I know there is this question which suggests looping through all canvas elements on each mouse move.
However, is there a more effective way than looping through all the elements?
I have quite a few elements on the canvas and looping through them all on each mouse move could be very, very slow.
Yes, you have to loop through all of your elements.
That's how nearly all hit testing/object picking works.
Now there are a lot of optimizations you can do, like making sure that the mouse coordinate is in the rectangular bounds of the object before you test its real bounds (unless they're all rectangles, which would make everything convenient and fast, even if there are 10,000 objects). If you have a million objects, you could also split up their location into quadrants, or otherwise add a layer of isolation.
But at the end of the day you need to loop through every relevant object and ask if its bounds intersect the mouse point. There's no way of getting around that. It ought to be fast, and if you've implemented something that is very slow then you should post it so we can take a look and give you pointers.
If you need to see a live example I made a simple tutorial on picking and moving shapes in a canvas exactly for explaining situations like this.
Looping through 10000 of elements is still no effort in javascript.
However you might consider looping throught them with some interval not on every mousemove.
var mouseX, mouseY;
$(document).on("mousemove", function(e) {
mouseX = e.pageX;
mouseY = e.pageY;
/* dont do any probing there */
});
setInterval(function() {
checkCollision();
}, 25);
Related
I´m programing a space ship side scroll in as3. The bottom of the stage are mountains and here comes the problem, when I try to detect the ship collision against the mountains..
Because the poor collision detection and the need of avoid large loops my idea is create an object that works as a collider itself detecting a collision and avoiding parse all the stage or more selective metod.
I place "by hand" in the flash stage several instances of circles with a class for manage them where I place the If(this.collider.hits(ship)....
I spent looong time but I can find the way to make it work some of the mistakes i get are like this
Error 1061: Call to a possibly undefined method hitTestObject through a reference with static type Class.
some Idea? Thanks in advance
when you hit test with points it is important that the point being tested is relative to the object being tested against, eg
if(mountain.hitTestPoint(this.x + circle1.x, this.y + circle1.y))
will return true if the circles are inside the object calling the function because their position relative to the mountain is now relative to it rather then relative to the ships xy position within the clip... hope that makes sense.
btw I have done this myself in the past but I would have to remind you that you can only hit test with the points so there is no need to have circles, use blank sprites instead and set the visible flag in the properties panel to false, no drawing will make it slightly faster... not that you will notice, also sprites/graphics use less memory then movie clips.
also I would recommend hard coding some points in the clips rather then actually adding the clips in the sprite/clip itself, this will make it easier to work with them and scale later on (believe me this will annoy the hair from your head to do something later and slow the game to scale on the fly)
try something like this... you can determine the points values by adding a clip to the movie clip and getting its position from the properties if you must.
private var hitPoints:Vector.<Point> = new Vector.<Point>
hitPoints.push(new Point(10, 40));
hitPoints.push(new Point(30, 40));
//...do this for all your points
//loop through all your points and check if the hit relative to the ships position.
for(var i:int = 0; i < hitPoints.length; i++)
{
if (scene.hitTestPoint(ship.x + hitPoints[i].x, ship.y + hitPoints[i].y))
{
//do your hit stuff here
break;//don't forget to break
}
}
in this code you will need to make sure the scene object is a reference to your scenery at the bottom of the screen.
I hope this helps but if this is not enough help then you should post some of your code here so we can have a look and see where it can be improved.
I simply added a sprite in AS3:
Sprite myspr = new Sprite();
myspr.addChild(mybitmap);
addChild(myspr);
Then I added an event. I did hitTestPoint for checking mouse is over my sprite or not.
stage.addEventListener(MouseEvent.MOUSE_MOVE, mouseCheck);
private function mouseCheck(evt:MouseEvent):void {
var xx:int = stage.mouseX;
var yy:int = stage.mouseY;
if(myspr.hitTestPoint(xx, yy, true)) {
...
// I'm checking mouse over here.
}
evt.updateAfterEvent();
}
Problem is: hitTestPoint gives true when mouse comes to full boundary box. But it should give true only if mouse comes on transparent isometric sprite.
Is there a solution for this, thanks in advance.
this should help. You need pixel perfect detection.
Actionscript 3 pixel perfect collision. How to? (learning purposes)
http://www.freeactionscript.com/2011/08/as3-pixel-perfect-collision-detection/
http://www.anotherearlymorning.com/2009/07/pixel-perfect-collision-detection-in-actionscript-3/
http://old.troygilbert.com/2009/08/pixel-perfect-collision-detection-revisited/
There's a few ways I usually do hit testing.
1) The easiest way is to use a an already made class that you can find online. Some people much smarter than me have created complex classes that allow for much better pixel to pixel interaction. The ones listed by Paras are all good. The problem with these is, for newer users, it can be hard to understand all the code and how to implement them. Usually it is simple once you understand what is going on though. You just replace your hit test with the class file and then enter in the correct arguments.
2) Another method is to actually go into the symbol, create a new layer, and then draw a rectangle(just turn the alpha down to 0%) where you want the hit test to work. This may seem like a stupid method, after all we are just confined to a square once again. BUT, it will actually work MUCH better than you'd expect. Just draw the square maybe slightly smaller than the height and width of your character you're detecting the hit test on, and you should be good to go. Give it an instance name (the hit square that is) and then just perform the hitTest with that square instead of the actual sprite. It works wonderfully and is a very simple solution. For what you're explaining though, this sounds like it might not work. This method is more from a gamer standpoint. It looks good when attacking and getting hit by enemies, but isn't necessarily exact. Also, if you want to do this with two characters (maybe a large attack hitting an enemy) simply draw a hit box for both sprites. This is probably a little more basic than using a pre-made pixel perfect hit detection test, but it works extremely well and takes only a few minutes.
