This article mainly introduces the WeChat applet widget in detail, and implements the live broadcast like bubble effect based on Canvas. It has a certain reference value. Interested friends can refer to it.

First post Canvas implements the live broadcast like bubble effect diagram:

## Implementation details:

1.JS:

drawImage:function(data){[/align]
????var?that?=?this
????var?p10=?data[0][0];??/*?三階貝塞爾曲線起點坐標(biāo)值*/
????var?p11=?data[0][1];??/*?三階貝塞爾曲線第一個控制點坐標(biāo)值*/
????var?p12=?data[0][2];??/*?三階貝塞爾曲線第二個控制點坐標(biāo)值*/
????var?p13=?data[0][3];??/*?三階貝塞爾曲線終點坐標(biāo)值*/
????var?p20=?data[1][0];
????var?p21=?data[1][1];
????var?p22=?data[1][2];
????var?p23=?data[1][3];
????var?p30=?data[2][0];
????var?p31=?data[2][1];
????var?p32=?data[2][2];
????var?p33=?data[2][3];
????var?t?=?factor.t;
????/*計算多項式系數(shù)?（下同）*/??
????var?cx1?=?3*(p11.x-p10.x);
????var?bx1?=?3*(p12.x-p11.x)-cx1;
????var?ax1?=?p13.x-p10.x-cx1-bx1;
????var?cy1?=?3*(p11.y-p10.y);
????var?by1?=?3*(p12.y-p11.y)-cy1;
????var?ay1?=?p13.y-p10.y-cy1-by1;
????var?xt1?=?ax1*(t*t*t)+bx1*(t*t)+cx1*t+p10.x;
????var?yt1?=?ay1*(t*t*t)+by1*(t*t)+cy1*t+p10.y;
????var?cx2?=?3*(p21.x-p20.x);
????var?bx2?=?3*(p22.x-p21.x)-cx2;
????var?ax2?=?p23.x-p20.x-cx2-bx2;
????var?cy2?=?3*(p21.y-p20.y);
????var?by2?=?3*(p22.y-p21.y)-cy2;
????var?ay2?=?p23.y-p20.y-cy2-by2;
????var?xt2?=?ax2*(t*t*t)+bx2*(t*t)+cx2*t+p20.x;
????var?yt2?=?ay2*(t*t*t)+by2*(t*t)+cy2*t+p20.y;
????var?cx3?=?3*(p31.x-p30.x);
????var?bx3?=?3*(p32.x-p31.x)-cx3;
????var?ax3?=?p33.x-p30.x-cx3-bx3;
????var?cy3?=?3*(p31.y-p30.y);
????var?by3?=?3*(p32.y-p31.y)-cy3;
????var?ay3?=?p33.y-p30.y-cy3-by3;
????/*計算xt?yt的值?*/
????var?xt3?=?ax3*(t*t*t)+bx3*(t*t)+cx3*t+p30.x;
????var?yt3?=?ay3*(t*t*t)+by3*(t*t)+cy3*t+p30.y;
????factor.t?+=factor.speed;
????ctx.drawImage("../../images/heart1.png",xt1,yt1,30,30);
????ctx.drawImage("../../images/heart2.png",xt2,yt2,30,30);
????ctx.drawImage("../../images/heart3.png",xt3,yt3,30,30);
????ctx.draw();
????if(factor.t>1){
??????factor.t=0;
??????cancelAnimationFrame(timer);
??????that.startTimer();
????}else{
??????timer?=requestAnimationFrame(function(){
????????that.drawImage([[{x:30,y:400},{x:70,y:300},{x:-50,y:150},{x:30,y:0}],[{x:30,y:400},{x:30,y:300},{x:80,y:150},{x:30,y:0}],[{x:30,y:400},{x:0,y:90},{x:80,y:100},{x:30,y:0}]])
?????})
????}}

2. Principle:

a. By drawing three different third-order Bezier curves, select three pictures and let them move along their respective Bezier curves. The movement trajectories are as follows:

b. Calculate the mathematical expression of third-order Bezier curve x(t), y(t).

The third-order Bezier curve forms a curve through four points, two control points, a starting point and an end point.

Use polynomial coefficients to get the mathematical expressions of x(t), y(t):

cx?=?3?*?(?x1?-?x0?)
bx?=?3?*?(?x2?-?x1?)?-?cx
ax?=?x3?-?x0?-?cx?-?bx
cy?=?3?*?(?y1?-?y0?)????
by?=?3?*?(?y2?-?y1?)?-?cy
ay?=?y3?-?y0?-?cy?-?by
x(t)?=?ax?*?t?^?3?+?bx?*?t?^?2?+?cx?*?t?+?x0
y(t)?=?ay?*?t?^?3?+?by?*?t?^?2?+?cy?*?t?+?y0

Three Bezier curves are drawn here, just apply the formula three times , no loop is used here. If there are many Bezier curves, you can use a loop to call ctx.drawImage, where factor.t is the parameter of the third-order Bezier curve, the value range is [0,1], and finally call ctx .draw(), and set the timer to realize the picture moving along the Bezier curve.

3.Tip:

The timer used here is implemented through the requestAnimationFrame() function. The reason for deprecating setInterval is that there is a frame stuck phenomenon in the actual test and the animation display has Subtle discontinuities.

For more WeChat applet widgets to implement live broadcast like bubble effect based on Canvas, please pay attention to the PHP Chinese website!