I am drawing lines using Canvas (HTML 5), since lines/shapes are not stored as objects in Canvas, I cannot attach unique events to it (eg onmouseclick)
I wish to attach a onmouseover event to a line, is it possible by getting to know if the mouse if over a particular line (using its 2 X and 2 Y co-ordinates) in Canvas using Javascript. Would this work for different line widths (eg: 2,5 pixels)
Want to avoid using SVG as the entire project is built on Canvas
Please advise.
You would need to use math formulas to calculate the area of the line and whether a certain point intersects with it.
Here's a basic example:
Find mouse coordinates relative to position of the canvas (How to find mouse pos on element)
Calculate whether mouse x/y is inside some rectangle (Point in rectangle formula)
Done.
There is a function isPointInPath(x,y). It will return true if a point is on the current path.
You will have to call that for every line you want to check and the best way to do that is at the same time as you draw.
The best way is using some canvas frameworks. Look at "LibCanvas :: Creating Lines" (dont forget to dblClick at canvas)
Related
The problem: I'm trying to create a simple drawing app using p5.js. Instead of the standard cursor image, I'd like to show a circle at my cursor location that represents the size of the drawing brush.
Potential solution 1: Replace the cursor using the cursor() function native to p5.
Why it doesn't work: The p5 cursor function only takes the following parameters:
ARROW, CROSS, HAND, MOVE, TEXT, or WAIT, or path for image
As such, there's no native way to replace the cursor using the ellipse class.
Potential solution 2: Use the noCursor() function and then draw the circle at the cursor location, while also drawing the background, as such:
var brushSize = 50;
function setup() {
createCanvas(1080,720);
noCursor();
}
function draw() {
background(100);
ellipse(mouseX,mouseY,brushSize);
}
Why it doesn't work: While this solution gets the desired effect i.e. replacing the cursor with a circle the size of the brush, the constantly updating background prevents me from actually drawing to the canvas with the brush when I want to.
Is there some way I can replace the cursor without actually drawing the ellipse to the canvas? Is there any way to save and then instantly reload a canvas in p5? I couldn't find such a method searching through the API docs. Any hints are appreciated.
According to the reference, you can pass a URL into the cursor() function to set an image.
If you want to use an image that you draw, you're going to have to draw them ahead of time and save them to files, and then use those files. Something like this:
cursor('images/ellipse-15.png');
Where ellipse-15.png is an image that you generated ahead of time, to match when brushSize is 15, for example.
Btw P5.js is just setting the cursor CSS property. You can read more about it here.
If you want to go with the noCursor() approach and draw the ellipse yourself, you could draw your drawing to a buffer (the createGraphics() function is your friend) and then draw the ellipse on top of that every frame. I'd still probably use a cross cursor just because there's going to be some annoying lag if you draw it yourself.
Create a circular DIV inside the canvas container and show it on top of the actual canvas.
Alright, so I have a good deal of experience with HTML and CSS, and some experience with Javascript (I can write basic functions and have coded in similar languages).
I'm looking to start some visual projects and am specifically interested in getting into particle systems. I have an idea for something similar to Codecademy's name generator here (https://www.codecademy.com/courses/animate-your-name/0/1) where particles are mapped to a word and move if hovered over. It seems as though alphabet.js is what's really behind Codecademy's demo however I can't understand exactly how they mapped the particles to a word, etc.
I've done some basic tutorials just creating rudimentary particles in a canvas but I'm not sure a canvas is the best way to go - demos that utilize one of the many libraries available (such as http://soulwire.github.io/sketch.js/examples/particles.html) don't use a canvas.
So my question is - what is the best way for a beginner/intermediate in Javascript to start with particle systems? Specifically to accomplish the Codecademy name effect or similar? Should I try to use canvas or which library would be best to start with and how would you recommend starting?
The code for this project is achievable for your intermediate JS programmer status.
How the CodeAcademy project works ...
Start by building each letter out of circles and saving each circle's centerpoint in an array. The alphabet.js script holds that array of circle centerpoints.