Is it possible to create an application using Kinetic.js where you create a shape, then scale it as you move the mouse around? I couldn't find anything in the Kinetic APIs, so I am mixing in "raw" JQuery. In particular, I use $("canvas").last().mousemove function, but it turns out this is actually very slow.
Here is the JSFiddle.
Any tips on making it faster?
I don't think the Kinetic.js has support for layer.on("mousemove", fn), because it seems to only apply to shapes.
yes. You would do something like this:
$('#container').on('mousemove', function(evt) {
shape.setScale(someValue);
layer.batchDraw();
});
In other words, attach a mousemove listener to the container div element (the one you pass into the Kinetic stage). set the shape scale with the setScale() method. Use batchDraw() instead of draw() so that the draw operation hooks into the KineticJS animation engine for much better performance. Otherwise, if you use draw(), you'll be redrawing the entire layer each time a mousemove event is detected, which could be hundreds of thousands of times per second depending on the browser
So this one is a tricky one (for me) vital to the development of my project due to the fact that we can't directly modify the position of mouseX and mouseY - they are read-only variables.
Basically, what I want to do is have a player able to move their mouse only within a certain triangular area when a specific instance is active. The latter bit I can manage just fine, however I am having trouble restricting mouse movement -- or apparent mouse movement.
Here's what I have done so far:
1. Assign a library moveclip to the mouseX and mouseY position in the Event.ENTER_FRAME event - although I acknowledge that this should be moved to Mouse.MOUSE_MOVE. (this does not matter yet)
2. Using Corey O'Neils Collision detection kit, do a hit test on the border instances of the area with the crosshair/cursor.
3. Offset the cursor appropriately, and then set a standard Boolean value to false so that the cursor will not keep bouncing back into the cursor over and over.
My problem is, I am not sure what the best way is to go about allowing mouse movement again. Can anyone give me some tips on the best way to do this, or if necessary, point me in another direction where restricting mouse movement is a little easier?
For what it's worth, this is to stop users from aiming in an unrealistic direction with a character in a top-down (ish) shooter.
For those unfamiliar with Corey O'Neil's Collision Detection Kit, I believe it is just a pre-built setup of bitmap (or maybe vector) collision testing - I could be wrong. I'm not sure on the details of how it works, just its basic implementation.
Here is my code regarding mouse movement thus far:
import flash.ui.Mouse;
import flash.events.event
import com.coreyoneil.collision.CollisionList;
Mouse.hide();
var c:crosshair = new crosshair();
addchild(c);
var myCollisionList:CollisionList;
myCollisionList = new CollisionList(c); //sets up detection for the object c
myCollisionList.addItem(mcB); // adds mcB to the list of objects to check c's hittest with
function aim(e:Event) {
var collisions:Array = myCollisionList.checkCollisions();
if (collisions.length>0)
{
hashit = true; // tells the program that the mouse has collided with a boundary
c.x += 1;
c.y += 1;
}
else
{
if (hashit == false)
{
c.x = mouseX;
c.y = mouseY;
}
}
}
Apologies for the code block, but I figure it is best to show all relevant code -- I'm not sure about the complexity of this issue due to the read-only nature of the mouse's X and Y position.
Also, I'm looking for a possible solution which will not be clunky - that is, as soon as the mouse is back in the area, mouse movement will be smooth as it is originally, and where the cursor will still be matching the mouse position (meaning, the cursor is ALWAYS relevant to the mouse and will not change position should the mouse leave the boundaries).
Could anyone please give me some pointers? Sorry for the long question. I gather there might be a bit to get my head around here, being relatively new to AS3 - but I still feel this is a problem I can get past, if one of you can show me the right direction and help me with both the logic and programming side of things slightly.
Here is a diagram of my stage to clarify the boundary areas etc.
Thanks very much for any help in advance, I really do appreciate it!
Cheers, Harry.
How about trying getObjectsUnderPoint which returns an array of objects under a certain point.
If your triangle object is within the array the cursor must be above it.
var pt:Point = new Point(c.x, c.y);
var objects:Array = stage.getObjectsUnderPoint(pt);
if (objects.indexOf(triangleObject) > -1) {
trace("still within bounds");
}
The workaround here could be to hide the system mouse cursor and add a bespoke cursor movieclip to the stage.
Using a MOUSE_MOVE event listener attached to the stage, set the bespoke cursor movieclip to match the stage.mouseX and stage.mouseY values and also test whether the movieclip is outside your bounds. If so, set it back within your bounds.
Say I want a ball bouncing at 5 frames per second and only want to have a square bouncing at 2 frames per second, how is this possible?
return setInterval(draw,10) is used in the current simulation to move 1000 particles around, but I also want to draw a radial gradient on a second canvas which gets data from the particle simulation. I cant figure out how to draw the gradient a frame per second and the particles at another framerate
What i do is create a Timer constructor, and everytime I make something animate, i make a var animateThing = new Timer().
It may not be necessary to do this, but it can be a useful peice of code as you get deeper into canvas with more moving parts.
Update
So something sorta like this.
function Timer(fps, callback) {
return setTimout(callback, 1000 / fps);
}
var timer1 = new Timer(33, callback1);
var timer2 = new Timer(55, callback2);
Now that's probably not gonna work, but it's the idea.