panCamera method
void
panCamera()
Implementation
void panCamera() {
final positionX = screenToWorldX(mousePositionX);
final positionY = screenToWorldY(mousePositionY);
final previousX = screenToWorldX(previousMousePositionX);
final previousY = screenToWorldY(previousMousePositionY);
final diffX = (previousX - positionX) * zoom;
final diffY = (previousY - positionY) * zoom;
cameraX += diffX;
cameraY += diffY;
}