d3.geoProjectionMutator(factory)
Constructs a new projection from the specified raw projection factory and returns a mutate function to call whenever the raw projection changes. The factory must return a raw projection. The returned mutate function returns the wrapped projection. For example, a conic projection typically has two configurable parallels. A suitable factory function, such as d3.geoConicEqualAreaRaw, would have the form:
1 2 3 4 5 6 | // y0 and y1 represent two parallelsfunction conicFactory(phi0, phi1) { return function conicRaw(lambda, phi) { return […, …]; };} |
Using d3.geoProjectionMutator, you can implement a standard projection that allows the parallels to be changed, reassigning the raw projection used internally by d3.geoProjection:
1 2 3 4 5 6 7 8 9 10 11 12 | function conicCustom() { var phi0 = 29.5, phi1 = 45.5, mutate = d3.geoProjectionMutator(conicFactory), projection = mutate(phi0, phi1); projection.parallels = function(_) { return arguments.length ? mutate(phi0 = +_[0], phi1 = +_[1]) : [phi0, phi1]; }; return projection;} |
When creating a mutable projection, the mutate function is typically not exposed.
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