opengl - 窗口调整大小/移动时顶点颜色发生了变化

Question

当我运行我的应用程序时，矩形的颜色为红色（这没关系），但是当我移动或调整窗口大小时，颜色会变为白色。 我不明白为什么会出现这种行为。

顶点着色器

attribute vec3 position;

void main(void) {

    gl_Position = gl_ModelViewProjectionMatrix * vec4(position, 1.0);
}

片段着色器

void main(void) {

    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}

来自glwindow.cpp的主渲染功能

void GLWindow::render(QPainter *painter)
    {
        Q_UNUSED(painter);

        glClearColor(0.0, 0.0, 0.0, 1.0);

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        GLfloat vertexes[] = {
            -0.5f, -0.5f, 0.0f,
            0.5f, -0.5f, 0.0f,
            -0.5f, 0.5f, 0.0,
            0.5f, 0.5f, 0.0f
        };

        glTranslatef(0.0f, 0.0f, -1.00f);

        unsigned int va;

        glGenBuffers(1, &va);

        glBindBuffer(GL_ARRAY_BUFFER, va);

        glEnableVertexAttribArray(0);

        glBufferData(GL_ARRAY_BUFFER, sizeof(vertexes), vertexes, GL_STATIC_DRAW);

        glVertexAttribPointer(program->attributeLocation("position"), 3, GL_FLOAT, GL_FALSE, 0, 0);

        glDrawArrays(GL_TRIANGLE_STRIP, 0, sizeof(vertexes)/(3*sizeof(GLfloat)));

        glDisableVertexAttribArray(0);

        glBindBuffer(GL_ARRAY_BUFFER, 0);

        glDeleteBuffers(1, &va);

    }

glwindow.cpp （http://qt-project.org/doc/qt-5/qtgui-openglwindow-example.html）

#include "glwindow.h"
#include <iostream>
#include <QApplication>


using namespace std;

GLWindow::GLWindow(QObject *parent)
    : QWindow((QWindow *)parent)
    , m_update_pending(false)
    , m_animating(false)
    , m_context(0)
    , m_device(0)
{
    setWidth(640);
    setHeight(480);
    setTitle("OpenGL window");
    setSurfaceType(QWindow::OpenGLSurface);
}

void GLWindow::render(QPainter *painter)
{
    Q_UNUSED(painter);

    glClearColor(0.0, 0.0, 0.0, 1.0);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    GLfloat vertexes[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        -0.5f, 0.5f, 0.0,
        0.5f, 0.5f, 0.0f
    };

    glTranslatef(0.0f, 0.0f, -1.00f);

    unsigned int va;

    glGenBuffers(0, &va);

    glBindBuffer(GL_ARRAY_BUFFER, va);

    glEnableVertexAttribArray(0);

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertexes), vertexes, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, sizeof(vertexes)/(3*sizeof(GLfloat)));

    glDisableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glDeleteBuffers(1, &va);

}

void GLWindow::initialize()
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    double aspect = (double)width()/height();
    glFrustum(-1.0, 1.0, -(2/(2*aspect)), (2/(2*aspect)), 1.0, 100.0);
    glMatrixMode(GL_MODELVIEW);

    program = new QOpenGLShaderProgram(m_context);
    program->addShaderFromSourceFile(QOpenGLShader::Vertex, "/Users/Krab/projects/qtProjects/gl/vertex.vert");
    program->addShaderFromSourceFile(QOpenGLShader::Fragment, "/Users/Krab/projects/qtProjects/gl/fragment.frag");
    program->link();
    program->bind();

}

void GLWindow::render()
{

    if (!m_device)
        m_device = new QOpenGLPaintDevice;

    m_device->setSize(size());

    QPainter painter(m_device);
    render(&painter);
}


void GLWindow::renderLater()
{
    if (!m_update_pending) {
        m_update_pending = true;
        QApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
    }
}

bool GLWindow::event(QEvent *event)
{
    switch (event->type()) {
    case QEvent::UpdateRequest:
        m_update_pending = false;
        renderNow();
        return true;
    default:
        return QWindow::event(event);
    }
}

void GLWindow::exposeEvent(QExposeEvent *event)
{
    Q_UNUSED(event);

    if (isExposed())
        renderNow();
}

void GLWindow::renderNow()
{
    if (!isExposed())
        return;

    bool needsInitialize = false;

    if (!m_context) {
        m_context = new QOpenGLContext(this);
        m_context->setFormat(requestedFormat());
        m_context->create();
        needsInitialize = true;
    }

    m_context->makeCurrent(this);

    if (needsInitialize) {
        initializeOpenGLFunctions();
        initialize();
    }

    render();

    m_context->swapBuffers(this);

    if (m_animating)
        renderLater();
}

void GLWindow::setAnimating(bool animating)
{
    m_animating = animating;

    if (animating)
        renderLater();
}

GLWindow::~GLWindow() {

}