I have a small project I am working on HTML5 canvas and I wanted to get some ideas how to accomplish it. I have built an outline of a tree using all the canvas line functions. lineTo, bezierCurveTo, quadracticCurve, etc. I have attached a picture of the outline. Now, what I would like to do is have some code that fills a percent of this outline. Kind of like a progress bar starting from the bottom. Does anyone have ideas on how to accomplish this?
Thanks
Rather than thinking of the problem as having to fill a percentage of the inside of the tree, why not split the image into two layers, the tree and the "fill", and then draw one over the other. See my image below for a quick and dirty example.
Of course, you will need to obscure the rest of the "fill" layer, so you will need to fill the outside of the tree shape white, but this should be fairly easy as you already have the path worked out. In essence, your path would instead of being the outside edge of a a tree shape, become the inside edge of a tree shaped hole!
Related
So... I have some sets of 6 pictures, like these http://www.humus.name/index.php?page=Textures , and I basically want to render them on an html5 canvas like this: http://www.allforthecode.co.uk/aftc/forum/user/modules/forum/article.php?index=5&subindex=4&aid=303
But I'd rather not use any 3d library such as webgl or three.js, since that's the only 3d-related feature I need and I want the whole thing to be as lightweight as possible.
I thought, "c'mon, it's just a rotating cube, can't be that hard!"
WRONG.
My original planwas to keep the camera position fixed, ant then to keep track of the x and y offset (in radians) of each vertex, and then to project them on my canvas and to deform the context accordingly to render each face of the cube.
That approach doesn't seem to work, tho, so... can someone give me a pseudocode algorithm?
I think a good way to tackle this problem is to use CSS3 3d transformations. There's quite a few turorials to be found on the web giving details on how to build a 3d cube with CSS. Instead of using <div>s to build the cube's sides, you could use <img> or even <canvas> elements. By playing around with perspective attributes you should be able to place the 'camera' inside the cube looking out.
I'm having trouble understand how DisplacementMapFilter works. Basically, I'm trying to create a revolving planet through a combination of fisheye/masking.
Also, how do I go about doing this via timeline? I'm not too familiar with coding within it, but this is more of an animation project than anything else, so classes are out of the question. Sorry for the lack of code -- I'm simply stuck.
As noted in the comments above, this probably only answers half the problem;
Generating a displacement map image isn't too difficult with the right tools. I'll assume you're using Photoshop, GIMP, Fireworks, or similar.
It's probably best to work on a 128x128 image or smaller with this method. Some editors have more specialised tools which let you work on pretty much any size of image, but this is a generic process that needs no special tools. You can always enlarge the end result, but the quality will begin to go down.
Start with a gradient fill. It should go from pure black on the left to dark red on the right (specifically 128,0,0). Add a vertical fill from black at the top to dark green at the bottom (specifically 0,128,0), and combine them with a LIGHTEN or ADD filter. You should now have an image which has black, red, green and yellow corners. Flatten it.
Copy this image to another layer / whatever the term-of-choice is for your editor. Apply whatever displacement filter you want to it (maybe a fish eye, maybe a manual smudge, maybe a perspective transform, anything)
Add a third layer between the two. Flood-fill it with dark yellow (128,128,0) and set it to ADD / ADDITION blend mode. Set the top layer to SUBTRACT / SUBTRACTION blend mode.
That's it. You should get a mostly yellow image which will function as a displacement map.
Update:
To use this in the example program (http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/filters/DisplacementMapFilter.html#includeExamplesSummary), replace the createBitmapData function with this:
private function createBitmapData():BitmapData {
return myBitmapObject.bitmapData;
}
where myBitmapObject is the instance name (I think) of your displacement Bitmap. There are tidier ways of setting that up, but this is the easiest.
this.context.drawImage(myimage, 0, 0);
Putting the image on the canvas is pretty well covered all over the web.
But how do I remove it after it's there?
Canvas is an immediate drawing surface. This means that you execute a command on it (drawImage or fillRect) and it does that command, and it doesn't give a damn what has just done. There is no undoing of something.
You had a hard time searching for it because there's no such thing as "removing" for a Canvas. All it knows is that it has some pixels of some color from somewhere. It has no idea where.
To simplify a bit, there are generally two ways:
Clear the entire canvas, and draw everything all over again EXCEPT the one image you do not want drawn
Use two canvases, one that only has the image and one with all the other stuff. Clear this canvas with clearRect(0,0,width,height) and you're done.
You'll notice in 1. that you will probably have to start keeping track of the things that you draw on canvas if you want some of them selectively removed or repositioned. Instilling object persistence, or rather turning canvas from an immediate drawing surface to a retained drawing surface, is something that a lot of canvas libraries do. If you want to do it yourself, I've written a few tutorails to help people get started.
If you want to look into libraries, take a peek at easel.js. It's pretty learnable.
Option 1:
Draw a rectangle over it of the same color as the background.
Option 2 (works for non-trivial background, but slower):
Get the pixel data from the canvas before drawing the image, then redraw that pixel data to remove the image.
So I came up with a quick and easy way to clear my canvas. I just put my <canvas> tags in between <p> tags with an Id, then each time i needed my canvas cleared I just rerendered my <p> tags by changing the innerHTML, works like a charm.
I have a basic paint application on a canvas, and I want to make a drawing-border and by that create a stencil. In other words, I want to make a shape, and then I want the user to be able to draw only inside it, even when he tries to draw outside.
Do you have any idea how can i do it?
thanks
This can be achieved by making a clipping region. The basic idea is that there is a path on the canvas that all drawing is constrained to.
Make the shape, and instead of calling stroke() or fill(), call clip()
If you don't quite get how clipping regions work, there are a few examples around.
Given an HTML canvas that has already been drawn to, what's the best way to shade the whole canvas except given circular regions? (in context: shadows except where are there light sources)
I was hoping it would be as simple as a rect() followed by subsequent arc()s, but AFAIK there's no way to "remove" those circular sections after the fact. I can get close ( http://jsfiddle.net/mW8D3/2/), but the overlapping regions of circles end up shaded (in XOR fashion, whereas I want OR). Using clip() has the same problem.
I've also tried using globalCompositeOperation but can't quite seem to achieve what I want.
Any ideas?
You could first create the shadow image on a second canvas and knock out holes from it with globalCompositeOperation 'copy' and a transparent fillStyle.
Like this: http://jsfiddle.net/mW8D3/4/