C++ SDL：全屏半透明背景

我试图写一个程序，有一个半透明的背景覆盖整个屏幕。经过一些研究，SDL似乎是一条可行之路

我已经编写了创建一个全屏窗口的代码，背景的alpha值等于100（255中的100），但出于某种原因，它只绘制纯色。我做错了什么

// Initialise SDL
if (SDL_Init(SDL_INIT_EVERYTHING) != 0) {
        this->throwSDLError("SDL_Init Error");
}

// Create the window and renderer
if (SDL_CreateWindowAndRenderer(0, 0, SDL_WINDOW_FULLSCREEN_DESKTOP, &(this->window), &(this->renderer)) != 0) {
        this->throwSDLError("Could not create the window and renderer");
}

// Set the blend mode to specify how the alpha channel is used
if (SDL_SetRenderDrawBlendMode(this->renderer, SDL_BLENDMODE_BLEND) != 0) {
        this->throwSDLError("Could not set render draw blend mode");
}

// Set the colour to draw
if (SDL_SetRenderDrawColor(this->renderer, 200, 200, 200, 100) != 0) {
        this->throwSDLError("Could not set the drawing colour");
}

// Clear the screen using the colour
if (SDL_RenderClear(this->renderer) != 0) {
        this->throwSDLError("Could not render the screen");
}

// Present the rendered screen
SDL_RenderPresent(this->renderer);

---

在Windows上，可以通过使用对无边框SDL窗口的背景色设置色度键来创建透明窗口

代码：

// SDL window with transparent background v1.2
#include <SDL.h>
#include <SDL_syswm.h>
#include <Windows.h>

// Makes a window transparent by setting a transparency color.
bool MakeWindowTransparent(SDL_Window* window, COLORREF colorKey) {
    // Get window handle (https://stackoverflow.com/a/24118145/3357935)
    SDL_SysWMinfo wmInfo;
    SDL_VERSION(&wmInfo.version);  // Initialize wmInfo
    SDL_GetWindowWMInfo(window, &wmInfo);
    HWND hWnd = wmInfo.info.win.window;

    // Change window type to layered (https://stackoverflow.com/a/3970218/3357935)
    SetWindowLong(hWnd, GWL_EXSTYLE, GetWindowLong(hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);

    // Set transparency color
    return SetLayeredWindowAttributes(hWnd, colorKey, 0, LWA_COLORKEY);
}

int main(int argc, char** argv) {
    // Get resolution of primary monitor
    int desktopWidth = GetSystemMetrics(SM_CXSCREEN);
    int desktopHeight = GetSystemMetrics(SM_CYSCREEN);

    SDL_Window* window = SDL_CreateWindow("SDL Transparent Window",
        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        desktopWidth, desktopHeight, SDL_WINDOW_BORDERLESS);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

    // Set background color to magenta and clear screen
    SDL_SetRenderDrawColor(renderer, 255, 0, 255, 255);
    SDL_RenderClear(renderer);

    // Draw blue square in top-left corner
    SDL_Rect rect1 = {0, 0, 100, 100};
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, 255);
    SDL_RenderFillRect(renderer, &rect1);

    // Draw red square in center of the screen
    SDL_Rect rect2 = {(desktopWidth-100)/2, (desktopHeight-100)/2, 100, 100};
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
    SDL_RenderFillRect(renderer, &rect2);

    // Add window transparency (Magenta will be see-through)
    MakeWindowTransparent(window, RGB(255, 0, 255));

    // Render the square to the screen
    SDL_RenderPresent(renderer);

    // Loop until user quits
    bool quit = false;
    SDL_Event event;
    while (!quit) {
       while (SDL_PollEvent(&event) != 0) {
           if (event.type == SDL_QUIT) {
               quit = true;
           }
       }
    }

