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  [Java2D] findind x and Y after Rotation  (Read 1962 times)
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Offline alaslipknot
« Posted 2013-04-23 16:31:28 »

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  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  Roll Eyes ?

thank you  

"It's not at all important to get it right the first time. It's vitally important to get it right the last time."
Offline Zhon

Junior Devvie

Medals: 4

« Reply #1 - Posted 2013-04-23 19:57:46 »

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;

Offline Roquen

JGO Kernel

Medals: 517

« Reply #2 - Posted 2013-04-23 20:18:17 »

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Offline h3ckboy

JGO Coder

Medals: 5

« Reply #3 - Posted 2013-04-26 12:36:46 »

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 Wink.

If I misunderstood your question, then please clarify Smiley.
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