DOC.md

Documentation

Here I'll try to explain why some methods in google map react are needed and how to use them.

For all examples I'll use recompose and you must have basic understanding what css-modules is.

Looks like to rewrite current api I need to create Documentation about current version, so it will be easier to detect wrong ideas and solutions

Simple example.

Simple example (source)

At Map.js you will see the smallest possible boilerplate for GoogleMapReact component,

And a MyMarker.js is a simple React component.

Open Log tab at the top of webpackbin and see the mapProps log. (see the withProps at Map.js)

First value is the { center and zoom } which is set by you (see withState at Map.js), and second value is the value provided by GoogleMapReact component at initialization in onChange callback.

{
  center: { lat, lng }, // current map center
  zoom: 4, // current map zoom
  bounds: { nw, se, sw... }, // map corners in lat lng
  size: { width, height... } // map size in px
}

Calling onChange at initialization is needed because map bounds can't be calculated without knowledge of map size, and bounds are really usefull in a lot of situations. (see Note below)

Please move and zoom the map to see log changes.

Be sure that onChange callback is not called at realtime, and only at idle google map api callback.

It's because google api itself provides changes with some delay and to avoid synchronization issues one of the ways was to use idle callback.

On creation map uses the space of parent container and if parent container has zero height or width the map will be not visible. (This is one of the most common issue)

If you want to place map inside display: flex container you need to pass style property with { flex: 1 } to the control as like as here

By default map will not raise onChange event if parent size has changed, to change such behavior add resetBoundsOnResize = {true} property.

NOTE: Now I think it was wrong decision to call onChange at initialization. In the future releases I'll remove such behavior and will provide helper to calculate size and bounds outside map control. I think about helper similar to AutoSizer it also will allow to remove resetBoundsOnResize, style properties

PS: I highly recommend you to use GoogleMapReact as a controllable component, and always provide center, zoom and onChange props. (see withState)

NOTE: In the future releases I'll remove usage of all defaultProps like defaultCenter

Whats wrong with "Simple example" above

The wrong part is that React components are placed on the map positioning from top, left corner.

In most cases it's not the expected behaviour, so we need to change the MyMarker position by changing it's position and left, top css properties, or use flex as like as in this example.

Good position

Now MyMarker centered well, see the myMarker.css css changes and MyMarker.js layout change.

Few markers with hover example.

Few markers with hover example

As we use ordinary React components we can use any methods we use for hover effects like

• css
• onMouseEnter, onMouseLeave

But the problem you will see in example that markers are uniformly distributed over the map only in designer pictures. In real life all that markers will be possibly in one place ;-)

And with ordinary hovers we have the problem, it's hard and sometimes impossible to hover on some markers. So the solution is to use some algorithm for hovering.

(Note: but I think there are a lot of cases exists there you can use ordinary hovers without any issues. Yes, sometimes real life is like a magazine picture)

Few markers with hover example done right.

Few markers with hover example done right

Now markers are hoverable even if placed under other marker.

Let's see what has changed,

• I've added four properties to map control distanceToMouse, hoverDistance, onChildMouseEnter, onChildMouseLeave
• Instead of using css hovers, I now pass hover property to marker directly.

So what does that properties means.

• distanceToMouse you need to pass a distance function which will compute distance based on mouse position, marker position, and any other properties you want.

  It can be non euclidean distance based on some of your internals. For example you can return a smaller distance for some markers making them more hoverable, or to return infinite distance for other markers making them unhoverable.

  For circle markers of equal radius it can be euclidean distance

  function distanceToMouse({ x, y }, { x: mouseX, y: mouseY }) {
    return Math.sqrt((x - mouseX) * (x - mouseX) + (y - mouseY) * (y - mouseY))
  }

  At the example above I use some kind of rectangular distance.

  Other distanceToMouse example

• hoverDistance: number distance threshold, system can decide that marker is hovered only if distanceToMouse for that marker returns value less than this threshold.

• onChildMouseEnter - similar to onMouseEnter but here it's a callback called with key and props arguments for marker which have the smallest distanceToMouse value below hoverDistance threshold.

• onChildMouseLeave - similar to onMouseLeave.

Be sure that onChildMouseEnter, onChildMouseLeave and any other method starting with onChild* are useless without hoverDistance and distanceToMouse props.

And even now system uses some defaults for both distanceToMouse and hoverDistance it's not a good idea to use them for your app.

Other onChild* methods onChildClick, onChildMouseDown, onChildMouseUp, onChildMouseMove.

(_onChildMouseDown, onChildMouseUp, onChildMouseMove are usefull for creating draggable markers, to prevent map from moving when you drag something over, you can set draggable map property to false _)

(Note: defaults for distanceToMouse and hoverDistance will be removed in future releases)

Helper utilities

import { meters2ScreenPixels } from 'google-map-react';
const { w, h } = meters2ScreenPixels(sizeInMeters, { lat, lng } /* marker coords*/, zoom /* map zoom*/);

meters2ScreenPixels it returns horizontal - w and vertical - h sizes for given size in meters, point and zoom.

Having the mercator map projection for some places w and h will be different, for most places almost the same.

To be continued