Good evening (at the time of writing)
The research I've done on this topic has turned up numerous fruitful code blocks regarding various situations similar to mine, but not quite identical. If one exists which I have not uncovered, I would be grateful for a link!
I have a few pertinent criteria, all on a 2d plane, and the question is related to 2d projectile pathing:
1) Object A: position ax,ay
2) Object B: position bx, by
3) Object P: (projectile) origin position bx,by
Object P leaves object B's X/Y position at a static velocity, traveling toward object A's X/Y position.
Objects A and B continue to move along their paths, irrespective of object P's trajectory. Object P continues to move from ax,ay to bx,by and beyond. I think I just need the angle and velocity, and don't need to continue to track beyond that (just increment movement steps accordingly till off-stage, where the object is disposed).
I'm working in Actionscript 3, any help would be greatly appreciated. Thanks!
In most case in 2D x-y plane, it is usually easier to handle movement and momentum in planar(separate in x-axis and y-axis) fashion than polar(angle+distance) fashion. I couldn't get the exact behaviour of projectile you want, so I assume you want a simple, dumbfire-rocket style projectile (which keeps initial direction).
:: 1. Projectile initiation ("Firing" of projectile)
var duration:int //(duration of flight(until getting to (ax,ay) described in number of frames)
var spdX:Number //(x-axis part of speed, described in pixels per frame)
var spdY:Number //(y-axis part of speed, described in pixels per frame)
spdX=(bx-ax)/duration;
spdY=(by-ay)/duration;
:: 2. Projectile movement (listen to ENTER_FRAME Event, executed once per frame)
projectile.x+=spdX;
projectile.y+=spdY;
:: if you want to change velocity of projectile, simple multiplication will handle it.
public function adjustSpeed(ratio:Number):void
{
spdX*=ratio;
spdY*=ratio;
}
Related
My player's arm is programmed to follow my mouse and rotate accordingly and I've programmed bullets to be fired using this rotational value
(Math.atan2(this._dy, this._dx) * 180 / Math.PI
where _dy is the y location of the mouse (-) the y of my player's arm and the _dx is the x location of mouse (-) the y of my player's arm.
However, when I program the player to reflect when the mouse has crossed the x-coordinates, the bullet angle is also reflected. How would I fix this issue?
I've already tried subtracting 180 from the angle but it still doesn't fire towards the direction of the mouse.
First, make sure you have this parent-child-sibling relationship:
"A" should be the parent of "B" and "C". "B" and "C" should have no direct link. Their connection is that they have the same parent. So when you want to move the character, move the parent, and both will move. Now, for the good stuff:
Use key frames and sibling relationship
beginner level approach
Make the character and the arm both children of the same parent display object container (Movie Clip in this case). Now, instead of flipping anything by xScale, which I assume you did, you can just have both MC children (arm and character) go to frame 2 (or whatever is available) where the graphics are flipped.
xScale body, move arm to frame 2, change z order
moderate level approach (best result)*
Alternatively, you could do that same "sibling" setup as above, and then scale the character but not the arm (I think scaling the arm will mess it up again, but you could have the arm go to frame 2 and have it drawn reversed so the thumb and handle are pointing the right way. Bonus points for changing the z stacking order so the arm goes to the other side of the body. xScale for only the body allows you to only have one set of frames for animation of his legs and torso etc. but also avoid scaling the arm at all).
Global properties
advanced approach
A third option is to use global rotation and global points. I won't illustrate that here because I'm not that advanced and it would take me a while to figure out the exact syntax. If you already have mastered global properties, try this; if not, try one of the ones above.
* Example (best result)
if (facingRight == true && stage.mouseX < totalChar.x){
// totalChar is on the stage
// and contains two children:
// armAndGun and bodyHeadLegs
totalChar.armAndGun.gotoAndStop(2);
// in frame 2 of the arm MC, draw the
// arm and gun in the flipped orientation
totalChar.addChild(bodyHeadLegs);
// re-ads body to parent so it's
// z-order is above the arm;
totalChar.bodyHeadLegs.xScale = -1;// flips body and any animation of legs and head
facingRight = false;
// use a variable or property like this
// to keep him from constantly flipping
}
You'll need similar code to flip him back the other way.