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

//具有透明背景的SDL窗口v1.2
#包括
#包括
#包括
//通过设置透明度颜色使窗口透明。
bool使窗口透明（SDL_窗口*窗口，COLORREF colorKey）{
//拿窗把手(https://stackoverflow.com/a/24118145/3357935)
SDL_SysWMinfo wmInfo；
SDL_VERSION（&wmInfo.VERSION）；//初始化wmInfo
SDL_GetWindowWMInfo（窗口和wmInfo）；
HWND HWND=wmInfo.info.win.window；
//将窗口类型更改为“分层”(https://stackoverflow.com/a/3970218/3357935)
SetWindowLong（hWnd，GWL_EXSTYLE，GetWindowLong（hWnd，GWL_EXSTYLE）| WS_EX_分层）；
//设置透明度颜色
返回SetLayeredWindowAttributes（hWnd、colorKey、0、LWA_colorKey）；
}
int main（int argc，字符**argv）{
//获取主监视器的分辨率
int desktopWidth=GetSystemMetrics（SM_CXSCREEN）；
int desktopHeight=GetSystemMetrics（SM\u CYSCREEN）；
SDL_Window*Window=SDL_CreateWindow（“SDL透明窗口”，
SDL_WINDOWPOS_居中，SDL_WINDOWPOS_居中，
桌面宽度、桌面高度、SDL_窗口（无边框）；
SDL_渲染器*渲染器=SDL_CreateRenderer（窗口，-1，SDL_渲染器加速）；
//将背景色设置为洋红色并清除屏幕
SDL_SetRenderDrawColor（渲染器，255,0,255,255）；
SDL_渲染器（渲染器）；
//在左上角画蓝色正方形
SDL_Rect rect1={0,0,100,100}；
SDL_SetRenderDrawColor（渲染器，0、0、255、255）；
SDL_RenderFillRect（渲染器和rect1）；
//在屏幕中央画红方块
SDL_Rect rect2={（桌面宽度-100）/2，（桌面高度-100）/2100}；
SDL_SetRenderDrawColor（渲染器，255,0,0,255）；
SDL_RenderFillRect（渲染器和rect2）；
//添加窗口透明度（洋红将透明）
使WindowTransparent（窗口，RGB（255，0，255））；
//将正方形渲染到屏幕上
SDL_渲染器呈现（渲染器）；
//循环直到用户退出
bool-quit=false；
SDL_事件；
而（！退出）{
while（SDL_PollEvent（&event）！=0）{
if（event.type==SDL\u QUIT）{
退出=真；
}
}
}
SDL_窗口（窗口）；
SDL_退出（）；
返回0；
}

结果：

// SDL window with transparent background v1.2
#include <SDL.h>
#include <SDL_syswm.h>
#include <Windows.h>

// Makes a window transparent by setting a transparency color.
bool MakeWindowTransparent(SDL_Window* window, COLORREF colorKey) {
    // Get window handle (https://stackoverflow.com/a/24118145/3357935)
    SDL_SysWMinfo wmInfo;
    SDL_VERSION(&wmInfo.version);  // Initialize wmInfo
    SDL_GetWindowWMInfo(window, &wmInfo);
    HWND hWnd = wmInfo.info.win.window;

    // Change window type to layered (https://stackoverflow.com/a/3970218/3357935)
    SetWindowLong(hWnd, GWL_EXSTYLE, GetWindowLong(hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);

    // Set transparency color
    return SetLayeredWindowAttributes(hWnd, colorKey, 0, LWA_COLORKEY);
}

int main(int argc, char** argv) {
    // Get resolution of primary monitor
    int desktopWidth = GetSystemMetrics(SM_CXSCREEN);
    int desktopHeight = GetSystemMetrics(SM_CYSCREEN);

    SDL_Window* window = SDL_CreateWindow("SDL Transparent Window",
        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        desktopWidth, desktopHeight, SDL_WINDOW_BORDERLESS);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

    // Set background color to magenta and clear screen
    SDL_SetRenderDrawColor(renderer, 255, 0, 255, 255);
    SDL_RenderClear(renderer);

    // Draw blue square in top-left corner
    SDL_Rect rect1 = {0, 0, 100, 100};
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, 255);
    SDL_RenderFillRect(renderer, &rect1);

    // Draw red square in center of the screen
    SDL_Rect rect2 = {(desktopWidth-100)/2, (desktopHeight-100)/2, 100, 100};
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
    SDL_RenderFillRect(renderer, &rect2);

