I'm using HTML5 lineTo but any stroke greater than 1 creates squarish looking corners on the lines (the stroke extends perpendicular to the path of the line you draw). I want to create a circular brush tip, similar to http://muro.deviantart.com.
Any ideas?
The corners can be rounded by setting the line cap.
ctx.lineCap = "round"
You can also apply a bezier curve to the overall line to create a smoother overall line, by, for each point in the line P'0, …, P'n + 1, applying the equation P'k = (k/(n+1))Pk-1+(1-(k/(n+1)))Pk [NB: You might do well to select which points to which you apply the smoothing of the bezier curve by setting a threshold, perhaps on the angle between Pn and Pn+1]
Combining these two techniques with a standard box blur to the line itself will give you a much smoother appearing line.
Edit
From what I can tell, there's actually a number of ways to do this – which you use is entirely up to you. I'll give you an example, and let you decide: Assume you have a path drawn from a beginning point pm (mousedown) to an endpoint (mouseup) pn. That path is made up of subpaths (the points joined by miters). We can draw the path to the context from p0 to p1 with lineTo() and stroke() as normal. Just from watching console output, the points at which the subpaths join is the mousemove event firing. Record these points in order in an array.
Of course if we draw this to the main context, we have a problem removing it, so this should be done to a buffer context (an additional canvas element, for instance). The buffer is cleared, and we use the points of the miters to calculate the curve. bezierCurveTo prints a cubic function (B(t) = (1-t)3P0+3(1-t)2P1+3(1-t)t2P2+t3P3, t ∈ [0,1]. Step through your array (think for loop) recalculating the line with those points, updating the curve from P0 to Pn-3. (Doing quick head-math. You might need to think over this endpoint. All of this is dependent upon which arcing equation you use).
So let me see if I can do something with this... I'm not testing it so I guarantee bugginess.
// Assume:
// bfr = buffer context.
// ctx = main context.
// md = boolean value for mousedown
// pts = []; <-- already contains lp (below) at pts[0];
// We've also recorded Pm in associative array lp [last point]
// Draw is fired on mousemove. Mousemove records a current point in associative array cp
draw = function() {
if(md) {
bfr.beginPath();
bfr.moveTo(lp.x-.5, lp.y-.5);
bfr.lineTo(cp.x-.5, cp.y-.5);
pts.push({cp.x, cp.y});
bfr.stroke();
}
}
// Optionally, you could make this function recursive.
// This assumes that you want to estimate the curve based on the whole line.
bezier = function(pts) {
ctx.beginPath();
ctx.moveTo(pts[0].x, pts[0].y);
for( var i = 0; i < pts.length - 3; i++ ) {
ctx.bezierCurveTo( pts[i+1].x, pts[i+1].y, pts[i+2].x, pts[i+2].y, pts[i+3].x, pts[i+3].y);
}
ctx.stroke();
}
Again, this is what I see – someone else may have an entirely different and I'm sure better interpretation. I'm trying to tear chunks of things I've done and put them together with some new code quickly to give you some idea.
Related
I'm working on a drawing app and the line quality seems to be very low and jagged compared to other drawing apps.
Or it might be that other apps are doing something different than I'm doing.
What I have done so far is use the graphics property to draw the lines. I also collect the mouse positions on the mouse move events for assigning to a path later on. Summarized it:
MouseDownHandler:
mouseDownPoint.x = event.stageX;
mouseDownPoint.y = event.stageY;
drawCommands.push(GraphicsPathCommand.MOVE_TO);
simplePath = "M " + mouseDownPoint.x + " " + mouseDownPoint.y;
MouseMoveHandler:
line.graphics.lineStyle(lineWeight, lineColor, lineAlpha, pixelHinting);
line.graphics.moveTo(previousPoint.x, previousPoint.y);
scaledPoint = new Point(localPoint.x/scaleX, localPoint.y/scaleY);
line.graphics.lineTo(scaledPoint.x, scaledPoint.y);
previousPoint.x = scaledPoint.x;
previousPoint.y = scaledPoint.y;
simplePath += " L " + scaledPoint.x + " " + scaledPoint.y;
MouseUpHandler:
myPath.data = simplePath;
As I draw I update the line (which is a UIComponent but could just as well be a Shape or Sprite - anything with a graphics property). At the same time I keep track of the mouse locations in the simplePath string.
