The elusive hitTest explained

Back by popular demand!

HitTest is a very useful, and can be used for just about anything (like ductape really). There are two main forms that it takes:

Code:

---

if(this.hitTest(another_clip)){
 // Something
}

---

This just tests the bounding boxes of this, and another_clip. If they hit, then the contents of the if will run.

Code:

---

if(this.hitTest(x, y, true)){
 // Something
}

---

This tests the point x,y against the contents of this, the actual shape and not the bounding box. The true is what makes it test against the shape and not the bounding box.

Anyone else want to continue?

(if it's an irrelevant post, it'll be edited out as this is a guide sticky, not just a general bantering one ;))

I am going to show you how to have a hitTest on your badguy so that if your hero touches it, it will decrease your life.

1.Goto your hero's instance box and name it "player"

2.Add a dynamic text box on your scene, and set it's variable to "life".

3.Add this code to Frame 1

Code:

---

life = 100;

---

Edit the life if you wish

4.Bring up the object actions panel for your enemy and add these actions:

Code:

---

onClipEvent (enterFrame) {
    if (this.hitTest(_root.player)) {
        _root.life -= 5;
        if (_root.life == 0) {
            _root.gotoAndStop(2);
        }
    }
}

---

These actions cause the variable "life" on _root (the one you set the dynamic text field to display) to go down by 5 each time the player and the enemy collide. It also makes the main timeline goto frame two, if the player runs out of life. You should put a gameover screen on frame two of _root.

There you go, test it out

[ed: Just tweaking a few readability things, thanks very much for this :D]

http://www.nlc.net.au/~oceana/games/bounding.gif

Thanks! Is there much more that we can do?

Here's code I'm quite fond of using for moving the player. It requires a clip on _root, called map containing the areas you're not allowed to walk on (It basically tests the bounding box of the object against an actual shape):

Code:

---

onClipEvent(load){
        s = 5;
        b = this.getBounds(this);

        function move(x,y){
                if(!_root.hit.hitTest(_x+x+b.xmin+1, _y+y+b.ymin+1, true)){
                        if(!_root.hit.hitTest(_x+x+b.xmax-1, _y+y+b.ymin+1, true)){
                                if(!_root.hit.hitTest(_x+x+b.xmin+1, _y+y+b.ymax-1, true)){
                                        if(!_root.hit.hitTest(_x+x+b.xmax-1, _y+y+b.ymax-1, true)){
                                                _x += x;
                                                _y += y;
                                        }
                                }
                        }
                }
        }
}

onClipEvent(enterFrame){
        if(Key.isDown(Key.UP)){
                move(0,-s);
        }
        if(Key.isDown(Key.DOWN)){
                move(0,s);
        }
        if(Key.isDown(Key.LEFT)){
                move(-s,0);
        }
        if(Key.isDown(Key.RIGHT)){
                move(s,0);
        }
}

---

Quote:

---

Code:

---

if(this.hitTest(x, y, true)){
 // Something
}

---

This tests the point x,y against the contents of this, the actual shape and not the bounding box. The true is what makes it test against the shape and not the bounding box.

---

This would be useful for, say, when leaving a level. Like your hero. once he hits a door or something, (this is for art-based), you would just set the right x and y coords and poof! Perfect for art based...

Ah well i'll gonna be a part of this to :)

This _x, _y, true thingy can also be used for games like this:
http://members.lycos.nl/saphua/games/newBouncy.swf

It will walk on the hill instead of on the bounding box :)

There are loads of files here on flashkit wich explain this very well (atleast bether than my [poor] english)

:doughnut::cow:

this works really nicely for art-based RPG's where you go from room to room, but is there any way to modify the code to make a large outdoor map that will start to scroll up/down/left/right as soon as the "hero" gets to the midpoint of the screen? If you still don't know what I'm talking about here's an example someone did that I'm trying to implement into my RPG engine, but i'm stumped on how to do it using the current script setup: http://www.geocities.com/mclelun/rpg.html

Any help would be appreciated. Thanx.

HI,
I just want to detect collision between two circles not with there bounding boxes but there actual shapes using shapeFlag property of flash.

I came acros this thread actual wherein the discussion is alrady on.
Anyway
we all know this is right
onCliEvent(enterFrame){
if(hitTest(_root._xmouse,_root._ymouse,true)){
trace(Hit is on);
}
}

This works fine with the _xmouse and _ymouse property.

