Qt 5.3. QWidget direct painting with OpenGL

Question

Good day. Is there any ways to paint QWidget -based window without QPainter . I try to use raw OpenGL for drawing with the following code:

1) Main function:

int main(int argc, char* argv[]) {
    QApplication app(argc, argv);
    GLWindow* window = new GLWindow;
    window->setMinimumSize(200, 200);
    window->initializeGLContext();
    window->show();
    return app.exec(); 
}

GLWindow inhereted from QMainWindow . I use glew library in order to work with OpenGL . Below is a simplified version of the code without error handling and stupid program flow.

namespace {
    GLfloat vertices[] = {
        0.0f, 0.5f,
        0.5f, -0.5f,
        -0.5f, -0.5f
    };
    const char* vertexShaderSource =
        "in vec2 position;"
         "void main() {"
         "gl_Position = vec4(position, 0.0, 1.0); }";

    const char* fragmentShaderSource =
        "out vec4 outColor;"
        "void main() {"
        "outColor = vec4(1.0, 0.0, 0.0, 1.0); }";
}

GLWindow::GLWindow() {
    setAttribute(Qt::WA_PaintOnScreen, true); }

void GLWindow::initializeGLContext() {

    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR), 1,
        PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
        PFD_TYPE_RGBA, 32, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0,
        24, 8, 0,
        PFD_MAIN_PLANE, 0, 0, 0, 0 };

    HDC hdc = GetDC((HWND)winId());

    int windowPixelFormat = ChoosePixelFormat(hdc, &pfd);
    SetPixelFormat(hdc, windowPixelFormat, &pfd);

    HGLRC hglrc = wglCreateContext(hdc);
    wglMakeCurrent(hdc, hglrc);
}

QPaintEngine* GLWindow::paintEngine() const { return 0; }

void GLWindow::paintEvent(QPaintEvent *) {

    glewInit();

    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glDrawArrays(GL_TRIANGLES, 0, 3);

    SwapBuffers(GetDC((HWND)winId()));
}

After program execution all that i have is black screen without triangle. I'm a novice in Qt and if you have any suggestions what is going wrong, please share them with me.

Best regards.

Answer 1

您应该使用基类QGLWidget并改写paintGL 。