On mousemove events, test which circles are within a specified radius of the mouse position. Then animate each of those discovered circles radially outward from the mouse position using simple trigonometry.
When the mouse moves again, test which circles are no longer within the specified radius of the current mouse position. Then animate each of those "outside" circles back towards their original positions.
You can also use native html5 canvas without any libraries...
Another approach allowing any text to be "dissolved" and reassembled
Start by drawing the text on the canvas. BTW, this approach will "dissolve" any drawing, not just text.
Use context.getImageData to fetch the opacity value of every pixel on the canvas. Determine which pixels on the canvas contain parts of the text. You can tell if a pixel is part of the text because it will be opaque rather than transparent.
Now do the same procedure that CodeAcademy did with their circles -- but use your pixels:
On mousemove events, test which pixels are within a specified radius of the mouse position. Then animate each of those discovered pixels radially outward from the mouse position using simple trigonometry.
When the mouse moves again, test which pixels are no longer within the specified radius of the current mouse position. Then animate each of those "outside" pixels back towards their original positions.
[Addition: mousemove event to test if circles are within mouse distance]
Note: You probably want to keep an animation frame running that moves circles closer or further from their original positions based on a flag (isInside) for each circle.
function handleMouseMove(e){
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
// calc the current mouse position
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
// test each circle to see if it's inside or outside
// radius of 40px to current mouse position
// circles[] is an array of circle objects shaped like this
// {x:,y:,r:,originalX:,originalY:,isInside:}
var radius=40;
for(var i=0;i<circles.length;i++){
var c=circles[i];
var dx=c.x-mouseX;
var dy=c.y-mouseY;
if(dx*dx+dy*dy<radius*radius){
c.isInside=true;
// move c.x & c.y away from its originalX & originalY
}else{
c.isInside=false;
// if the circle is not already back at it's originalX, originalY
// then move c.x & c.y back towards its originalX, originalY
}
}
}
I have two canvases. I have made them circular using border-radius. The 2nd is positioned inside the first one (using absolute position).
I have click events on both circles. If you click on inside canvas, the color at the point of the click is loaded in the outside canvas with opacity varying from white to the picked color and finally to black. If you click on outer canvas the exact color value at that point is loaded in the text-box at the bottom
I am unable to click in red zones (as shown in figure below) of the outer canvas when using chrome. I tried z-idex, arcs but nothing is helping me. But In Firefox everything is working fine.
Note: You can drag the picker object in the outer circle. But if you leave it in red zones, you would not be able to click it again in Chrome. Clicking in green zone will get you its control again
Code in this JSFiddle
Edit
I excluded all irrelevant code to make it easy. Now there is only a container having two canvas.
Filled simply with two distinct colors. Open following fiddle link in both chrome and firefox. Click on both cirles in different zones and see difference in chrome and firefox. I want them to behave in chrome as they do in firefox
Note I will ultimately draw an image in inner canvas.
Updated Fiddle Link
-
Your problem is because canvases currently are always rectangular, even if they don't look rectangular. Border radius makes the edges except the circle transparent, but it still doesn't stop events in Chrome on the corner areas. This is why you cannot click the bottom circle in those areas
I even tried putting it inside of a container that had a border-radius instead but the click event still goes through
With that being said, you have two options. You could either change your code to only use one canvas with the same type of layout, just drawing the background circle before the other each time. Essentially you'd draw a circle, draw your black to color to white gradient, use the xor operation to combine the two into one circle, then do the same with the rainbox gradient. You must draw the background circle first because canvas paints over the old layers every time
or
You could use javascript to only detect clicks in the circular area which takes just a little bit of math (: This solution is featured in edit below
In the future, CSS Shapes may allow canvases to be non-rectangular elements to be used, I'm actually not sure, but we don't have that capability yet at least
Edit
Alright, so after going through your code a bit it seems there are some things I should cover before I offer a solution
Setup all your finite variables outside of the functions that run every time. This means you don't put them (like radiuses, offsets, etc.) in the click function or something that runs often since they don't change
Your "radius"es are actually "diameter"s. The format of .rect goes .rect(x, y, width (diameter of circle), height (diameter of circle))
Almost always when overlaying canvases like you are you want to make them equal dimensions and starting position to prevent calculation error. In the end it makes it easier, doing all relative positioning with javascript instead of mixing it with CSS. In this case, however, since you're using border-radius instead of arc to make a circle, keep it like it is but position it using javascript ....
