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index.js
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'use strict';
var colorSpaces = require('./color_spaces');
function identityFunction(x) {
return x;
}
function createFunction(parameters, defaultType) {
var fun;
if (!isFunctionDefinition(parameters)) {
fun = function() { return parameters; };
fun.isFeatureConstant = true;
fun.isZoomConstant = true;
} else {
var zoomAndFeatureDependent = parameters.stops && typeof parameters.stops[0][0] === 'object';
var featureDependent = zoomAndFeatureDependent || parameters.property !== undefined;
var zoomDependent = zoomAndFeatureDependent || !featureDependent;
var inputType = parameters.stops && typeof (zoomAndFeatureDependent ? parameters.stops[0][0].property : parameters.stops[0][0]);
var type = parameters.type || defaultType || (inputType === 'string' ? 'categorical' : 'exponential');
var innerFun;
if (type === 'exponential') {
innerFun = evaluateExponentialFunction;
} else if (type === 'interval') {
innerFun = evaluateIntervalFunction;
} else if (type === 'categorical') {
innerFun = evaluateCategoricalFunction;
} else if (type === 'identity') {
innerFun = evaluateIdentityFunction;
} else {
throw new Error('Unknown function type "' + type + '"');
}
var outputFunction;
// If we're interpolating colors in a color system other than RGBA,
// first translate all stop values to that color system, then interpolate
// arrays as usual. The `outputFunction` option lets us then translate
// the result of that interpolation back into RGBA.
if (parameters.colorSpace && parameters.colorSpace !== 'rgb') {
if (colorSpaces[parameters.colorSpace]) {
var colorspace = colorSpaces[parameters.colorSpace];
// Avoid mutating the parameters value
parameters = JSON.parse(JSON.stringify(parameters));
for (var s = 0; s < parameters.stops.length; s++) {
parameters.stops[s] = [
parameters.stops[s][0],
colorspace.forward(parameters.stops[s][1])
];
}
outputFunction = colorspace.reverse;
} else {
throw new Error('Unknown color space: ' + parameters.colorSpace);
}
} else {
outputFunction = identityFunction;
}
if (zoomAndFeatureDependent) {
var featureFunctions = {};
var featureFunctionStops = [];
for (s = 0; s < parameters.stops.length; s++) {
var stop = parameters.stops[s];
if (featureFunctions[stop[0].zoom] === undefined) {
featureFunctions[stop[0].zoom] = {
zoom: stop[0].zoom,
type: parameters.type,
property: parameters.property,
stops: []
};
}
featureFunctions[stop[0].zoom].stops.push([stop[0].value, stop[1]]);
}
for (var z in featureFunctions) {
featureFunctionStops.push([featureFunctions[z].zoom, createFunction(featureFunctions[z])]);
}
fun = function(zoom, feature) {
return outputFunction(evaluateExponentialFunction({
stops: featureFunctionStops,
base: parameters.base
}, zoom)(zoom, feature));
};
fun.isFeatureConstant = false;
fun.isZoomConstant = false;
} else if (zoomDependent) {
fun = function(zoom) {
return outputFunction(innerFun(parameters, zoom));
};
fun.isFeatureConstant = true;
fun.isZoomConstant = false;
} else {
fun = function(zoom, feature) {
return outputFunction(
innerFun(parameters, feature[parameters.property]));
};
fun.isFeatureConstant = false;
fun.isZoomConstant = true;
}
}
return fun;
}
function evaluateCategoricalFunction(parameters, input) {
for (var i = 0; i < parameters.stops.length; i++) {
if (input === parameters.stops[i][0]) {
return parameters.stops[i][1];
}
}
return parameters.stops[0][1];
}
function evaluateIntervalFunction(parameters, input) {
for (var i = 0; i < parameters.stops.length; i++) {
if (input < parameters.stops[i][0]) break;
}
return parameters.stops[Math.max(i - 1, 0)][1];
}
function evaluateExponentialFunction(parameters, input) {
var base = parameters.base !== undefined ? parameters.base : 1;
var i = 0;
while (true) {
if (i >= parameters.stops.length) break;
else if (input <= parameters.stops[i][0]) break;
else i++;
}
if (i === 0) {
return parameters.stops[i][1];
} else if (i === parameters.stops.length) {
return parameters.stops[i - 1][1];
} else {
return interpolate(
input,
base,
parameters.stops[i - 1][0],
parameters.stops[i][0],
parameters.stops[i - 1][1],
parameters.stops[i][1]
);
}
}
function evaluateIdentityFunction(parameters, input) {
return input;
}
function interpolate(input, base, inputLower, inputUpper, outputLower, outputUpper) {
if (typeof outputLower === 'function') {
return function() {
var evaluatedLower = outputLower.apply(undefined, arguments);
var evaluatedUpper = outputUpper.apply(undefined, arguments);
return interpolate(input, base, inputLower, inputUpper, evaluatedLower, evaluatedUpper);
};
} else if (outputLower.length) {
return interpolateArray(input, base, inputLower, inputUpper, outputLower, outputUpper);
} else {
return interpolateNumber(input, base, inputLower, inputUpper, outputLower, outputUpper);
}
}
function interpolateNumber(input, base, inputLower, inputUpper, outputLower, outputUpper) {
var difference = inputUpper - inputLower;
var progress = input - inputLower;
var ratio;
if (base === 1) {
ratio = progress / difference;
} else {
ratio = (Math.pow(base, progress) - 1) / (Math.pow(base, difference) - 1);
}
return (outputLower * (1 - ratio)) + (outputUpper * ratio);
}
function interpolateArray(input, base, inputLower, inputUpper, outputLower, outputUpper) {
var output = [];
for (var i = 0; i < outputLower.length; i++) {
output[i] = interpolateNumber(input, base, inputLower, inputUpper, outputLower[i], outputUpper[i]);
}
return output;
}
function isFunctionDefinition(value) {
return typeof value === 'object' && (value.stops || value.type === 'identity');
}
module.exports.isFunctionDefinition = isFunctionDefinition;
module.exports.interpolated = function(parameters) {
return createFunction(parameters, 'exponential');
};
module.exports['piecewise-constant'] = function(parameters) {
return createFunction(parameters, 'interval');
};