大佬教程收集整理的这篇文章主要介绍了html5 – 在HTML 5 2d Canvas上下文中查找曲线上的点,大佬教程大佬觉得挺不错的,现在分享给大家,也给大家做个参考。
我的目的是在曲线的中点绘制一个物体.使用SVG DOM,我可以使用方法getPointAtLength& getTotALLENgth,但我看不到HTML画布中的等价物.
HTML画布中没有等效的东西.你必须用简单的旧数学自己找到中点.
我做了一个如何为你找到贝塞尔曲线中点的例子.在jsfiddle here上看到它.下面粘贴了一个javascript的副本.
实曲线为红色,中点为微小的绿色矩形.其他一切只是一种视觉辅助.
var ctx = $("#test")[0].getContext("2d") function mid(a,b) { return (a+b) / 2; } var cp1x = 100; var cp1y = 150; var cp2x = 175; var cp2y = 175; var x = 200; var y = 0; ctx.lineWidth = 4; ctx.strokeStyle = "red"; ctx.fillStyle = "rgba(0,0.6)"; ctx.beginPath(); ctx.moveTo(0,0); ctx.bezierCurveTo(cp1x,cp1y,cp2x,cp2y,x,y); ctx.stroke(); //line goes from start to control point 1 ctx.strokeStyle = "rgba(0,200,0.4)"; ctx.beginPath(); ctx.moveTo(0,0); ctx.lineTo(cp1x,cp1y); ctx.stroke(); //line goes from end to control point 2 ctx.beginPath(); ctx.moveTo(x,y); ctx.lineTo(cp2x,cp2y); ctx.stroke(); //line goes from control point to control point ctx.strokeStyle = "rgba(200,0.4)"; ctx.beginPath(); ctx.moveTo(cp1x,cp1y); ctx.lineTo(cp2x,cp2y); ctx.stroke(); // Now find the midpoint of each of those 3 lines var ax = mid(cp1x,0); var bx = mid(cp2x,X) var cx = mid(cp1x,cp2X) var ay = mid(cp1y,0) var by = mid(cp2y,y) var cy = mid(cp1y,cp2y) // draw midpoints for visual aid // not gonna look exact 'cause square // will be drawn from top-right instead of center ctx.fillRect(ax,ay,4,4); ctx.fillRect(bx,by,4); ctx.fillRect(cx,cy,4); //Now draw lines between those three points. these are green ctx.strokeStyle = "rgba(0,0.4)"; ctx.beginPath(); ctx.moveTo(ax,ay); ctx.lineTo(cx,cy); ctx.stroke(); ctx.beginPath(); ctx.moveTo(bx,by); ctx.lineTo(cx,cy); ctx.stroke(); //Now the midpoint of the green lines: // so g1 and g2 are the green line midpoints var g1x = mid(ax,cX); var g2x = mid(bx,cX); var g1y = mid(ay,cy); var g2y = mid(by,cy); //draw them to make sure: ctx.fillRect(g1x,g1y,4); ctx.fillRect(g2x,g2y,4); //Now one final line,in gray ctx.strokeStyle = "rgba(20,20,0.4)"; ctx.beginPath(); ctx.moveTo(g1x,g1y); ctx.lineTo(g2x,g2y); ctx.stroke(); //whew! We made it! var FinallyTheMid@R_417_7616@ = mid(g1x,g2X); var FinallyTheMidpointy = mid(g1y,g2y); //draw something at the midpoint to celebrate ctx.fillStyle = "rgba(0,255,1)"; ctx.fillRect(FinallyTheMid@R_417_7616@,FinallyTheMidpointy,4);
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