Question

我成功读取了OpenGL渲染的DC像素。这是我的代码的一部分。

void COpenGLWnd::OffscreenRender
    (/* IN parameters */ int transitionID, int counts, int directionID,
    /* OUT parameters */ BYTE* pPixelArray)
{
    HDC hDC = ::GetDC(m_hWnd);
    SetDCPixelFormat(hDC);

    HGLRC hRC = wglCreateContext(hDC);
    VERIFY(wglMakeCurrent(hDC, hRC));

    for(int i = 0; i < counts; i++)
    {
        GLFadeinRender((GLfloat)(i+1) / (GLfloat)counts);

        BYTE* data = (BYTE*) malloc(m_BmpSize);
        glReadBuffer(GL_BACK);
        glReadPixels(0,0,m_BmpWidth,m_BmpHeight,GL_BGR_EXT,GL_UNSIGNED_BYTE, data);

        memcpy(&pPixelArray[i * m_BmpSize], data, m_BmpSize);
        free(data);
    }

    wglMakeCurrent(hDC, NULL);
    wglDeleteContext(hRC);
    ::ReleaseDC(m_hWnd, hDC);
}

它工作得很好，但我想在没有hWnd的情况下使用glReadPixels。我听说PBO或FBO可能会对这种情况有所帮助，但我无法做到。这是我尝试使用PBO呈现的代码。

void COpenGLWnd::OffscreenRender
    (/* IN parameters */ int transitionID, int counts, int directionID,
    /* OUT parameters */ BYTE* pPixelArray)
{
    GLuint pbo;
    glGenBuffersARB(1,&pbo);
    glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pbo);
    glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, m_BmpSize, NULL, GL_STREAM_READ_ARB);
    glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);

    for(int i = 0; i < counts; i++)
    {
        glReadBuffer(GL_BACK);
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pbo);

        GLFadeinRender((GLfloat)(i+1) / (GLfloat)counts);

        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pbo);
        //glReadBuffer(GL_BACK);
        glReadPixels(0,0,m_BmpWidth,m_BmpHeight,GL_BGR_EXT,GL_UNSIGNED_BYTE, 0);
        BYTE* data = (BYTE*) glMapBufferARB(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY_ARB);

        memcpy(&pPixelArray[i * m_BmpSize], data, m_BmpSize);

        if(data)
        {
            glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_ARB);
        }

        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB,0);
    }

    glDeleteBuffers(1,&pbo);
}

但glReadPixels没有发生任何事。没有像素读取。那么我可以在不使用hWnd的情况下屏幕渲染和读取像素吗？

如何在没有hWnd的情况下使用glReadPixels？

0 个答案: