技术教程 编程教程 使用Canvas基于手势可以使树秋千 正文

使用Canvas基于手势可以使树秋千

2023-06-02,,

用Canvas制作能够依据手势摆动的树

依据工作的须要。制作一个摆动的树做为页面的背景。为了添加页面的交互性，我又为背景中的树添加了鼠标（触控）事件，使他可以依据鼠标（触控）做出对应的动作，当手指做上下或者左右滑动的时候树会跟着摆动。先看看终于效果。

Step1.完毕HTML页面。新建一个Tree类

完毕HTML页面后新建一个Tree类用来记录树的各个属性。当中x,y为树根部的坐标值。branchLen,branchWidth各自是树枝的长度与宽度，depth为树枝的层数。canvas用来接页面中的canvas元素（默认是ID为canvas的元素）。

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    this.canvas = canvas || document.getElementById('canvas');

    this.ctx = this.canvas.getContext('2d');

    this.x = x||0;

    this.y = y||0;

    this.branchLen = branchLen||0;

    this.branchWidth = branchWidth||0;

    var depth = depth || 5;

}

点击查看历史代码

Step2.加入drawRoot方法，用来绘制树干

首先在drawRoot中画第一个枝干。

drawRoot的參数意义同上。而且在Tree类的构造函数中执行drawRoot并把Tree接受到的參数传入。最后new一个Tree类，使树根位于屏幕的底部正中心。树枝长100px，树枝宽度为8px，树枝层数为8层（临时用不上）。

var atree = new Tree(canvas.width/2-4,canvas.height,100,8,8,canvas);

在drawRoot中我们须要用lineTo()画出树枝。树枝的起始的坐标值(x,y)已经给出，结束的坐标值(toX,toY)须要进行计算。第一个画的是树干，因为树干垂直于地面所以结束坐标toX等于初始坐标x,而结束坐标toY等于初始y减去树干长度branchLen(注意坐标的0,0点在canvas的左上角)。var
toX = x;var toY = y-branchLen;

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    this.canvas = canvas || document.getElementById('canvas');

    this.ctx = this.canvas.getContext('2d');

    this.x = x||0;

    this.y = y||0;

    this.branchLen = branchLen||0;

    this.branchWidth = branchWidth||0;

    var depth = depth || 5;

    this.drawRoot(this.x,this.y,this.branchLen,this.branchWidth);

}

Tree.prototype.drawRoot = function(x,y,branchLen,branchWidth){

    var toX = x;

    var toY = y-branchLen;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

}

var atree = new Tree(canvas.width/2-4,canvas.height,100,8,8,canvas);

执行代码：

点击查看历史代码

Step3.加入drawBranch方法，用来绘制树枝

drawBranch相同是依据初始与结束坐标画出一条直线代表树枝。

与树干不同的是树枝不再是垂直与地面而是与树干保持一定的角度。并且树枝的初始值是树干的结束点(toX,toY)。所以在drawBranch中我们增加新參数angle用来表示树枝与树干的垂直夹角α，这样就能够依据α算出toX与toY。请看图。

这样我们在画完树干后再分别画两个不同角度的树枝。一个是30°一个-30°。并将传给树枝的宽度branchWidth减小一个像素。使其与树干粗细不同。

Tree.prototype.drawRoot = function(x,y,branchLen,branchWidth){

    var toX = x;

    var toY = y-branchLen;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

    this.drawBranch(toX,toY,branchLen,branchWidth-1,30);

    this.drawBranch(toX,toY,branchLen,branchWidth-1,-30);

}

Tree.prototype.drawBranch = function(x,y,branchLen,branchWidth,angle){

    var angle = angle || 0;

    var radian = (90-angle)*(Math.PI/180);

    var toX = x+Math.cos(radian)*branchLen;

    var toY = y-Math.sin(radian)*branchLen;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

}

执行代码：

点击查看历史代码

Step4.改动drawBranch函数，反复画树枝

在drawBranch函数的最后再次调用两次drawBranch

this.drawBranch(toX,toY,branchLen,branchWidth-1,angle+30);

this.drawBranch(toX,toY,branchLen,branchWidth-1,angle-30);

使其调用自己完毕递归,注意这里传入的角度是在之前的角度的基础上在添加或者降低30度。

为了使递归停下来我们须要一个停止条件，就是之前一直没实用到的depth參数。我们在每次画下一层之前使其减1表示已经完毕了一层树枝的绘制，直至depth减小到0表示绘制全然部的层数。

