[Java2D] findind x and Y after Rotation

Newbie & Debugging Questions
#1

Hello everyone,

Determinate the rotation angle


angle = Math.atan2(gun.getY() - my, gun.getX() - mx) - Math.PI / 2;

Rotate :


g2d.rotate(gun.getA(), gun.getX() + 5, gun.getY() + 60);
g2d.drawRect(gun.getX(), gun.getY(), gun.getW(), gun.getH());

but when i trace the X and Y of the rotated rectangle, it always show the same values (unless if i moved left-right/up-down)
but during the rotation nothing changes
is there a way to find it ?
to clarify the problem :
the rectangle is a “gun” and therefore i need to know the x and y value during the rotation to be able to launch bullets

PS :
i tried to rotate the bullets (i don’t think it’s the right way) but after i tried it, the result is very annoying,
i had to write the code in the bottom of the paint method, otherwise, everything that i draw after it will rotate with it,(i tried drawing it with a different Graphics2D variable but still the same result) it should be a fix for that and am sure am going to ask about it later :stuck_out_tongue: but for now, is there a way to find the new X and Y after rotation ??

Edit :
“ps” is fixed,
look at this post

now how to know the new X and Y ::slight_smile: ?

thank you

#2

I don’t think I fully understood your problem, but this is what I do.

float angle = … (you already have)
float velX = (float)Math.cos(angle) * speed;
float velY = (float)Math.sin(angle) * speed;

In the bullet’s update method:

posX += velX;
posY += velY;

#3

Angles hate you, hate them back (local search).

#4

I’m also not sure about your question, but I’m gonna make an assumption that you are looking for the tip of the gun’s x and y?

If that is the case, then you just use your basic trigonometry knowledge:

Sin means the y value of an angle on a unit circle (r=1).
Cos means the x value.

In order to find the tip of the gun you would do this:


gunTipX = math.sin(gun.angle)*gun.length + gun.x;
gunTipY = math.cos(gun.angle)*gun.length + gun.y;

Hope I could be of help ;).

If I misunderstood your question, then please clarify :).