问题
I'm styling some chartjs bar charts which need rounded corners at the bar's values (not their base), In most cases this means rounded corners at the top of the bar's however there are also instances where the bars have negative values.
I've used the answer here: How to create rounded bars for Bar Chart.js v2? provided by jordanwillis (https://stackoverflow.com/users/7581592/jordanwillis) which works great when values are positive but not when values are negative.
See attached example: bars with negative values get inverted corners
I need to update the extension so that the quadraticCurves's in canvas calculate correctly for negatives.
回答1:
I also faced the same issue. use below code for rounded corners-
Chart.elements.Rectangle.prototype.draw = function () {
var ctx = this._chart.ctx;
var vm = this._view;
var left, right, top, bottom, signX, signY, borderSkipped, radius;
var borderWidth = vm.borderWidth;
// Set Radius Here
// If radius is large enough to cause drawing errors a max radius is imposed
var cornerRadius = 20;
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.
var barSize = Math.min(Math.abs(left - right), Math.abs(top - bottom));
borderWidth = borderWidth > barSize ? barSize : borderWidth;
var halfStroke = borderWidth / 2;
// Adjust borderWidth when bar top position is near vm.base(zero).
var borderLeft = left + (borderSkipped !== 'left' ? halfStroke * signX : 0);
var borderRight = right + (borderSkipped !== 'right' ? -halfStroke * signX : 0);
var borderTop = top + (borderSkipped !== 'top' ? halfStroke * signY : 0);
var 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;
}
}
ctx.beginPath();
ctx.fillStyle = vm.backgroundColor;
ctx.strokeStyle = vm.borderColor;
ctx.lineWidth = borderWidth;
// Corner points, from bottom-left to bottom-right clockwise
// | 1 2 |
// | 0 3 |
var corners = [
[left, bottom],
[left, top],
[right, top],
[right, bottom]
];
// Find first (starting) corner with fallback to 'bottom'
var borders = ['bottom', 'left', 'top', 'right'];
var startCorner = borders.indexOf(borderSkipped, 0);
if (startCorner === -1) {
startCorner = 0;
}
function cornerAt(index) {
return corners[(startCorner + index) % 4];
}
// Draw rectangle from 'startCorner'
var corner = cornerAt(0);
var width, height, x, y, nextCorner, nextCornerId
var x_tl, x_tr, y_tl, y_tr;
var x_bl, x_br, y_bl, y_br;
ctx.moveTo(corner[0], corner[1]);
for (var i = 1; i < 4; i++) {
corner = cornerAt(i);
nextCornerId = i + 1;
if (nextCornerId == 4) {
nextCornerId = 0
}
nextCorner = cornerAt(nextCornerId);
width = corners[2][0] - corners[1][0];
height = corners[0][1] - corners[1][1];
x = corners[1][0];
y = corners[1][1];
radius = cornerRadius;
// Fix radius being too large
if (radius > Math.abs(height) / 2) {
radius = Math.floor(Math.abs(height) / 2);
}
if (radius > Math.abs(width) / 2) {
radius = Math.floor(Math.abs(width) / 2);
}
if (height < 0) {
// Negative values in a standard bar chart
x_tl = x; x_tr = x + width;
y_tl = y + height; y_tr = y + height;
x_bl = x; x_br = x + width;
y_bl = y; y_br = y;
// Draw
ctx.moveTo(x_bl + radius, y_bl);
ctx.lineTo(x_br - radius, y_br);
ctx.quadraticCurveTo(x_br, y_br, x_br, y_br - radius);
ctx.lineTo(x_tr, y_tr + radius);
ctx.quadraticCurveTo(x_tr, y_tr, x_tr - radius, y_tr);
ctx.lineTo(x_tl + radius, y_tl);
ctx.quadraticCurveTo(x_tl, y_tl, x_tl, y_tl + radius);
ctx.lineTo(x_bl, y_bl - radius);
ctx.quadraticCurveTo(x_bl, y_bl, x_bl + radius, y_bl);
} else if (width < 0) {
// Negative values in a horizontal bar chart
x_tl = x + width; x_tr = x;
y_tl = y; y_tr = y;
x_bl = x + width; x_br = x;
y_bl = y + height; y_br = y + height;
// Draw
ctx.moveTo(x_bl + radius, y_bl);
ctx.lineTo(x_br - radius, y_br);
ctx.quadraticCurveTo(x_br, y_br, x_br, y_br - radius);
ctx.lineTo(x_tr, y_tr + radius);
ctx.quadraticCurveTo(x_tr, y_tr, x_tr - radius, y_tr);
ctx.lineTo(x_tl + radius, y_tl);
ctx.quadraticCurveTo(x_tl, y_tl, x_tl, y_tl + radius);
ctx.lineTo(x_bl, y_bl - radius);
ctx.quadraticCurveTo(x_bl, y_bl, x_bl + radius, y_bl);
} else {
//Positive Value
ctx.moveTo(x + radius, y);
ctx.lineTo(x + width - radius, y);
ctx.quadraticCurveTo(x + width, y, x + width, y + radius);
ctx.lineTo(x + width, y + height - radius);
ctx.quadraticCurveTo(x + width, y + height, x + width - radius, y + height);
ctx.lineTo(x + radius, y + height);
ctx.quadraticCurveTo(x, y + height, x, y + height - radius);
ctx.lineTo(x, y + radius);
ctx.quadraticCurveTo(x, y, x + radius, y);
}
}
ctx.fill();
if (borderWidth) {
ctx.stroke();
}
};
I used it for horizontal bar chart. It will draw the chart like below image-
来源：https://stackoverflow.com/questions/47186273/rounded-corners-on-chartjs-v-2-bar-charts-with-negative-values