Aim of my code:
Draw a small rectangle on a HTML canvas whenever a user clicks the canvas. The rectangle should have a small number representing the number of rectangles made by the user.
The user should be able to connect any two rectangles using a straight line. (Preferably by just pressing left mouse button, and taking the mouse from first rectangle to second rectangle)
Approach and my attempt
As you can see in this jsFiddle , I have been able to achieve the first part of above very well. On clicking on the canvas, a rectangle with a number inside of it is made. But I am really clueless about the second part.
How do I make the user connect any two made rectangles? I want the connection to be made only if a rectangle is there ( So I would need to store coordinates of every rectangle that has been made, that's okay as I can use an array for that ).
Basically, I just want to check if the mousedown was at one place and mouseup at the other.
How do I get these two different coordinates ( one of mousedown and other of mouseup ) , and draw a line between them?
I have given the Fiddle above but still here's my jquery:
$(function () {
var x, y;
var globalCounter = 0;
$('#mycanvas').on("click", function (event) {
x = event.clientX + document.body.scrollLeft + document.documentElement.scrollLeft;
x -= mycanvas.offsetLeft;
y = event.clientY + document.body.scrollTop + document.documentElement.scrollTop;
y -= mycanvas.offsetLeft;
// alert("x:"+x+"y: "+y);
drawRectangle(x, y);
});
function drawRectangle(x, y) {
var acanvas = document.getElementById("mycanvas");
var context = acanvas.getContext("2d");
context.strokeRect(x, y, 25, 25);
globalCounter++;
writeNo(x, y, globalCounter);
}
function writeNo(x, y, n) {
var acanvas = document.getElementById("mycanvas");
var context = acanvas.getContext("2d");
context.font = "bold 14px sans-serif";
context.fillText(n, x + 8, y + 12.5);
}
});
The main question is therefore: connecting the two made rectangles by mousedrag
How do I achieve this?
Thank You.
How about this: http://jsfiddle.net/4jqptynt/4/
Ok, first I did a little refactoring for your code to make things easier. Just stuff like putting the code that gets the canvas coordinates into it's own function, and caching some variables (like the canvas context) in the outer function's scope. Oh, and defining your rectangle dimensions as constants because we'll be using the same numbers in a couple of different places.
As you said, the first thing we need is to keep track of the existing rectangles using an array rects (easy enough to do within drawRectangle). Then we need a function to check if a particular pair of coordinates are within some rectangle:
function inRectangle(x, y) {
for (var i = 0, l = rects.length; i < l; i++) {
if ((x - rects[i].x) <= RECT_X && (y - rects[i].y) <= RECT_Y &&
(x - rects[i].x) >= 0 && (y - rects[i].y) >= 0) {
return i;
}
}
}
where RECT_X & RECT_Y define the sides of the rectangle. If the coordinates do exist within some rectangle then this will return the index of that rectangle within the rects array.
Then it's a case of checking whether or not a mousedown occurred within a rectangle, noting that inRectangle will only return a number if the mousedown event was within a rectangle:
$acanvas.on("mousedown", function (event) {
var coords = getCoords(event),
rect = inRectangle(coords.x, coords.y);
if (typeof rect === "number") {
dragStart = rect + 1;
} else {
drawRectangle(coords.x, coords.y);
}
});
if so, make a note of which rectangle using dragStart, if not draw a rectangle as before.
Then to complete the drag, we need to attach a handler to mouseup:
$acanvas.on("mouseup", function (event) {
if (!dragStart) { return; }
var coords = getCoords(event),
rect = inRectangle(coords.x, coords.y);
if (typeof rect === "number") {
drawConnection(dragStart - 1, rect);
}
dragStart = 0;
});
If no drag was started, then it does nothing. If it's coordinates aren't within a rectangle, then it does nothing but reset dragStart. If however, it is within a rectangle, then it draws a connecting line:
function drawConnection(rect1, rect2) {
context.strokeStyle = "black";
context.lineWidth = 1;
context.beginPath();
context.moveTo(rects[rect1].x + RECT_X/2, rects[rect1].y + RECT_Y/2);
context.lineTo(rects[rect2].x + RECT_X/2, rects[rect2].y + RECT_Y/2);
context.stroke();
context.closePath();
}
Related
Have a class with methods that draws rectangular shapes with random lengths.
