我试图从左到右划出一条穿过画布的线.即时通讯还处于早期阶段,要做到这一点,使用以下功能来做一步一步的动画
@H_301_5@timer = window.setInterval(draw_line,30);
我的绘图功能是这样的
@H_301_5@function draw_line()
{
context.fillStyle = "#000";
context.fillRect(0,canv.width,canv.height);
context.beginPath();
context.lineWidth = 2;
context.strokeStyle = '#fff';
//Where p1,p2,cp1,cp2 are point objects that has x & y values already defined
context.moveTo(p1.x,p1.y);
context.bezierCurveTo(cp1.x,cp1.y,cp2.x,cp2.y,p2.x,p2.y);
context.stroke();
context.closePath();
// now i have to move p1,cp2
// now here is my problem
}
我知道我需要移动p1.x =一个随机数;对于cp1和cp2来说也是一样的,但是p2的终点应该跟着同一条轨道一样！我怎么能实现这一目标？
谢谢
最佳答案
编辑回答
有了你的澄清,我想我现在可以适当地回答这个问题了.
为了使终点遵循起点通过画布的路径,您必须存储历史值.在这个例子中,http://jsfiddle.net/mobidevelop/bGgHQ/,我使用鼠标移动来填充最后16个位置的缓冲区,然后通过迭代RingBuffer使用它来形成穿过点的贝塞尔曲线.
@H_301_5@function RingBuffer(length) {
this.length = length;
this.pointer = 0;
this.buffer = [];
}
RingBuffer.prototype.get = function(index) {
if (index < 0) {
index += this.length;
}
return this.buffer[index];
}
RingBuffer.prototype.push = function(value) {
this.buffer[this.pointer] = value;
this.pointer = (this.length + this.pointer +1) % this.length;
}
var c = document.getElementById("myCanvas");
var context =c.getContext("2d");
timer = window.setInterval(draw_line,30);
function Point(x,y) {
this.x = x;
this.y = y;
}
Point.prototype.translateX = function(x) {
return this.x += x;
};
Point.prototype.translateY = function(y) {
return this.y += y;
};
function draw_line()
{
context.fillStyle = "#000";
context.fillRect(0,c.width,c.height);
var pointer = history.pointer;
context.beginPath();
context.lineWidth = 2;
context.strokeStyle = '#F00';
for (iteration = 0,count = 15; iteration < count; iteration += 3) {
var p1 = history.get(--pointer);
var p2 = history.get(--pointer);
var p3 = history.get(--pointer);
var p4 = history.get(--pointer);
if (p1 && p2 && p3 && p4) {
context.moveTo(p1.x,p1.y);
context.bezierCurveTo(p2.x,p2.y,p3.x,p3.y,p4.x,p4.y);
}
pointer++;
}
context.stroke();
context.closePath();
}
var history = new RingBuffer(16);
var lastGrab = new Date();
c.addEventListener('mousemove',function() {
now = new Date();
if (now - lastGrab > 15) {
history.push(new Point(event.clientX - c.offsetLeft,event.clientY - c.offsetTop));
lastGrab = now;
}
});
出于历史目的,上面的答案留在下面.
我不确定我是否完全理解你想要实现的目标,但我认为你需要做的就是用相同的值翻译你的所有点数.这将导致遍历画布的线保持相同的形状.这样的事情：
@H_301_5@var c = document.getElementById("myCanvas");
var context =c.getContext("2d");
timer = window.setInterval(draw_line,y) {
this.x = x;
this.y = y;
}
Point.prototype.translateX = function(x) {
return this.x += x;
};
Point.prototype.translateY = function(y) {
return this.y += y;
};
var p1 = new Point(0,0);
var p2 = new Point(100,100);
var cp1 = new Point(15,45);
var cp2 = new Point(85,45);
function draw_line()
{
context.fillStyle = "#000";
context.fillRect(0,c.height);
context.beginPath();
context.lineWidth = 2;
context.strokeStyle = '#fff';
//Where p1,cp2 are point objects that has x & y values already defined
context.moveTo(p1.x,p1.y);
context.bezierCurveTo(cp1.x,p2.y);
context.stroke();
context.closePath();
p1.translateX(1);
p2.translateX(1);
cp1.translateX(1);
cp2.translateX(1);
if (p1.x > 300) {
p1.translateX(-400);
p2.translateX(-400);
cp1.translateX(-400);
cp2.translateX(-400);
}
}
除非我误解目标……
