Is there a possibility to fill a rectangle with a picture and not with color in jCanvas?
I would repeat the pic in the rectangle like in css for example:
background-repeat: repeat;
To fill a pattern with an image, use the createPattern() method built into jCanvas. However, due to the limitations of the HTML5 canvas API, you cannot offset a pattern (so as to move it with a draggable layer).
-Caleb
Related
I'm using html5 canvas to manipulate individual pixels. The canvas is zoomable and draggable, and each pixel is a rectangle, basically I do the following:
pixels.forEach(p => {
context.fillStyle = p.color;
context.fillRect(toScreenX(p.x), toScreenY(p.y), 1*scale, 1*scale);
});
where toScreenX and toScreenY determine the position of the rectangle based on the position of the pixel and the actual scale and offset.
When the zoom scale is 1, everything is okay as shown on picture below:
However, when I start to zoom in, thin white lines start to appear between pixels, and the picture gets distorted as shown in the two figure below:
Here's a short video about the effect: https://imgur.com/a/dvEaZIy
I also tried to use context.putImageData instead of fillRect but for individual pixels, it gets terribly slow.
I'm not requiring a full answer to this question, just an idea on how to approach it.
Let's say that a user on my site wants to cut out the background from this image:
Normally this would be a job for some magic outline tool, but this site already carries something that would provide a perfect cutout pattern, namely this:
As you can see this car will fit perfectly over the top one.
If the user could somehow fit the bottom picture over the top one and cut out everything outside that, it would be a perfect background removal.
How do I go about building something like this? Or are there already software out that does something similar?
The bottom picture could be anything, for examle a completely black model for easier recognition, but I'd think that it would be smarter if it used the outline of the transparent .png image and cut out everything outside it.
(The picture itself doesn't need to be used either if there is some way to extract the important bits of it needed for the cutout, of course).
Here's how to do your knockout with html5 canvas
If you have an exact image that defines the desired cut and you also know the position where the cut is to be made, then you can use compositing to do you cut-out. With destination-in compositing, new drawings will keep existing pixels only where new & old pixels are non-transparent.
Here's a few notes, example code and a Demo:
Notes:
Your car on your car-only image is not exactly the size of the car on the car+background image -- the car-only is a bit wider. This causes the cut-out to have some extra pixels. But if you had exact sizing the cutout would be perfect.
Your car on your car-only image has semi-transparent shadowing. This causes the cutout to have some extra semi-transparent pixels where the shadow was on the car-only image.
Example & demo using a different exactly sized cutout with no shadow:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var bk=new Image();
bk.onload=start;
bk.src='https://dl.dropboxusercontent.com/u/139992952/multple/model-t-car.png';
var cut=new Image();
cut.crossOrigin='anonymous';
cut.onload=start;
cut.src="https://dl.dropboxusercontent.com/u/139992952/multple/model-t-cutout.png";
var imgcount=2;
function start(){
if(--imgcount>0){return;}
canvas.width=bk.width;
canvas.height=bk.height;
ctx.drawImage(bk,0,0);
ctx.globalCompositeOperation='destination-in';
ctx.drawImage(cut,125,40);
// always clean up -- reset the default compositing mode
ctx.globalCompositeOperation='source-over';
}
body{ background-color: ivory; }
canvas{border:1px solid red; margin:0 auto; }
<h4>Original with background</h4>
<img src='https://dl.dropboxusercontent.com/u/139992952/multple/model-t-car.png'>
<h4>Exactly sized cutout</h4>
<img src='https://dl.dropboxusercontent.com/u/139992952/multple/model-t-cutout.png'>
<br>
<h4>With background removed</h4>
<canvas id="canvas" width=300 height=300></canvas>
There's no easy plug-and-play way. I can think of 2 methods:
(1) SVGs. Plot the different points on the outline of the car yourself (very time-consuming), or import the car into Illustrator (or similar), export it as an SVG, and use the points it calculated for you with clip-path.
(2) PNG (or GIF).
Create a rectangle of solid color in Illustrator/Photoshop.
Paste the car image on top of it as a new layer.
Select the outline of the car.
Delete the selection from the rectangle of color. This will leave a rectangle with a transparent car-shaped hole in it.
Save the rectangle as a PNG or GIF or other format supporting transparent backgrounds.
Use CSS to overlay that PNG on various images of cars.
This is useful if, for instance, you have 5 photos of cars in different colors, all with the same dimensions and taken from the same angle, and want to display the 5 cars with the same background. No need to copy the same background 5 times in Photoshop; just re-use the PNG 5 times in CSS.
Now if you want to change the "background" (which is actually an overlay and not really a background) you need only change it in one place.
Keep in mind: The image you provided is not a perfect outline because it has a shadow.
I'd like to know if there is some way in Kinetic to have an image merged with another image on a lower layer, creating a kind of crop effect based on the shape of the "cropping" image.
