Fix macOS click-through for transparent shaped windows

Transparent.mm

@@ -1,21 +1,79 @@
 #include <SFML/Graphics.hpp>
 #import <Cocoa/Cocoa.h>
-
 @implementation NSOpenGLView (Opaque)
 -(BOOL)isOpaque
 {
     return NO;
 }
 @end
+// Global variables to hold the window and image state
+static const sf::Image* g_windowShapeImage = nullptr;
+static NSWindow* g_shapedWindow = nil;
+static NSTimer* g_mouseTrackingTimer = nil;
+
+// A helper class to run our 60FPS mouse tracking loop
+@interface MouseTracker : NSObject
++ (void)checkMousePosition:(NSTimer*)timer;
+@end
+
+@implementation MouseTracker
++ (void)checkMousePosition:(NSTimer*)timer {
+    if (!g_shapedWindow || !g_windowShapeImage) return;
+
+    // Get the global mouse location on the screen
+    NSPoint mouseLoc = [NSEvent mouseLocation];
+    NSRect windowFrame = [g_shapedWindow frame];
+
+    // Calculate the mouse point relative to the bottom-left of the window
+    NSPoint localPoint = NSMakePoint(mouseLoc.x - windowFrame.origin.x, mouseLoc.y - windowFrame.origin.y);
+
+    // Flip the Y-axis (macOS maps bottom-to-top, SFML images map top-to-bottom)
+    int x = (int)localPoint.x;
+    int y = (int)g_windowShapeImage->getSize().y - (int)localPoint.y - 1;
+
+    // Default to transparent if the mouse is outside the window bounds entirely
+    bool isTransparent = true; 
+
+    if (x >= 0 && x < (int)g_windowShapeImage->getSize().x &&
+        y >= 0 && y < (int)g_windowShapeImage->getSize().y) {
+
+        const sf::Uint8* pixelData = g_windowShapeImage->getPixelsPtr();
+
+        // Read the alpha channel (index 3 in RGBA)
+        unsigned int index = (y * g_windowShapeImage->getSize().x * 4) + (x * 4) + 3;
+        isTransparent = (pixelData[index] == 0);
+    }
+
+    // Dynamically tell the OS whether to ignore clicks based on the exact pixel
+    [g_shapedWindow setIgnoresMouseEvents:isTransparent];
+}
+@end
 
 bool setShape(sf::WindowHandle handle, const sf::Image& image)
 {
     NSWindow* wnd = (NSWindow*)handle;
 
+    g_windowShapeImage = &image;
+    g_shapedWindow = wnd;
+
+    // Make the window background transparent
     GLint opaque = 0;
     [[[wnd contentView] openGLContext] setValues:&opaque forParameter:NSOpenGLCPSurfaceOpacity];
     [wnd setBackgroundColor:[NSColor clearColor]];
     [wnd setOpaque:NO];
+    [wnd setHasShadow:NO];
+
+    // Start tracking the mouse position at ~60 times a second
+    if (!g_mouseTrackingTimer) {
+        g_mouseTrackingTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/60.0
+                                                                target:[MouseTracker class]
+                                                              selector:@selector(checkMousePosition:)
+                                                              userInfo:nil
+                                                               repeats:YES];
+
+        // Ensure the timer keeps firing even if the user is interacting with standard OS UI
+        [[NSRunLoop currentRunLoop] addTimer:g_mouseTrackingTimer forMode:NSRunLoopCommonModes];
+    }
 
     return true;
 }