圆圈跟随鼠标HTML5画布jQuery
圆圈跟随鼠标HTML5画布jQuery
提问于 2019-01-20 23:56:16
我正试着在游戏中使用的HTML画布上跟着鼠标画一个圆圈。我试图让圆在每次迭代中移动5px，但它在水平移动时速度较慢，垂直移动时速度较快。下面是我使用的数学公式：
x=distance between mouse and circle on the x-axis
y=distance between mouse and circle on the y-axis
z=shortest distance between mouse and circle
a=number of units circle should move along the x-axis
b=number of units circle should move along the y axis
x^2 + y^2=z^2
Want the total distance traveled every iteration to be five pixels
a^2 + b^2 = 25
b/a=y/x
b=ay/x
a=sqrt(25-ay/x^2)
a^2+ay/x-25=0
Use Quadratic formula to find both answers
a=(-y/x+-sqrt(y/x)^2+100)/2我在下面的代码中重复了这个问题
$(function(){
let canvas = $("canvas")[0];
let ctx = canvas.getContext("2d");
//Gets position of mouse and stores the value in variables mouseX and mouseY
let mouseX = mouseY = 0;
$("canvas").mousemove(function(e){
mouseX = e.pageX;
mouseY = e.pageY;
}).trigger("mousemove");
let circleX = 0;
let circleY = 0;
function loop(t){
//Background
ctx.fillStyle="blue";
ctx.fillRect(0, 0, canvas.width, canvas.height);
let xFromMouse = mouseX-circleX;
let yFromMouse = mouseY-circleY;
let yxRatio = yFromMouse/xFromMouse;
let xyRatio = xFromMouse/yFromMouse;
let speed = 25;
let possibleXValues = [(-yxRatio+Math.sqrt(Math.pow(yxRatio,2)+(4*speed)))/2,(-yxRatio-Math.sqrt(Math.pow(yxRatio,2)+(4*speed)))/2];
//I use this code as a temporary fix to stop the circle from completely disappearing
if(xFromMouse === 0 || isNaN(yxRatio) || isNaN(possibleXValues[0]) || isNaN(possibleXValues[1])){
possibleXValues = [0,0];
yxRatio = 0;
}
//Uses b=ay/x to calculate for y values
let possibleYValues = [possibleXValues[0]*yxRatio,possibleXValues[1]*yxRatio];
if(xFromMouse >= 0){
circleX += possibleXValues[0];
circleY += possibleYValues[0];
} else {
circleX += possibleXValues[1];
circleY += possibleYValues[1];
}
ctx.beginPath();
ctx.arc(circleX, circleY, 25, 0, 2 * Math.PI,false);
ctx.fillStyle = "red";
ctx.lineWidth = 0;
ctx.fill();
window.requestAnimationFrame(loop);
}
window.requestAnimationFrame(loop);
});<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<canvas width="450" height="250"></canvas>
Stack Overflow用户
回答已采纳
发布于 2019-01-21 09:44:46
我认为你最好使用笛卡尔到极坐标的转换。这是我之前做的一个例子。这将允许你在每次迭代中都有一个一致的步长“速度”。
//Canvas, context, mouse.
let c, a, m = { x:0, y:0};
//onload.
window.onload = function(){
let circle = {},
w, h,
speed = 5; //step speed = 5 "pixels" (this will be fractional in any one direction depending on direction of travel).
//setup
c = document.getElementById('canvas');
a = c.getContext('2d');
w = c.width = window.innerWidth;
h = c.height = window.innerHeight;
function move(){
//get distance and angle from mouse to circle.
let v1m = circle.x - m.x,
v2m = circle.y - m.y,
vDm = Math.sqrt(v1m*v1m + v2m*v2m),
vAm = Math.atan2(v2m, v1m);
//if distance is above some threshold, to stop jittering, move the circle by 'speed' towards mouse.
if(vDm > speed) {
circle.x -= Math.cos(vAm) * speed;
circle.y -= Math.sin(vAm) * speed;
}
}
function draw(){
//draw it all.
a.fillStyle = "blue";
a.fillRect(0,0,w,h);
a.fillStyle = "red";
a.beginPath();
a.arc(circle.x, circle.y, circle.r, Math.PI * 2, false);
a.closePath();
a.fill();
}
circle = {x:w/2, y:h/2, r:25};
function animate(){
requestAnimationFrame(animate);
move();
draw();
}
c.onmousemove = function(e){
m.x = e.pageX;
m.y = e.pageY;
};
animate();
}<canvas id="canvas" width="450" height="250"></canvas>
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/54278218
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