svg 实践之屏幕坐标与svg元素坐标转换

Posted 2021-03-06 smedas

近期在做svg相关项目，很好用的东西要记下来：

1、基础知识就是根据 矩阵进行坐标转换，如下：

： 屏幕坐标 = 矩阵* svg对象坐标

2、javascript有个方法用于获取 svg对象 的转换矩阵CTM ：svgObj.getScreenCTM(); 该矩阵将svg坐标转换为屏幕坐标

3、所以以上公式：已知屏幕坐标，已知矩阵，求svg对象坐标

4、如下：
5、javascript方法：矩阵.inverse() =矩阵的逆矩阵
6、代码如下：
api：
/*屏幕坐标转为svg坐标*/

coordinateTransform(screenPoint, someSvgObject) {
var CTM = someSvgObject.getScreenCTM();
return screenPoint.matrixTransform(CTM.inverse());
}
reportMouseCoordinates(svgElement, pageX, pageY, svgChild) {
var point = svgElement.createSVGPoint();
point.x =pageX; 
point.y = pageY;
point = coordinateTransform(point, svgChild); 
return point;
}

调用：

bindEvent(){
this.grid.addEventListener(‘click‘,(event) => {
let pageX = event.pageX;
let pageY = event.pageY;
let point = utils.reportMouseCoordinates(this.svg, pageX, pageY, this.grid);
}
}

dom：

<svg xmlns="http://www.w3.org/2000/svg" preserveAspectRatio="xMidYMid meet">
<defs>
<pattern id="gridDot" x="0" y="0" width="1" height="1" patternUnits="userSpaceOnUse">
<path d="M0,0H1V1" stroke="#ccc" stroke-width="0.1" fill="none"></path>
</pattern>
<pattern id="gridBlock" x="0" y="0" width="1" height="1" patternUnits="userSpaceOnUse">
<path d="M0,0H1V1" stroke="#ccc" stroke-width="0.1" fill="none"></path>
</pattern>
</defs>


<rect id="grid_10X10" x="0" y="0" width="100%" height="100%" fill="url(#gridDot)">
</rect>
<!-- <rect id="grid_20X20" x="0" y="0" width="100%" height="100%" fill="url(#gridBlock)">
</rect> -->
<!-- <text x="100" y="100" dx="20 20 20 20" dy="20" style="font-size:20px; font-family: ‘Arial‘">ABCDE</text>
<path d="M100,0V200M0,100H200" stroke="red"></path> -->
</svg>