If I have two instances called block1 and block2. And they move off the stage. It scrolls down the y position and it respawns back on top. But I don't want the x/y position colliding with the other blocks? I want it to respawn back to position, but I want it randomized but at the same time I don't want it touching each other?
Heres my code:
if (block1.y > stage.stageHeight)
{
block1.y = -550;
block1.x = (Math.floor(Math.random() * (maxNum - minNum + 5)) + minNum);
}
I'm pretty sure I'm calculating the respawn coordinates the wrong way, but I'm not sure how to put it in a random x and y position without colliding with other blocks.
A very simple method can be just to spawn your box, do a collision check, then if collision, remove and respawn and recheck until you find an empty spot where it fits
This is obviously quite inefficient, but is pretty simple to implement quickly if you have some sort of collision detection already working. Keep in mind if there is no spot that it can fit in, then it'll loop forever so you may want to set a max try count or something of that sort.
How fast/well it'll actually work will depend on if the spawn area is pretty sparse or pretty dense, which will increase/decrease the percentage that it'll find a good empty spot the first few times.
There is some room for improvement, going down this path though, such as if your collision detection system gives a minimum translation vector, you could just move the new shape over and use that position to spawn.
Other simple methods could involve keeping track of known occupied positions and adjusting your random range to avoid those values.
I've been able to apply a smooth animation to my sprite and control it using the accelerometer. My sprite is fixed to move left and right along the x-aixs.
From here, I need to figure out how to create a vertical infinite wavy line for the sprite to attempt to trace. the aim of my game is for the user to control the sprite's left/right movement with the accelerometer in an attempt to trace the never ending wavy line as best they can, whilst the sprite and camera both move in a vertical direction to simulate "moving along the line." It would be ideal if the line was randomly generated.
I've researched about splines, planes, bezier curves etc, but I can't find anything that seems to relate close enough to what I'm trying to achieve.
I'm just seeking some guidance as to what methods I could possibly use to achieve this. Any ideas?
You could use sum of 4 to 5 sine waves (each with different amplitude, wavelength and phase difference). All 3 of those parameters could be random.
The resulting curve would be very smooth (since it is primarily sinusoidal) yet it'll look random (it's time period would be LCM of all 4 to 5 random wavelengths which is a huge number).
So the curve won't repeat for a long time, yet it will not be hard on memory. Concerning computational complexity, you can always tune it by changing number of sine terms with FPS.
It should look like this.
It's really easy to implement too. (even I could generate above image.. haha)
Hope this helps. Maths rocks. :D
(The basic idea here is a finite Fourier series which I think should be ideal for your use case)
Edit:
You can create each term like this and assign random values to all terms.
public class SineTerm {
private float amplitude;
private float waveLength;
private float phaseDifference;
public SineTerm(float amplitude, float waveLength, float phaseDifference) {
this.amplitude = amplitude;
this.waveLength = waveLength;
this.phaseDifference = phaseDifference;
}
public float evaluate(float x) {
return amplitude * (float) Math.sin(2 * Math.PI * x / waveLength + phaseDifference);
}
}
Now create an array of SineTerms and add all values returned by evaluate(x) (use one coordinate of sprite as input). Use the output as other coordinate of sprite. You should be good to go.
The real trick would be in tuning those random numbers.
Good luck.
I have a MovieClip, that is representing a character in my game. Id like to "create bullets" shooting out from the tip of my characters gun. Problem is that when my character turns around, also the point rotates around the MovieClips pivot.
Is it possible to anyhow easily track this point, so that I could dynamically create new objects at the same location.
I tried to add a new MC as a child to my character, with the initial position at the guntip. In some systems child-objects "follow" their parents around, but it didnt seem to work here.
Is there any other "native" way of doing this, or do I just have to have a Polar-coordinates representation of the point relative to character-MovieClips origin, and add the MC rotation to theta, so that I can calculate the X and Y coordinates?
Try localToGlobal() and globalToLocal() methods to transform coordinates from your character movieclip to its parent.
Set up the movie clip with the gun (I'm assuming it's at the end of an arm?) so that the gun tip is straight across from the pivot point.
Then pass the method that fires the bullet three parameters: the x and y position of the gun MC, and its current angle.
