Chart.js v2

Question

我试图在Chart.js v2中制作带圆角的水平条形图。 在这里看到这个答案：https://stackoverflow.com/a/43281198/6935580，它显示了如何创建带圆角的垂直条形图。

这是我的代码。

Chart.helpers.drawRoundedTopRectangle = function (ctx, x, y, width, height, radius) {
      ctx.beginPath();
      ctx.moveTo(x + radius, y);
      // top right corner
      ctx.lineTo(x + width - radius, y);
      ctx.quadraticCurveTo(x + width, y, x + width, y + radius);
      // bottom right   corner
      ctx.lineTo(x + width, y + height);
      // bottom left corner
      ctx.lineTo(x, y + height);
      // top left
      ctx.lineTo(x, y + radius);
      ctx.quadraticCurveTo(x, y, x + radius, y);
      ctx.closePath();
    };

    Chart.elements.RoundedTopRectangle = Chart.elements.Rectangle.extend({
      draw: function () {
        const ctx = this._chart.ctx;
        const vm = this._view;
        let left, right, top, bottom, signX, signY, borderSkipped;
        let borderWidth = vm.borderWidth;

        if (!vm.horizontal) {
          // bar
          left = vm.x - vm.width / 2;
          right = vm.x + vm.width / 2;
          top = vm.y;
          bottom = vm.base;
          signX = 1;
          signY = bottom > top ? 1 : -1;
          borderSkipped = vm.borderSkipped || 'bottom';
        } else {
          // horizontal bar
          left = vm.base;
          right = vm.x;
          top = vm.y - vm.height / 2;
          bottom = vm.y + vm.height / 2;
          signX = right > left ? 1 : -1;
          signY = 1;
          borderSkipped = vm.borderSkipped || 'left';
        }

        // Canvas doesn't allow us to stroke inside the width so we can
        // adjust the sizes to fit if we're setting a stroke on the line
        if (borderWidth) {
          // borderWidth shold be less than bar width and bar height.
          const barSize = Math.min(Math.abs(left - right), Math.abs(top - bottom));
          borderWidth = borderWidth > barSize ? barSize : borderWidth;
          const halfStroke = borderWidth / 2;
          // Adjust borderWidth when bar top position is near vm.base(zero).
          const borderLeft = left + (borderSkipped !== 'left' ? halfStroke * signX : 0);
          const borderRight = right + (borderSkipped !== 'right' ? -halfStroke * signX : 0);
          const borderTop = top + (borderSkipped !== 'top' ? halfStroke * signY : 0);
          const borderBottom = bottom + (borderSkipped !== 'bottom' ? -halfStroke * signY : 0);
          // not become a vertical line?
          if (borderLeft !== borderRight) {
            top = borderTop;
            bottom = borderBottom;
          }
          // not become a horizontal line?
          if (borderTop !== borderBottom) {
            left = borderLeft;
            right = borderRight;
          }
        }

        // calculate the bar width and roundess
        const barWidth = Math.abs(left - right);
        // const roundness = this._chart.config.options.barRoundness || 0.5;
        const roundness = 1.0;
        const radius = barWidth * roundness * 0.5;

        // keep track of the original top of the bar
        const prevTop = top;

        // move the top down so there is room to draw the rounded top
        top = prevTop + radius;
        const barRadius = top - prevTop;

        ctx.beginPath();
        ctx.fillStyle = vm.backgroundColor;
        ctx.strokeStyle = vm.borderColor;
        ctx.lineWidth = borderWidth;

        // draw the rounded top rectangle
        Chart.helpers.drawRoundedTopRectangle(ctx, left, (top - barRadius + 1), barWidth, bottom - prevTop, barRadius);

        ctx.fill();
        if (borderWidth) {
          ctx.stroke();
        }

        // restore the original top value so tooltips and scales still work
        top = prevTop;
      },
    });

    Chart.defaults.roundedBar = Chart.helpers.clone(Chart.defaults.bar);

    Chart.controllers.roundedBar = Chart.controllers.bar.extend({
      dataElementType: Chart.elements.RoundedTopRectangle
    });

这是codepen链接：https://codepen.io/anon/pen/MGPYPX

我意识到我必须修改drawRoundedTopRectangle助手函数。我不知道二次曲线是如何工作的。 有关如何修改水平图表的任何想法？ 感谢