Implement function to set macOS dock icon

src/_cocoalayer.mm

@@ -0,0 +1,20 @@
+#if defined(__APPLE__)
+#import <Cocoa/Cocoa.h>
+#import <objc/runtime.h>
+#include "_cocoalayer.h"
+// Example: make a global function you can call
+extern "C" void _cocoasetdockicon(unsigned char* data, int width, int height)
+{
+    NSImage *dockIcon = [[NSImage alloc] initWithSize:NSMakeSize(width, height)];
+    CGDataProviderRef provider = CGDataProviderCreateWithData(nullptr, data, width*height*4, nullptr);
+    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
+    CGImageRef cgImage = CGImageCreate(width, height, 8, 32, width*4, colorSpace,
+                                       kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big,
+                                       provider, nullptr, false, kCGRenderingIntentDefault);
+    [dockIcon addRepresentation:[[NSBitmapImageRep alloc] initWithCGImage:cgImage]];
+    [NSApp setApplicationIconImage:dockIcon];
+    CGImageRelease(cgImage);
+    CGColorSpaceRelease(colorSpace);
+    CGDataProviderRelease(provider);
+}
+#endif