本文介绍了获取没有边框的边界客户端矩形的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我创建了一个将鼠标坐标转换为画布像素坐标的函数:

I made a function that transforms mouse coordinates to canvas pixel coordinates:

/* Returns pixel coordinates according to the pixel that's under the mouse cursor**/
HTMLCanvasElement.prototype.relativeCoords = function(event) {
  var x,y;
  //This is the current screen rectangle of canvas
  var rect = this.getBoundingClientRect();

  //Recalculate mouse offsets to relative offsets
  x = event.clientX - rect.left;
  y = event.clientY - rect.top;
  //Also recalculate offsets of canvas is stretched
  var width = rect.right - rect.left;
  //I use this to reduce number of calculations for images that have normal size
  if(this.width!=width) {
    var height = rect.bottom - rect.top;
    //changes coordinates by ratio
    x = x*(this.width/width);
    y = y*(this.height/height);
  }
  //Return as an array
  return [x,y];
}

你可以看到。问题是图像的解决方案无效。

You can see demonstration of the pixel coordinate calculation. The problem is that the solutions fails for images having border property set.

如何从矩形中减去边框宽度?性能确实很重要,因为此计算通常在鼠标移动事件期间执行。

How can I subtract the border width from rectangle? Performance does matter, as this calculation is often performed during mouse move events.

推荐答案

getComputedStyle 包含您想要的信息:

getComputedStyle contains the information you desire:

在应用开始时获取一次边框信息设置画布边框后。

Fetch the border information once at the beginning of your app after the canvas border has been set.

// get a reference to the canvas element
var canvas=document.getElementById('yourCanvasId');

// get its computed style
var styling=getComputedStyle(canvas,null);

// fetch the 4 border width values
var topBorder=styling.getPropertyValue('border-top-width');
var rightBorder=styling.getPropertyValue('border-right-width');
var bottomBorder=styling.getPropertyValue('border-bottom-width');
var leftBorder=styling.getPropertyValue('border-left-width');

如果您在app-wide范围内设置这些边框宽度变量,则可以在HTMLCanvasElement中使用这些预取变量.prototype.relativeCoords。

If you scope these border-width variables app-wide, you can use these prefetched variables in your HTMLCanvasElement.prototype.relativeCoords.

祝你的项目好运!

这篇关于获取没有边框的边界客户端矩形的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-20 07:30
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