Rendering to full size of an NSWindow using GLFW3

In one of my projects I wanted to render (using OpenGL) to the full area of a window, including the title bar. This would enable me to create a more custom look for my tool, similar to how Spotify looks;

Spotify having a custom window color.

After digging around it seemed possible by setting titlebarAppearsTransparent and backgroundColor properties for the NSWindow. Easy stuff if you have full control of your window code, but if you are using a third party windowing library, such as GLFW, you need to do some more work.

If you also want to be able to move the window by draging the title bar, it gets even trickier. But thanks to something called method swizzling it’s possible to solve it in runtime, without any code changes!

Below is what I ended up using for GLFW; just call HackFullContentView(GLFWwindow* window) once for every GLFW window you open. It will set the needed properties for the NSWindow, but also override/swizzle the mouseDownCanMoveWindow property getter (otherwise a read only property) of the GLFWContentView class.

#include <GLFW/glfw3.h>
#include <GLFW/glfw3native.h>

#import <objc/runtime.h>

// Dummy class for supplying a fake mouseDownCanMoveWindow selector.
@interface FakeView : NSView
@implementation FakeView
- (BOOL)fakeMouseDownCanMoveWindow { return YES; }

void HackFullContentView(GLFWwindow* window)
    // For each new window we open, the following code needs to be run.
    NSWindow* wnd = glfwGetCocoaWindow(window);
    wnd.titlebarAppearsTransparent = YES;
    wnd.titleVisibility = NSWindowTitleHidden;
    wnd.backgroundColor = NSColor.blackColor;

    // We only need override/swizzle the selector once.
    static bool run_once = true;
    if (run_once)
        run_once = false;
        NSView* glView = [wnd contentView];
        Method originalMethod = class_getInstanceMethod([glView class], @selector(mouseDownCanMoveWindow));
        Method categoryMethod = class_getInstanceMethod(FakeView.class, @selector(fakeMouseDownCanMoveWindow));
        method_exchangeImplementations(originalMethod, categoryMethod);

Here is a quick screenshot of the result, a GLFW window rendering dear imgui:

GLFW window with custom color.