When the mouse is up I clear the line graphics and show a path graphic element. The Path isn't important to this but I noticed it looks slightly cleaner than the line that had been drawn. That might be because it has pixel hinting (it's not much cleaner). Sometimes there are artifacts. And I'm including it in case I need to use a path for some reason.
Here is the screen shot:
The pixel hinted version looks crisper but it still is far below the quality of the line drawing in other apps and in some cases it makes it look more jagged. Is there something I'm missing?
Note: I included graphics2d and canvas2d because I believe this may not be related to the specific language or platform but might be related to drawing graphics in general.
The green line is produced by Graphics.cubicCurveTo(...) method. Initially you have a list of user-provided points A1,A2,A3...An. In order to use cubic curves you also need to figure 2 control points CFk (forward) and CBk (backward), for each Ak respectively, so you draw that big curve starting from A1 and every curve piece from Ak-1 to Ak will take arguments .cubicCurveTo(CFk-1, CBk, Ak);
For each Ak (except for A1 and An) you can calculate CFk and CBk as following:
(vector)AForward = (vector)(Ak+1 - Ak-1)
(vector)AForward.length = (vector)(Ak+1 - Ak).length / 3
CFk = Ak + (point)AForward
(vector)ABackward = (vector)(Ak-1 - Ak+1)
(vector)ABackward.length = (vector)(Ak-1 - Ak).length / 3
CBk = Ak + (point)ABackward
Then, there are A1 and An that are left out, but I am sure you can figure them on your own.
For vector math you can use ru.delimiter.math.Vector2D class (works with both Cartesian and Polar coordinates) from my small collection of useful things: https://bitbucket.org/thydmitry/ru.delimiter/src/9083fb46ce1c/classes/ru/delimiter/math/
P.S. Maybe you don't need to go that extreme and will be fine with the red line, that is a simple .curveTo(Ak, (Ak + Ak+1)/2);
UPD: a simple algorithm to inscribe a curve into zigzag provided by an array of points.
function middle(A:Point, B:Point):Point
{
return new Point((A.x + B.x) / 2, (A.y + B.y) / 2);
}
function drawTo(target:Point):void
{
graphics.lineTo(target.x, target.y);
}
function bendTo(control:Point, target:Point):void
{
graphics.curveTo(control.x, control.y, target.x, target.y);
}
// This should contain at least 2 points before you start drawing.
var PP:Vector.<Point>;
// Go to the start position.
graphics.lineStyle(0, 0xFF0000);
graphics.moveTo(PP[0].x, PP[0].y);
// Draw a straight line to the center of the first zigzag segment.
drawTo(middle(PP[0], PP[1]));
// For each 3 consequent points A,B and C, connect
// the middle of AB and the middle of BC with a curve.
for (var i:int = 2; i < PP.length; i++)
{
bendTo(PP[i - 1], middle(PP[i - 1], PP[i]));
}
// Connect the center of the last zigzag segment with the end point.
drawTo(PP[PP.length - 1]);
There are multiple reasons:
Stage quality. In Flash Player you can set the stage quality to LOW, MEDIUM, HIGH, BEST, 8x8, 8x8Linear, 16x16 and 16x16Linear. This affects if there is antialiasing applied on lines / paths and how many times it's applied. Increasing the quality helps but in 8x8 and higher quality there are bugs in the Flash Player (font size reduced by 25% on non-embedded fonts, graphics artifacts, gradient fills color count reduced).
Pixel snapping. If you have a 1px line that ends up positioned on a half pixel it is anti aliased over two lines. Normally antialiasing increases quality but in the case of an offset single pixel line it reduces quality. Setting pixel snapping helps.
Using curveTo and cubicCurveTo instead of line points as #Organis suggested. Not sure how to do this yet.
Will try to post images of the difference in each case when I get a chance.
So the issue that I'm having is that in developing an HTML5 canvas app I need to use a lot of transformations (i.e. translate, rotate, scale) and therefore a lot of calls being made to context.save() and context.restore(). The performance drops very quickly even with drawing very little (because the save() and restore() are being called as many times as possible in the loop). Is there an alternative to using these methods but still be able to use the transformations? Thank you!
Animation and Game performance tips.
Avoid save restore
Use setTransform as that will negate the need for save and restore.
There are many reasons that save an restore will slow things down and these are dependent on the current GPU && 2D context state. If you have the current fill and/or stroke styles set to a large pattern, or you have a complex font / gradient, or you are using filters (if available) then the save and restore process can take longer than rendering the image.
