Introduced a new Metal renderer implementation and a new example illustrating usage of Metal on macOS and iOS (partially addresses #1873)

examples/example_apple_metal/Shared/ViewController.mm

@@ -0,0 +1,130 @@
+
+#import "ViewController.h"
+#import "Renderer.h"
+#include "imgui.h"
+
+#if TARGET_OS_OSX
+#include "imgui_impl_osx.h"
+#endif
+
+@interface ViewController ()
+@property (nonatomic, readonly) MTKView *mtkView;
+@property (nonatomic, strong) Renderer *renderer;
+@end
+
+@implementation ViewController
+
+- (MTKView *)mtkView {
+    return (MTKView *)self.view;
+}
+
+- (void)viewDidLoad
+{
+    [super viewDidLoad];
+    
+    self.mtkView.device = MTLCreateSystemDefaultDevice();
+    
+    if (!self.mtkView.device) {
+        NSLog(@"Metal is not supported");
+        abort();
+    }
+
+    self.renderer = [[Renderer alloc] initWithView:self.mtkView];
+
+    [self.renderer mtkView:self.mtkView drawableSizeWillChange:self.mtkView.bounds.size];
+
+    self.mtkView.delegate = self.renderer;
+
+#if TARGET_OS_OSX
+    // Add a tracking area in order to receive mouse events whenever the mouse is within the bounds of our view
+    NSTrackingArea *trackingArea = [[NSTrackingArea alloc] initWithRect:NSZeroRect
+                                                                options:NSTrackingMouseMoved | NSTrackingInVisibleRect | NSTrackingActiveAlways
+                                                                  owner:self
+                                                               userInfo:nil];
+    [self.view addTrackingArea:trackingArea];
+    
+    // If we want to receive key events, we either need to be in the responder chain of the key view,
+    // or else we can install a local monitor. The consequence of this heavy-handed approach is that
+    // we receive events for all controls, not just ImGui widgets. If we had native controls in our
+    // window, we'd want to be much more careful than just ingesting the complete event stream, though
+    // we do make an effort to be good citizens by passing along events when ImGui doesn't want to capture.
+    NSEventMask eventMask = NSEventMaskKeyDown | NSEventMaskKeyUp | NSEventMaskFlagsChanged | NSEventTypeScrollWheel;
+    [NSEvent addLocalMonitorForEventsMatchingMask:eventMask handler:^NSEvent * _Nullable(NSEvent *event) {
+        BOOL wantsCapture = ImGui_ImplOSX_HandleEvent(event, self.view);
+        if (event.type == NSEventTypeKeyDown && wantsCapture) {
+            return nil;
+        } else {
+            return event;
+        }
+        
+    }];
+    
+    ImGui_ImplOSX_Init();
+#endif
+}
+
+#if TARGET_OS_OSX
+
+- (void)mouseMoved:(NSEvent *)event {
+    ImGui_ImplOSX_HandleEvent(event, self.view);
+}
+
+- (void)mouseDown:(NSEvent *)event {
+    ImGui_ImplOSX_HandleEvent(event, self.view);
+}
+
+- (void)mouseUp:(NSEvent *)event {
+    ImGui_ImplOSX_HandleEvent(event, self.view);
+}
+
+- (void)mouseDragged:(NSEvent *)event {
+    ImGui_ImplOSX_HandleEvent(event, self.view);
+}
+
+- (void)scrollWheel:(NSEvent *)event {
+    ImGui_ImplOSX_HandleEvent(event, self.view);
+}
+
+#elif TARGET_OS_IOS
+
+// This touch mapping is super cheesy/hacky. We treat any touch on the screen
+// as if it were a depressed left mouse button, and we don't bother handling
+// multitouch correctly at all. This causes the "cursor" to behave very erratically
+// when there are multiple active touches. But for demo purposes, single-touch
+// interaction actually works surprisingly well.
+- (void)updateIOWithTouchEvent:(UIEvent *)event {
+    UITouch *anyTouch = event.allTouches.anyObject;
+    CGPoint touchLocation = [anyTouch locationInView:self.view];
+    ImGuiIO &io = ImGui::GetIO();
+    io.MousePos = ImVec2(touchLocation.x, touchLocation.y);
+    
+    BOOL hasActiveTouch = NO;
+    for (UITouch *touch in event.allTouches) {
+        if (touch.phase != UITouchPhaseEnded && touch.phase != UITouchPhaseCancelled) {
+            hasActiveTouch = YES;
+            break;
+        }
+    }
+    io.MouseDown[0] = hasActiveTouch;
+}
+
+- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
+    [self updateIOWithTouchEvent:event];
+}
+
+- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
+    [self updateIOWithTouchEvent:event];
+}
+
+- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
+    [self updateIOWithTouchEvent:event];
+}
+
+- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
+    [self updateIOWithTouchEvent:event];
+}
+
+#endif
+
+@end
+