But what If I want to do this witha movie clip but checking the actual shape of the movieclip not the bounding box.

something like :
onCliEvent(enterFrame){
if(hitTest(_root.mov._x,_root.mov._y,true)){
trace(Hit is on);
}
}

This also works but it works only when the center of the "mov" clip which is basically a circle is hit by the host movie clip i:e _x and _y of mov.

I want it to happen when the mov actaully collides iwth the host movielcip

So I treid

onCliEvent(enterFrame){
if(hitTest(_root.mov._x-_root.mov._width/2,_root.mov._x-
_root.mov._width/2,_root.mov._y-_root.mov._height/2,_root.mov._y+
_root.mov._height/2){
trace(Hit is on);
}
}


This is to detect the actual collison of the mov movie clip.
But this isnt happening.

Also I have heard that this type of hitTest method in flash consumes quiet an amount of memory resulting in lower fps.

Pls guide me if I am wrong somewhere.

thx

The easiest way to check if two circles hit, is to work out the distance between the two circle's centers, and check if it less than both circle's radias (?) added together.

that worked, that really worked.

thx edmack that was gr8 help.

this is what I tried and got it. The important thing is that I have totally eluded the hitTest function of flash.

onClipEvent (enterFrame) {
x = _x-_root.two._x;
y = _y-_root.two._y;
h = Math.sqrt((x*x)+(y*y));
rad = _width/2;
radTwo = _root.two._width/2;
sumRad = rad+radTwo;
if (sumRad>=h) {
trace("yes");
}
}
onClipEvent(load){
startDrag("", true);
}

two is the other movie clip on the stage.

Infact I am working on a pool game with this help I can really move ahead. I will start posting threads based on this.

thx again.

Quote:

---

Originally posted by Ed Mack

It requires a clip on _root, called map containing the areas you're not allowed to walk on (It basically tests the bounding box of the object against an actual shape):

---

Could you explain that code a lil better, im not sure exactly how it works...?

NeotiK, your engine is looking sweet.
Ed Mack, I think someone got an 'A' in geometry. ;)

is there a proper way to do a hitTest that checks if some one is clicking on the object? if not are you supposed to use buttons to do this? i have seen many games where a click alters a MC... (shoot-em-up types obviously)

-joe

try this

PHP Code:

---

onClipEvent(mouseUp){

if(hitTest(_root._xmouse,_root._ymouse)){
//Your statements here;
}
} 


---

Copy Paste the above code in movieclip.

don't need a "this." before the hitTest?
that's something good to know. just implied when inside a movieClip script?

If you do not write "this", ActionScript assumes you mean "this". I for one write it anyways, as it is just good coding practice. You can go back to it, and glide right over code and know whats happening because the "this" is highlighted.

a simple way of checking circles against all other shapes is to put an invisible edge round your shapes, that is the radius of the circle) and test the mid point of the circle, giving the impression of seamless collision detection

nb only works if one shape is a circle

Quote:

---

Originally posted by Psytrix
Could you explain that code a lil better, im not sure exactly how it works...?

---

Have a look at the fla (one of my faves):

The only problem is that the movement in computer is not the same as in realLife...

In realLife when an object goes for about 5 meter per second and then hits a very strong wall... a hit has been done...

But with the computer, when an object moevs for 50 pixels and between that 'jump' is a small wall... theres no hit

could someone please fix this? (I.m trying to but with no succes :S

heres a small .fla with my problem (if you didn;t understand hat I ment :)) (ITs MX!!!)

For this there are two fixes:

Define the walls as sets of points (a bent line) and the balls movement as a vector. Then just test the vector against the line(s). This requires a good bit of algebra knowledge, but can be a better system in the long run for collisions (just find the gradient of the line) and mass hitTesting.

OR

Do a set of checks, ie. one for every 10px the ball will travel that frame.

Hey, does this work with Flash 4? If not, is there an alternative?

Quote:

---

Originally posted by Ed Mack
For this there are two fixes:

Define the walls as sets of points (a bent line) and the balls movement as a vector. Then just test the vector against the line(s). This requires a good bit of algebra knowledge, but can be a better system in the long run for collisions (just find the gradient of the line) and mass hitTesting.

OR

Do a set of checks, ie. one for every 10px the ball will travel that frame.

---

And... how should I do that :)?

Quote:

---

Originally posted by Psytrix
Could you explain that code a lil better, im not sure exactly how it works...?

