setFocusDistance method
Manually fixes the focus distance: distance 0.0 (far / infinity) to
1.0 (nearest). Pass a negative value to restore continuous auto-focus.
Fixed-focus lenses (and iOS devices without custom-lens-position support)
ignore it. See CameraDeviceInfo.minFocusDistanceCm for the near limit.
Implementation
void setFocusDistance(double distance) {
_requireInitialized();
_native.setFocusDistance(_textureId!, distance);
}