When writing for animations and games performance is everything, for me it is about sprite counts. The more sprites I can draw per frame (60th second) the more FX I can add, the more detailed the environment, and the better the game.
I leave the state open ended, that is I do not keep a detailed track of the current 2D context state. This way I never have to use save and restore.
ctx.setTransform rather than ctx.transform
Because the transforms functions transform, rotate, scale, translate multiply the current transform, they are seldom used, as i do not know what the transform state is.
To deal with the unknown I use setTransform that completely replaces the current transformation matrix. This also allows me to set the scale and translation in one call without needing to know what the current state is.
ctx.setTransform(scaleX,0,0,scaleY,posX,posY); // scale and translate in one call
I could also add the rotation but the javascript code to find the x,y axis vectors (the first 4 numbers in setTransform) is slower than rotate.
Sprites and rendering them
Below is an expanded sprite function. It draws a sprite from a sprite sheet, the sprite has x & y scale, position, and center, and as I always use alpha so set alpha as well
// image is the image. Must have an array of sprites
// image.sprites = [{x:0,y:0,w:10,h:10},{x:20,y:0,w:30,h:40},....]
// where the position and size of each sprite is kept
// spriteInd is the index of the sprite
// x,y position on sprite center
// cx,cy location of sprite center (I also have that in the sprite list for some situations)
// sx,sy x and y scales
// r rotation in radians
// a alpha value
function drawSprite(image, spriteInd, x, y, cx, cy, sx, sy, r, a){
var spr = image.sprites[spriteInd];
var w = spr.w;
var h = spr.h;
ctx.setTransform(sx,0,0,sy,x,y); // set scale and position
ctx.rotate(r);
ctx.globalAlpha = a;
ctx.drawImage(image,spr.x,spr.y,w,h,-cx,-cy,w,h); // render the subimage
}
On just an average machine you can render 1000 +sprites at full frame rate with that function. On Firefox (at time of writing) I am getting 2000+ for that function (sprites are randomly selected sprites from a 1024 by 2048 sprite sheet) max sprite size 256 * 256
But I have well over 15 such functions, each with the minimum functionality to do what I want. If it is never rotated, or scaled (ie for UI) then
function drawSprite(image, spriteInd, x, y, a){
var spr = image.sprites[spriteInd];
var w = spr.w;
var h = spr.h;
ctx.setTransform(1,0,0,1,x,y); // set scale and position
ctx.globalAlpha = a;
ctx.drawImage(image,spr.x,spr.y,w,h,0,0,w,h); // render the subimage
}
Or the simplest play sprite, particle, bullets, etc
function drawSprite(image, spriteInd, x, y,s,r,a){
var spr = image.sprites[spriteInd];
var w = spr.w;
var h = spr.h;
ctx.setTransform(s,0,0,s,x,y); // set scale and position
ctx.rotate(r);
ctx.globalAlpha = a;
ctx.drawImage(image,spr.x,spr.y,w,h,-w/2,-h/2,w,h); // render the subimage
}
if it is a background image
function drawSprite(image){
var s = Math.max(image.width / canvasWidth, image.height / canvasHeight); // canvasWidth and height are globals
ctx.setTransform(s,0,0,s,0,0); // set scale and position
ctx.globalAlpha = 1;
ctx.drawImage(image,0,0); // render the subimage
}
It is common that the playfield can be zoomed, panned, and rotated. For this I maintain a closure transform state (all globals above are closed over variables and part of the render object)
// all coords are relative to the global transfrom
function drawGlobalSprite(image, spriteInd, x, y, cx, cy, sx, sy, r, a){
var spr = image.sprites[spriteInd];
var w = spr.w;
var h = spr.h;
// m1 to m6 are the global transform
ctx.setTransform(m1,m2,m3,m4,m5,m6); // set playfield
ctx.transform(sx,0,0,sy,x,y); // set scale and position
ctx.rotate(r);
ctx.globalAlpha = a * globalAlpha; (a real global alpha)
ctx.drawImage(image,spr.x,spr.y,w,h,-cx,-cy,w,h); // render the subimage
}
All the above are about as fast as you can get for practical game sprite rendering.
General tips
Never use any of the vector type rendering methods (unless you have the spare frame time) like, fill, stroke, filltext, arc, rect, moveTo, lineTo as they are an instant slowdown. If you need to render text create a offscreen canvas, render once to that, and display as a sprite or image.
