(0);
yvel = al_itofix(0);
}

void CPlayer::Update(){
Move();
}

void CPlayer::Move(){
if(keyboard->key_flag[KEY_NAME_LEFT]){angle_deg--;}
if(keyboard->key_flag[KEY_NAME_RIGHT]){angle_deg++;}

if(keyboard->key_flag[KEY_NAME_UP]){speed_current =1;}
if(keyboard->key_flag[KEY_NAME_DOWN]){speed_current -= speed_acc;}

if(angle_deg < 0)
angle_deg += 360;
else if(angle_deg > 360)
angle_deg -= 360;

angle_rad = (angle_deg * PI) / 180;

xvel = al_fixmul(speed_current, al_fixcos(angle_rad));
yvel = al_fixmul(speed_current, al_fixsin(angle_rad));

xpos+=xvel;
ypos+=yvel;
}

void CPlayer::Draw(){
al_draw_rotated_bitmap(my_ship->my_image,64,64,SCREEN_WIDTH/2,SCREEN_HEIGHT/2,(angle_rad),NULL);
al_draw_textf(myfont,al_map_rgb(255,255,255),10,100,NULL,"ANGLE RADIANS : %f",angle_rad);
al_draw_textf(myfont,al_map_rgb(255,255,255),10,144,NULL,"ANGLE DEGREES : %f",angle_deg);

al_draw_textf(myfont,al_map_rgb(255,255,255),10,188,NULL,"SPEED : %f",al_fixtof(speed_current));
al_draw_textf(myfont,al_map_rgb(255,255,255),10,222,NULL,"X POS : %f",al_fixtof(xpos));
al_draw_textf(myfont,al_map_rgb(255,255,255),10,266,NULL,"Y POS : %f",al_fixtof(ypos));
}
</code>

Thanks

Edgar Reynaldo

Major Reynaldo

May 2007

There is no reason to use the 'fixed' class anymore. Just use regular floats or doubles, don't mess around with converting back and forth between ftofix.

As a rule, you can always regenerate your speed and heading from your rotation value.

You can use transforms or just regular sin and cos and rotation matrices. Generally I keep a speed (magnitude of velocity) and angle in radians, since that's what the C library works with.

Here's a treat from old days about working with angles :

angles, how I hate them

And here's sin and cos, a programmer's pal, except I think they give you bad advice about using fixed numbers.

Eagle and Allegro 5 binaries | Older Allegro 4 and 5 binaries | Allegro 5 compile guide
King Piccolo will make it so Then I could just flip it with some sweet, sweet matrix math. In either case, I’ll ride this wagon until the wheels fall off. Thanks to those that keep it running

Neil Roy

Member #2,229

April 2002

I highly recommend reading the following series of blog posts which cover things like rotations and the like using vectors which is the best way to represent locations and to do rotations etc. This is probably one of the best posts on the subject I have seen.

http://blog.wolfire.com/2009/07/linear-algebra-for-game-developers-part-1/

---
“I love you too.” - last words of Wanda Roy

dakatt

Member #10,695

February 2009

I'll check that blog out later today Neil, it looks interesting and I don't know much about vectors but it looks user friendly. You were right Edgar, I replaced all the fixeds and it works as it should. Also the code I posted wasn't right since I was playing around with some variables and pasted it after. Here's the working code for anyone interested

class CPlayer{
public:
CPlayer(CKeyboard*,CMouse*);
~CPlayer(){}

void Update();
void Move();

void Draw();

CShip* my_ship;

CKeyboard* keyboard;
CMouse* mouse;

float angle_deg,angle_rad;
float xpos,ypos,speed,xvel,yvel;
};

CPlayer::CPlayer(CKeyboard* k,CMouse* m){
keyboard = k;
mouse = m;

my_ship = new CShip();

xpos = 0;
ypos = 0;
speed = 0;

angle_deg = 0.0;
angle_rad = 0.0;

}

void CPlayer::Update(){
Move();
}

void CPlayer::Move(){
if(keyboard->key_flag[KEY_NAME_LEFT]){angle_deg--;}
if(keyboard->key_flag[KEY_NAME_RIGHT]){angle_deg++;}

if(angle_deg >= 360)angle_deg-=360;
if(angle_deg < 0) angle_deg+=360;

angle_rad = (angle_deg * PI) / 180;

if(keyboard->key_flag[KEY_NAME_UP]){speed = 1;}
else if(keyboard->key_flag[KEY_NAME_DOWN]){speed = -1;}
else speed = 0;

xvel = speed * cos(angle_rad);
yvel = speed * sin(angle_rad);

xpos += xvel;
ypos += yvel;
}

</code>

Thanks guys

Edgar Reynaldo

Major Reynaldo

May 2007

<code>code goes here...</code> tags are helpful

It was probably because there are only 256 allegro degrees in a circle, so you have to convert as well.

LennyLen

Member #5,313

December 2004

Edgar Reynaldo said:

code goes here... tags are helpful

He used code tags, but he has '="1"' instead of 'start="1"'.

Edgar Reynaldo

Major Reynaldo

May 2007

Sorry, I'm half blind sometimes...

I saw that and my brain acknowledged it, but still posted it anyway.

dakatt

Member #10,695

February 2009

Damn it, I tried using the formatting help. Hopefully this is better

Also you can't edit a post?

LennyLen

Member #5,313

December 2004

dakatt said:

Also you can't edit a post?

Yes click on the edit post button at the top of the post: 611325

edit: ok, that is NOT the image I uploaded.

edit2: the image isn't showing, but it's the correct one now.