---

There seems to be a mistake....I used this link as an example. It is not my work. Sorry if I made it sound like it is. I am working on a game similar to this (creating my on custom sprites...zelda ones are too old) but the example I showed was used to illustrate what I'm trying to achieve: Map scrolling- when your character moves a certain distance and the screen begins to scroll.

This is my script in the "hero" mc using ed mack's tutorials with some adjustments:

onClipEvent(load){
this.sendmessage("I need to get to the village square.");
this.liftItem("map1");
s = 5;
b = this.getBounds(this);
movespeed = 5
function move(x,y){
if(!_root.hyrossia.hitTest(_x+x+b.xmin+1,_y+y+b.ym in+1,true)){
if(!_root.hyrossia.hitTest(_x+x+b.xmax-1,_y+y+b.ymin+1,true)){
if(!_root.hyrossia.hitTest(_x+x+b.xmin+1,_y+y+b.ym ax-1,true)){
if(!_root.hyrossia.hitTest(_x+x+b.xmax-1,_y+y+b.ymax-1,true)){
_x += x;
_y += y;
}
}
}
}
}
}

onClipEvent(enterFrame){
if(Key.isDown(Key.UP)){
if(_root.hero._y<180){
_root.hyrossia._y+=movespeed
_root.road._y+=movespeed
}else if{
_root.hyrossia.hitTest
}else{
move(0,-s);
}
}
if(Key.isDown(Key.DOWN)){
if(_root.hero._y>220){
_root.hyrossia._y-=movespeed
_root.road._y-=movespeed
}else{
move(0,s);
}
}
if(Key.isDown(Key.LEFT)){
if(_root.hero._x<330){
_root.hyrossia._x+=movespeed
_root.road._x+=movespeed
}else{
move(-s,0);
}
}
if(Key.isDown(Key.RIGHT)){
if(_root.hero._x>330){
_root.hyrossia._x-=movespeed
_root.road._x-=movespeed
}else{
move(s,0);
}
}
}

Now, "hyrossia" is the map mc. I have the map scrolling the way I want it now....but the problem now is the collision detection is out of whack (if the map is scrolling while you hit a wall you begin to go through it). Any solutions for this?

Quote:

---

Originally posted by SMcClure34
Hey, does this work with Flash 4? If not, is there an alternative?

---

Not in flash 4, with that I think the only way to check collisions is to set up some variables representing the edges of the target, a left edge, right edge top and bottom, then check if another point falls within this area.
That is, the x position of the point you test is greater than the leftedge variable and less than the rightedge variable. The y position of the point is greater than the topedge variable and less than the bottomedge variable.

Well, there is "_droptarget", look at this:

http://www.moock.org/webdesign/books...dragndrop.html

It basically tells you what MC the movie hit when dropped last

Quote:

---

Originally posted by Ed Mack
For this there are two fixes:

Define the walls as sets of points (a bent line) and the balls movement as a vector. Then just test the vector against the line(s). This requires a good bit of algebra knowledge, but can be a better system in the long run for collisions (just find the gradient of the line) and mass hitTesting.

OR

Do a set of checks, ie. one for every 10px the ball will travel that frame.

---

Theres still no answer on the most importand question in the d*mn hitTest thing!!! It's just the question of the quesions!!!

Plz help me for my dog's sake!!!
:doughnut::cow:

I have a question. Maybe this is simple. How about performing hitTest on multiple objects on multiple levels?

mulitple objects just needs a test for each one. maybe a for loop with an array of your objects like:

for (var i=0; i<numObjects;i++)
if (this.hitTest(hitObject[i]){
...

levels are easy too, just specify the level:

if (this.hitTest(_level1.object))

For the lines, having a solid knowledge of Algebra would be best... if I get time later I'll do an example of two lines and their gradients, then work out the intersection (through direct substitution).

Thanks for the insight. I have a good understanding of Algebra but I'm not sure about the hitTest. So far I have a gun:

Code:

---


if(_root.gun = "machine"){
counter++;
_root.bullet.duplicateMovieClip("bullet"+counter,counter);
_root["bullet" + _level0.counter]._visible = true;
_root["bullet" + _level0.counter]._x = this._x;
_root["bullet" + _level0.counter]._y = this._y;
_root.machineammo = _root.machineammo - 1;
}

---

so each bullet is incremented to a new level to prevent a new bullet from overwriting an old bullet. Is there a way around this? Then in my hit detection:

Code:

---

n = 1;
if (n < 20){
if (this.hitTest(eval("_root.person"+n))){
            if (_root.gun == "machine"){
                eval("_root.person"+n).hitpoint = eval("_root.person"+n).hitpoint+1
            }
}
this.removeMovieClip();
n++
}

---

Works fine for the first object I'm shooting but doesn't detect a collision for any object after the first. I've tried different ways of loading the objects into levels but I'm stumped on this one. How can I track the levels and make the hitTest detect them dynamically, i.e. I shoot person1 first and it takes damage but is not destroyed then I shoot person2 and it takes damage and both objects are still on stage but moving. Am I going in the right direction? Is there a better method for doing this in flash?

