I have a canvas that I'm creating with KineticJS and I am adding transparent PNG images to that canvas. When stacked on top of each other, this makes one image of an outfit with all the different parts.
What I then want to do is allow the user to click on a pattern and then change a specific piece of that outfit with that pattern. So I need to fill in the non-transparent parts of one of the images with that pattern. I found a way to do this that didn't use KineticJS and it looks something like this:
ctx.globalCompositeOperation = 'source-in';
var ptrn = ctx.createPattern(fabricA, 'repeat');
ctx.fillStyle = ptrn;
ctx.fillRect(0, 0, 375, 260);
My question is, is there a way to do the same steps outlined above with KineticJS?
Also, I did first try to just do this without using KineticJS, but when I applied the above code to the layer, it filled in all of the images because they were all on the same layer. So I'm guessing that I will need to change my code to either use multiple layers or to add the images to groups in a single layer. Is my thinking right here? And which would be the better option for what I'm trying to accomplish? Multiple Layers? Or Multiple Groups on a single Layer?
Thanks for any help that anyone can provide.
If you want to do custom drawing then use the KineticJS Shape Object
This is a KineticJS object that lets you control exactly how it's drawn.
You create your overlays using your compositing method. Then put that drawing code in a function and give that function to Kinetic Shape's drawFunc.
Here's a skeleton of Kinetic.Shape:
var outfit1 = new Kinetic.Shape({
drawFunc: function(canvas) {
// you are passed a canvas to draw your custom shape on
// so new-up a context and get drawing!
var context = canvas.getContext();
context.beginPath();
// Draw stuff--including your composited overlays
// You can use any canvas.context drawing commands
},
id:"myCustomOutfit"
});
You can get started with an example here: http://www.html5canvastutorials.com/kineticjs/html5-canvas-kineticjs-shape-tutorial/
Related
What I would like to do is draw a circle on a canvas and then when a function is called delete the previous circle and draw a new one. Is this possible without having to redraw the whole canvas?
Take the code below for example
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95, 50, 40, 0, 2 * Math.PI);
ctx.stroke();
A canvas is a collection of pixels (it's exactly like an image, however it's computed from code instead of being just loaded from file).
The only way to remove the old circle and draw the new one (if you want pixel perfect result) is repainting everything with the circle in the new position.
A possible solution could be using three distinct canvas elements layered one on top of the other:
whatever is behind the changing parts
the changing parts
whatever is covering the changing parts
1 and 3 can be kept fixed, you need to redraw only the second canvas.
This is a question about fabric.js. I have been trying to create some shapes on the contextTop. When you create some shapes on contextTop(not using add), how to merge them with the fabric.js canvas?
let canvas = new fabric.Canvas('C');
canvas.contextTop.StrokeRect(12,12,30,30);
Then, I want to make the Rect appear on the canvas. What should I do? Could anybody tell me how to use canvas API in fabric.js?
I do not understand contextTop, contextContainer...
You can't use canvas API directly.
FabricJS is a framework to work on the canvas and you have to use the framework rules, or it will break.
ContextTop is the result of getContext('2d') from the upperCanvas, where the upperCanvas is a canvas layered on top of the main one to do some quick drawing that does not require full canvas refresh.
All the html5 canvas drawing that are done outside the provided API will be wiped at the next frame.
To draw a rect you have to create the rect class and add it to the canvas, that is the correct way to do it:
var rect = new fabric.Rect({ width: 200, height: 300 });
canvas.add(rect);
I'm two days into js,html and css programming. So very newbie!
Following and building upon this TUTORIAL
Q1: How can I add this male into the background (see figuere 1.) and prohibit any strokes outside of the borders?
Adding image to background was no biggy!
function make_base()
{
base_image = new Image();
base_image.src = 'img/bmapFront.gif';
base_image.onload = function(){
context.drawImage(base_image, 0,0);
}
}
There is a context.clip function, not sure if I can use pixel form as clipping path. Making tons of "image substractions" isn't the best way.
Any suggestions
Edit:
Did the Job for me: VeryHelpful
var frontPath = new Path2D ("M 133.41,17.00 C 141.37,2.41 160.66, !VERY LONG! ")
context.clip(frontPath);
Messy strokes!
He should look like this. Then I want to save him.
Although there is such a thing as ctx.clip(), this is sometimes not what's wanted as it's impractical to use a path.
The solution that I like involves creating a virtual empty canvas onto which you draw your pixel image. Through various manipulations, like using ctx.getImageData and similar to make sure you only get one kind of color or apply other filters only once, you can obtain an image that seems to be empty (alpha of 0, mostly) in the places where you want to clip other images or paths out.
At that point, you'd use ctx.globalCompositeOperation = 'source-atop', or pick another one you might want to use from mdn's list of globalCompositeOperations.
At this point, you can just draw this virtual canvas image onto the main canvas
I have a polygon object (say a car) drawn inside a HTML5 canvas with help of methods moveTo and lineTo. I want to repeatedly draw that object at different positions in the canvas (simulating a moving object). My problem is that the previous drawn object is not getting cleared. Instead, multiple images are drawn on the canvas. How can I fix this issue?
You have to clear the canvas at the start of every draw frame
context.clearRect(0, 0, canvas.width, canvas.height);
Canvases are just arrays of pixels, they know nothing of the shapes you have drawn.
There are animation tricks that used to be used on bitmapped displays (e.g. "xor drawing") that can be used to remove the old shape before you draw the new one, but on modern machines it's generally far simpler (and perfectly fast) to just erase the canvas and start again for each frame.
Given your comments to other answers, I'd suggest just using two Canvases - one for the static background and one for the car. If the background image is static it could even be an <img> element instead of a Canvas.
If the car image is static you could also just draw that once, and then use CSS positioning to set its position relative to the background for each frame.
suppose your shape is car then you first have to assign a new graphic like:
car.graphics = new createjs.Graphics();
car.graphics
.setStrokeStyle(1)
.beginStroke("#000000")
.moveTo()
.lineTo()
.lineTo()
Is there a way to use an image as a clipping mask instead of creating a shape like this:
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
// Clip a rectangular area
ctx.rect(50,20,200,120);
ctx.stroke();
ctx.clip();
I have tried to context.drawImage('myimg.png') on top of the context and clip but that did not work.
You can only directly clip using a path.
If you have an image that you wish to clip by, you can probably achieve this by drawing your content in another canvas, and then using globalCompositeOperation combined with drawImage (with the mask) to remove the bits you don't want.
You would then then use .drawImage again (possibly with a different globalCompositeOperation) to merge that clipped image with your original content.
See for example http://www.html5canvastutorials.com/advanced/html5-canvas-global-composite-operations-tutorial/