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    this.canvas = canvas || document.getElementById('canvas');

    this.ctx = this.canvas.getContext('2d');

    this.x = x||0;

    this.y = y||0;

    this.branchLen = branchLen||0;

    this.branchWidth = branchWidth||0;

    var depth = depth || 5;

    this.drawRoot(this.x,this.y,this.branchLen,this.branchWidth,depth);

}

Tree.prototype.drawRoot = function(x,y,branchLen,branchWidth,depth){

    var toX = x;

    var toY = y-branchLen;

    var depth = depth||5;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

    depth--;

    if(depth>0){

      this.drawBranch(toX,toY,branchLen,branchWidth-1,30,depth);

      this.drawBranch(toX,toY,branchLen,branchWidth-1,-30,depth);

    }

}

Tree.prototype.drawBranch = function(x,y,branchLen,branchWidth,angle,depth){

    var angle = angle || 0;

    var radian = (90-angle)*(Math.PI/180);

    var toX = x+Math.cos(radian)*branchLen;

    var toY = y-Math.sin(radian)*branchLen;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

    depth--;

    if(depth>0){

      this.drawBranch(toX,toY,branchLen,branchWidth-1,angle+30,depth);

      this.drawBranch(toX,toY,branchLen,branchWidth-1,angle-30,depth);

    }

}

执行代码：

因为树之间角度过大，并且全部树枝长度都相等，看起来并不像一棵树。所以我们须要在Tree的构造函数中增加几个參数用来调整树的姿态。

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    ......

    this.branchLenFactor = 0.8;

    this.rootLenFactor = 1.2;

    this.branchAngle = 20;

    ......

}

branchLenFactor:画每一层树枝的时候乘在branchLen上面，用来控制树枝长度。

rootLenFactor:画树根的时候乘在branchLen上面，用来控制树根长度。branchAngle: 用来控制树枝之间的角度。

Tree.prototype.drawRoot = function(x,y,branchLen,branchWidth,depth){

    var toX = x;

    var toY = y-branchLen*this.rootLenFactor;

    var depth = depth||5;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

    depth--;

    if(depth>0){

      this.drawBranch(toX,toY,branchLen*this.branchLenFactor,branchWidth-1,this.branchAngle,depth);

      this.drawBranch(toX,toY,branchLen*this.branchLenFactor,branchWidth-1,-this.branchAngle,depth);

    }

  }

  Tree.prototype.drawBranch = function(x,y,branchLen,branchWidth,angle,depth){

    var angle = angle || 0;

    var radian = (90-angle)*(Math.PI/180);

    var toX = x+Math.cos(radian)*branchLen;

    var toY = y-Math.sin(radian)*branchLen;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

    depth--;

    if(depth>0){

      this.drawBranch(toX,toY,branchLen*this.branchLenFactor,branchWidth-1,angle+this.branchAngle,depth);

      this.drawBranch(toX,toY,branchLen*this.branchLenFactor,branchWidth-1,angle-this.branchAngle,depth);

    }

  }

执行代码：

点击查看历史代码

Step5.使树枝晃动起来

为了使树枝有摇晃的效果。我们仅仅须要改变树枝之间的角度branchAngle就能够了。我须要在Tree的构造函数中添加三个新属性：oBranchAngle用来记录初始角度。branchAngleFactor用来控制角度随时间变化的变化量；swingAngle:随时间添加用来记录摇动的角度。

同一时候改动下drawRoot函数使其不用接受參数。调用更加方便。

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    ......

    this.branchAngle = 20;

    this.oBranchAngle = this.branchAngle;

    this.branchAngleFactor = 5;

    this.swingAngle = 0;

    ......

    this.drawRoot();

}

Tree.prototype.drawRoot = function(){

    var x = this.x,y=this.y,branchLen = this.branchLen,depth = this.depth,branchWidth = this.branchWidth;

    var toX = x;

    var toY = y-branchLen*this.rootLenFactor;

    var depth = depth||5;

    this.ctx.save();

    this.ctx.strokeStyle="rgba(37, 141, 194, 0.93)";

    this.ctx.beginPath();

    this.ctx.lineCap = "butt";

    this.ctx.lineJoin="round";

    this.ctx.lineWidth = this.branchWidth;

    this.ctx.moveTo(x,y);

    this.ctx.lineTo(toX,toY);

    this.ctx.closePath();

    this.ctx.stroke();

    this.ctx.restore();

    depth--;

    if(depth>0){

      this.drawBranch(toX,toY,branchLen*this.branchLenFactor,branchWidth-1,this.branchAngle,depth);

      this.drawBranch(toX,toY,branchLen*this.branchLenFactor,branchWidth-1,-this.branchAngle,depth);