I'm thinking something like:

Code:

---

if(eval("_root.bullet"+n).hitTest(eval("_root.person"+n)._x+n,eval("_root.person"+n)._y+n,true){
//statement;
}

---

Any suggestions? My brain is about to run out of my ear. :D

Well, I would do it somthing like this:

To add bullets:

bc++; // bullet count
_root.attachMovie("bullet","bullet"+bc,bc); // make sure you goto the bullet clip in the library, right click on it, goto linkage and set the linkage name as "bullet"
bull = _root["bullet"+bc]; // save typing
bull._x = _x; // we are here
bull._y = _y;
_root.machineammo--;

For hitTesting:

for(i in _root){
if(i.substring(0, 2) == "per"){ // must be person clip
if(this.hitTest(_root[i])){
if(_root.gun == "machine"){
_root[i].hitpoint++;
}
}
}
}

Much the same as you...

In the people clips, put enterframe loops (onclipevent kind), and just make them test if(hitpoint < 10){ //keep walking }else{ //splutter and die

You have to place all the clips on different depths to keep everything working smoothly.

What are levels used for anyway? :D

This is from the ActionScript dictionary.
//start
The initial movie loaded into an instance of the Flash Player is automatically loaded into _level0. The movie in _level0 sets the frame rate, background color, and frame size for all subsequently loaded movies. Movies are then stacked in higher-numbered levels above the movie in _level0.

You must assign a level to each movie that you load into the Flash Player using the loadMovieNum action. You can assign levels in any order. If you assign a level that already contains a SWF file (including _level0) the movie at that level is unloaded and replaced by the new movie.
//end

Everything in Flash resides on a level. You can think of it as sheets of paper stacked on top of each other. Hope that helps.

If you don't understand how to make solid objects (stuff that your character can't walk through) then do this: Go here: HERE . I guarantee that you won't be dissapointed. Look at the "lastish" post, there I explain it pretty well - I think.

It's one of those pointless functions in Flash that need not exist.

this is how I do collision detection:


if((_x+_width/2>_root.object2._x-_root.object2._width/2 && _x-_width/2<_root.object2._x+_root.object2._width/2) && _root.object2.dead == false){
_root.object2.dead = true
}


that way you don't have to bother with stupid things like drawing boxs for hitTest and crap.

the only thing I've seen hitTest do that impressed me was "contour collision" in other words shapeflag.

but still you don't really need that for 90% of the games you will create.

congratulations segavenger, you just rewrote hitTest... well a simplified version of it with no shapeflag and which only works left and right on clips with centered registration points (and which takes longer to type out when used in your code).

yeah hitTest is like one of those other pointless functions, Math.cos. Id much rather use

Math.sqrt((Math.pow(b,2)+Math.pow(a,2)-Math.pow(a,2))/2*b*c)

I dont have Flash MX, so please dont punch me if this has already been fixed. i hope that macromedia can make the .hitTest() only work for the actual shape, not the bounding area(was that right?). another thing i noticed was that squaring a negative number produced a negative number. thats wrong. -2 squared is 4. another useful thing would be the inverse of sin, cos and tan, so that i can find the angel between two lines. if there is a formula for this already, can anyone tell me.

thnx

well yeah that was just a basic explanation. I didn't add the Y collision detection. I guess the reason I like to use this form of hitTest() is because I don't have to bother with boxes and things...
plus it makes me feel more like a 1337 coder :mrpimp:

I have three questions:

1. How can I have a shield meter above the health meter, and have it so that once my shield meter reaches 0, the health starts to go down?

2. How can I have enemies shoot lasers that hurt the player?

3. How can I have enemies with hit points?

I'm having trouble with my pacman clone, see it here.

My problem is that pacman and my ghost are getting caught up on the rounded corners. Anyone have any suggestions?

Thanks in advance