However, is unable to only do rotate() on the shapes without translating ( translate() ), which translate will make the shapes draw off the canvas.
So are there anyways to make it so no translation occurs while rotating?
The code:
class rect {
constructor(range) {
this.boundary = 100;
this.x = random(this.boundary, width - this.boundary);
this.y = random(this.boundary, height - this.boundary);
this.xu = this.x + random(50, 200);
this.yu = this.y + random(50, 200);
this.range = range;
this.limit = random(-range, range);
this.rand_color1 = random(255);
this.rand_color2 = random(255);
this.rand_color3 = random(255);
}
custom_shapes() {
// how to make no translations occur while only perform rotation on shapes?
translate(this.x-this.margin,this.y-this.margin);
rotate(30);
fill(this.rand_color1, this.rand_color2, this.rand_color3)
quad(this.x, this.y, this.xu + this.limit, this.y, this.xu, this.yu, this.x, this.yu + this.limit);
}
}
If you mean that your rectangular is going of the screen when rotating, it's rotating around x = 0, y= 0 point, so i guess you could do something like:
push() //push and pop acts as a way to "seperate" any style and translate and so on...
rectMode(CENTER) // basically the middle of the rect = x , y
translate(this.x,this.y) // **OR** translate(this.x - this.rectSizeX / 2, this.y - this.rectSizeY / 2)
//quad() // if you're not using the rectMode()
pop() // also you'll have to fill() and so on in here i believe, not too sure
also if you know it's allways going to be a long or tall square, you can just use rect(x,y,xSize,ySize) // if think it's the size anyways
If you just want to separate translate() in general, just put push() and pop() around it...
Oh yeah and translate() basically just makes whatever x and y you give it into 0,0... Dunno if i said that already i'm just editing this the next day.
I'm using the JavaScript canvas API for free drawing. I'm stuck at masking the area that is allowed to be drawn on - in my example it should only be the speechbubble area.
I'm using this Vue component: https://github.com/sametaylak/vue-draw/blob/master/src/components/CanvasDraw.vue
draw(event) {
this.drawCursor(event);
if (!this.isDrawing) return;
if (this.tools[this.selectedToolIdx].name === 'Eraser') {
this.canvasContext.globalCompositeOperation = 'destination-out';
} else {
this.canvasContext.globalCompositeOperation = 'source-over';
this.canvasContext.strokeStyle = this.tools[this.selectedToolIdx].color;
}
this.canvasContext.beginPath();
this.canvasContext.moveTo(this.lastX, this.lastY);
this.canvasContext.lineTo(event.offsetX, event.offsetY);
this.canvasContext.stroke();
[this.lastX, this.lastY] = [event.offsetX, event.offsetY];
},
drawCursor(event) {
this.cursorContext.beginPath();
this.cursorContext.ellipse(
event.offsetX, event.offsetY,
this.brushSize, this.brushSize,
Math.PI / 4, 0, 2 * Math.PI
);
this.cursorContext.stroke();
setTimeout(() => {
this.cursorContext.clearRect(0, 0, this.width, this.height);
}, 100);
},
There is a built-in clip() method which sets a path as the clipping region.
var ctx=document.getElementById("cnv").getContext("2d");
ctx.lineWidth=2;
ctx.strokeStyle="red";
ctx.moveTo(0,0);
ctx.lineTo(100,100);
ctx.stroke(); // 1.
ctx.strokeStyle="black";
ctx.beginPath();
ctx.moveTo(10,10);
ctx.lineTo(100,10);
ctx.lineTo(100,60);
ctx.lineTo(30,60);
ctx.lineTo(10,80);
ctx.closePath();
ctx.stroke(); // 2.
ctx.clip(); // 3.
ctx.strokeStyle="green";
ctx.beginPath();
ctx.moveTo(0,100);
ctx.lineTo(100,0);
ctx.stroke(); // 4.
