How to create a ring shape in Box2d - libgdx

Circles are solid and there's no way to create an empty space inside them, is there?
It is possible to create it using a combination of the basic shapes (Chains/Edges) but I was wondering if there was an easier way?

The easiest way to make a ring would be draw a larger circle of the primary color, then draw a smaller circle inside of the background color (if it's a solid color.) Otherwise, use a texture with a transparent center.

No, there is no way to create a space inside a circle in box2d. ChainShape and EdgeShape will work, but only if you are creating a ring that doesn't move. If you want a dynamic body your only option is compound polygon shape (Body with few convex polygon fixtures). Compound polygon shape is a good idea for static ring too.

Related

How to implement rotating rectangle around circle in libGDX Box2D?

I want to implement rotating rectangle around cicrle in such way, that circle has no rotation, and rectangle has. All object's are Box2D Body objects. Here is picture, what I want to have:
In my case rectangle touches circle, but I think it doesn't matter.
At first I tried to do it with two Fictures for same Body, but there was a problem with rotation: I couldn't have one ficture with rotation and another without.
I think, it should be somehow connected with joints, but I don't know what exactly Joint I should use. Maybe are there another solutions?
I think DistanceJointDef will do the tricks
you could put the radius if the circle as the distance with a little margin if you want
you also have to reduce the friction of bodies so the rectangle can move smoothly
DistanceJointDef djd = new DistanceJointDef();
djd.bodyA = bodyRactangle;
djd.bodyB = bodyCirlce;
djd.length = radius + margin;
world.createJoint(djd);
bodyRactangle is a dynamic body
bodyCirlce is a static body
try that for a start, hope it is helpful
Good luck !!

actionscript: creating a soft mask using vector shape

I have an hourglass like vector shape and I'd like to use it to mask an image. I'd like to feather the edges - have a soft falloff in transparency that follows the contours of the hour glass. Any ideas how I can do this?
I tried using a gradient fill on a closed shape (using beginGradientFill() and curveTo() functions) but that falloff doesn't follow the contour of the vector shape, it can only go one direction.
Maybe there is a better solution but until somebody comes up with it... I assume you could do the following:
Draw whatever shape you want to use as mask into a transparent bitmap.
Scale a bit the bitmap down (or use a matrix while drawing its bitmapdata).
Apply a blur filter to it.
Put the bitmap's center to the masked clip's center so they are aligned.
Set the masked clip's cacheAsBitmap property to true.

Masking in ActionScript3

I am trying to understand masks in actionscript..Everything seems to make sense to me but one part of the code
function mouseM(event:MouseEvent):void {
if (mouseclick == 1) {
mask_mc.graphics.beginFill(0x000000);
mask_mc.graphics.drawEllipse(mouseX, mouseY, 70, 60);
mask_mc.graphics.endFill();
}
}
I am not sure how to exactly ask this question but here it goes. why does the mask have "begin fill" with a black color? wouldn't that paint the the image in black (I know it doesn't, it just reveals it)? what is the exact function of beginfill (besides revealing the image lool)? like how does it exactly work? sorry if it sounds ridiculously off.. but that part of the code was really screwing me up in understanding masks
What you are doing is drawing a shape to be used as a mask. In this case, a circle.
It doesn't matter what colour it is as Flash is only interested in the shape of the mask, not the colour.
Once the circle is drawn, Flash checks what part of the circle overlap the object you're masking so that every pixel the circle is not covering will be invisible. I guess it should really be called an anti-mask as the circle dictates which parts of your image wont be masked but it's just become the general convention to call the circle (or whatever shape you use) the mask.
Again, you're just creating a shape to be used as a mask. Setting the colour is just so the object can essentially exist.. because you can't exactly have a transparent circle.
Feel free to change the colour to anything and you'll see it makes no difference, the shape is all that matters.

how to set one continuous background image for multiple elements

I've been wrecking my brain trying to figure this out. is there any way to set one background image in css for multiple elements? I have a square-ish speech bubble, made with regular css, the triangle made with the border technique, but i want an background image to fill them both so it looks like a cut out all together.
I dont know any other way to design a solid shape using html/css other than squares and rectangles. If i could create a speech bubble as one solid shape, then giving it a bg would be simple lol.
I was wondering about html5's drawing capabilites, but im not sure...
Any ideas?
Edit: No, there's no option to do what you want. But if you wanna do spech bubbles, you can check any of these links:
http://nicolasgallagher.com/pure-css-speech-bubbles/demo/
http://konigi.com/tools/css-tooltips-and-speech-bubbles
http://desandro.com/resources/css-speech-bubble-icon/

Creating a canvas on top of an SVG (or other image)

The reason for asking this question is because I want to be able to draw an arrow between two svg images. I want to use canvas to create the arrows, so firstly I generate the svgs then place a canvas on top of them to be able to draw the arrows.
I've tried using style=... but haven't had any luck as everytime I add the canvas element it just pushes my svg images to another pl
If there's no easy way to do this I'll just create arrows using SVG, I figured it would be more efficient to use canvas if I had to do lots of arrows in a short amount of time.
You need position:absolute on the CSS for the canvas to take it out of the flow, and then you can layer it as you like using z-index.
However, I instead suggest that you can use one or two tiny canvases to create the arrowheads and use toDataURL() on them to create a url you can use for <image> tags in the SVG. This way all your graphics are in SVG but you can use the canvas for complex raster effects if you need to.
have you tried z-index? it's a useful css trick
#svgcontent
{
z-index:1
}
#html5content
{
z-index:3
}
EDIT: accidentally screwed the #s up. 'scuse me.