I'm adding multiple rectangles in canvas which could collide with each other. The outer stroke should be displayed on the outer part of both rectangles or the rectangle shapes should be merged in to one producing the expected result.
See picture bellow
It has to be cut because it will display the content under the canvas. See live example with background image: https://jsfiddle.net/0qpgf5un/
In the code example bellow rectangles are being added on top of each other as you can see in the first example of the picture.
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var offsetX = 150;
var offsetY = 150;
var w = 200;
var h = 100;
ctx.fillStyle = "red";
ctx.rect(0, 0, 600, 600);
ctx.fill();
ctx.clearRect(offsetX,offsetY, w, h);
ctx.strokeRect(offsetX, offsetY, w, h);
ctx.clearRect(offsetX-50,offsetY+50, w, h);
ctx.strokeRect(offsetX-50, offsetY+50, w, h);
Is there ways to achieve it without writing complex calculations of each path, since the collision of rectangles can be unintentional and diverse ?
Edit:
What I am trying to achieve is a similar functionality like in youtube's feedback form where when editing screenshot you can highlight items and the border then is merged.
Just add one more clearRect() (the first one)
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var offsetX = 150;
var offsetY = 150;
var w = 200;
var h = 100;
ctx.fillStyle = "red";
ctx.rect(0, 0, 600, 600);
ctx.fill();
ctx.clearRect(offsetX,offsetY, w, h);
ctx.strokeRect(offsetX, offsetY, w, h);
ctx.clearRect(offsetX-50,offsetY+50, w, h);
ctx.strokeRect(offsetX-50, offsetY+50, w, h);
ctx.clearRect(offsetX,offsetY, w, h);
https://jsfiddle.net/kt3yjhpc/
You can skip clearing the first rectangle and then clear it after you stroke the second one.
The clearPrev function will clear the area inside the strokes of the initial rectangle.
let canvas = document.getElementById('canvas'),
ctx = canvas.getContext('2d'),
offsetX = 70,
offsetY = 20,
w = 200,
h = 100,
strokeWidth = 5;
ctx.fillStyle = '#F00'
ctx.rect(0, 0, 600, 600);
ctx.fill();
ctx.strokeStyle = '#0FF';
ctx.lineWidth = strokeWidth;
//ctx.clearRect(offsetX, offsetY, w, h); <-- Do not need to do this, if we clear below...
ctx.strokeRect(offsetX, offsetY, w, h);
ctx.clearRect(offsetX - 50, offsetY + 50, w, h);
ctx.strokeRect(offsetX - 50, offsetY + 50, w, h);
clearPrev(ctx, offsetX, offsetY, w, h); // Clear previous
function clearPrev(ctx, x, y, w, h) {
let startOffset = Math.round(ctx.lineWidth / 2) - 1,
endOffset = strokeWidth - 1;
ctx.clearRect(x + startOffset, y + startOffset, w - endOffset, h - endOffset);
}
<canvas id="canvas" width="290" height="190"></canvas>
When you want to clear the canvas with complex shapes, forget about clearRect, it's not the only one able to produce transparent pixels.
Instead, have a look at compositing.
So your shape is really border-line, but I think you'll benefit from using this already:
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var offsetX = 150;
var offsetY = 150;
var w = 200;
var h = 100;
ctx.lineWidth = 2;
ctx.fillStyle = "red";
ctx.fillRect(0, 0, 600, 600);
// declare our complex shape as a single sub-path
ctx.beginPath()
ctx.rect(offsetX,offsetY, w, h);
ctx.rect(offsetX-50, offsetY+50, w, h);
// now we can paint it
// first the stroke, because we want to erase what's inside the fill-area
ctx.stroke();
// now to erase, we switch to destination-out compositing mode
ctx.globalCompositeOperation = 'destination-out';
// fill the inner path
ctx.fill();
// we're done
// If you wish to go back to normal mode later
ctx.globalCompositeOperation = 'source-over';
body { background: linear-gradient(blue,yellow); }
<canvas id="canvas" width="600" height="600"></canvas>
Related
I was trying to make two different shapes that are different colors but it isn't working. Both of the shapes are the same colors. Please help!(Please note that I am not the best coder in the world)
I've looked for other examples on this website, but all of them use the lineTo() method and I would like to use the rect() method just to make things easier.