<canvas id="cnv"></canvas>
red line is drawn between 0,0 and 100,100, without clipping
bubble is drawn in black
bubble is set as clipping region
green line is drawn between 0,100 and 100,0, and correctly clipped into the bubble.
In practice you may want to have the clipping region one pixel inside the bubble, so a separate path (which is not stroke()-d, just clip()-ped), so drawing can not modify the bubble itself. If you zoom in now as it is, you will see that the green line actually overdraws the inner pixels of the bubble (linewidth is 2 pixels, and the outer one is "unharmed").
Establishing if a given point belongs to polygon's area is a quite tricky and solved problem in Computer Science.
In this concrete scenario, where you have canvas with above image set as background and 500x300 dimension you don't really need to use ray casting algorithm.
You can for example divide speech bubble area to a rectangle and a triangle, and then using event.offsetX, event.offsetY check if any given point lies inside of any of these two figures.
Code example:
isPointInArea(event) {
const x = event.offsetX;
const y = event.offsetY;
// For rectangle it is straightforward
if (x >= 60 && x <= 325 && y >= 60 && y <= 215) {
return true;
}
/* Since two sides of this triangle are parallel to canvas
It is enough to check y coordinate with one linear function of a third one
in form of y = ax + b */
if(x >= 60 && x <= 120 && y >= 215) {
const boundaryY = -0.81818181818 * x + 313.181818182;
if (y <= boundaryY) {
return true;
}
}
return false;
}
In draw function of CanvasDraw.vue
draw(event) {
if(!this.isPointInArea(event)) {
return;
}
this.drawCursor(event);
if (!this.isDrawing) return;
...
Working example on codesandbox
Result:
Edit:
As pointed out by #tevemadar you can also use simply clip() method of Canvas API. If there is nothing else you want to render (And since it is not a game, so probably that is the case), then you can just execute clip() once and you are all set. Otherwise remember to use save() method (and then of course restore(), so that you can render stuff also outside of speech bubble clipping region.
I need your advice, I have a html with canvas, in this html you can add circles and then link these to make a figure, I also want to insert a search where you can find the different figures and focussed on it, so I don't know if it'll be better : to overlay the figures or use different canvas for each figure.
(I'm not implement the search function yet.)
What do you think?
Here is the functions that makes de draws
//this function puts the circles on a <table>, and then the other function takes the img coordinates and link it making a figure.
function position(year, mon)
{
$('#' + year + ' .' + mon).prepend('<img class="black_point" src="./images/circle.png"/>');
}
var table = document.getElementById("tabla");
var images = table.getElementsByTagName("img");
var canvas = document.getElementById("miCanvas");
var ctx = canvas.getContext("2d");
var x,y; // Remember coordinates
canvas.width = table.offsetWidth;
canvas.height = table.offsetHeight;
function connect(image, index) { //this function link the images
var tabBcr = table.getBoundingClientRect();
var imgBcr = image.getBoundingClientRect();
x = imgBcr.left + (imgBcr.width / 2) - tabBcr.left;
y = imgBcr.top + (imgBcr.height / 2) - tabBcr.top;
index === 0 ? ctx.moveTo(x, y) : ctx.lineTo(x, y);
}
//this function add a new canvas
function figure(){
/*$('#miCanvas').prepend('<canvas id="myCanvas">Su navegador no soporta Canvas.</canvas>');
//this is the property who overlay the figures
cxt.globalCompositeOperation="source-over";/*
//which it will be better to implement a search function?
}
// new path here
ctx.beginPath();
for(var i=0; i<images.length; i++){
connect( images[i], i); // provide index so we can sep. move/line
}
// then at the end:
ctx.fill();
Use 1 html canvas to hold all your connected circles.
This simplifies the event handling when focusing / blurring your figures.