The image must have a transparent background as a result, which is the main source of difficulty for me. I would otherwise just have used a mask with dragging turned off... I've made a diagram to explain what I want a bit better. Any suggestions welcome.
diagram
I've also made a quick jsfiddle, where I would like the contents of the image to be displayed inside the box. I feel like one layer is the way to go on this one.
You can use an offscreen Canvas element plus compositing to create your clipped image for use by your Kinetic.Image. Note that the offscreen canvas can be used as an image source for your Kinetic.Image.
Example code and a Demo: http://jsfiddle.net/m1erickson/ks1xxqfL/
var canvas=document.createElement('canvas');
var ctx=canvas.getContext('2d');
canvas.width=background.width;
canvas.height=background.height;
ctx.drawImage(mask,0,0,mask.width*2.25,mask.height*2.25);
ctx.globalCompositeOperation='source-in';
ctx.drawImage(background,0,0);
var support=new Kinetic.Image({
draggable:true,
image:canvas,
});
layer.add(support);
layer.draw();
Illustrations
Left: the background image,
Center: the image to be used as a clipping mask
Right: the background clipped by the mask (mask was scaled by 2.25X)
I have a canvas <canvas></canvas> that displays a graphic of an unclean window. I need to be able to 'clean' the window with my cursor, displaying another image behind it. Just as this website uses their brushes: http://mudcu.be/sketchpad/ but rather than adding to the page, I need to remove content to display the image behind it.
Here's an example of the before and after 'rubbing out':
http://www.titaniumwebdesigns.com/images/forums/before.png http://www.titaniumwebdesigns.com/images/forums/after.png
See this complete DEMO
globalCompositeOperation is one of the most nice features in canvas api.
To achieve the desired effect, I use multiple canvas layers and globalCompositeOperation.
In this solution we have 3 layers:
Layer 1 - bottom Layer 2 - middle
Layer 3 - top
Middle and Top layers are static and only the middle layer is dynamically cleared using globalCompositeOperation.
middleCtx.globalCompositeOperation = "xor";
With globalCompositeOperation = "xor", the brush is drawn over the layer and clears the portion of canvas where it was drawn.
The final result is:
UPDATE:
To verify if the window is fully cleaned I create a hidden canvas with the same size of the others layers and drawn a black rectangle on it. When dragging the mouse over the canvas the layer 2 (middle) is cleared with a circle with transparent gradient color and now we also draw over the hidden canvas a circle with white color (might be any color different of black).
So on, we just verify the pixels of the hidden canvas and if there is no black pixels, the window is cleaned.
To get the image data we need to use something like:
imageData = context.getImageData(x, y, width, height)
and then get the pixels from the image data:
pixels = imageData.data;
The requestAnimationFrame routine is used for performance reason, because getImageData might be slow. The major change in the code is put the brush action inside an animation frame when dragging the mouse instead of do that action in each mouse move event. This allows the processor to have more time to do the pixel data verification.
Here is the modified fiddle with pixel data verification and an alert when the window is cleaned:
jsFiddle link
If you have a canvas where you have drawn a blurred image into it once, you should be able to create that effect by creating a "brush" image (an image containing a semi-transparent circle, with soft edges), and then draw that image in the canvas at the mouse coordinate using:
canvasContext.globalCompositeOperation = "destination-out";
https://developer.mozilla.org/samples/canvas-tutorial/6_1_canvas_composite.html
As soon as you have drawn the blurred image to the canvas, you just need to call the line above once and all drawn images after will use the specified composite operation.
I am writing a colouring game for small children, where I have a black and white image shown on a canvas initially, and as the user moves the drawing tool (mouse) over the canvas, the black and white surface gets over-painted with the colour information from the corresponding coloured image.
In particular, on every mouse move I need to copy a circular area from the coloured image to my canvas. The edge of the circle should be a little blurry to better immitate the qualities of a real drawing tool.
The question is how to accomplish this?
One way I see is to use a clipping region, but this approach does not let me have blurry edges. Or does it?
So I was thinking about using an alpha mask to do that and copy only pixels that correspond to the pixels in the mask that have non zero alpha. Is it feasible?
My suggestion is to have your drawable canvas in front of the coloured image you wish to reveal. (You could use your coloured image as a CSS background image for the canvas.)
Initially have the canvas containing the black and white image with 100% opacity. Then, when you draw, actually erase the contents of the canvas to show the image behind.
Like this:
var pos_x, pos_y, circle_radius; // initialise these appropriately
context.globalCompositeOperation = 'destination-out';
context.fillStyle = "rgba(0,0,0, 1.0)";
// And "draw" a circle (actually erase it to reveal the background image)
context.beginPath();
context.arc(pos_x, pos_y, circle_radius, 0, Math.PI*2);
context.fill();
I would probably use multiple clipping regions with varying alpha (one dab for each) to mimic the effect you are after. Render the low opacity one first (paste using drawImage) and render the rest after that till you reach alpha=1.0.
Have you considered using radial gradients that go from an opaque color to a fully transparent one?
Here is a demo from Mozilla. The circles are drawn the way you need. - https://developer.mozilla.org/samples/canvas-tutorial/4_10_canvas_radialgradient.html