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!
Related
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 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 have a function in script that draws a rectangular on canvas.I want to clean the rectangular drew in the "if" condition.
I also have text on the canvas(its coordinates are 0,80) and it shouldn't be cleaned. Only the rectangular must be cleaned.
function red_stroke_2(yy)
{
//Red color edges
context.strokeStyle = "#f00";
context.strokeRect(0,yy,800,40);
}
if (Option1==answers[qnumber])
{
red_stroke_2(80);
}
Canvas is "stateless" in the sense that it does not know about the primitives that have been drawn or the calls that have been made. As such it is impossible to undo only a certain drawing call. If you need to modify the drawing, you need to redraw all of the items that you don't want to change. Of course you have the option to change single pixels, so if your text is black and the rectangle is red, you can replace all red pixels, but this won't work so good if antialiasing is enabled and is utterly complicated.
So either redraw the whole area (omit the rectangle drawing but render the text). Or consider using 2 Canvases on top of each other (one with the text, one with the background), then of course you can rerender the background without having to worry about the text.
Last but not least using SVG might be also an alternative, since this is stateful and consists of DOM elements that you can modify/insert/remove and the browser will do the compositing. In that case you would have a rect element and a textelement and you could simply remove the former.
This will put transparent pixels instead of your rectangle:
function clean_red_stroke(yy)
{
context.clearRect(0,yy,800,40);
}
//Call it with the same 'yy' you used in the drawing method
clean_red_stroke(80);
However I think you code could be improved, by using more variables (and consequently a most generic function) for exemple.
I have an inner div inside an outer div. The inner div is draggable and outer is rotated through 40 degree. This is a test case. In an actual case it could be any angle. There is another div called point which is positioned as shown in the figure. ( I am from a flash background . In Flash if I were to drag the inner div it would follow the mouse even if its contained inside an outer rotated div.) But in HTML the inner div does not follow the mouse as it can be seen from the fiddle. I want the div 'point' to exactly follow the mouse. Is this possible. I tried to work it using trignometry but could not get it to work.
http://jsfiddle.net/bobbyfrancisjoseph/kB4ra/8/
Here is my approach to this problem.
http://jsfiddle.net/2X9sT/21/
I put the point outside the rotated div. That way I'm assured that the drag event will produce a normal behavior (no jumping in weird directions). I use the draggable handler to attach the point to the mouse cursor.
In the drag event, I transform the drag offset to reflect the new values. This is done by rotating the offset around the outer div center in the opposite direction of the rotation angle.
I tested it and it seems to be working in IE9, Firefox, and Chrome.
You can try different values for angle and it should work fine.
I also modified the HTML so it is possible to apply the same logic to multiple divs in the page.
Edit:
I updated the script to account for containment behavior as well as cascading rotations as suggested in the comments.
I'm also expirementing with making the outer div draggable inside another div. Right now it is almost working. I just need to be able to update the center of the dragged div to fix the dragging behavior.
Try Dragging the red div.
http://jsfiddle.net/mohdali/kETcE/39/
I am at work now, so I can't do the job for you, but I can explain the mathematics behind the neatest way of solving your problem (likely not the easiest solution, but unlike some of the other hacks it's a lot more flexible once you get it implemented).
First of all you must realize that the rotation plugin you are using is applying a transformation to your element (transform: rotate(30deg)), which in turn is changed into a matrix by your browser (matrix(0.8660254037844387, 0.49999999999999994, -0.49999999999999994, 0.8660254037844387, 0, 0)).
Secondly it is necessary to understand that by rotating an element the axis of the child elements are rotate absolutely and entirely with it (after looking for a long time there isn't any real trick to bypass this, which makes sense), thus the only way would be to take the child out of the parent as some of the other answers suggest, but I am assuming this isn't an option in your application.