//make canvas and set it up
var canvas = document.createElement('canvas');
document.body.appendChild(canvas);
var ctx = canvas.getContext('2d');
canvas.height = window.innerHeight;
canvas.width = window.innerWidth;
canvas.style.position = 'absolute';
canvas.style.left = '0px';
canvas.style.top = '0px';
canvas.style.backgroundColor = '#D0C6C6';
var cH = canvas.height;
var cW = canvas.width;
//draw paddles
//variables
var paddleLength = 120;
var redPaddleY = window.innerHeight / 2;
var bluePaddleY = window.innerHeight / 2;
var paddleWidth = 20;
//drawing starts
function drawPaddles() {
//RED PADDLE
var redPaddle = function(color) {
ctx.fillStyle = color;
ctx.clearRect(0, 0, cW, cH);
ctx.rect(cH / 12, redPaddleY - paddleLength / 2, paddleWidth, paddleLength);
ctx.fill();
};
//BLUE PADDLE
var bluePaddle = function(color) {
ctx.fillStyle = color;
ctx.clearRect(0, 0, cW, cH);
ctx.rect(cH / 12 * 14, bluePaddleY - paddleLength / 2, paddleWidth, paddleLength);
ctx.fill();
};
redPaddle('red');
bluePaddle('blue');
};
var interval = setInterval(drawPaddles, 25);
Whenever you add a shape to the canvas it becomes part of the current path. The current path remains open until you tell the canvas to start a new one with beginPath(). This means that when you add your second rect() it is combined with the first and filled with the same colour.
The simplest fix would be to use the fillRect() function instead of rect which begins, closes and fills a path in one call.
var redPaddle = function(color) {
ctx.fillStyle = color;
ctx.fillRect(cH / 12, redPaddleY - paddleLength / 2, paddleWidth, paddleLength);
};
If you still want to use rect() you should tell the canvas to begin a new path for each paddle.
var redPaddle = function(color) {
ctx.fillStyle = color;
ctx.beginPath();
ctx.rect(cH / 12, redPaddleY - paddleLength / 2, paddleWidth, paddleLength);
ctx.fill();
};
I would also suggest moving the clearRect() outside of the drawing functions too. Clear once per frame and draw both paddles.
...
ctx.clearRect(0, 0, cW, cH);
redPaddle();
bluePaddle();
...
You should also investigate requestAnimationFrame() to do your animation loop as it provides many performance improvements over intervals.
I am trying to write the description of each edge along the rectangle. The reason is to describe the length of each edge inside and outside rectangles (alongside). Is there a way I can achieve it?
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Clip a rectangular area
ctx.rect(50, 20, 200, 120);
ctx.stroke();
ctx.clip();
// Draw red rectangle after clip()
ctx.fillStyle = "red";
ctx.fillRect(0, 0, 150, 100);
This should show 200 above the top edge (outside) and 150 along the left edge (outside)
Using #stealththeninja's comment (pointing to this answer - text in html canvas) and this jsfiddle (for text rotation), I was able to build the code below. Hope it fits within your specs.
Screenshot of the result attached.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
const rectPosX = 50;
const rectPosY = 50;
const rectLength = 200;
const rectHeight = 150;
ctx.fillStyle = "red";
ctx.fillRect(rectPosX, rectPosY, rectLength, rectHeight);
ctx.fillStyle = "blue";
ctx.fillText('200', rectPosX + rectLength / 2, rectPosY);
ctx.fillText('150', rectPosX, rectPosY + rectHeight / 2);
ctx.fillText('200', rectPosX + rectLength / 2, rectPosY + rectHeight);
ctx.save();
ctx.translate(rectPosX + rectLength, rectPosY + rectHeight / 2);
ctx.rotate(0.5*Math.PI);
ctx.fillText('150', 0, 0);
ctx.restore();
<canvas id="myCanvas" width="400" height="300"></canvas>
Inside canvas I draw a line, that line will create dynamically. In the end of line, i want to create an HTML button. But I don't know how to create.
Plz, help me.
HTML
<canvas id="c"></canvas>
<input id="btn" type="button">
Javascript
var line = document.createElement("canvas");
var ctx = line.getContext("2d");
document.getElementById("c").style.height = "300px";
ctx.fillStyle = "red";
ctx.fillRect(10, 1, line.width, line.height);
var ctx = c.getContext("2d");
drawLine(20, 20, 150, 70);
function drawLine(x1, y1, x2, y2) {
var dx = x2 - x1,
dy = y2 - y1,
len = (Math.sqrt(dx*dx+dy*dy)-1)|0,
ang = Math.atan2(dy, dx);
ctx.translate(x1|0, y1|0);
ctx.rotate(ang);
ctx.drawImage(line, 0, 0, len, 1);
ctx.setTransform(1,0,0,1,0,0)
}
ctx.arc(20, 20, 5, 0, 2 * Math.PI);
ctx.fillStyle = 'green';
ctx.fill();
ctx.strokeStyle = 'red'
ctx.stroke();
DEMO
You can't put or draw an HTML element in a canvas. You can create the button and then use position: absolute with the same left and top as the end of the line's x and y.
