Creation of a game like String Avoider tutorial
Filed Under Flash •
A really interesting "avoidance game" that was made in those days is String Avoider. The author of this "More than 1 million views" game in Newgrounds explains it in 12 words: "Avoid colliding with walls and guide your string through each unique level".
And that's it. The aim of the game is guiding your string through some levels without touching the walls.
It's very similar to the ball game I am discussing in this site, but this time the ball is controlled by the mouse and has a "tail" that responses in a very "real life" way.
Something very hard to code, you may say. It's not that hard to reproduce a string movement in Flash, even if the built-in string class does not help us...
(laugh)
... but let's start with the tutorial.
The string
A string is made of two objects: the head and the tail. The player will control the head, while the tail will follow the head. That's it.
So, the first thing to do is the creation of the head. The picture below shows how to draw, position and link the head
Then in main scene first frame simply drop this actionscript
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tail_len = 2;
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tail_nodes = 100;
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nodes = new Array();
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_root.attachMovie("the_head", "the_head", 1, {_x:250, _y:200});
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_root.createEmptyMovieClip("the_tail", 2);
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for (x=1; x<tail_nodes; x++) {
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nodes[x] = {x:the_head._x, y:the_head._y};
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}
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the_head.onEnterFrame = function() {
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this._x = _root._xmouse;
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this._y = _root._ymouse;
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the_tail.clear();
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the_tail.lineStyle(2, 0x00ff00);
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the_tail.moveTo(the_head._x, the_head._y);
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nodes[0] = {x:the_head._x, y:the_head._y};
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for (var x = 1; x<tail_nodes-1; ++x) {
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rotation = Math.atan2(nodes[x].y-nodes[x-1].y, nodes[x].x-nodes[x-1].x);
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pos_x = nodes[x-1].x+tail_len*Math.cos(rotation);
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pos_y = nodes[x-1].y+tail_len*Math.sin(rotation);
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nodes[x] = {x:pos_x, y:pos_y};
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the_tail.lineTo(pos_x, pos_y);
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}
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};
Line 1: Defining tail_len variable at 2. What is tail_len? It's the length in pixels of the fixed part between two nodes.
Line 2: Defining tail_nodes as the number of nodes that will contain the tail.
Time to give some explication: in real world, a string can bend in any of its points. In flash world, we do not want it because it will use too much computer resources and we do not need it because it's just a game. So, if we want a string 200 pixels wide, we can use the "real world" method defining tail_len at 1 and tail_nodes at 200, or we can simplify computer's work setting tail_len at 2 and tail_nodes at 100. Just remember that tail_nodes*tail_len = real tail length for high values of tail_nodes.
Line 3: Declaration of the array where will store all nodes positions
Line 4: Attaching the "head" movie on the stage positioning it in middle of it.
Line 5: Creation of an empty movie clip called "tail" that will contain the tail of the string
Lines 6-8: Cycle that creates all nodes positions. Their starting positions, defined as coordinates, at the beginning are equals to head's _x and _y coordinates
Line 9: Function to be executed at every frame
Lines 10-11: Placing the head at current mouse x and y positions
Line 12: Clearing the tail movieclip
Line 13: Setting the line style of the tail movieclip with a stroke height of 2 filled with green. For more information about drawing and line styles, check this tutorial.
Line 14: Placing the "pen" that will draw the tail on the same head _x and _y positions
Line 15: Defining the first node coordinates (nodes[0]) and the same head _x and _y positions. The first node actually could be the head itself, but I wanted a bigger head so I designed it as a separate movieclip.
Line 16: Beginning of the main loop, that will scan all nodes except nodes[0]. In this case, nodes[1] to nodes[99]
Line 17: Obtaining the angle between the xth and the (x-1)th node. This is done using trigonometry. I wrote a tutorial about it here. You may notice that is a bit different than the atan formulas used in that tutorial, but I discovered atan2 is often more useful than atan in applications involving rotation by a specified amount, because it returns a positive beta for all angles between 0 and 180 degrees (even when x is negative).
Thus it eliminates the need for extra code to deal with different values in different quadrants of the circle.
Lines 18-19: Here trigonometry is involved to calculate new node[x] x and y positions according to its angle with node[x-1]
Line 20: New x and y positions are saved in node[x]
Line 21: Drawing a line from the previous pen position to new x and y positions
And that's it! We have our moving string. Time to test for some collisions!
Collisions
I created a movieclip linked as wall and placed it on the stage.
