Performance improvement with zoom/scale

[monsieurtanuki]

What do you want implemented?

Not sure how much performance improvements we can get from this.

We have a couple of methods for projecting LatLng.

  (double, double) latLngToXY(LatLng latlng, double scale);

  /// Similar to [latLngToXY] but converts the XY coordinates to an [Offset].
  Offset latLngToOffset(LatLng latlng, double zoom) {
    final (x, y) = latLngToXY(checkLatLng(latlng), scale(zoom));
    return Offset(x, y);
  }

The most used method is latLngToOffset, that computes a scale.

  /// Zoom to Scale function.
  double scale(double zoom) => 256.0 * math.pow(2, zoom);

The thing is that we constantly compute math.pow(2, zoom).
Given that most of the time (always?) we work on a single zoom level for all points, we could cache the latest zoom/scale values.
Something like that:

  double _latestZoom = -1;
  double _latestScale = -1;

  double scale(double zoom) {
    if ((_latestZoom == -1 && _latestScale == -1) || _latestZoom != zoom) {
      _latestZoom = zoom;
      return _latestScale = 256.0 * math.pow(2, zoom);
    }
    return _latestScale;
  }

What other alternatives are available?

No response

Can you provide any other information?

No response

[monsieurtanuki]

And of course, the zoom method could be improved similarly:

double zoom(double scale) => math.log(scale / 256) / math.ln2;

[monsieurtanuki]

Looks like it would mean making Crs not const anymore. Which is problematic as we have default Crs constructor parameters: we need the default Crs value to be const.
Or... we create not const classes on top, that just override methods scale and zoom. As "optimized" versions.