Basic vectors questions http://www.allegro.cc/forums/view/605230 Allegro.cc Forum Thread matthew@allegro.cc (Matthew Leverton) Fri, 08 Oct 2010 16:45:00 +0000

Can somebody explain me basics of vectors please a lot?
I know how to calculate lenght of vector (lenght=sqrt(x*x+y*y)). I want to explain angles and how to get the new x and y. Please show me how on some simple example with this picture.
I want to use left and right keys to set the angle and up nad down to move forward and backward. But I want only know how to calculate angle and new x, y. The best solution will be show it on some example picture. Thanks a lot everybody. ???::)

]]> no-reply@allegro.cc (Ad@m22) Wed, 06 Oct 2010 17:47:40 +0000

wikipedia to the rescue ?
ask google ?

]]> no-reply@allegro.cc (GullRaDriel) Wed, 06 Oct 2010 17:56:37 +0000

x = length * cos(angle)
y = length * sin(angle)

]]> no-reply@allegro.cc (KnightWhoSaysNi) Wed, 06 Oct 2010 17:56:54 +0000

I tried wikipedia and google but nothing please explain it to me ::) yes I found new x and y as you but it did not work for me perhaps because I used wrong angle so can you show me it on some example in picture please?

edit
Is this right code? ::)

#SelectExpand
1#include <cmath> 2#include <iostream> 3 4#define PI 3.14159265 5 6int main() { 7 8 using namespace std; 9 10 int x=100, y=100, angle=45, lenght=0; 11 // next x=110, next y = 110 12 lenght=sqrt(10*10+10*10); 13 14 cout<<"lenght: "<<lenght<<endl; 15 16 x=x+lenght*cos(angle*PI/180); 17 y=y+lenght*sin(angle*PI/180); 18 19 cout<<"x: "<<x<<endl; 20 cout<<"y: "<<y<<endl; 21 22 return 0; 23 24}

]]> no-reply@allegro.cc (Ad@m22) Wed, 06 Oct 2010 18:06:42 +0000

Length. :P If I knew the answer to what you are asking then I would help with that, but I don't. :-X

]]> no-reply@allegro.cc (bamccaig) Wed, 06 Oct 2010 18:36:34 +0000
Ad@m22 said:

The best solution will be show it on some example picture.

Perhaps you should draw an illustration to let us know what you're trying to calculate. I can't understand what you're trying to say.

]]> no-reply@allegro.cc (LennyLen) Wed, 06 Oct 2010 18:49:59 +0000

There's a Windows bitmap in the paperclip in the original post, but it looks like a simple transposition.

]]> no-reply@allegro.cc (Arthur Kalliokoski) Wed, 06 Oct 2010 18:52:01 +0000

I am only asking that is my source code of calculating the new x and y right? ::) that was my question

]]> no-reply@allegro.cc (Ad@m22) Wed, 06 Oct 2010 19:06:43 +0000

Yes, you are calculating the new x and y values correctly. Not too sure why you are calculating the length that way, however...

Basically, if you want to move distance 'lenght' in the direction 'angle' you do: 

x=x+lenght*cos(angle*PI/180);
y=y+lenght*sin(angle*PI/180);

Which is exactly what you do anyway.

]]> no-reply@allegro.cc (SiegeLord) Wed, 06 Oct 2010 19:18:02 +0000

Thanks, that is it. :)
Do you know about better way to calculate length? :-X

]]> no-reply@allegro.cc (Ad@m22) Wed, 06 Oct 2010 19:21:45 +0000

No, the way you calculate it is right if you want to calculate the length of the vector (10, 10). I'm not sure why you are calculating it.

]]> no-reply@allegro.cc (SiegeLord) Wed, 06 Oct 2010 19:23:00 +0000

Where are X and Y on your picture ?

What kind of data do you already know for computing X and Y ?

]]> no-reply@allegro.cc (GullRaDriel) Wed, 06 Oct 2010 19:25:18 +0000

That is only example,the important thing is the way to do it :)
Thanks for all.
I tried this code but it doesn t work, where I am doing mistake please?
The length is in every case 10, the object move about 10 pixels. Can somebody fix me it? :'(

