How to rotate an image on HTML5 canvas when the right and left arrow keys are pressed
Question
I need help trying to rotate the rectangle that I have drawn on the canvas. I would like the top of the rectangle to pivot either to the right or left once I press on the arrow keys on my keyboard. This is my code so far:
HTML:
<body >
<div id="canvas-container">
<canvas id="canvas" width="500" height="400"></canvas>
</div>
</body>
CSS:
canvas {
display: inline;
}
Javascript:
document.addEventListener("DOMContentLoaded", function() {
drawBorder();
});
var canvas;
var context;
var size;
drawRectangle();
drawHalfCircle();
function drawBorder() {
canvas = document.getElementById("canvas");
context = canvas.getContext('2d');
size = {
x: canvas.width,
y: canvas.height
};
//have to set colors etc befor it is drawn
context.strokeStyle = 'black';
//takes 4 parameters
context.strokeRect(0, 0, size.x, size.y);
}
function drawRectangle() {
var c = document.getElementById("canvas");
var ctx = c.getContext("2d");
ctx.rect(246, 290, 8, 80);
ctx.stroke();
}
function drawHalfCircle(){
var c= document.getElementById("canvas");
var ctx=c.getContext("2d");
ctx.beginPath();
ctx.arc(250,579,308,1.2*Math.PI, 1.8*Math.PI);
ctx.stroke();
}
1 answers
solution1
2 ACCPTED 2015-10-01 06:31:08
I have mocked something up is this along the correct lines of what you are wanting.
document.addEventListener("DOMContentLoaded", function() {
drawBorder();
});
var canvas = document.getElementById("canvas");
var context = canvas.getContext('2d');
var size;
var angle = 0;
setInterval(function () {
context.save();
context.clearRect(0, 0, canvas.width, canvas.height);
drawBorder();
drawHalfCircle();
drawRectangle();
context.restore();
}, 100);
function drawBorder() {
size = {
x: canvas.width,
y: canvas.height
};
//have to set colors etc befor it is drawn
context.strokeStyle = 'black';
//takes 4 parameters
context.strokeRect(0, 0, size.x, size.y);
}
function drawRectangle() {
context.rotate(Math.PI / 180 * (angle));
context.rect(246, 290, 8, 80);
context.stroke();
}
function drawHalfCircle(){
context.beginPath();
context.arc(250,579,308,1.2*Math.PI, 1.8*Math.PI);
context.stroke();
}
document.onkeydown = function(e) {
var event = window.event ? window.event : e;
if (e.keyCode == '37') {
angle += 5;
}
else if (e.keyCode == '39') {
angle -= 5;
}
}
Basically set an interval and redraw (ie frames like in a movie) and rotate via a variable.
See a demo here https://jsbin.com/qititacazu/edit?js,output
If you want to translate it so it will rotate around a different point do something like this.
context.translate(246, 290);
context.rotate(Math.PI / 180 * (angle));
context.rect(-4, 0, 4, 80);
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.