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html5 canvas 绘制圆角矩形

html5没有圆角矩形的绘制函数，不过可以通过arc和line组合成圆角矩形，或者quadraticCurveTo和lineTo组合成圆角矩形。

下面是示例代码：

//-------------------------------------

/**

* 绘制圆角矩形,用arc和LineTo函数

*/

function roundRectanglePath(context,rect,radius)

{

context.beginPath();

context.moveTo( rect.getX()+radius,rect.getY() );

context.lineTo( rect.getRight()-radius,rect.getY() );

context.arc( rect.getRight()-radius,rect.getY()+radius, radius, 3*Math.PI/2,2*Math.PI, false);

context.lineTo( rect.getRight(),rect.getBottom()-radius);

context.arc( rect.getRight()-radius,rect.getBottom()-radius, radius, 0, Math.PI/2, false);

context.lineTo( rect.getX()+radius,rect.getBottom() );

context.arc( rect.getX()+radius,rect.getBottom()-radius, radius, Math.PI/2, Math.PI, false);

context.lineTo( rect.getX(),rect.getY()+radius);

context.arc( rect.getX()+radius,rect.getY()+radius, radius,Math.PI, 3*Math.PI/2, false);

context.closePath();

}

/**

* 绘制圆角矩形，用quadraticCurveTo和lineTo函数

*/

function roundRectanglePath2(context,rect,radius)

{

context.beginPath();

context.moveTo( rect.getX()+radius,rect.getY() );

context.lineTo( rect.getRight()-radius,rect.getY() );

context.quadraticCurveTo( rect.getRight(), rect.getY(), rect.getRight(), rect.getY() + radius);

context.lineTo( rect.getRight(),rect.getBottom()-radius);

context.quadraticCurveTo( rect.getRight(), rect.getBottom(), rect.getRight()-radius, rect.getBottom());

context.lineTo( rect.getX()+radius,rect.getBottom() );

context.quadraticCurveTo( rect.getX(), rect.getBottom(), rect.getX(), rect.getBottom()-radius);

context.lineTo( rect.getX(),rect.getY()+radius);

context.quadraticCurveTo( rect.getX(), rect.getY(), rect.getX()+radius, rect.getY());

context.closePath();

}

//这是两个函数用到的矩形对象------------------------------------

function Rect(x,y,width,height)

{

this.x = x;

this.y = y;

this.width = width;

this.height= height;

}

Rect.prototype.getX = function()

{

return this.x;

}

Rect.prototype.getY = function()

{

return this.y;

}

Rect.prototype.getWidth = function()

{

return this.width;

}

Rect.prototype.getHeight = function()

{

return this.height;

}

Rect.prototype.getLeft = function()

{

return this.x;

}

Rect.prototype.getTop = function()

{

return this.y;

}

Rect.prototype.getRight = function()

{

return (this.x + this.width);

}

Rect.prototype.getBottom = function()

{

return (this.y + this.height);

}

//----------------------------------------

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