tidy up method call handler and add example project with camera panning

ios/Classes/filament/FilamentMethodCallHandler.mm

@@ -0,0 +1,97 @@
+#import "FilamentMethodCallHandler.h"
+#import "FilamentViewController.h"
+#import "FilamentNativeViewFactory.h"
+
+static const FilamentMethodCallHandler* _handler;
+
+static mimetic::ResourceBuffer loadResourceGlobal(const char* name) {
+  return [_handler loadResource:name];
+}
+
+static void* freeResourceGlobal(void* mem, size_t size, void* misc) {
+  [_handler freeResource:mem size:size misc:misc ];
+  return nullptr;
+}
+
+@implementation FilamentMethodCallHandler {
+  FilamentViewController *_controller;
+  FlutterMethodChannel* _channel;
+  mimetic::FilamentViewer* _viewer;
+  void* _layer;
+  
+  NSObject<FlutterPluginRegistrar>* _registrar;
+}
+- (instancetype)initWithController:(FilamentViewController*)controller
+                         registrar:(NSObject<FlutterPluginRegistrar>*)registrar
+                         viewId:(int64_t)viewId
+                         layer:(void*)layer
+{
+  _layer = layer;
+  _registrar = registrar;
+  _controller = controller;
+  NSString* channelName = [NSString stringWithFormat:@"%@_%d",VIEW_TYPE,viewId];
+  _channel = [FlutterMethodChannel
+    methodChannelWithName:channelName
+          binaryMessenger:[registrar messenger]];
+  [_channel setMethodCallHandler:^(FlutterMethodCall * _Nonnull call, FlutterResult  _Nonnull result) {
+    [self handleMethodCall:call result:result];
+  }];
+  _handler = self;
+  return self;
+}
+
+- (void)handleMethodCall:(FlutterMethodCall* _Nonnull)call result:(FlutterResult _Nonnull )result {
+  if([@"initialize" isEqualToString:call.method]) {
+	    _viewer = new mimetic::FilamentViewer(_layer, loadResourceGlobal, freeResourceGlobal);
+      [_controller setViewer:_viewer];
+      [_controller startDisplayLink];
+      result(@"OK");
+  } else if([@"loadSkybox" isEqualToString:call.method]) {
+    if(!_viewer)
+      return;
+    _viewer->loadSkybox([call.arguments[0] UTF8String], [call.arguments[1] UTF8String]);
+    result(@"OK");
+  } else if([@"loadGltf" isEqualToString:call.method]) {
+    if(!_viewer)
+      return;
+    _viewer->loadGltf([call.arguments[0] UTF8String], [call.arguments[1] UTF8String]);
+    result(@"OK");
+  } else if([@"panStart" isEqualToString:call.method]) {
+    if(!_viewer)
+      return;
+    _viewer->manipulator->grabBegin([call.arguments[0] intValue], [call.arguments[1] intValue], true);
+  } else if([@"panUpdate" isEqualToString:call.method]) {
+    if(!_viewer)
+      return;
+    _viewer->manipulator->grabUpdate([call.arguments[0] intValue], [call.arguments[1] intValue]);
+  } else if([@"panEnd" isEqualToString:call.method]) {
+    if(!_viewer)
+      return;
+    _viewer->manipulator->grabEnd();
+  } else {
+    result(FlutterMethodNotImplemented);
+  }
+}
+
+- (mimetic::ResourceBuffer)loadResource:(const char* const)path {
+    NSString* p = [NSString stringWithFormat:@"%s", path];
+    NSString* key = [_registrar lookupKeyForAsset:p];
+    NSString* nsPath = [[NSBundle mainBundle] pathForResource:key
+                                                      ofType:nil];
+    if (![[NSFileManager defaultManager] fileExistsAtPath:nsPath]) {
+        NSLog(@"Error: no file exists at %@", nsPath);
+        exit(-1);
+    }
+
+    NSData* buffer = [NSData dataWithContentsOfFile:nsPath];
+    void* cpy = malloc([buffer length]);
+    memcpy(cpy, [buffer bytes],  [buffer length]); // can we avoid this copy somehow?
+    mimetic::ResourceBuffer rbuf(cpy, [buffer length]);
+    return rbuf;
+}
+
+- (void)freeResource:(void*)mem size:(size_t)s misc:(void *)m {
+    free(mem);
+}
+
+@end