Then the actionscript is:
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tail_len = 2;
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tail_nodes = 100;
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nodes = new Array();
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_root.attachMovie("the_head", "the_head", 1, {_x:250, _y:200});
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_root.createEmptyMovieClip("the_tail", 2);
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_root.attachMovie("wall", "wall", 3, {_x:250, _y:200});
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for (x=1; x<tail_nodes; x++) {
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nodes[x] = {x:the_head._x, y:the_head._y};
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}
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the_head.onEnterFrame = function() {
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this._x = _root._xmouse;
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this._y = _root._ymouse;
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the_tail.clear();
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the_tail.lineStyle(2, 0x00ff00);
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the_tail.moveTo(the_head._x, the_head._y);
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nodes[0] = {x:the_head._x, y:the_head._y};
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for (var x = 1; x<tail_nodes-1; ++x) {
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rotation = Math.atan2(nodes[x].y-nodes[x-1].y, nodes[x].x-nodes[x-1].x);
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pos_x = nodes[x-1].x+tail_len*Math.cos(rotation);
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pos_y = nodes[x-1].y+tail_len*Math.sin(rotation);
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nodes[x] = {x:pos_x, y:pos_y};
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if (wall.hitTest(pos_x, pos_y, true)) {
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the_tail.lineStyle(2, 0xff0000);
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}
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the_tail.lineTo(pos_x, pos_y);
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}
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};
Line 6: Placing the wall on stage
Line 22: Hit test between pos_x, pos_y coordinates and the wall
Line 23: If the test is positive, then change the line color to red. In this way you can view where you collided.
And now you're ready to create some string game... download the source code and send me your works!
Tell me what do you think about this post. I'll write better and better entries.
(2 votes, average: 5 out of 5)
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33 Responses to “Creation of a game like String Avoider tutorial”
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Awesome!
nice but what is the code so when it hits the wall it goes back to the begning position! And same for exit it goes to end
thanks
heelo emanuele, i have posted a link to this tutorial at http://www.beedigital.net/blog I hope you don´t mind…
Nice blog you have here, great tutorials….
See you around.
Awesome, cannot believe how simple you make it seem, lol.
To Mousey:
Simply reset the head’s X and Y to wherever your start is inside the hitTest.
if(wall.hitTest(pos_x, pos_y, true)){
this._x = 250;
this._y = 200;
}
Cooool!!!
good but what abount a second to youre platform game linke have enemys but good tut
I apologize, but in my mind this isn’t your best tutorial… I have no clue about how the string actually follows the mouse as it does, when the tail snail it’s way like it does. Could you post a part 2 that explains the calculations? :)
Let me try to explain the trigonometry, Emanuele will correct me if I’m wrong:
1.rotation = Math.atan2(nodes[x].y-nodes[x-1].y, nodes[x].x-nodes[x-1].x);
Finds the angle(direction) between the current node and the previous
node. This happens because the position of each node depends on the position of
the previous node. This way, the nodes remain tail_len pixels apart.
_
nodes[x-1]->(_)
\
\
\ (_)
———————————————————————–
_
(_)_____
\ |
\ |
Man, my comment was cut if half.
Let me try again.
Let me try to explain the trigonometry, Emanuele will correct me if I’m wrong:
1.rotation = Math.atan2(nodes[x].y-nodes[x-1].y, nodes[x].x-nodes[x-1].x);
Finds the angle(direction) between the current node and the previous
node. This happens because the position of each node depends on the position of
the previous node. This way, the nodes remain tail_len pixels apart.
_
nodes[x-1]->(_)
\
\
\ <— angle of this line from the
\ horizontal is calculated
\
\_
nodes[x]—>(_)
———————————————————————–
_
(_)_____
\ |
\ | <– distance equals tail_len
\ |
\__|
nodes[x] will be moved here ____/\
so that the distance remains \_
tail_len (_)
=======================================================================
2.pos_x = nodes[x-1].x tail_len*Math.cos(rotation);
Calculates the x position of the current node after it has been moved.
___length of this line equals
_ | _tail_len * Math.sin(rotation)
(_)__(_)
\ |\
\ | currently, the node would be moved
\ | here
\|
\
\
=======================================================================
3.pos_y = nodes[x-1].y tail_len*Math.sin(rotation);
Calculates the y position of the current node after it has been moved.
_
(_)___
\ |
\ |<— length of this line equals
\ | tail_len * Math.cos(rotation)
\|
(_) <— this is where the node finally ends up
\
<— As you can see, the node just
moves straight towards the previous node
=======================================================================
4.nodes[x] = {x:pos_x, y:pos_y};
Updates the nodes[x] coordinates
=======================================================================
5.the_tail.lineTo(pos_x, pos_y);
Draws a line (tail_len long) from current pen position
(nodes[x-1].x,nodes[x-1].y), to the current nodes position
(nodes[x].x,nodes[x].y or pos_x,pos_y)
=======================================================================
Hope this helps you out. Why the sin and cos statements work are
explained in the tutorial Emanuele mentioned
Do these files work in Flash MX? I can’t get any of these to work. If not, is there a quick fix to make them work in Flash MX? I’d love to try these out…
I’ve been looking how to make a game like this. Thanks.
