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area-label.js
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area-label.js
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import fits from './fits';
import { max, extent, bisector, range } from 'd3-array';
import { scaleLinear } from 'd3-scale';
// Returns a transform string that will
// translate and scale the label to the computed position and size.
function toTransformString() {
return [
'translate(' + this.xTranslate + ',' + this.yTranslate + ')',
'scale(' + this.scale + ')'
].join(' ');
};
function areaLabel(area) {
var x,
y0,
y1,
bisectorX,
minHeight = 2,
epsilon = 0.01,
maxIterations = 100,
interpolate = true,
interpolateResolution = 800,
paddingLeft = 0,
paddingRight = 0,
paddingTop = 0,
paddingBottom = 0,
numIterations;
// Gets the height of the area for a particular datum.
function getHeight(d) {
return y0(d) - y1(d);
}
// Finds the largest value that passes the test
// within some epsilon tolerance.
// https://en.wikipedia.org/wiki/Bisection_method#Algorithm
function bisection(a, b, test, epsilon, maxIterations) {
var i, c, passesTest, withinEpsilon;
for(i = 0; i < maxIterations; i++){
c = (a + b) / 2;
passesTest = test(c);
withinEpsilon = (b - a) / 2 < epsilon;
// In our case, the returned value *must* pass the test,
// so it's not enough only to check if the value is within epsilon.
if ( passesTest && withinEpsilon) {
numIterations = i;
return c;
}
if (passesTest) {
a = c;
} else {
b = c;
}
}
return null;
}
function interpolateY(data, xValue, y) {
var i = bisectorX(data, xValue, 0, data.length - 1),
a = data[i - 1],
b = data[i],
ax = x(a),
ay = y(a),
bx = x(b),
by = y(b),
t = (xValue - ax) / (bx - ax);
return ay * (1 - t) + by * t;
}
// Returns true if there is at least one rectangle
// of the given aspect ratio and scale
// that fits somewhere within the area.
function my(data) {
// The bounding box of the text label as-is.
var box = this.getBBox();
// Account for padding.
var paddingFactorX = 1 + paddingLeft + paddingRight;
var paddingFactorY = 1 + paddingTop + paddingBottom;
var boxWidth = box.width * paddingFactorX;
var boxHeight = box.height * paddingFactorY;
// The aspect ratio of the text label bounding box.
var aspect = boxWidth / boxHeight;
// Compute maximum possible label bounding box height in pixels.
var maxHeight = max(data, getHeight);
// Compute the X extent once, to be reused for every height test.
var xExtent = extent(data, x);
// The test function for use in the bisection method.
var options = {
justTest: true,
xMax: xExtent[1]
};
if (interpolate) {
var interpolateResolutionScale = scaleLinear()
.domain([0, interpolateResolution - 1])
.range(xExtent);
var interpolatedData = range(interpolateResolution)
.map(function (i) {
var xValue = interpolateResolutionScale(i);
return {
x: xValue,
y0: interpolateY(data, xValue, y0),
y1: interpolateY(data, xValue, y1)
};
});
options.xIndex = function (x) {
return Math.ceil(interpolateResolutionScale.invert(x));
};
options.data = interpolatedData;
options.x = function (d) { return d.x; };
options.y0 = function (d) { return d.y0; };
options.y1 = function (d) { return d.y1; };
} else {
options.xIndex = function (x) {
return bisectorX(data, x);
},
options.data = data;
options.x = x;
options.y0 = y0;
options.y1 = y1;
}
var test = function (testHeight){
options.height = testHeight;
options.width = aspect * testHeight;
return fits(options);
};
// Use the bisection method to find the largest height label that fits.
var height = bisection(minHeight, maxHeight, test, epsilon, maxIterations);
// If there's not any position that works,
// return an object that will scale the label down to nothing,
// and indicate that the algorithm failed.
if (height === null) {
return {
failed: true,
numIterations: maxIterations,
scale: 0,
xTranslate: 0,
yTranslate: 0,
toString: toTransformString
};
}
// Get the (x, y, width, height) for the largest height label that fits.
options.justTest = false;
var fit = fits(options);
// Account for padding.
var xInner = fit.x + fit.width / paddingFactorX * paddingLeft;
var yInner = fit.y + fit.height / paddingFactorY * paddingTop;
// Compute the scale and translate.
fit.scale = height / boxHeight;
fit.xTranslate = xInner - fit.scale * box.x;
fit.yTranslate = yInner - fit.scale * box.y;
// Expose the toString method, which generates a transform string.
fit.toString = toTransformString;
// Expose how many iterations the bisection method took.
fit.numIterations = numIterations;
return fit;
}
my.x = function(_) {
if (arguments.length) {
x = _;
bisectorX = bisector(x).right;
return my;
}
return x;
};
my.y0 = function(_) {
return arguments.length ? (y0 = _, my) : y0;
};
my.y1 = function(_) {
return arguments.length ? (y1 = _, my) : y1;
};
my.area = function(area) {
return my.x(area.x()).y0(area.y0()).y1(area.y1());
};
my.minHeight = function(_) {
return arguments.length ? (minHeight = +_, my) : minHeight;
};
my.epsilon = function(_) {
return arguments.length ? (epsilon = +_, my) : epsilon;
};
my.maxIterations = function(_) {
return arguments.length ? (maxIterations = +_, my) : maxIterations;
};
my.interpolate = function(_) {
return arguments.length ? (interpolate = +_, my) : interpolate;
};
my.interpolateResolution = function(_) {
return arguments.length ? (interpolateResolution = +_, my) : interpolateResolution;
};
my.paddingLeft = function(_) {
return arguments.length ? (paddingLeft = +_, my) : paddingLeft;
};
my.paddingRight = function(_) {
return arguments.length ? (paddingRight = +_, my) : paddingRight;
};
my.paddingTop = function(_) {
return arguments.length ? (paddingTop = +_, my) : paddingTop;
};
my.paddingBottom = function(_) {
return arguments.length ? (paddingBottom = +_, my) : paddingBottom;
};
my.paddingX = function(_) {
return my.paddingLeft(_).paddingRight(_);
};
my.paddingY = function(_) {
return my.paddingTop(_).paddingBottom(_);
};
my.padding = function(_) {
return my.paddingX(_).paddingY(_);
};
if (area) {
my.area(area);
}
return my;
};
export default areaLabel;