Image sizes and GPU RAM
When creating content, always use the power rule for image sizes. GPU handle images in sizes that are powers of 2. (2,4,8,16,32,64,128....) so the width and height have to be a power of two. ie 1024 by 512, or 2048 by 128 are good sizes.
When you do not use these sizes the 2D context does not care, what it does is expand the image to fit the closest power. So if I have an image that is 300 by 300 to fit that on the GPU the image has to be expanded to the closest power, which is 512 by 512. So the actual memory footprint is over 2.5 times greater than the pixels you are able to display. When the GPU runs out of local memory it will start switching memory from mainboard RAM, when this happens your frame rate drops to unusable.
Ensuring that you size images so that you do not waste RAM will mean you can pack a lot more into you game before you hit the RAM wall (which for smaller devices is not much at all).
GC is a major frame theef
One last optimisation is to make sure that the GC (garbage collector) has little to nothing to do. With in the main loop, avoid using new (reuse and object rather than dereference it and create another), avoid pushing and popping from arrays (keep their lengths from falling) keep a separate count of active items. Create a custom iterator and push functions that are item context aware (know if an array item is active or not). When you push you don't push a new item unless there are no inactive items, when an item becomes inactive, leave it in the array and use it later if one is needed.
There is a simple strategy that I call a fast stack that is beyond the scope of this answer but can handle 1000s of transient (short lived) gameobjects with ZERO GC load. Some of the better game engines use a similar approch (pool arrays that provide a pool of inactive items).
GC should be less than 5% of your game activity, if not you need to find where you are needlessly creating and dereferencing.
I'm doing a motion detection program and want to determine if a person is moving their hand in a clockwise or counterclockwise motion. Would someone know the best way to do this? (I'm coding in AS3, but any ECMA-like code would help).
I believe one way would be to determine if, for instance, a left-right is followed by a top-bottom or a bottom-top, and so on — is there a better way?
If you have a point of reference (0,0), you can sample the change in angle over time:
var sprite:Sprite = new Sprite();
var samples:Array = [];
setInterval(function(){
var len = samples.push(Math.atan2(sprite.mouseY,sprite.mouseX));
if ( len >=2 ) {
if ( samples[len-2]-samples[len-1] > 0 ) {
// clockwise
} else {
// counter-clockwise
}
}
},1000/stage.frameRate);
The reference is the top-left of the sprite (or its natural 0,0 point by atan2), so this snippet samples the mouse coordinate relative to the sprite.
Also, the more samples you consider (I'm only sampling 2 samples[len-2] and samples[len-1]) the better the decision for cw or ccw.
Lastly, and most importantly, my script does consider negative numbers in the radian calculations, it assumes everything is positive - this would require some tweeking.
PS: You'll want to clear samples every now and again since the array length will max out.
My script is incomplete, and I'd welcome edits, suggestions and elaborations. My hope is that it gives you something to consider and work from.
I'm currently struggling on a problem that seems far beyond my maths capacities (been a long time since I've made some proper maths...) and I would appreciate some help on that.
Here's my setting :
I got some simple shapes (rectangles), and I "project" their bottom points on a line, coming from an Origin point.
Up to this point everything is fine.
But now I'd like to draw the original shape distorted as if it was projected with some perspective on a plane.
Please consider that I have nothing related to any rotation, isometric or any 3D or fake 2D perspective in my code, I'm only trying to draw some shapes using the graphics library to only have a feeling of something real.
Here's a quick drawing of what I'm trying to do :
What I know :
Origin point coordinates
the rect position & sizes
the red line position
the A & B points coordinates
What I want to determine is the coordinates of the C & D points, thing that could be easy if I wasn't struggling to find the "Origin bis" coordinates.
What I'm trying to do is to fake the projection of my rectangle on something that can be considered as a "floor" (related to the plane where my original rectangle is that can be seen as a wall).
Maybe I'm over-complicating the problem or maybe I fail to see any other easier way to do it, but I'm really not good anymore in any geometry or maths thing... :-(
Thanks a lot for your answers !
hmm i don't know if I undestood it correctly but I think you have too few input parameters:
you said the following information is given:
Origin point coordinates
the rect position & sizes
the red line position
the A & B points coordinates
I don't think it is possible to get your projected rectangle with this information alone.
Additionally, I think your green lines and the 'origin Bis' aren't helpful as well.
Perhaps, try this:
Supose, a blue line going through the points C & D is given as well.
Then you could find your projected rectangle by projecting the top of the rectangle onto that blue line.
So in summary:
You define an origin + two parallel lines, a red and a blue one.
