Forgotten mana...

Forgotten mana...

Don Freeman

Member #5,110

October 2004

Ok...this topic has been punished enough, but I can't find it using allegro/forums/search at the moment.

Questions is:

I am rotating a sprite using allegro's rotate_sprite(...) function. I want the image to move in the same direction as the angle is. I've done this before, but it's been a long time ago. I know it's got something to do with converting radians to degrees...converting degrees to allegro degrees...conjuring magical dragons...and all that, but I can't remember.

////////////////////////////////////////////////////////////////
// in the update routine:
xVel = cos( angle ) * vel;
yVel = sin( angle ) * vel;
x += xVel;
y += yVel;
////////////////////////////////////////////////////////////////
// then in drawing routine:
rotate_sprite(pDest,pBmp,x+pBmp->w/2,y+pBmp->h/2,ftofix(angle));
////////////////////////////////////////////////////////////////

--
"Everyone tells me I should forget about you, you don’t deserve me. They’re right, you don’t deserve me, but I deserve you."
"It’s so simple to be wise. Just think of something stupid to say and then don’t say it."

ReyBrujo

Moderator

January 2001

Sin & Cos: The Programmer's Pals!, see the Using atan2(): homing missiles section.

--
RB
光子「あたしただ…奪う側に回ろうと思っただけよ」
Mitsuko's last words, Battle Royale

Don Freeman

Member #5,110

October 2004

Here is my code sample:

The image is a simple triangle with a white line facing north.

1//////////////////////////////////////////////////////////////////////////////////////////////////
2Player::Player()
3{
4  x = 0.0f;
5  y = 0.0f;
6  vel = 0.0f;
7  xVel  = 0.0f;
8  yVel  = 0.0f;
9  angle = GetRadians(0.0f);
10  pWeapon = new Weapon;
11  pBmp = NULL;
12}
13Player::~Player()
14{
15  if ( pWeapon )
16    delete pWeapon;
17  pWeapon = NULL;
18  if ( pBmp )
19    destroy_bitmap(pBmp);
20  pBmp = NULL;
21}
22void Player::Display( BITMAP *pDest )
23{
24  if ( !pBmp )
25    return;
26  if ( !pDest )
27    return;
28  rotate_sprite(pDest,pBmp,x+pBmp->w/2,y+pBmp->h/2,ftofix(GetDegrees(angle)*(40.74366543153)));
29}
30void Player::Update( void )
31{
32  xVel = cos( GetDegrees( angle ) ) * vel;
33  yVel = sin( GetDegrees( angle ) ) * vel;
34  x += xVel;
35  y += yVel;
36  pWeapon->Update(*this);
37}
38// Degrees = radians * 180 / PI
39// Radians = degrees * PI / 180
40// const float Rad2AllegroDeg = 40.74366543153; 
41// float radian = whatever;
42// float AllegroDeg = radians * Rad2AllegroDeg; 
43//////////////////////////////////////////////////////////////////////////////////////////////////
44float GetDegrees( float radians )
45{
46  return (radians * 180 / PI);
47}
48//////////////////////////////////////////////////////////////////////////////////////////////////
49float GetRadians( float degrees )
50{
51  return (degrees * PI / 180);
52}
53//////////////////////////////////////////////////////////////////////////////////////////////////

I know I am just doing a conversion wrong somewhere...

Arthur Kalliokoski

Second in Command

February 2005

angle = 1.0; //radians
angle *= 180.0/M_PI; //now it's degrees
angle *= 65536.0; //now it's suitable for rotate_sprite

That should work, money back guarantee

They all watch too much MSNBC... they get ideas.

amarillion

Member #940

January 2001

Arthur: that doesn't work. rotate_sprite needs a value between 0 and 255.

  xVel = cos( GetDegrees( angle ) ) * vel;
  yVel = sin( GetDegrees( angle ) ) * vel;

These functions take radians, not degrees. Assuming angle is in radians (can't deduce that from the code), you can use it directly here without converting.

And you can use this (shorter) code:

  rotate_sprite(pDest,pBmp,x+pBmp->w/2,y+pBmp->h/2, ftofix(angle * 128 / PI));

edit:
Here are they all:

1//radians to degrees:
2float degrees = radians * 180 / PI;
3 
4//degrees to radians:
5float radians = degrees * PI / 180;
6 
7//degrees to allegro degrees
8fix al_deg = ftofix (degrees * 256 / 360);
9 
10//allegro degrees to degrees
11float degrees = fixtof (al_deg) * 360 / 256;
12 
13//radians to allegro degrees
14fix al_deg = ftofix (radians * 128 / PI);
15 
16//allegro degrees to radians
17float radians = fixtof (al_deg) * PI / 128;

--
Martijn van Iersel | My Blog | Sin & Cos | Food Chain Farm | TINS 2023 is Jun 2-5

OICW

Member #4,069

November 2003

But you need to convert radians into the fixed angle. Fixed angle is number between 0-255 and therefore you must multiple angle in radians by radtofix() constant. I advice you to have angle in fixed format because it will remove you many headaches.

[My website][CppReference][Pixelate][Allegators worldwide][Who's online]
"Final Fantasy XIV, I feel that anything I could say will be repeating myself, so I'm just gonna express my feelings with a strangled noise from the back of my throat. Graaarghhhh..." - Yahtzee
"Uhm... this is a.cc. Did you honestly think this thread WOULDN'T be derailed and ruined?" - BAF
"You can discuss it, you can dislike it, you can disagree with it, but that's all what you can do with it"

amarillion

Member #940

January 2001

OICW: Only one conversion is necessary in the code above, i.e. when using rotate_sprite. All the other functions use radians.

--
Martijn van Iersel | My Blog | Sin & Cos | Food Chain Farm | TINS 2023 is Jun 2-5