Moving an object to the center of the screen.

[ciuffolo]

Hi, i'm going to create an "asteroid remake", but i have another question.
I created the space shuttle and i made the random spawn of the rocks, but i wonder how to move the rocks all in the center of the screen, this is the code that i wrote for the random spawning:

Code: [Select]

TouchAdd(0,0,50,50,rotasinistra,0);
TouchAdd(430,0,50,50,rotadestra,0);
int randomnumber=rand() % 480+1;
int randomnumber2=rand() % 480+1;
int randomnumber3=rand() % 480+1;
int view2;
int view3;
int view4;
view2=ViewAdd("Images/rocks.png",randomnumber,310);
view3=ViewAdd("Images/rocks.png",randomnumber2,310);
view4=ViewAdd("Images/rocks.png",randomnumber3,310);
Thanks

[tim]

Check out this tutorial on Trigonometry for Developers:

http://active.tutsplus.com/tutorials/games/quick-tip-trigonometry-for-flash-game-developers-basix/

It's in Flash, but the concepts are the same.

Cheers,

[ciuffolo]

m ... thanks, but i can not do it on c + + Because It Is not really my best language
I know, I'm going to try it but it will very difficult, and if you have a c + + tutorial trigonometry may be better ...
thank you for the support you are giving me

[graham]

it's not difficult (and you don't need any trigonometry )

to move an object in a straight line, just compute coordinates as a linear combination of the start and end points:

Code: [Select]

float x1, y1;  // starting position
float x2, y2;  // end position
float x, y;      // the point that moves
float alpha;

for (alpha=0.0; alpha<=1.0; alpha+=0.1) {
   x = alpha*x1+(1.0-alpha)*x2;
   y = alpha*y1+(1.0-alpha)*y2;
}


this will move (x,y) from (x1,y1) to (x2,y2) in a straight line using ten equidistant steps.

[ciuffolo]

Thank you, i'm going to try it, but i have to study trigonometry too because it can help me in the future.

and how to apply it to an image?
do i have to put in x1 and y1 the location of the image?
m...i don't think...

[ciuffolo]

thank you, did it, but still have some problems now.How to use it in a for cicle?
i did it:

Code: [Select]

for (int i = 0; i < 20; i++)
    {
if(alpha<=1.0)
{
ENX=ViewGetx(EN[i]);
ENY=ViewGety(EN[i]);

       
alpha+=0.01; // aumentando questo valore aumenti la velocità
x = alpha*240+(1.0-alpha)*ENX;
y = alpha*160+(1.0-alpha)*ENY;
ViewSetxy(EN[i],x,y);

}
    }
but doesn't work...

[graham]

i dont know what you mean by "How to use it in a for cicle?"

there is a bug in your code: you should increment alpha outside the i loop.

[ciuffolo]

i was wrong, i wanted to mean in  a "for loop".
I'm going to try if that was the problem

[ciuffolo]

In short I have to create a ball and start it, and after a second I need to create another one and get it started, but I also make sure that they travel at the same time.
i only want to know how to do it, not the code.

[graham]

i can't think how to describe it concisely without using code, so here is a suggestion:

Code: [Select]

#include "DragonFireSDK.h"
#include <string.h>
#include <math.h>
#include <time.h>


const int CenterX = 160;
const int CenterY = 240;
const int INVISIBLE = 0;
const int VISIBLE = 1;


int AsteroidX[10];
int AsteroidY[10];
float Alpha[10];
int Counter;
int AsteroidI;
int AsteroidV[10];
int Tick;
int AsteroidStartX[10];
int AsteroidStartY[10];
float Delta = 0.002;


void Initialize()
{
int i;
float Angle;
float Distance;

RandomSetSeed(TimerGetMs());
AsteroidI = ImageAdd("Images/Asteroid.png");
for (i=0; i<10; i++) {
Angle = 2.0*3.1416*0.01*Random(100);
Distance = Random(30)+130;
AsteroidStartX[i] = 160+Distance*cos(Angle);
AsteroidStartY[i] = 240+Distance*sin(Angle);
AsteroidV[i] = ViewAdd(AsteroidI, AsteroidStartX[i], AsteroidStartY[i]);
ViewSetVisible(AsteroidV[i], INVISIBLE);
Alpha[i] = 0.0;
}
ViewSetVisible(AsteroidV[0], VISIBLE);
Counter = 1;
Tick = 0;
}


void Step()
{
int i;
int x, y;

for (i=0; i<Counter; i++)
if (Alpha[i] < 1.0) {
Alpha[i] += Delta;
x = (1.0 - Alpha[i]) * AsteroidStartX[i] + Alpha[i] * (CenterX-15);
y = (1.0 - Alpha[i]) * AsteroidStartY[i] + Alpha[i] * (CenterY-15);
ViewSetxy(AsteroidV[i], x, y);
}
}


void AppMain()
{
Initialize();
}


void AppExit()
{
}


void OnTimer()
{
int i;

Tick++;
Step();
if ((Tick % 30) == 0)
if (Counter < 10) {
ViewSetVisible(AsteroidV[Counter], VISIBLE);
Counter++;
}
}


[ciuffolo]

thanks, I'm going to try it.
There is only one thing that leaves me perplexed, the part of the sine and cosine ... but it doesn't seems something excessively complicated, thanks again

[graham]

that's just one possible way to determine starting positions for the asteroids: choose an angle and a distance from the centre of the screen at random and then convert those two numbers to (x,y) coordinates. it can easily be done without using trigonometric functions.

[ciuffolo]

oh yes, but i alredy have the random starting position, i only want to know how to move two asteroids togheter, but you helped me a alot, thanks!
i didn't think to making alpha an array.
I am a self-taught, that's why i'm not so good with these things...i'm studying it at school.

[ciuffolo]

for now I used the random function and my orthodox methods that i will semplify later, but in doing that they do not move anymore, they only create ... and I left the rest unchanged
the method that you use to create the rocks in this part of the code has to do with moving them or can I also use a random function? Maybe I've made some mistakes ...

[ciuffolo]

sorry,sorry i solved:
i have made
INT delta=0.002
then it takes only the 0...
i must make
FLOAT delta=0.002