1、角度和弧度转换
radius = degrees * Math.PI / 180;
degrees = radius *180 / Math.PI
2、图形跟随鼠标转动
dx = mouse.x - obj.x;
dy = mouse.y - obj.y;
obj.rotation = Math.atan2(dy,dx)*180 / Math.PI
3、创建波动
(function drawFrame() {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
ball.x += xspeed;
ball.y = centerY / 2 + Math.sin(angle) * range;
ball.draw(context)
}())
4、创建圆形
(function drawFrame() {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
ball.x = centerX + Math.sin(angle) * radius;
ball.y = centerY + Math.cos(angle) * radius;
angle += speed;
ball.draw(context)
}())
5、创建椭圆
(function drawFrame() {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
ball.x = centerX + Math.sin(angle) * radiusX;
ball.y = centerY + Math.cos(angle) * radiusY
angle += speed
ball.draw(context)
}())
6、两点之间的距离:
dx = x1 - x2;
dy = y1 - y2;
dist = Math.sqrt(dx*dx + dy*dy);
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