The code for your bullets initial position might look something like this:
public function CreateBullet(x,y:Number, degree:Number)
{
// set start position
this.x = x + ARMLENGTH*Math.cos((degree/180)*Math.PI);
this.y = y + ARMLENGTH*Math.sin((degree/180)*Math.PI);
}
Where ARMLENGTH is the distance from the pivot point to the end of the gun.
Two caveats, Flash can do weird things with angles, so you might have to make an if statement in CreateBullet() with inverted degrees if the player if facing backwards. Also, if you have the gun MC as a child of your character, you might have to make a Point where the pivot point is then do a localToGlobal on it. There's a good reference for that here.
I need to do an endless horizontal scroll of elements within a parent MovieClip.
No matter what ever method I try, an element of 'drift' occurs and eventually the elements start to overlap.
I've tried using relative recursive tweening for each element according
but this method seems prone to quite a bit of error after repeated starts and stops.
//CODE START
function doScroll():void {
TweenLite.to(this, .25, {x:"20", ease:Linear.easeNone,onUpdate:checkPos,onComplete:doScroll});
}
//CODE END
I've reverted to doing absolute tweens to a predefined position using a contant speed. This seems to be more accurate but still some 'drift' occurs.
//CODE START
//_dest is predefined
var speed:Number = 500;
var dist:Number = this.x - _dest;
var distAbs:Number = dist < 0 ? -dist : dist;
//kludge to get constant velocity by recalculating time every frame
_time = distAbs / speed;
TweenLite.to(this, _time, {x:_dest, ease:Linear.easeNone,onComplete:reset});
//CODE END
Thought this should be very simple.
Can anyone point me to any possible tutorials or make any suggestions?
Any help appreciated.
Solution/Discussion at http://forums.greensock.com/viewtopic.php?f=1&t=6800
(warning: this is gonna require a rather lengthy explanation...)
It's a logic problem in your code. In your onUpdate, you were running conditional logic such that if the x position is beyond 980, it kills the tween and moves x back to -980 and starts things over. You're doing that for each individual item, each of which begins at a different position. That initial position affects when it crosses that threshold, thus when they reposition, the offsets are different.
For example, let's say item1 starts at an x position of 0 and item2 starts at 490 and both start moving at 400 pixels per second and your frame rate is 60, thus they'll move 6.66666 pixels per frame. Item1 will take 147 frames to hit 980. However, item2 will take 74 frames (actually 73.5, but there's no such thing as a half-frame) to cross the 980 threshold, but when it does so it will be at an x position of 983.333333. At that point it jumps back to -980 due to your conditional logic, but notice that it traveled an EXTRA 3.333333 pixels. You intended Item1 and item2 to travel at the exact same velocities and they do during the tween, but your onUpdate logic is misaligning them on the reposition such that in the end, some are traveling more than others which affects their overall velocity.
Another issue has to do with the fact that Flash rounds x/y coordinates of DisplayObjects to the nearest 0.05. So when you do your manual reposition (wrap), small rounding errors creep in. For example, let's say TweenLite sets the exact x value to 980.799. Flash will actually round that to 980.75. Then when you reposition it like this.x -= 980 and then tween it, the value would have just lost almost 0.05 pixels on that round. Do that many times and it can add up to a half-pixel or whole pixel (or more). All your items are crossing the threshold at slightly different spots, thus the rounding errors aren't the same, thus you start seeing slight variances in the spacing. Again, this is NOT an issue with the tweening engine. You'll see that the engine itself sets the values correctly, but Flash rounds them internally when applied to DisplayObjects.
A solution was posted at http://forums.greensock.com/viewtopic.php?f=1&t=6800 that includes an FLA and support files.
As others have suggested, I'd recommend having a single chunk of code that manages ALL the items that you're aligning/scrolling. It would lay things out from a single reference point so that everything lines up perfectly every time. You could tween a getter/setter that applies the logic. I use that technique all the time and it works great. You can see a smaller-scale example in the code I attached in the above URL (the scrollX getter/setter in ItemBase.as)
If you will be tweening all background elements at the same rate indefinitely on a single dimension - why not use a Timer and bypass tweening libraries entirely?