Mac平台下，如何为SDL_CreateWindow创建的无边框SDL2窗口添加圆角？

Hey there! Great question—SDL doesn’t include a native API for setting rounded corners on borderless windows, but since SDL wraps macOS’s Cocoa framework under the hood, we can tap into native Objective-C APIs to make this work. Here’s a step-by-step guide:

Prerequisites #

• Target macOS 10.10 or later (the setCornerRadius API was introduced here)
• Your project must link against the Cocoa framework
• If mixing C/C++ with Objective-C, use .mm as your source file extension (to enable Objective-C++ compilation)

Step-by-Step Implementation #

1. Include Required Headers #

You’ll need SDL’s window management headers plus Cocoa’s framework headers:

#include <SDL2/SDL.h>
#include <SDL2/SDL_syswm.h>
#import <Foundation/Foundation.h>
#import <AppKit/AppKit.h>

2. Initialize SDL and Create Your Borderless Window #

Standard SDL setup, with code added to fetch the native Cocoa window handle:

int main(int argc, char* argv[]) {
    // Initialize SDL video subsystem
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        SDL_LogError(SDL_LOG_CATEGORY_ERROR, "SDL init failed: %s", SDL_GetError());
        return 1;
    }

    // Create borderless window
    SDL_Window* window = SDL_CreateWindow(
        "Rounded Borderless Window",
        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        800, 600,
        SDL_WINDOW_BORDERLESS
    );

    if (!window) {
        SDL_LogError(SDL_LOG_CATEGORY_ERROR, "Failed to create window: %s", SDL_GetError());
        SDL_Quit();
        return 1;
    }

3. Fetch the Native NSWindow Pointer #

Use SDL_GetWindowWMInfo() to access the underlying Cocoa NSWindow instance:

SDL_SysWMinfo wmInfo;
    SDL_VERSION(&wmInfo.version); // Critical: Initialize version info before use

    if (!SDL_GetWindowWMInfo(window, &wmInfo)) {
        SDL_LogError(SDL_LOG_CATEGORY_ERROR, "Failed to get window WM info: %s", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }

    // Convert the void* handle to an NSWindow* (use __bridge to avoid ARC issues)
    NSWindow* nsWindow = (__bridge NSWindow*)wmInfo.info.cocoa.window;

4. Set the Corner Radius #

Call Cocoa’s setCornerRadius: method to apply rounded corners. Adjust the value to your preference:

// Set corner radius (20.0 is a reasonable starting point)
    [nsWindow setCornerRadius:20.0];

    // Optional: If your window has transparent content, set a clear background
    // [nsWindow setBackgroundColor:[NSColor clearColor]];

5. Run Your Main Loop #

Finish with standard SDL cleanup:

// Main event loop
    bool running = true;
    SDL_Event event;
    while (running) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                running = false;
            }
        }

        // Add your rendering logic here
        SDL_Delay(16); // ~60 FPS
    }

    // Cleanup
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}

Compilation Notes #

When compiling, link against the Cocoa framework and use SDL’s config flags:

gcc -o rounded_window rounded_window.mm `sdl2-config --cflags --libs` -framework Cocoa

Key Notes #

• Version Compatibility: If you need to support macOS versions older than 10.10, wrap the setCornerRadius call in a version check:

  if (@available(macOS 10.10, *)) {
      [nsWindow setCornerRadius:20.0];
  }
  

• Content Clipping: The NSWindow’s corner radius will automatically clip your SDL-rendered content, so you don’t need to adjust your rendering code unless you’re drawing outside the window bounds.

内容的提问来源于stack exchange，提问作者John