You can test if the mouse is inside one of your circles like this:
// given a circle defined by centerX, centerY, radius
var dx = mouseX - centerX;
var dy = mouseY - centerY;
var isInside = dx*dx+dy*dy <= radius*radius;
Here's an outline of how to focus on a figure:
Create a javascript object defining each circle. If a set of objects makes up a figure, then add a group property to each circle-object representing which group that circle is a member of.
Put all your circle-objects in an array.
In your mouse event handlers, iterate through the circle-objects-array and find which circle is under the mouse. That circle's group has been focused.
So i want to make a line follow mouse and on click to draw that line, i need this for drawing polygons. My idea was to draw a line every time mouse moves but then it makes mess with a lot of lines, so i decided to draw over old lines after mouse moves with white lines to clean up and so that there would be only one line that goes from a point of last clicked spot to current mouse location.My jsFiddle for this. but it doesn't work the way i want yes i draws polygons on clicking but there is no line following the mouse so i can't see what line I'm drawing. I don't see where is it wrong ? Maybe there is some ready solution that i didn't find ? Mycode :
var polygonX = [];
var polygonY = [];
var lineReady = 0;
var whileLineX;
var whiteLineY;
$("#body").bind('mousemove', function (ev) {
if (lineReady >= 2) {
var context;
//clear old lines
if (whiteLineX !== null && whiteLineY !== null) {
context = $("#canvas")[0].getContext('2d');
context.moveTo(polygonX[lineReady - 1], polygonY[lineReady - 1]);
context.lineTo(whiteLineX, whiteLineY);
context.strokeStyle = '#ffffff';
context.stroke();
}
//draw a new line
context = $("#canvas")[0].getContext('2d');
var offset = $('#body').offset();
var x = ev.clientX - offset.left;
var y = ev.clientY - offset.top;
context.beginPath();
context.moveTo(polygonX[lineReady - 1], polygonY[lineReady - 1]);
context.strokeStyle = '#000000';
context.lineTo(x, y);
context.stroke();
whileLineX = x;
whiteLineY = y;
}
});
$("#body").bind('click', function (ev) {
var offset = $('#body').offset();
var x = ev.clientX - offset.left;
var y = ev.clientY - offset.top;
polygonX
.push(x);
polygonY.push(y);
lineReady++;
if (lineReady >= 2) {
var context = $("#canvas")[0].getContext('2d');
context.beginPath();
context.moveTo(polygonX[lineReady - 2], polygonY[lineReady - 2]);
context.lineTo(polygonX[lineReady - 1], polygonY[lineReady - 1]);
context.stroke();
}
});`
The best way to do this is to use a bit of animation.
Everytime you draw a line, push its coordinates (first point and last point) in an array. Then draw your array at every animation loop(check out this link which will explain you how to animate)
. Then you'll want to draw a single line, say colored in red, from the last point of the last line of the array where you're pushing lines to your mouse position.
Doing it this way will allow you to have a red line following your mouse at all times, giving you a "preview" of a line.
Algo-wise it would look like:
var arrayOflines = [];
canvas.onclick ->
var coordinates = mouseposition()
arrayOfLines.push(coordinates)
function mouseposition(){
returns x and y of your mouse on the canvas
}
function draw(array){
loop through array
draw line from array[0] to array[1], then from array[1] to array[2] on canvas
}
function drawPreview(){
draw line from last point of arrayOflines to mouseposition;
}
//so here we are:
function animationloop{
erase your canvas
draw(arrayOfLines); //draw your array
drawPreview(); //draw your 'preview' line
requestAnimationFrame(animationloop); //animate
}
Doing things this way will allow you to achieve a clean result.
I bumped into the following problem, hope someone will know how to help me:
I work with the JavaScript library Raphael. Now, what I want to do is, when I have many Raphael SVG elements, to simply select more elements with "rectangle selection", i.e. by dragging the mouse starting from the graph's background to create a selection rectangle (I hope I was clear enough), and move the elements which are in this rectangle.