Then you can project the top of the rect onto the blue line and the bottom of the rect onto the red line, yielding the points A,B,C,D
I hope this helps.
If I'm right, this code will show what you wanted to see.
First of all, I've ignored your initial setup of objects and information, and focused on the example situation itself; fake-projecting shadow for a "monolith" (any object is possible with the example below, even textured)
My reason was that it's really quite easy with the Matrix class of ActionScript, a handy tool worth learning.
Solution:
You can use the built-in Matrix class to do skew transform on DisplayObjects.
Try this example:
(The "useful" part lies in the _EF EnterFrame handler ;) )
import flash.display.MovieClip;
import flash.geom.Matrix;
import flash.events.Event;
import flash.display.BitmapData;
const PIP180:Number = Math.PI / 180;
const MAX_SHADOW_HEIGHT_MULTIPLIER:Number = 0.25; // you can also calculate this from an angle, like ... = Math.sin(angle * PIP180);
const ANIM_DEG_PER_FRAME:Number = 1.0 * PIP180; // the shadow creeps at a +1 degree per frame rate
var tx:BitmapData = new MonolithTexture(); // define this BitmapData in the library
var skew:Number = -10 * PIP180; // initial
var mono:MovieClip = new MovieClip();
mono.graphics.beginBitmapFill(tx);
// drawn that way the registration point is 0,0, so it's standing on the ground
mono.graphics.drawRect(0, -tx.height, tx.width, tx.height);
mono.graphics.endFill();
// align monolith to the "ground"
mono.x = stage.stageWidth / 2;
mono.y = stage.stageHeight - 100;
// make it be 100x300 pixel
mono.width = 100;
mono.height = 300;
var shad:MovieClip = new MovieClip();
// colored:
shad.graphics.beginFill(0x000000);
// or textured:
//shad.graphics.beginBitmapFill(tx);
shad.graphics.drawRect(0, -tx.height, tx.width, tx.height);
shad.graphics.endFill();
addChild(shad); // shadow first
addChild(mono); // then the caster object
addEventListener(Event.ENTER_FRAME, _EF);
function _EF(e:Event):void {
// animate skew on the positive half circle
skew = (skew + ANIM_DEG_PER_FRAME) % Math.PI;
// Matrix takes 6 parameters: a, b, c, d, x, y
// for this shadow trick, use them as follows:
// a = width scaling (as mono and shad are drawn in the same way, copy mono.scaleX for a perfect fit
// b = 0, because we don't want to project the vertical axis of transformation to the horizontal
// c = horizontal skew
// d = height scaling * skew * making it a bit flat using the constant
// x = mono.x, ...
// y = mono.y since originally mono and shad look alike, only the Matrix makes shad render differently
var mtx:Matrix = new Matrix(mono.scaleX, 0, Math.cos(skew), mono.scaleY * Math.sin(skew) * MAX_SHADOW_HEIGHT_MULTIPLIER, mono.x, mono.y);
shad.transform.matrix = mtx;
}
Now all you got to know to utilize this in your case, is the following N factors:
Q1: from what angle you want to project the shadow?
A1: horizontal factor is the skew variable itself, while vertical angle is stored as constant here, called MAX_SHADOW_HEIGHT_MULTIPLIER
Q2: do you want to project shadow only "upwards", or freely?
A2: if "upwards" is fine, keep skew in the positive range, otherwise let it take negative values as well for a "downward" shadow
P.S.: if you render the internals of the objects that they don't snap to 0 y as a base point, you can make them seem float/sink, or offset both objects vertically with a predefined value, with the opposite sign.
You face 1 very simple problem, as you said:
'What I want to determine is the coordinates of the C & D points, thing that could be easy if I wasn't struggling to find the "Origin bis" coordinates.'
But these co-ordinates relate to each other, so without one (or another value such as an angle) you cannot have the other. If you are to try this in 3D you are simply allowing the 3D engine to define 'Origin bis' and do your calculating for C and D itself.
So regardless you will need an 'Original bis', another value relating to the redline or your Rect for which to calculate the placement of C and D.
I remember making stuff like this and sometimes it's better to just stick with simple, you either make an 'Original bis' defines by yourself (it can be either stationary or move with the player/background) and get C and D the way you got A and B only that you use a lower line than the red line, or as I would of done, once you have A and B, simple skew/rotate your projection from those points down a bit further, and you get something the same as an 'Original bis' that follows the player. This works fine at simulating 'feeling of something real' but sadly as has been said, it looking real depends on what you are portraying. We do not know what the areas above or below the red line are (sky/ground, ground/water) and whether 'Origin' and 'Origin bis' is your light source, vanishing point, etc.
