Hi i am building a windows store app with html5 and javascript in my app i am trying to implement an eraser tool but this is problematic because if the user moves an image or another layer to where they've previously erased, they see the white drawing where they erased.
i have been trying to do the eraser tool from different ways for example i have changed the default globalCompositeOperation to "destination-out" like this code
//Here is the error.
if (clickTool[j] == "eraser") {
ctx.globalCompositeOperation = 'destination-out';
ctx.fillStyle = 'rgba(255,0,0,0.5);';
ctx.strokeStyle = 'rgba(255,0,0,0.5);';
}
else {
ctx.globalCompositeOperation = "source-over";
ctx.strokeStyle = clickColor[j];
}
but unfortunately it doesn´t work for me. i have uploaded all my code to this link:
My code
Please i would like to somebody could help me.
Thanks and i'm sorry for my speech , i'm mexican.
Use multiple layers. Have one canvas for the background image and another for the drawing; that why you never erase any of the background image.
If you need to, you can have multiple layers as they don't generally impact performance.
And of course if you can combine layers, say the last drawn squiggle to the background layer, if you deem a drawing to be "permanent".
Maintain a array of mid points. Use the globalCompositeOperation as 'destination-out' first and 'source-over' later to make a transparent eraser trail .
Following is the code that you need to use with a mouse move function
var handleMouseMove = function (event) {
midPt = new createjs.Point(oldPt.x + stage.mouseX>>1, oldPt.y+stage.mouseY>>1);
if(curTool.type=="eraser"){
var tempcanvas = document.getElementById('drawcanvas');
var tempctx=tempcanvas.getContext("2d");
tempctx.beginPath();
tempctx.globalCompositeOperation = "destination-out";
tempctx.arc(midPt.x, midPt.y, 20, 0, Math.PI * 2, false);
tempctx.fill();
tempctx.closePath();
tempctx.globalCompositeOperation = "source-over";
drawingCanvas.graphics.clear();
// keep updating the array for points
arrMidPtx.push(midPt.x);
arrMidPty.push(midPt.y);
stage.addChild(drawingCanvas);
stage.update();
}
};
I use this code to make a eraser that behaves like pen and fills up transparent color instead of white
Related
I want to create a Welcome Page with a responsive background like this fiddle
https://codepen.io/JulianLaval/pen/KpLXOO/.
I tried using
var ctx = canvasDiv.getContext("2d");
ctx.fillStyle = "RGBA(255, 255, 255, 0.8)";
ctx.fillText("Hi", canvasDiv.width / 2, canvasDiv.height / 2);
But it is not working.
Any help?
The problem is that you can not simply reuse the canvas of the particle library - at least not without modifications to the particle library itself.
This library has it's own update() function which we can see at this github link: ParticleNetwork.prototype.update
So initially it clears it's canvas, draws the particles and finally schedules a call to itself - so it constantly repaints the canvas with the displays refresh rate.
No here's the problem - if you simply draw something to it's canvas it will ultimately be overwritten by this update function.
If you want to draw text on it's canvas, you have to do it inside this function.
For example, find these lines of code:
if (this.options.velocity !== 0) {
requestAnimationFrame(this.update.bind(this));
}
if you add the following lines before:
this.ctx.fillStyle = "RGBA(255, 255, 255, 0.8)";
this.ctx.fillText("Hi", this.canvas.width / 2, this.canvas.height / 2);
You will have your desired text.
I made a double pendulum with canvas.
Here is the result: https://jsfiddle.net/zndo9vh4/
As you guys can see a trace is drawn everytime the second part of the pendulum moves, and my way of doing that is by appending each coordinate to a "trace" array.
var trace = []
trace.push([x2,y2]);
And then I draw the trace by joining each coordinate with the last one:
for (let i = 1; i < trace.length; i++) {
c.moveTo(trace[i][0], trace[i][1])
c.lineTo(trace[i-1][0], trace[i-1][1])
}
I want to improve it. What i've tried so far is only adding coordinates that aren't already in the array, but it's not a big improvent because the lines are drawn every loop
var trace = []
if(trace.includes([x2, y2]) != true){
trace.push([x2,y2]);
}
The way I think could be a good improvement is by having 2 canvas (I don't know if its possible) and then draw each point but only in that canvas so I doesnt have to be redrawn. But I dont know how to implement that.
Thanks in advice
Your improvement idea is great. You can indeed have two canvases!
There are two ways to go about it.
Offscreen canvas
Using what's called an offscreen canvas (a canvas that is created in JavaScript but not added to the DOM), you can draw all the points onto it and then using drawImage (which can accept a canvas element) pass the canvas to the main context.
var offscreenCanvas = document.createElement('canvas');
var offscreenC = offscreenCanvas.getContext('2d');
offscreenCanvas.width = canvas.width;
offscreenCanvas.height = canvas.height;
// in animate function, draw points onto the offscreen canvas instead
// of the regular canvas as they are added
if(trace.includes([x2, y2]) != true){
trace.push([x2,y2]);
var i = trace.length-1;
if (i > 1) {
offscreenC.strokeStyle = 'white'
offscreenC.beginPath();
offscreenC.moveTo(trace[i][0], trace[i][1])
offscreenC.lineTo(trace[i-1][0], trace[i-1][1])
offscreenC.stroke();
}
}
c.drawImage(offscreenCanvas, 0, 0);
Layered Canvases
One of the downsides to the offscreen canvas approach is that you have to draw it to the main canvas every frame. You can further improve the approach by layering two canvases on top of one another, where the top one is just the pendulum and the bottom one the trace.