#SelectExpand
1#include <cmath> 2#include <allegro.h> 3 4#define PI 3.14159265 5 6int main() { 7 8 allegro_init(); 9 install_keyboard(); 10 11 set_color_depth(desktop_color_depth()); 12 if (set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0) != 0) { 13 14 allegro_message("Couldn't set graphics mode: 640x480.\n"); 15 return 1; 16 17 } 18 19 int x=100, y=100, angle=105, lenght=0; 20 // next x=110, next y = 110 21 lenght=10; 22 23 BITMAP *bmp=load_bitmap("pic.bmp",NULL); 24 25 rotate_sprite(screen, bmp, x, y, itofix(angle/1.40625)); 26 x=x+lenght*cos(angle*PI/180); 27 y=y+lenght*sin(angle*PI/180); 28 29 while(!key[KEY_ESC]) { 30 if(key[KEY_RIGHT]||key[KEY_LEFT]||key[KEY_UP]||key[KEY_DOWN]) { 31 if(key[KEY_UP]) { 32 x=x+lenght*cos(angle*PI/180); 33 y=y+lenght*sin(angle*PI/180); 34 clear_to_color(screen,makecol(0,0,0)); 35 rotate_sprite(screen, bmp, x, y, itofix(angle/1.40625)); 36 } 37 38 39 if(key[KEY_DOWN]){ 40 x=x-lenght*cos(angle*PI/180); 41 y=y-lenght*sin(angle*PI/180); 42 clear_to_color(screen,makecol(0,0,0)); 43 rotate_sprite(screen, bmp, x, y, itofix(angle/1.40625)); 44 } 45 46 47 } 48 rest(10); 49 } 50 51 return 0; 52 53} 54END_OF_MAIN()

]]> no-reply@allegro.cc (Ad@m22) Wed, 06 Oct 2010 22:07:44 +0000
Ad@m22 said:

I tried this code but it doesn t work, where I am doing mistake please?

In just using the hated phrase "doesn't work". :P
How does it not work?

]]> no-reply@allegro.cc (gnolam) Wed, 06 Oct 2010 22:41:54 +0000

Okey, it moves to opposite directions
Here is picture to show you how it works, up and down mean keys
{"name":"14scvi0.jpg","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/8\/c\/8c0097e3ed90fff4b1188fc8d9745fc0.jpg","w":646,"h":512,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/8\/c\/8c0097e3ed90fff4b1188fc8d9745fc0"}14scvi0.jpg

]]> no-reply@allegro.cc (Ad@m22) Wed, 06 Oct 2010 22:46:18 +0000

Line of enquiry :-

You program says that when UP is pressed y gets incremented by

lenght*sin( 105 *PI/180);

which is a posiive value so the sprite should move down the screen.

Is this what's happening ?

]]> no-reply@allegro.cc (William Labbett) Thu, 07 Oct 2010 00:54:49 +0000

Yes, that's right

]]> no-reply@allegro.cc (Ad@m22) Thu, 07 Oct 2010 09:08:52 +0000

Checklist:

  • use the right angle unit at every point

  • be sure of direction at zero angle value

  • be sure of direction of rotation when angle value increases

  • be sure of screen coordinates, where's origo, at what direction does x grow, at what direction does y grow

  • sin(0) == 0, cos(0) == 1, sin(π/2) == 1, cos(π/2) == 0

Your problems seem to relate to this checklist, not to your understanding of vectors. Someone continue my checklist. Or improve it.

]]> no-reply@allegro.cc (Johan Halmén) Thu, 07 Oct 2010 11:21:27 +0000

Okey, but does anybody know how to fix my source code? ::)

]]> no-reply@allegro.cc (Ad@m22) Thu, 07 Oct 2010 17:04:18 +0000

Follow Halméns checklist. It will tell you exactly what's wrong with your code.

]]> no-reply@allegro.cc (gnolam) Thu, 07 Oct 2010 17:06:02 +0000
Ad@m22 said:

Okey, but does anybody know how to fix my source code?

People here don't make a habit of writing other people's source code for them, but we'll happily give you the tools to do it yourself (which has already been done in this case).

]]> no-reply@allegro.cc (LennyLen) Thu, 07 Oct 2010 17:07:24 +0000

When I rotate my image in own image file it works good and all int are float :-/
rotated about 90 deegres to right

]]> no-reply@allegro.cc (Ad@m22) Thu, 07 Oct 2010 21:22:38 +0000

Why hasn't anyone linked to this?
http://pixwiki.bafsoft.com/mags/5/articles/circle/sincos.htm

Read that article, it explains about all of the basics you need to know.

A quick summery for once you know what you're doing:

theta - the angle of your vector

Polar to Cartesian Coordinents

x=magnitude * cosine(theta)
y=magnitude * sine(theta)

Cartesian to Polar Coordinents
magnitude_of_x_y = sqrt(x^2 + y^2)
theta = atan2(x,y) *it's atan2(y,x) in MATLAB and some other languages.

]]> no-reply@allegro.cc (Chris Katko) Thu, 07 Oct 2010 23:39:14 +0000

Thank you for that link and explain of it :)

]]> no-reply@allegro.cc (Ad@m22) Fri, 08 Oct 2010 16:45:00 +0000