我创建了一个小程序,在其中显示一个圆圈并允许用户在 HTML5 Canvas 中拖动该圆圈。
我能够显示圆圈,但只有当我单击圆圈的右下角时,拖动功能才起作用,如果我尝试通过单击圆圈的其他任何位置来拖动它,那么它就不起作用。我不知道如何解决其中的问题。
这是我的完整代码:
<script>
// handle mousedown events
function myDown(e) {
// tell the browser we're handling this mouse event
e.preventDefault();
e.stopPropagation();
// get the current mouse position
var mx = parseInt(e.clientX - offsetX);
var my = parseInt(e.clientY - offsetY);
// test each circle to see if mouse is inside
dragok = false;
for (var i = 0; i < circles.length; i++) {
var r = circles[i];
if (mx > r.x && mx < r.x + r.radius && my > r.y && my < r.y + r.height) {
// if yes, set that circles isDragging=true
dragok = true;
r.isDragging = true;
}
}
// save the current mouse position
startX = mx;
startY = my;
}
// handle mouseup events
function myUp(e) {
// tell the browser we're handling this mouse event
e.preventDefault();
e.stopPropagation();
// clear all the dragging flags
dragok = false;
for (var i = 0; i < circles.length; i++) {
circles[i].isDragging = false;
}
}
// handle mouse moves
function myMove(e) {
// if we're dragging anything...
if (dragok) {
// tell the browser we're handling this mouse event
e.preventDefault();
e.stopPropagation();
// get the current mouse position
var mx = parseInt(e.clientX - offsetX);
var my = parseInt(e.clientY - offsetY);
// calculate the distance the mouse has moved
// since the last mousemove
var dx = mx - startX;
var dy = my - startY;
// move each circle that isDragging
// by the distance the mouse has moved
// since the last mousemove
for (var i = 0; i < circles.length; i++) {
var r = circles[i];
if (r.isDragging) {
r.x += dx;
r.y += dy;
}
}
// redraw the scene with the new circle positions
draw();
// reset the starting mouse position for the next mousemove
startX = mx;
startY = my;
}
}
</script>
我猜,问题在于 function myDown(e)
,但我无法弄清楚如何修复坐标,这样如果我单击圆圈的任何位置,它应该可拖动。
最佳答案
尝试将函数 myDown(e) 中的 for 循环内的 if 更改为:
if (mx > r.x - r.radius && mx < r.x + r.radius && my > r.y - r.radius && my < r.y + r.radius)
关于javascript - 使用鼠标拖动 HTML5 Canvas 中的元素,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31161804/