Now, what we thus need to do is cancel out the original matrix of the parent, which is a two step process. First we need to find the matrix using code along the following lines:
var styles = window.getComputedStyle(el, null);
var matrix = styles.getPropertyValue("-webkit-transform") ||
styles.getPropertyValue("-moz-transform") ||
styles.getPropertyValue("-ms-transform") ||
styles.getPropertyValue("-o-transform") ||
styles.getPropertyValue("transform");
Next the matrix will be a string as shown above which you would need to parse to an array with which you can work (there are jquery plugins to do that). Once you have done that you will need to take the inverse of the matrix (which boils down to rotate(-30deg) in your example) which can be done using for example this library (or your math book :P).
Lastly you would need to do the inverse matrix times (use the matrix library I mentioned previously) a translation matrix (use this tool to figure out how those look (translations are movements along the x and y axis, a bit like left and top on a relatively positioned element, but hardware accelerated and part of the matrix transform css property)) which will give you a new matrix which you can apply to your child element giving you the a translation on the same axis as your parent element.
Now, you could greatly simplify this by doing this with left, top and manual trigonometry1 for specifically rotations only (bypassing the entire need for inverse matrices or even matrices entirely), but this has the distinct disadvantage that it will only work for normal rotations and will need to be changed depending on each specific situation it's used in.
Oh and, if you are now thinking that flash was a lot easier, believe me, the way the axis are rotated in HTML/CSS make a lot of sense and if you want flash like behavior use this library.
1 This is what Mohamed Ali is doing in his answer for example (the transformOffset function in his jsFiddle).
Disclaimer, it has been awhile since I have been doing this stuff and my understanding of matrices has never been extremely good, so if you see any mistakes, please do point them out/fix them.
For Webkit only, the webkitConvertPointFromPageToNode function handles the missing behavior:
var point = webkitConvertPointFromPageToNode(
document.getElementById("outer"),
new WebKitPoint(event.pageX, event.pageY)
);
jsFiddle: http://jsfiddle.net/kB4ra/108/
To cover other browsers as well, you can use the method described in this StackOverflow answer: https://stackoverflow.com/a/6994825/638544
function coords(event, element) {
function a(width) {
var l = 0, r = 200;
while (r - l > 0.0001) {
var mid = (r + l) / 2;
var a = document.createElement('div');
a.style.cssText = 'position: absolute;left:0;top:0;background: red;z-index: 1000;';
a.style[width ? 'width' : 'height'] = mid.toFixed(3) + '%';
a.style[width ? 'height' : 'width'] = '100%';
element.appendChild(a);
var x = document.elementFromPoint(event.clientX, event.clientY);
element.removeChild(a);
if (x === a) {
r = mid;
} else {
if (r === 200) {
return null;
}
l = mid;
}
}
return mid;
}
var l = a(true),
r = a(false);
return (l && r) ? {
x: l,
y: r
} : null;
}
This has the disadvantage of not working when the mouse is outside of the target element, but it should be possible to extend the area it covers by an arbitrary amount (though it would be rather hard to guarantee that it covers the entire window no matter how large).
jsFiddle: http://jsfiddle.net/kB4ra/122/
This can be extended to apply to #point by adding a mousemove event:
$('#outer').mousemove(function(event){
var point = convertCoordinates(event, $("#outer"));
$("#point").css({left: point.x+1, top: point.y+1});
});
Note that I adjust the x and y coordinates of #point by 1px to prevent it from being directly underneath the mouse; if I didn't do that, then it would block dragging #inner. An alternative fix would be to add handlers to #point that detect mouse events and pass them on to whichever element is directly underneath #point (and stopPropagation, so that they don't run twice on larger page elements).
jsFiddle: http://jsfiddle.net/kB4ra/123/
It seems to me that if you do not rotate the div, the div exactly follows the mouse.
This might be a problem with the plugin..maybe you could simulate the draggable function corretly?
This basically will do what you need though it is buggy. Bind the drag event handler, intercept the ui object and modify it to use the offset X and Y of the parent element. All of the X, Y, top, left etc. are in those objects. I will try to get you a better example sometime when today when I get a bit more time. Good luck!
http://jsfiddle.net/kB4ra/107/
may be this is issue of your jquery library or you can check this by assigning z-order value of inner div and outer div make sure that you give higher number to inner div.
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)