SDL 实现透明悬浮窗

最近一直想用SDL实现弹幕功能，但是一直没法实现悬浮窗和透明背景功能。

在一个老外的博客上发现了思路：EthioProgrammer: Applying transparency using win32 api, C++/SDL code

就是通过SDL_GetWindowWMInfo函数获取到窗口的HWND句柄，然后调用win32 api设置窗口的属性即可。

在别的平台也一样，调用系统api设置窗体属性。

有一点需要注意，目测只能用Surface，不能用Renderer,不然无法通过窗体colorKey实现透明背景。

代码如下：

#include <SDL2/SDL.h>

#include <SDL2/SDL_syswm.h>

#include <SDL2/SDL_video.h>

#include <windows.h>

int main(int argc, char *argv[])

{

    SDL_Window *window;

    SDL_Renderer *renderer;

    SDL_Surface *winSurface;

    SDL_Event event;

    int quit = ;

    SDL_Rect rectRect = {,,,};

    SDL_Rect backRect = {};

    SDL_SysWMinfo info;

    HWND hwnd;

    SDL_Init(SDL_INIT_EVERYTHING);

    window   = SDL_CreateWindow("Test",SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,,,SDL_WINDOW_SHOWN|SDL_WINDOW_BORDERLESS);

    SDL_VERSION(&info.version);

    if(SDL_GetWindowWMInfo(window,&info))

    {

        hwnd = info.info.win.window;

    }

/*设置窗口colorkey*/

    SetWindowLong( hwnd, GWL_EXSTYLE, GetWindowLong(hwnd, GWL_EXSTYLE)|WS_EX_LAYERED);

    SetLayeredWindowAttributes( hwnd, RGB(,,),, LWA_COLORKEY);

/*设置窗口为悬浮窗 */

    SetWindowPos ( hwnd, HWND_TOPMOST, , , , , SWP_NOMOVE|SWP_NOSIZE);

/*--------------*/

    winSurface = SDL_GetWindowSurface(window);

    SDL_GetWindowSize(window,&backRect.w,&backRect.h);

    UINT32 keyColor = SDL_MapRGB(winSurface->format,,,);

    SDL_SetSurfaceBlendMode(winSurface,SDL_BLENDMODE_NONE);

    while(!quit){

        while(SDL_PollEvent(&event))

        {

            if(event.type == SDL_QUIT)

                quit = ;

        }

        SDL_FillRect(winSurface,&backRect,keyColor);

        rectRect.x+=;

        SDL_FillRect(winSurface,&rectRect,SDL_MapRGB(winSurface->format,0xff,0x00,0x00));

        SDL_UpdateWindowSurface(window);

        SDL_Delay(/);

    }

    SDL_Quit();

    return ;

}

效果图：

巴特西

SDL 实现透明悬浮窗

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