This way, you never have to redraw the offscreen canvas onto the main canvas, and save yourself some rendering time.
Updated jsfiddle
I'm trying to use a canvas image as background here: http://www.cphrecmedia.dk/musikdk/stage/prelisten.php
The code is as below:
window.onload=function(){
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var imageObj = new Image();
stackBoxBlurImage('coverbgblur', 'canvas', 19, false, 2);
}
Beside the layout stuff that needs to be fixed, I need to darken the image a little bit, so the text will always be visible, also if I use a white album-cover. Can I somehow in the code above add a line or 2 that will darken the image? I know I can use CSS3, but its seems unsmart to create an extra layer of processing instead of doing it right the first time.
I'm quite new with canvas, so every kind of help is hugely appreciated!
You can make the canvas appear darker by drawing a semi-transparent dark rectangle over the image when after you draw the image
context.fillStyle = "rgba(0, 0, 0, 0.4)";
context.fillRect(0, 0, 700, 500);
Here is an example jsFiddle
You may also be able to use context.globalAlpha or context.globalCompositeOperation = "lighter"; as described in this SO post
I have a problem and I have potential solution. But I wanted to confirm if there is an easy and simple way to solve my problem.
App type:
Isometric Game
Problem statement:
I am loading images in my flash app and have mouse events attached to them.
The images I load are prop images like vehicles, trees, buildings etc., and all of them are transparent.
Example: Red ball asset (please ignore the yellow background which I applied to describe the problem)
If I click on the actual image area (colored in red), then every thing works perfect
I don't want to trigger mouseevent when I click on empty image part (or transparent area, which I have shown in yellow color)
There is one way I know by creating masks in flash. I don't want to do it unless that is the final option left because I load image assets instead of flash assets and I don't want to create a new mask asset for all the assets
There is another method I was going to adopt by using getPixel method of Bitmap. Which is discussed here.
But there is another problem with this method.
I might be able to ignore the click event when I click on the empty part of the asset but if there is some other asset is behind the image in the same location, then I need to process the click event for the occluded image.
Well, thinking of solution to this problem takes me to the getObjectsUnderPoint where I can scan the occluded assets
Well, what you proposed as a solution is 100% valid. Just move the logic of determining what game object is clicked outside of that object.
Listen for MOUSE_DOWN/MOUSE_UP events at container which contains your game objects.
Catch an event
Check if the game object which is the target of this event is transparent at this point using BitmapData.getPixel32
If it is use getObjectsUnderPoint to find out all other game objects at this point
Find in a loop the first object which is not transparent at this point
Now you got the actual object which is hit.
One interesting solution is to use Sprite objects with the individual non-transparent pixels burnt onto them.
Suppose this is your Loader "complete" handler:
private function loaderCompleteHandler(event:Event):void
{
// Loader is not our child, we use a Sprite instead (below).
var loader:Loader = Loader(event.target);
var sprite:Sprite = new Sprite();
addChild(sprite);
var w:Number = loader.content.width;
var h:Number = loader.content.height;
// Use transparent bitmap.
var bitmapData:BitmapData = new BitmapData(w, h, true, 0);
bitmapData.draw(loader.content);
// Now burn the image onto the Sprite object, ignoring
// the transparent pixels.
for (var xPos:int = 0; xPos < w; xPos++) {
for (var yPos:int = 0; yPos < h; yPos++) {
var pixel32:uint = bitmapData.getPixel32(xPos, yPos);
var alpha:int = pixel32 >>> 24;
if (alpha != 0) {
sprite.graphics.beginFill(pixel32 & 0xFFFFFF, alpha / 0xFF);
sprite.graphics.drawRect(xPos, yPos, 1, 1);
sprite.graphics.endFill();
}
}
}
}
Essentially you want "empty" pixels that aren't clickable, and fully transparent pixels aren't quite the same thing. With this solution you get empty pixels.
Only problem is that this might be slow. Give it a shot.
I have to draw a graph with 3 different lines. A line graph.
I tried doing this:
function draw()
{
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.lineWidth=10;
ctx.strokeStyle="teal";
ctx.moveTo(10,CompanyA[0]);
ctx.lineTo(110,CompanyA[1]);
ctx.lineTo(210,CompanyA[2]);
ctx.stroke();
ctx.strokeStyle="green";
ctx.moveTo(10,CompanyB[0]);
ctx.lineTo(110,CompanyB[1]);
ctx.lineTo(210,CompanyB[2]);
ctx.stroke();
ctx.strokeStyle="yellow";
ctx.moveTo(10,CompanyC[0]);
ctx.lineTo(110,CompanyC[1]);
ctx.lineTo(210,CompanyC[2]);
ctx.stroke();
}
But apparently, the last stroke draws for all the lines. So I get 3 yellow lines, instead of a Teal, a Green and a Yellow one.
I tried creating three different Context (ctx1, ctx2 and ctx3), but for some reason, all were drawn with the "ctx3.stroke()" call.
What would be the correct way to do this?
Add a ctx.beginPath() call before every line, and also a ctx.closePath() after every ctx.stroke()
If you don't, every time you call the stroke() method, not only the new line will be drawn but also all the previous lines will be drawn again (with the new strokeStyle), since it's the same line path that is still open.
Although there is a functional answer here, I'd just like to add this.
var ctx1 = canvas.getContext("2d");
var ctx2 = canvas.getContext("2d");
var ctx3 = canvas.getContext("2d");
They all refer to the same object. It does not create a new context, it uses the one that's already attached to the canvas element. Delta is totally right in saying that it strokes yellow over the entire path because you did not begin a new path. ctx.beginPath() will solve your troubles.