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 Particle X:Y Spawn Coords Based on Rotation  (Read 4919 times) 0 Members and 1 Guest are viewing this topic.
Slyth2727
 « Posted 2013-03-01 23:24:12 »

Alright, I got a good one for you guys here. I have worked on this for a while to no avail so I thought some more math savvy people on here could point me in the right direction. So I've got a missile for my TD game that, when shot, rotates and follows it's target like a real missile. Now I want to use my particle system to spawn particles in at the base of the rocket so it looks like a nice smoke trail. I already have all the particle and color fade coded, but I have no clue how to get the X and Y to pass it to spawn based on the rotation of the missile. Here is the code for it:

 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44 `   public void move(Graphics g) {      if (inGame) {         if ((xBullet >= targetX - 4 && xBullet <= targetX + 4) && (yBullet <= targetY + 4 && yBullet >= targetY - 4)) {            inGame = false;            Screen.currLevel.mobs[shotMob].looseHealth(damage);            new Explosion((int) xBullet - 26, (int) yBullet - 12);            xBullet = 900;            yBullet = 900;         }         targetX = Screen.currLevel.mobs[shotMob].x + Screen.currLevel.mobs[shotMob].width / 4;         targetY = Screen.currLevel.mobs[shotMob].y + Screen.currLevel.mobs[shotMob].width / 4;         distanceX = (int) ((double) targetX - xBullet);         distanceY = (int) ((double) targetY - yBullet);         sep = Math.sqrt((distanceX * distanceX) + (distanceY * distanceY));         scale = 3;         xBullet += (distanceX / sep) * scale;         yBullet += (distanceY / sep) * scale;         slope = (targetY - yBullet) / (targetX - xBullet);         damage = tower.damage;         Graphics2D g2d = (Graphics2D) g.create();         double correction = 270;         float rotation;         rotation = (float) (Math.atan2(yBullet - targetY, xBullet - targetX) * (180 / Math.PI));         Screen.room.block[y][x].drawImage = false;         g2d.setTransform(AffineTransform.getRotateInstance(Math.toRadians(rotation + correction), xBullet + Screen.room.blockSize / 2, yBullet + Screen.room.blockSize / 2));         g2d.drawImage(Screen.tileset_air[Value.missile], (int) xBullet, (int) yBullet, Screen.room.blockSize, Screen.room.blockSize, null);         Screen.addParticle(XCOORDINATE, YCOORDINATE, .2, 4, 80, 100, false, Color.orange, Color.BLACK, 20);         g2d.dispose();      }   }   public void draw(Graphics g) {      if (!Screen.currLevel.mobs[shotMob].isDead() && Screen.inGame) {         if (timeF >= timeS) {            move(g);            timeF = 0;         } else {            timeF++;         }      } else {         // inGame = false;      }   }`
jonjava
 « Reply #1 - Posted 2013-03-02 00:27:25 »

Basically we need a bit of trigonometry

Where the distance should be the distance from the missiles rotation point to the point you want the missile to appear.

Something like that.

relminator
 « Reply #2 - Posted 2013-03-02 00:45:39 »

You could use atan2(diry,dirx) to get the angle.
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Slyth2727
 « Reply #3 - Posted 2013-03-02 01:20:32 »

what would be dirx and diry? I mean I know it is short for direction but I am not sure which variables you mean by it.
jonjava
 « Reply #4 - Posted 2013-03-02 01:23:06 »

 1 `rotation = (float) (Math.atan2(yBullet - targetY, xBullet - targetX) * (180 / Math.PI));`

jonjava
 « Reply #5 - Posted 2013-03-02 01:29:56 »

dirx would actually be delta x and diry you delta y or dx and dry. Whatever you call them it should be the the distance between point A and point B in the X lane and the distance between point A and point B in the Y lane. Because we can imagine that there is a 90 degree triangle between the two points.

Basic trigonometry for 90 degree angled triangles.

Slyth2727
 « Reply #6 - Posted 2013-03-02 01:43:37 »

Ah ok I understand.. I have already done this to get the angle, look up in the code I posted. For your suggestion on the spawn position for the particles, I have tried and failed to use it many different ways. For some reason none of them seem to work.
Slyth2727
 « Reply #7 - Posted 2013-03-02 19:58:57 »

Aaannd I slept on it and figured it out the next day (with the help you guys gave me ). So for anyone viewing this thread in the future, what I realized I had to do was plug in half the width and height of the image where missile_x and missile_y was so the final equations were these:

 1  2 `double particleX = (xBullet + Screen.room.blockSize / 2) - Math.toRadians(Math.cos((rotation) + correction)) * (Screen.room.blockSize / 2);double particleY = (yBullet + Screen.room.blockSize / 2) - Math.toRadians(Math.sin((rotation) + correction)) * (Screen.room.blockSize / 2);`
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