Take a look at this snippet:
var canvas = document.getElementById("c");
var ctx = canvas.getContext("2d");
ctx.fillStyle = 'green';
ctx.strokeStyle = 'red';
drawLine(20, 20, 150, 70);
ctx.arc(20, 20, 5, 0, 2 * Math.PI);
ctx.fill();
ctx.stroke();
function drawLine(x1, y1, x2, y2) {
var button = createButtonOnCanvas(x2, y2);
ctx.beginPath();
ctx.moveTo(x1, y1);
ctx.lineTo(x2, y2);
ctx.stroke();
ctx.closePath();
}
function createButtonOnCanvas(x, y) {
var btn = document.createElement("button");
document.body.appendChild(btn);
btn.style.position = "absolute";
btn.style.left = x + "px";
btn.style.top = y + "px";
btn.innerHTML = "btn";
return btn;
}
<canvas id="c" width="300" height="100"></canvas>
Since you want to create a button, instead of moving an already existing one, I made a function that creates a completely new button and moves it over a certain (x, y) of the canvas.
You should also use the lineTo() method to draw a line and resize the canvas' width and height attributes. If the width and height attributes are 100 and 100 while the CSS width and height styles are 200px and 200px, those 100x100 pixels will be stretched to fill a 200x200 canvas and everything drawn will get blurry. For more information, take a look at this question.
I'm trying to just make a rectangle but nothing will appear, just the background. I've tried ctx.fill, ctx.fillStyle etc. nothing works:
I'm refering to this part
fill(77, 66, 66);
rect(10,200,100,100);
Here is the whole code for the page
var ctx, W, H;
window.onload = function() {
var canvas = document.getElementById("canvas");
W = window.innerWidth;
H = window.innerHeight;
canvas.width = W;
canvas.height = H;
ctx = canvas.getContext("2d");
setInterval(draw, 1);
function draw() {
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "#E6E6FF"; // this part does appear
ctx.fillRect(0, 0, W, H);
fill(77, 66, 66); // this doesn't appear
rect(10,200,100,100);
}
}
Thanks
You need to call fill and rect on the canvas context.
Also you need to change the fillStyle otherwise you're drawing a rectangle with the same color as the background and it won't show.
var ctx, W, H;
window.onload = function() {
var canvas = document.getElementById("canvas");
W = window.innerWidth;
H = window.innerHeight;
canvas.width = W;
canvas.height = H;
ctx = canvas.getContext("2d");
setTimeout(draw, 1);
function draw() {
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "#E6E6FF";
ctx.fillRect(0, 0, W, H);
ctx.fillStyle = "red"; // need this otherwise the rect will be the same color as the background
ctx.rect(10, 200, 100, 100); // needs to be called on the canvas context
ctx.fill(); // needs to be called on the canvas context, it will fill any path not already filled in.
}
}
You are filling both areas with the same color, and you have to use the context to perform fill functions. you also need to create the rect BEFORE you fill it.
Try this on for size: https://jsfiddle.net/szbk6f67/3/
var ctx, W, H;
window.onload = function () {
var canvas = document.getElementById("canvas");
W = 400;
H = 400;
canvas.width = W;
canvas.height = H;
ctx = canvas.getContext("2d");
setInterval(draw, 1);
function draw() {
ctx.globalCompositeOperation = 'source-over';
ctx.fillStyle = 'gray';
ctx.fillRect(0, 0, W, H);
ctx.fillStyle = 'black';
ctx.rect(10, 200, 100, 100);
ctx.fill();
}
}
I made a cylinder gauge, very similar to this one:
It is drawn using about 7 or so functions... mine is a little different. It is very fleixble in that I can set the colors, transparency, height, width, whether there is % text shown and a host of other options. But now I have a need for the same thing, but all rotated 90 deg so that I can set the height long and the width low to generate something more like this:
I found ctx.rotate, but no mater where it goes all the shapes fall apart.. ctx.save/restore appears to do nothing, I tried putting that in each shape drawing function. I tried modifying, for example, the drawOval function so that it would first rotate the canvas if horizontal was set to one; but it appeared to rotate it every single iteration, even with save/restore... so the top cylinder would rotate and the bottom would rotate twice or something. Very tough to tell what is really happening. What am I doing wrong? I don't want to duplicate all this code and spend hours customizing it, just to produce something I already have but turned horizontal. Erg! Help.