jQuery isn't needed for something this simple. If you're worried about any load speed I'd recommend doing it in vanilla javascript, essentially just changing the .click() functions into .onclick functions, but I left jQuery for now
You can declare multiple variables in a row without declaring var each time by using the following format:
var name1 = value1,
name2 = value2;
Variables with the same value you can declare like so:
var name1 = name2 = sameValue;
When children have position:absolute and you want it to be positioned relative to the parent, the parent can have position:relative, position:fixed, or position:absolute. I would think you'd want position:relative in this case
When you don't declare var for a variable it becomes global (unlessed chained with a comma like above). For more on that read this question
Now, onto the solution.
After talking with a friend I realized I could sort do the math calculation a lot easier than I originally thought. We can just calculate the center of the circles and use their radiuses and some if statements to make sure the clicks are in the bounds.
Here's the demo
After everything is set up correctly, you can use the following to detect whether or not it's in the bounds of each
function clickHandler(e, r) {
var ex = e.pageX,
ey = e.pageY,
// Distance from click to center
l = Math.sqrt(Math.pow(cx - ex, 2) + Math.pow(cy - ey, 2));
if(l > r) { // If the distance is greater than the radius
if(r === LARGE_RADIUS) { // Outside of the large
// Do nothing
} else { // The corner area you were having a problem with
clickHandler(e, LARGE_RADIUS);
}
} else {
if(r === LARGE_RADIUS) { // Inside the large cirle
alert('Outer canvas clicked x:' + ex + ',y:' + ey);
} else { // Inside the small circle
alert('Inner canvas clicked x:' + ex + ',y:' + ey);
}
}
}
// Just call the function with the appropriate radius on click
$(img_canvas).click(function(e) { clickHandler(e, SMALL_RADIUS); });
$(wheel_canvas).click(function(e) { clickHandler(e, LARGE_RADIUS); });
Hopefully the comments above and code make enough sense, I tried to clean it up as best as I could. If you have any questions don't hesitate to ask!
I have problem with canvas createPattern. I have two boxes, both will move after pressing a keyarrow:
Example:
http://jsfiddle.net/wA73R/1/
The problem is that the box background filled by createPattern also is moving. How to avoid that? Is there any solution? The big box is only an example (drawImage is not the good solution for me, I need something that will repeat background image).
Thank you for help
The problem is that the box background filled by createPattern also is moving.
Actually your problem is that the background is not moving - it is static, while you are drawing your rectangle to different positions.
How to avoid that?
The pattern will always be drawn at the coordinate origin, whose actual position is defined by the current transformation. In future you will be able to transform the pattern itself with the setTransform method, but since that currently is not implemented anywhere you instead will have to change the global transformation matrix.
In your case it means, that instead of drawing your rectangle at x/y, you translate the whole context to x/y and draw your rectangle at 0/0 then:
ctx.fillStyle=pattern;
ctx.save();
ctx.translate(boxes[i].x - left , boxes[i].y);
ctx.fillRect(0, 0, boxes[i].width, boxes[i].height);
ctx.restore();
(updated demo)
I the speech bubbles to be next to the person who says them but how do I change the position? I don't want to have any more animations for that, is it possible?
link: http://www.tlu.ee/~kristo93/Eritamine%20-%20puhas/p6hi.html
for example the next tere would be positioned next to the students.
There is always an X-Y co-ordinate of any group or element you create using the kinetic.js
You just need to manipulate X-Y property of the group containing your speech cloud.
suppose your reference to that cloud group is called cloudGroup then set the X and Y property using the method as follows:
cloudGroup.setX(100);
cloudGroup.setY(100);
So just insert anything instead of 100, which suits the position you desire.