    // Add window transparency (Magenta will be see-through)
    MakeWindowTransparent(window, RGB(255, 0, 255));

    // Render the square to the screen
    SDL_RenderPresent(renderer);

    // Loop until user quits
    bool quit = false;
    SDL_Event event;
    while (!quit) {
       while (SDL_PollEvent(&event) != 0) {
           if (event.type == SDL_QUIT) {
               quit = true;
           }
       }
    }

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

说明：

// SDL window with transparent background v1.2
#include <SDL.h>
#include <SDL_syswm.h>
#include <Windows.h>

// Makes a window transparent by setting a transparency color.
bool MakeWindowTransparent(SDL_Window* window, COLORREF colorKey) {
    // Get window handle (https://stackoverflow.com/a/24118145/3357935)
    SDL_SysWMinfo wmInfo;
    SDL_VERSION(&wmInfo.version);  // Initialize wmInfo
    SDL_GetWindowWMInfo(window, &wmInfo);
    HWND hWnd = wmInfo.info.win.window;

    // Change window type to layered (https://stackoverflow.com/a/3970218/3357935)
    SetWindowLong(hWnd, GWL_EXSTYLE, GetWindowLong(hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);

    // Set transparency color
    return SetLayeredWindowAttributes(hWnd, colorKey, 0, LWA_COLORKEY);
}

int main(int argc, char** argv) {
    // Get resolution of primary monitor
    int desktopWidth = GetSystemMetrics(SM_CXSCREEN);
    int desktopHeight = GetSystemMetrics(SM_CYSCREEN);

    SDL_Window* window = SDL_CreateWindow("SDL Transparent Window",
        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        desktopWidth, desktopHeight, SDL_WINDOW_BORDERLESS);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

    // Set background color to magenta and clear screen
    SDL_SetRenderDrawColor(renderer, 255, 0, 255, 255);
    SDL_RenderClear(renderer);

    // Draw blue square in top-left corner
    SDL_Rect rect1 = {0, 0, 100, 100};
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, 255);
    SDL_RenderFillRect(renderer, &rect1);

    // Draw red square in center of the screen
    SDL_Rect rect2 = {(desktopWidth-100)/2, (desktopHeight-100)/2, 100, 100};
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
    SDL_RenderFillRect(renderer, &rect2);

    // Add window transparency (Magenta will be see-through)
    MakeWindowTransparent(window, RGB(255, 0, 255));

    // Render the square to the screen
    SDL_RenderPresent(renderer);

    // Loop until user quits
    bool quit = false;
    SDL_Event event;
    while (!quit) {
       while (SDL_PollEvent(&event) != 0) {
           if (event.type == SDL_QUIT) {
               quit = true;
           }
       }
    }

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

首先，创建一个覆盖整个桌面的无边框窗口。选择纯色遮罩颜色并将其用作背景。（在我的例子中，我使用了洋红）。然后，您可以使用Win32 API函数键入遮罩颜色

使用这种颜色的窗口的任何部分都将完全透明。程序后面的其他窗口可以正常交互。默认情况下，其他应用程序可以移动到无边界窗口的顶部

如果希望SDL窗口始终位于其他窗口的顶部，则可以在创建窗口时设置

SDL\u window\u always\u on\u top

标志

另见

• 堆栈溢出：
• 堆栈溢出：
• 微软：

---

要绘制部分不透明的背景以查看其他窗口和下方的桌面吗？我不相信SDL（或任何其他类型的抽象库）能够做到这一点。您需要访问特定于平台的窗口库（例如Windows、Mac/Cocoa、Linux/Xorg），但跨平台库可以将对setWindowTransparency方法的调用转换为平台的相应本机调用。谢谢，是否也有方法使矩形单击通过？因此，当您单击矩形时，它不会抓住焦点。我知道这是一条旧注释，但您（或其他带着相同问题来到这里的人）可能希望看看如何实现回调以返回

SDL\u HitTestResult

，并使用

SDL\u SetWindowHitTest

使窗口使用它。（，）谢谢@Stevoisiak这太棒了：）