Option 1
To rotate everything just apply a transform to the element itself:
canvas.style.transform = "rotate(90deg)"; // or -90 depending on need
canvas.style.webkitTransform = "rotate(90deg)";
Option 2
Rotate context before drawing anything and before using any save(). Unlike the CSS version you will first need to translate to center, then rotate, and finally translate back.
You will need to make sure width and height of canvas is swapped before this is performed.
ctx.translate(ctx.canvas.width * 0.5, ctx.canvas.height * 0.5); // center
ctx.rotate(Math.PI * 0.5); // 90°
ctx.translate(-ctx.canvas.width * 0.5, -ctx.canvas.height * 0.5);
And of course, as an option 3, you can recalculate all your values to go along the other axis.
Look at the rotate function in this example. You want to do a translation to the point you want to rotate around.
example1();
example2();
function rotate(ctx, degrees, x, y, fn) {
ctx.save();
ctx.translate(x, y);
ctx.rotate(degrees * (Math.PI / 180));
fn();
ctx.restore();
}
function rad(deg) {
return deg * (Math.PI / 180);
}
function example2() {
var can = document.getElementById("can2");
var ctx = can.getContext('2d');
var w = can.width;
var h = can.height;
function drawBattery() {
var percent = 60;
ctx.beginPath();
ctx.arc(35,50, 25,0,rad(360));
ctx.moveTo(35+percent+25,50);
ctx.arc(35+percent,50,25,0,rad(360));
ctx.stroke();
ctx.beginPath();
ctx.fillStyle = "rgba(0,255,0,.5)";
ctx.arc(35,50,25,0,rad(360));
ctx.arc(35+percent,50,25,0,rad(360));
ctx.rect(35,25,percent,50);
ctx.fill();
ctx.beginPath();
ctx.lineWidth = 2;
ctx.strokeStyle = "#666666";
ctx.moveTo(135,25);
ctx.arc(135,50,25, rad(270), rad(269.9999));
//ctx.moveTo(35,75);
ctx.arc(35,50,25,rad(270),rad(90), true);
ctx.lineTo(135,75);
ctx.stroke();
}
drawBattery();
can = document.getElementById("can3");
ctx = can.getContext('2d');
w = can.width;
h = can.height;
rotate(ctx, -90, 0, h, drawBattery);
}
function example1() {
var can = document.getElementById('can');
var ctx = can.getContext('2d');
var color1 = "#FFFFFF";
var color2 = "#FFFF00";
var color3 = "rgba(0,155,255,.5)"
var text = 0;
function fillBox() {
ctx.save();
ctx.fillStyle = color3;
ctx.fillRect(0, 0, can.width / 2, can.height);
ctx.restore();
}
function drawBox() {
ctx.save();
ctx.beginPath();
ctx.strokeStyle = ctx.fillStyle = color1;
ctx.rect(10, 10, 50, 180);
ctx.font = "30px Arial";
ctx.fillText(text, 25, 45);
ctx.stroke();
ctx.beginPath();
ctx.strokeStyle = color2;
ctx.lineWidth = 10;
ctx.moveTo(10, 10);
ctx.lineTo(60, 10);
ctx.stroke();
ctx.restore();
}
fillBox();
rotate(ctx, 90, can.width, 0, fillBox);
text = "A";
drawBox();
color1 = "#00FFFF";
color2 = "#FF00FF";
text = "B";
rotate(ctx, 90, can.width, 0, drawBox);
centerRotatedBox()
function centerRotatedBox() {
ctx.translate(can.width / 2, can.height / 2);
for (var i = 0; i <= 90; i += 10) {
var radians = i * (Math.PI / 180);
ctx.save();
ctx.rotate(radians);
ctx.beginPath();
ctx.strokeStyle = "#333333";
ctx.rect(0, 0, 50, 50)
ctx.stroke();
ctx.restore();
}
}
}
#can,
#can2,
#can3 {
border: 1px solid #333333
}
<canvas id="can" width="200" height="200"></canvas>
<canvas id="can2" width="200" height="100"></canvas>
<canvas id="can3" width="100" height="200"></canvas>