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adds midpoint interpolation to stepped plots #5908

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Dec 18, 2018
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1 change: 1 addition & 0 deletions docs/charts/line.md
Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,7 @@ The following values are supported for `steppedLine`.
* `true`: Step-before Interpolation (eq. 'before')
* `'before'`: Step-before Interpolation
* `'after'`: Step-after Interpolation
* `'middle'`: Step-middle Interpolation

If the `steppedLine` value is set to anything other than false, `lineTension` will be ignored.

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4 changes: 4 additions & 0 deletions samples/charts/line/stepped.html
Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,10 @@
steppedLine: 'after',
label: 'Step After Interpolation',
color: window.chartColors.purple
}, {
steppedLine: 'middle',
label: 'Step Middle Interpolation',
color: window.chartColors.blue
}];

steppedLineSettings.forEach(function(details) {
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9 changes: 7 additions & 2 deletions src/helpers/helpers.canvas.js
Original file line number Diff line number Diff line change
Expand Up @@ -184,8 +184,13 @@ var exports = module.exports = {
},

lineTo: function(ctx, previous, target, flip) {
if (target.steppedLine) {
if ((target.steppedLine === 'after' && !flip) || (target.steppedLine !== 'after' && flip)) {
var stepped = target.steppedLine;
if (stepped) {
if (stepped === 'middle') {
var midpoint = (previous.x + target.x) / 2.0;
ctx.lineTo(midpoint, flip ? target.y : previous.y);
ctx.lineTo(midpoint, flip ? previous.y : target.y);
} else if ((stepped === 'after' && !flip) || (stepped !== 'after' && flip)) {
ctx.lineTo(previous.x, target.y);
} else {
ctx.lineTo(target.x, previous.y);
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137 changes: 137 additions & 0 deletions test/specs/element.line.tests.js
Original file line number Diff line number Diff line change
Expand Up @@ -376,6 +376,143 @@ describe('Chart.elements.Line', function() {
});
});

it('should draw stepped lines, with "middle" interpolation', function() {

var mockContext = window.createMockContext();

// Create our points
var points = [];
points.push(new Chart.elements.Point({
_datasetindex: 2,
_index: 0,
_view: {
x: 0,
y: 10,
controlPointNextX: 0,
controlPointNextY: 10,
steppedLine: 'middle'
}
}));
points.push(new Chart.elements.Point({
_datasetindex: 2,
_index: 1,
_view: {
x: 5,
y: 0,
controlPointPreviousX: 5,
controlPointPreviousY: 0,
controlPointNextX: 5,
controlPointNextY: 0,
steppedLine: 'middle'
}
}));
points.push(new Chart.elements.Point({
_datasetindex: 2,
_index: 2,
_view: {
x: 15,
y: -10,
controlPointPreviousX: 15,
controlPointPreviousY: -10,
controlPointNextX: 15,
controlPointNextY: -10,
steppedLine: 'middle'
}
}));
points.push(new Chart.elements.Point({
_datasetindex: 2,
_index: 3,
_view: {
x: 19,
y: -5,
controlPointPreviousX: 19,
controlPointPreviousY: -5,
controlPointNextX: 19,
controlPointNextY: -5,
steppedLine: 'middle'
}
}));

var line = new Chart.elements.Line({
_datasetindex: 2,
_chart: {
ctx: mockContext,
},
_children: points,
// Need to provide some settings
_view: {
fill: false, // don't want to fill
tension: 0, // no bezier curve for now
}
});

line.draw();

expect(mockContext.getCalls()).toEqual([{
name: 'save',
args: [],
}, {
name: 'setLineCap',
args: ['butt']
}, {
name: 'setLineDash',
args: [
[]
]
}, {
name: 'setLineDashOffset',
args: [0.0]
}, {
name: 'setLineJoin',
args: ['miter']
}, {
name: 'setLineWidth',
args: [3]
}, {
name: 'setStrokeStyle',
args: ['rgba(0,0,0,0.1)']
}, {
name: 'beginPath',
args: []
}, {
name: 'moveTo',
args: [0, 10]
}, {
name: 'lineTo',
args: [2.5, 10]
}, {
name: 'lineTo',
args: [2.5, 0]
}, {
name: 'lineTo',
args: [5, 0]
}, {
name: 'lineTo',
args: [10, 0]
}, {
name: 'lineTo',
args: [10, -10]
}, {
name: 'lineTo',
args: [15, -10]
}, {
name: 'lineTo',
args: [17, -10]
}, {
name: 'lineTo',
args: [17, -5]
}, {
name: 'lineTo',
args: [19, -5]
}, {
name: 'stroke',
args: [],
}, {
name: 'restore',
args: []
}]);
});

it('should draw stepped lines, with "after" interpolation', function() {

var mockContext = window.createMockContext();
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