I am making an achtung die kurve-like game in AS3.0. So far I've done the movements of the 4 different players, and it works alright.
I am now to make collision detection, in order to test if a 'worm'-so to speak, is colliding with eachother or its own tail.
As I understand it, if I use hitTestObject(); it will use the registration area of the whole object, which would be a huge problem, seeing since this registration makes a 4-sided registration that contains all of the object. So if this is used, it will 'collide' just by entering this rectangle instead of hitting the actual worm. Is this correctly understood?
I've been looking through different methods of collision detection, and can't seem to find an optimal one for my project.
My thought were to check if the 'worms' are drawing their new sprites on a white background. if they aren't, then it must have hit something.
You can see how I used my code here: code in .as format linked to an .fla file
Sorry for my ill-formulated question, hope it makes somewhat sense.
Any help is greatly appreciated!!
Best regards - Jesper
Try this function if you want a Pixel Perfect Collision Detection with efficient CPU usage:
trace("Collided: " + (areaOfCollision(mc1, mc2) != null));
trace("Where: " + areaOfCollision(mc1, mc2));
function areaOfCollision(object1:DisplayObject, object2:DisplayObject, tolerance:int = 255):Rectangle {
if (object1.hitTestObject(object2)) {
var limits1:Rectangle = object1.getBounds(object1.parent);
var limits2:Rectangle = object2.getBounds(object2.parent);
var limits:Rectangle = limits1.intersection(limits2);
limits.x = Math.floor(limits.x);
limits.y = Math.floor(limits.y);
limits.width = Math.ceil(limits.width);
limits.height = Math.ceil(limits.height);
if (limits.width < 1 || limits.height < 1) return null;
var image:BitmapData = new BitmapData(limits.width, limits.height, false);
var matrix:Matrix = object1.transform.concatenatedMatrix;
matrix.translate(-limits.left, -limits.top);
image.draw(object1, matrix, new ColorTransform(1, 1, 1, 1, 255, -255, -255, tolerance));
matrix = object2.transform.concatenatedMatrix;
matrix.translate(-limits.left, -limits.top);
image.draw(object2, matrix, new ColorTransform(1, 1, 1, 1, 255, 255, 255, tolerance), BlendMode.DIFFERENCE);
var intersection:Rectangle = image.getColorBoundsRect(0xFFFFFFFF, 0xFF00FFFF);
if (intersection.width == 0) return null;
intersection.offset(limits.left, limits.top);
return intersection;
}
return null;
}
After a successful preliminary hitTestObject(), this function backgroundly takes a snapshot from the shapes of both objects painted with different colors each, then overlays them intersecting the colors on a new one, returning the Rectangle of the resulting shape. So cool.
To learn more about Pixel Perfect Collision Detection you can google Collision Detection followed by one of these names: "The ActionScript Man", "Troy Gilbert", "Boulevart (wim)", "Grant Skinner (gSkinner)" or "Senocular". Those guys are awesome AS3 references by the way.
The problem you discribe is a very common problem for collission detection because the object has a set width and height and therefor defines a rectangle as the object.
There is a solution however to make a colission detection system on pixel level I have found this on the official site and this made me able to make collission detection for bitmaps on pixel level.
http://help.adobe.com/en_US/ActionScript/3.0_ProgrammingAS3/WS5b3ccc516d4fbf351e63e3d118a9b90204-7d55.html
hope it helps you out in the same way.
Looking at the screenshots of that game, I think the best model would be to describe each worm as a chain of circles. Then divide the world/level in a grid with cells somewhat larger than the circle radii.
The collision check would then be:
clear grid
place each circle into the 1 or more grid cells it falls in
iterate over all cells, for each cell:
for each pair of circles (partially) in this cell, check if they intersect. If they do; collision.
Note that this may result in more than 1 collision occurrence between circle A and B, so you'd also need to check that to avoid duplicates.
Step 1 and 2 can be optimized by not clearing the grid, and instead of step 2, updating each circle's cell after it moves. If you size your cells like 5x the size of a circle, a circle can stay in the same cell for a few frames, avoiding excessive add/remove operations.
I'm doing something similar in a project of mine right now, except with space ships! My grid cells are currently 256x256 (too big for your project I think) and my units have radii of about 20.