如何制作透明背景的 OpenGL 渲染上下文？

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Abstract

Keywords OpenGL  C++ 

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Citation Yao Qing-sheng.如何制作透明背景的 OpenGL 渲染上下文？.FUTURE & CIVILIZATION Natural/Social Philosophy & Infomation Sciences,20220613. https://yaoqs.github.io/20220613/ru-he-zhi-zuo-tou-ming-bei-jing-de-opengl-xuan-ran-shang-xia-wen/

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转载自腾讯云社区

这是一个古老的问题，但由于新版本的 Windows 有合成和对 opengl 的支持，正如 datenwolf 所暗示的那样，我们可以使用一些特殊的调料来实现这一点。尽管这对于 DirectX 来说也是微不足道的 (如图所示) 微软确实在 opengl 上下文中添加了合成提示。耶，反垄断的恐惧！

因此，您必须使用指定 alpha 通道的像素格式创建一个 opengl 上下文，并且它应该使用合成 (第 82 行)。然后，使用 DwmApi.h 例程启用一个模糊窗口 (第 179 行)，其中指定了一个完全无效的区域，这将模糊任何内容并使窗口保持透明。(您需要在窗口类上指定一个 black+transparent 笔刷！奇怪！) 然后，您实际上只是使用 opengl，就像您习惯使用它一样。在事件循环中，只要有机会，您就可以绘制和交换缓冲区 (第 201 行)，并记住启用 GL_BLEND！😃

请查看 /fork https://gist.github.com/3644466，或者只查看基于 OP 自己的答案的以下代码片段，而不是使用此技术 (您可以将其放在一个空项目中)：

#define _WIN32_WINNT 0x0500

#include <windows.h>
#include <windowsx.h>
#include <GL/gl.h>
#include <GL/glu.h>

#include <dwmapi.h>

#pragma comment (lib, "opengl32.lib")
#pragma comment (lib, "glu32.lib")

#pragma comment (lib, "dwmapi.lib")

#include <assert.h>
#include <tchar.h>

#ifdef  assert
#define verify(expr) if(!expr) assert(0)
#else verify(expr) expr
#endif

const TCHAR szAppName[]=_T("TransparentGL");
const TCHAR wcWndName[]=_T("TransparentGL");

HDC hDC;
HGLRC m_hrc;
int w = 240;
int h = 240;

BOOL initSC() {
    glEnable(GL_ALPHA_TEST);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_COLOR_MATERIAL);

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glClearColor(0, 0, 0, 0);

    return 0;
}

void resizeSC(int width,int height) {
    glViewport(0,0,width,height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glMatrixMode(GL_MODELVIEW );
    glLoadIdentity();
}

BOOL renderSC() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glPushMatrix();

    glColor3f(0, 1, 1);
    glBegin(GL_TRIANGLES);                              // Drawing Using Triangles
        glColor3f(1.0f,0.0f,0.0f);                      // Set The Color To Red
        glVertex3f( 0.0f, 1.0f, 0.0f);                  // Top
        glColor3f(0.0f,1.0f,0.0f);                      // Set The Color To Green
        glVertex3f(-1.0f,-1.0f, 0.0f);                  // Bottom Left
        glColor3f(0.0f,0.0f,1.0f);                      // Set The Color To Blue
        glVertex3f( 1.0f,-1.0f, 0.0f);                  // Bottom Right
    glEnd();

    glPopMatrix();
    glFlush();

    return 0;
}

BOOL CreateHGLRC(HWND hWnd) {
    PIXELFORMATDESCRIPTOR pfd = {
      sizeof(PIXELFORMATDESCRIPTOR),
      1,                                // Version Number
      PFD_DRAW_TO_WINDOW      |         // Format Must Support Window
      PFD_SUPPORT_OPENGL      |         // Format Must Support OpenGL
      PFD_SUPPORT_COMPOSITION |         // Format Must Support Composition
      PFD_DOUBLEBUFFER,                 // Must Support Double Buffering
      PFD_TYPE_RGBA,                    // Request An RGBA Format
      32,                               // Select Our Color Depth
      0, 0, 0, 0, 0, 0,                 // Color Bits Ignored
      8,                                // An Alpha Buffer
      0,                                // Shift Bit Ignored
      0,                                // No Accumulation Buffer
      0, 0, 0, 0,                       // Accumulation Bits Ignored
      24,                               // 16Bit Z-Buffer (Depth Buffer)
      8,                                // Some Stencil Buffer
      0,                                // No Auxiliary Buffer
      PFD_MAIN_PLANE,                   // Main Drawing Layer
      0,                                // Reserved
      0, 0, 0                           // Layer Masks Ignored
   };

