javascript - About canvas rotation-PHP Chinese Network Q&A

Article Topic Learning Download Q&A Programming Dictionary Game Recent Updates

简体中文(ZH-CN) English(EN) 繁体中文(ZH-TW) 日本語(JA) 한국어(KO) Melayu(MS) Français(FR) Deutsch(DE)

javascript - About canvas rotation

女神的闺蜜爱上我 2017-06-28 09:28:14

718

$("#bt-lottery").one("click",function(){ var reg=1; setInterval(function(){ ctx.save(); ctx.translate(249.5,249.5);//将原点移动到画布中心 ctx.rotate(reg*Math.PI/180); ctx.clearRect(-pin.width/2,-pin.height/2,pin.width,pin.height); ctx.drawImage(pin,-pin.width/2,-pin.height/2); ctx.restore(); reg++; },5); });

I want to realize the function of the pointer (pin.png) rotating on the turntable (pan.png), but if ctx.clearRect(); will appearAs shown in the figure; The result I want is, how to achieve it? ? Ask for advice

女神的闺蜜爱上我

reply all (1)

Ty802017-06-28 09:30:14 1 floor

Due to insufficient information, I can only give my judgment.

png is not transparent, the probability is very small
You are divided into two canvases, but the canvas with the pointer has a background color, the probability is also very small
Code problem:

setInterval(function(){ ctx.clearRect(0,0,canvas.width,canvas.height); //这里你需要绘制背景图片（转盘），或者将转盘作为离屏canvas分离出去（因为转盘不会变动），只绘制指针。 ---我猜你缺少了这一步。。 ctx.save(); ctx.translate(249.5,249.5);//将原点移动到画布中心 //ctx.clearRect(-pin.width/2,-pin.height/2,pin.width,pin.height);至于为什么清理出来的区域是个圆形跟你代码执行的顺序有关，先旋转后清理和先清理后旋转是不一样的。 ctx.rotate(reg*Math.PI/180); ctx.drawImage(pin,-pin.width/2,-pin.height/2); ctx.restore(); reg++; },5);