    }

  }

添加循环函数，在循环函数中重绘整个树。而且每次重绘都要改动branchAngle值，使大树摇动起来。atree.swingAngle++;使摇动角度随时间变化。这里使用Math.sin(atree.swingAngle*(Math.PI/180))能够获得一个-1至1之间的连续变化值。atree.branchAngle = Math.sin(atree.swingAngle*(Math.PI/180))*atree.branchAngleFactor+atree.oBranchAngle;乘以系数并加在原角度上。

function loop(time){

    ctx.clearRect(0,0,canvas.width,canvas.height);

    atree.branchAngle = Math.sin(atree.swingAngle*(Math.PI/180))*atree.branchAngleFactor+atree.oBranchAngle;

    atree.drawRoot()

    requestAnimFrame(loop);

  }

  loop(0);

执行代码：

点击查看历史代码

Step6.加入手势

这里为了省事仅仅加入了touch事件，mouse事件与touch事件的处理方法大体一致。

首先为Tree新加一个属性swingSwitch = true用来表示大树是否摆动。当手指触控到屏幕的时候摆动停止，离开屏幕的时候摆动继续。

加入strengthX,strengthY两个属性;分别表示树在x轴与y轴因受到的力而移动的距离。

加入strengthXFactor,strengthYFactor；分别用来表示再一次滑动中x轴与y轴移动的最大距离。

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    ......

    this.swingSwitch = true;

    ......

    this.strengthX = 0;

    this.strengthY = 0;

    ......

  }
//记录触控開始时的信息

var touchStart = {x:0,y:0,strengthX:0,strengthY:0};

document.addEventListener('touchstart',function(e){

    //让树停止摆动

    atree.swingSwitch = false;

    touchStart.x = e.touches[0].clientX;

    touchStart.y = e.touches[0].clientY;

    //记录触控開始时,原strength的值

    touchStart.strengthX = atree.strengthX;

    touchStart.strengthY = atree.strengthY;

});

document.addEventListener('touchmove',function(e){

    //阻止浏览器默认动作

    e.preventDefault();

    //(touchStart.x-e.touches[0].clientX)/canvas.width能够依据滑动距离获得一个0-1的值

    atree.strengthX = touchStart.strengthX-(touchStart.x-e.touches[0].clientX)/canvas.width*atree.strengthXFactor;

    atree.strengthY = touchStart.strengthY-(touchStart.y-e.touches[0].clientY)/canvas.height*atree.strengthYFactor;

});

document.addEventListener('touchend',function(e){

    //恢复摆动

    atree.swingSwitch = true;

});

改动drawBranch将strength的变化加入到角度与toX，toY的计算中，详情见凝视。

Tree.prototype.drawBranch = function(x,y,branchLen,branchWidth,angle,depth){

    var angle = angle || 0;

    //用strengthX乘以(depth/this.depth)使得树枝末梢对角度的变化不敏感

    angle += this.strengthX*(depth/this.depth)/this.strengthXFactor*this.branchAngle;

    var radian = (90-angle)*(Math.PI/180);

    //用strengthX乘以(1-depth/this.depth)使得树枝末梢对角度的变化敏感

    var toX = x+Math.cos(radian)*branchLen+this.strengthX*(1-depth/this.depth);

    var toY = y-Math.sin(radian)*branchLen+this.strengthY*(1-depth/this.depth);

    ......

}

在动画循环中加入恢复代码，使strengthX，strengthY恢复为0。并添加swingSwitch的推断。

function loop(time){

    ......

    //当swingSwitch开启时開始摆动

    if(atree.swingSwitch){

        //将strength恢复到0

      if(atree.strengthX >0){

        atree.strengthX -= 1;

      }

      if(atree.strengthX <0){

        atree.strengthX += 1;

      }

      if(atree.strengthY >0){

        atree.strengthY -= 1;

      }

      if(atree.strengthY <0){

        atree.strengthY += 1;

      }

      atree.swingAngle++;

      atree.branchAngle = Math.sin(atree.swingAngle*(Math.PI/180))*atree.branchAngleFactor+atree.oBranchAngle;

    }

    ......