   HDC hdc = GetDC(hWnd);
   int PixelFormat = ChoosePixelFormat(hdc, &pfd);
   if (PixelFormat == 0) {
      assert(0);
      return FALSE ;
   }

   BOOL bResult = SetPixelFormat(hdc, PixelFormat, &pfd);
   if (bResult==FALSE) {
      assert(0);
      return FALSE ;
   }

   m_hrc = wglCreateContext(hdc);
   if (!m_hrc){
      assert(0);
      return FALSE;
   }

   ReleaseDC(hWnd, hdc);

   return TRUE;
}

LRESULT CALLBACK WindowFunc(HWND hWnd,UINT msg, WPARAM wParam, LPARAM lParam) {
    PAINTSTRUCT ps;

    switch(msg) {
        case WM_CREATE:
        break;

        case WM_DESTROY:
            if(m_hrc) {
                wglMakeCurrent(NULL, NULL);
                wglDeleteContext(m_hrc) ;
            }
            PostQuitMessage(0) ;
        break;

        default:
            return DefWindowProc(hWnd,msg,wParam,lParam);
    }

    return 0;
}

int WINAPI _tWinMain(HINSTANCE hThisInst, HINSTANCE hPrevInst, LPSTR str,int nWinMode) {
    WNDCLASSEX wc;
    memset(&wc, 0, sizeof(wc));
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = (WNDPROC)WindowFunc;
    wc.cbClsExtra  = 0;
    wc.cbWndExtra  = 0;
    wc.hInstance = hThisInst;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)CreateSolidBrush(0x00000000);
    wc.lpszClassName = szAppName;

    if(!RegisterClassEx(&wc)) {
        MessageBox(NULL, _T("RegisterClassEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
        return FALSE;
    }

    HWND hWnd = CreateWindowEx(WS_EX_APPWINDOW, szAppName, wcWndName,
                    WS_VISIBLE | WS_POPUP, 200, 150, w, h,
                    NULL, NULL, hThisInst, NULL);

    if(!hWnd) {
        MessageBox(NULL, _T("CreateWindowEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
        return FALSE;
    }

    DWM_BLURBEHIND bb = {0};
    HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
    bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
    bb.hRgnBlur = hRgn;
    bb.fEnable = TRUE;
    DwmEnableBlurBehindWindow(hWnd, &bb);

    CreateHGLRC(hWnd);

    HDC hdc = GetDC(hWnd);
    wglMakeCurrent(hdc, m_hrc);
    initSC();
    resizeSC(w, h);
    ReleaseDC(hWnd, hdc);

    MSG msg;
    while(1) {
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
        else {
            HDC hdc = GetDC(hWnd);
            wglMakeCurrent(hdc, m_hrc);

            renderSC();

            SwapBuffers(hdc);
            ReleaseDC(hWnd, hdc);
        }
    }

    return (FALSE);
}

References

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*Corresponding Author: Yao Qing-sheng <Email: 350788415@qq.com> BY-NC-SA .

1. Yao Qing-sheng.如何制作透明背景的 OpenGL 渲染上下文？.FUTURE & CIVILIZATION.Natural/Social Philosophy & Infomation Sciences,20220613.https://yaoqs.github.io/20220613/ru-he-zhi-zuo-tou-ming-bei-jing-de-opengl-xuan-ran-shang-xia-wen/
2. 版权声明：本文为「LordYao」的原创文章，遵循 CC 4.0 BY-NC-SA 版权协议，转载请附上原文出处链接及本声明。
   原文链接： https://yaoqs.github.io/20220613/ru-he-zhi-zuo-tou-ming-bei-jing-de-opengl-xuan-ran-shang-xia-wen/