I noticed that actually there will be one less node than defined. What is causing this.
Ok sorry for posting this question since it’s explained already. But if you want the same amount of nodes you defined, in line 16, remove the “-1″
I created a game where the nodes would actually go where the node in front of it in the last frame. Though I’m wordering how to convert it so it will be like the nodes in this tutorial instead of manually making each mode.
_root.attachMovie(”node”,”node1″,1,{_x:20, _y:100})
_root.attachMovie(”node”,”node2″,2,{_x:275, _y:200})
_root.attachMovie(”node”,”node3″,3,{_x:375, _y:300})
_root.createEmptyMovieClip(”line1″,4)
_root.createEmptyMovieClip(”line2″,5)
_root.createEmptyMovieClip(”line3″,6)
Mouse.hide()
onEnterFrame = function() {
node1._x = _xmouse
node1._y = _ymouse
node2._x = pos_x1
node2._y = pos_y1
node3._x = pos_x2
node3._y = pos_y2
line1.clear()
line2.clear()
line1.lineStyle(10, 0xabcdef)
line2.lineStyle(10, 0xabcdef)
line1.moveTo(node1._x,node1._y)
line2.moveTo(node2._x,node2._y)
line1.lineTo(node2._x,node2._y)
line2.lineTo(node3._x,node3._y)
pos_x1 = node1._x
pos_y1 = node1._y
pos_x2 = node2._x
pos_y2 = node2._y
}
I tried in the first time as u said in the turorial…but seems somewhere i m not doing the correct coding or misspelled something ….anyways..nice tutorial..!!
it doesnt work!!
when i apply the first script it doesnt work y?
wow this tuturial is nice!!!
guyz can anyone tell me how can i make the tail become red when the head touch my own tail?
I made String Avoider :D
Nice tutorial
Hi! I liked this tutorial very much - as like all the rest of your tutorials…
Anyway, I’ve been trying to make something similar to the string you made here, but waht I want was not a string, but a text following the mouse, and then I found this:
http://www.a-to-s.co.uk/home.php
click on N and you’ll see… would you please help me? I need this for a graduation project =)
thanks in advance
Flavio
what action script is this?
Hi Guys, i have this working, i have a timer also set, but everytime i get the game to move to a diff “scene” in Flash the sting allways appears to start from the centre, i have only added a “gotoandplay” function and this just carrys on the action script for the string creation..can you please help me with how to stop this script from being carried over to the other “scene’s” in flash
thank you
to make the line follow the mouse without the head, just make the colour of the heads alpha 0%. This will make it invisible
Could anyone post something for color codes?
I can make the tail black, otherwise it is a hit and miss situation.
i need a action script to make the wall move
—————–
blahblah
i am willing to help, i am sorry if i am too late, but what do you want to happen exactly?
I’m making a game with this code
http://dev.mrnat.com/bomb_sorter.swf
It’s not done yet, but do you want me to credit you?
it would be very kind…
Are you sure I can use it?
I really don’t like copying other people’s work…
hey how do you keep the wall not moving with the mouse but so it stays in one place
Does anyone know the code to make the tail (last node of the string) stationary (fixed) at a certain x,y coordinate? I want the string to follow the head but be limited to the tail_len… I am also trying to have the head drag rather than follow the mouse.
Is this possible?
Thanks!
PS: Great tutorial…
hey I put it all in and got a problem with the actionscript for the wall this is what it says
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 1: Statement must appear within on/onClipEvent handler
tail_len = 2;
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 2: Statement must appear within on/onClipEvent handler
tail_nodes = 100;
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 3: Statement must appear within on/onClipEvent handler
nodes = new Array();
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 4: Statement must appear within on/onClipEvent handler
_root.attachMovie(”the_head”, “the_head”, 1, {_x:250, _y:200});
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 5: Statement must appear within on/onClipEvent handler
_root.createEmptyMovieClip(”the_tail”, 2);
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 6: Statement must appear within on/onClipEvent handler
_root.attachMovie(”wall”, “wall”, 3, {_x:250, _y:200});
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 7: Statement must appear within on/onClipEvent handler
for (x=1; x<tail_nodes; x++) {
Scene=Scene 1, Layer=Layer 1, Frame=1: Line 10: Statement must appear within on/onClipEvent handler
the_head.onEnterFrame = function() {
please email me the answer
Does someone know how to convert this code to AS3?? I’m struggling with it for the whole week now but can’t get a clue out of it! please help!