For now, I've found something like this (someone posted it from a previous question of mine):
var paper = Raphael(0, 0, '100%', '100%');
var circle = paper.circle(75, 75, 50);
var rect = paper.rect(150, 150, 50, 50);
var set = paper.set();
set.push(circle, rect);
set.attr({
fill: 'red',
stroke: 0
});
var ox = 0;
var oy = 0;
var dragging = false;
set.mousedown(function(event) {
ox = event.screenX;
oy = event.screenY;
set.attr({
opacity: .5
});
dragging = true;
});
set.mousemove(function(event) {
if (dragging) {
set.translate(event.screenX - ox, event.screenY - oy);
ox = event.screenX;
oy = event.screenY;
}
});
set.mouseup(function(event) {
dragging = false;
set.attr({
opacity: 1
});
});
This code can be executed on jsfiddle. But, as you can see, this selects ALL the elements, by simply adding them to a Raphael set.
Now, I think that my problem will be solved by:
Making a rectangle selection
Adding the nodes which are in the rectangle to a Raphael set
Move only the selected items (i.e. move only the items which are in the Raphael set with set.mousemove)
My problem for now would be the first two issues.
Any ideas how to do this?
Thank you in advance!
Fun problem. You can do this by placing a rectangular "mat" the size of the canvas behind all of your other objects and attaching a drag event to it for selecting other elements. (Note this solution uses the newer version of Raphael, 2.1.0:
var paper = Raphael(0, 0, '100%', '100%');
//make an object in the background on which to attach drag events
var mat = paper.rect(0, 0, paper.width, paper.height).attr("fill", "#FFF");
var circle = paper.circle(75, 75, 50);
var rect = paper.rect(150, 150, 50, 50);
var set = paper.set();
set.push(circle, rect);
set.attr({
fill: 'red',
stroke: 0
});
//the box we're going to draw to track the selection
var box;
//set that will receive the selected items
var selections = paper.set();
Now, we add a drag event -- similar to the mouseover events but with three functions (see documentation), and draw a box to track the selection space:
//DRAG FUNCTIONS
//when mouse goes down over background, start drawing selection box
function dragstart (x, y, event) {
box = paper.rect(x, y, 0, 0).attr("stroke", "#9999FF");
}
// When mouse moves during drag, adjust box.
// If the drag is to the left or above original point,
// you have to translate the whole box and invert the dx
// or dy values since .rect() doesn't take negative width or height
function dragmove (dx, dy, x, y, event) {
var xoffset = 0,
yoffset = 0;
if (dx < 0) {
xoffset = dx;
dx = -1 * dx;
}
if (dy < 0) {
yoffset = dy;
dy = -1 * dy;
}
box.transform("T" + xoffset + "," + yoffset);
box.attr("width", dx);
box.attr("height", dy);
}
function dragend (event) {
//get the bounds of the selections
var bounds = box.getBBox();
box.remove();
reset();
console.log(bounds);
for (var c in set.items) {
// Here, we want to get the x,y vales of each object
// regardless of what sort of shape it is.
// But rect uses rx and ry, circle uses cx and cy, etc
// So we'll see if the bounding boxes intercept instead
var mybounds = set[c].getBBox();
//do bounding boxes overlap?
//is one of this object's x extremes between the selection's xe xtremes?
if (mybounds.x >= bounds.x && mybounds.x <= bounds.x2 || mybounds.x2 >= bounds.x && mybounds.x2 <= bounds.x2) {
//same for y
if (mybounds.y >= bounds.y && mybounds.y <= bounds.y2 || mybounds.y2 >= bounds.y && mybounds.y2 <= bounds.y2) {
selections.push(set[c]);
}
}
selections.attr("opacity", 0.5);
}
}
function reset () {
//empty selections and reset opacity;
selections = paper.set();
set.attr("opacity", 1);
}
mat.drag(dragmove, dragstart, dragend);
mat.click(function(e) {
reset();
});
Just like that, you have a new set (selections) that contains every object that was selected by the mouse drag. You can then apply your mouseover events from the original to that set.
Note that this will select circle objects if you nick the corner of their bounding box with your selection box, even if it doesn't overlap with the area of the circle. You could make a special case for circles if this is a problem.
jsFiddle