}

loop(0);

执行代码：

点击查看历史代码

Step7.加入缓动效果

Step6中的恢复strengthX,strengthY的代码过于简单，动画匀速恢复到0，显得过于突兀。比較真实的情况应该是由快变慢的恢复，所以我们要为恢复代码加上缓动。首先在Tree中加入recoverStartTime = 0用来记录恢复開始的时间。在手指离开屏幕的时候(touchend)将其赋为0，同一时候用oStrengthX,oStrengthY记录下来strengthX与strengthY的目标值。

function Tree(x,y,branchLen,branchWidth,depth,canvas){

    ......

    this.recoverStartTime = 0;

    ......

}

function loop(time){

    ......

    if(atree.swingSwitch){

      if(atree.strengthX > 0){

        if(atree.recoverStartTime == 0){

          atree.recoverStartTime = time;

        }

        var t = time-atree.recoverStartTime;

        //五次方的缓动

        atree.strengthX =  Math.max(atree.oStrengthX-atree.oStrengthX*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      if(atree.strengthX < 0){

        if(atree.recoverStartTime == 0){

          atree.recoverStartTime = time;

        }

        var t = time-atree.recoverStartTime;

        //五次方的缓动

        atree.strengthX =  Math.min(atree.oStrengthX-atree.oStrengthX*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      if(atree.strengthY > 0){

        if(atree.recoverStartTime == 0){

          atree.recoverStartTime = time;

        }

        var t = time-atree.recoverStartTime;

        //五次方的缓动

        atree.strengthY =  Math.max(atree.oStrengthY-atree.oStrengthY*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      if(atree.strengthY < 0){

        if(atree.recoverStartTime == 0){

          atree.recoverStartTime = time;

        }

        var t = time-atree.recoverStartTime;

        //五次方的缓动

        atree.strengthY =  Math.min(atree.oStrengthY-atree.oStrengthY*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

    }

    ......

}

document.addEventListener('touchend',function(e){

  atree.recoverStartTime = 0;

  atree.oStrengthX = atree.strengthX;

  atree.oStrengthY = atree.strengthY;

  ......

});

执行代码：

点击查看历史代码

Step7.使树干摇动并移至屏幕左边

改动drawRoot使树干也能够晃动，并改动var atree = new Tree(10,canvas.height,100,8,8,canvas);使其移至左边。

Tree.prototype.drawRoot = function(){

    ......

    //添加strength

    var angle = 0;

    angle += this.strengthX/this.strengthXFactor*this.branchAngle;

    var radian = (90-angle)*(Math.PI/180);

    var toX = x+Math.cos(radian)*branchLen*this.rootLenFactor;

    var toY = y-Math.sin(radian)*branchLen*this.rootLenFactor;

    ......

}

var atree = new Tree(10,canvas.height,100,8,8,canvas);

执行代码：

点击查看历史代码

Step8.

将动画循环中处理角度的部分加入到Tree的swing()中。

Tree.prototype.swing = function(time){

    this.ctx.clearRect(0,0,this.canvas.width,this.canvas.height);

    if(this.swingSwitch){

      if(this.strengthX > 0){

        if(this.recoverStartTime == 0){

          this.recoverStartTime = time;

        }

        var t = time-this.recoverStartTime;

        this.strengthX =  Math.max(this.oStrengthX-this.oStrengthX*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      if(this.strengthX < 0){

        if(this.recoverStartTime == 0){

          this.recoverStartTime = time;

        }

        var t = time-this.recoverStartTime;

        this.strengthX =  Math.min(this.oStrengthX-this.oStrengthX*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      if(this.strengthY > 0){

        if(this.recoverStartTime == 0){

          this.recoverStartTime = time;

        }

        var t = time-this.recoverStartTime;

        this.strengthY =  Math.max(this.oStrengthY-this.oStrengthY*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      if(this.strengthY < 0){

        if(this.recoverStartTime == 0){

          this.recoverStartTime = time;

        }

        var t = time-this.recoverStartTime;

        this.strengthY =  Math.min(this.oStrengthY-this.oStrengthY*((t=t/2000-1)*t*t*t*t + 1)+0,0);

      }

      this.swingAngle++;

      this.branchAngle = Math.sin(this.swingAngle*(Math.PI/180))*this.branchAngleFactor+this.oBranchAngle;

    }

    this.drawRoot();

}

var atree = new Tree(10,canvas.height,100,8,8,canvas);

function loop(time){

    atree.swing(time);

    requestAnimFrame(loop);

}

loop(0);

执行代码：

查看全部代码请去Github

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