QPixmap运行在我的glScissor(..)设置上

Question

如果这不准确，我深表歉意。我正在尽我所能手动将代码从一台计算机复制到另一台计算机，而目标计算机没有编译器(不要问(。

头文件

#ifndef MYOPENGLWIDGET_H
#define MYOPENGLWIDGET_H
#include <qopenglwidget.h>
class MyOpenGlWidget : public QOpenGLWidget
{
    Q_OBJECT
public:
    explicit MyOpenGlWidget(QWidget *parent = 0, Qt::WindowFlags f = Qt::WindowFlags());
    virtual ~MyOpenGlWidget();
protected:
    // these are supposed to be overridden, so use the "override" keyword to compiler check yourself
    virtual void initializeGL() override;
    virtual void resizeGL(int w, int h) override;
    virtual void paintGL() override;
private:
    QPixmap *_foregroundPixmap;
}
#endif 

源文件

QOpenGLFunctions_2_1 *f = 0;

MyOpenGlWidget::MyOpenGlWidget(QWidget *parent, Qt::WindowFlags f) :
    QOpenGLWidget(parent, f)
{
    _foregroundPixmap = 0;
    QPixmap *p = new QPixmap("beveled_texture.tiff");
    if (!p->isNull())
    {
        _foregroundPixmap = p;
    }
}
MyOpenGlWidget::~MyOpenGlWidget()
{
    delete _foregroundPixmap;
}
void MyOpenGlWidget::initializeGL()
{
    // getting a deprecated set of functions because such is my work environment 
    // Note: Also, QOpenGLWidget doesn't support these natively.
    f = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_2_1>();
    f->glClearColor(0.0f, 1.0f, 0.0f, 1.0f);    // clearing to green
    f->glEnable(GL_DEPTH_TEST);
    f->glEnable(GL_CULL_FACE);  // implicitly culling front face
    f->glEnable(GL_SCISSOR_TEST);
    // it is either copy the matrix and viewport code from resizeGL or just call the method
    this->resizeGL(this->width(), this->height());
}
void MyOpenGlWidget::resizeGL(int w, int h)
{
    // make the viewport square
    int sideLen = qMin(w, h);
    int x = (w - side) / 2;
    int y = (h - side) / 2;
    // the widget is 400x400, so this random demonstration square will show up inside it
    f->glViewport(50, 50, 100, 100);
    f->glMatrixMode(GL_PROJECTION);
    f->glLoadIdentity();
    f->glOrtho(-2.0f, +2.0f, -2.0f, +2.0f, 1.0f, 15.0f);    // magic numbers left over from a demo
    f->glMatrixMode(GL_MODELVIEW);
    // queue up a paint event
    // Note: QGLWidget used updateGL(), but QOpenGLWidget uses update().
    this->update();
}
void MyOpenGlWidget::paintGL()
{
    f->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // I want to draw a texture with beveled edges the size of this widget, so I can't 
    // have the background clearing all the way to the edges
    f->glScissor(50, 50, 200, 200);     // more magic numbers just for demonstration
    // clears to green in just scissored area (unless QPainter is created)
    f->glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
    // loading identity matrix, doing f->glTranslatef(...) and f->glRotatef(...)
    // pixmap loaded earlier in another function
    if (_foregroundPixmap != 0)
    {
        // QPixmap apparently draws such that culling the back face will cull the entire 
        // pixmap, so have to switch culling for duration of pixmap drawing
        f->glCullFace(GL_FRONT);
        QPainter(this);
        painter.drawPixmap(0, 0, _foregroundPixmap->scaled(this->size()));
        // done, so switch back to culling the front face
        f->glCullFace(GL_BACK);
    }
QOpenGLFunctions_2_1 *f = 0;
void MyOpenGlWidget::initializeGL()
{
    // getting a deprecated set of functions because such is my work environment 
    // Note: Also, QOpenGLWidget doesn't support these natively.
    f = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_2_1>();
    f->glClearColor(0.0f, 1.0f, 0.0f, 1.0f);    // clearing to green
    f->glEnable(GL_DEPTH_TEST);
    f->glEnable(GL_CULL_FACE);  // implicitly culling front face
    f->glEnable(GL_SCISSOR_TEST);
    // it is either copy the matrix and viewport code from resizeGL or just call it directly
    this->resizeGL(this->width(), this->height());
}
void MyOpenGlWidget::resizeGL(int w, int h)
{
    // make the viewport square
    int sideLen = qMin(w, h);
    int x = (w - side) / 2;
    int y = (h - side) / 2;
    // the widget is 400x400, so this random demonstration square will show up inside it
    f->glViewport(50, 50, 100, 100);
    f->glMatrixMode(GL_PROJECTION);
    f->glLoadIdentity();
    f->glOrtho(-2.0f, +2.0f, -2.0f, +2.0f, 1.0f, 15.0f);    // magic numbers left over from a demo
    f->glMatrixMode(GL_MODELVIEW);
    // queue up a paint event
    // Note: QGLWidget used updateGL(), but QOpenGLWidget uses update().
    this->update();
}
void MyOpenGlWidget::paintGL()
{
    f->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // I want to draw a texture with beveled edges the size of this widget, so I can't 
    // have the background clearing all the way to the edges
    f->glScissor(50, 50, 200, 200);     // more magic numbers just for demonstration
    // clears to green in just scissored area (unless QPainter is created)
    f->glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
    // loading identity matrix, doing f->glTranslatef(...) and f->glRotatef(...), drawing triangles
    // done drawing, so now draw the beveled foreground
    if (_foregroundPixmap != 0)
    {
        // QPixmap apparently draws such that culling the back face will cull the entire 
        // pixmap, so have to switch culling for duration of pixmap drawing
        f->glCullFace(GL_FRONT);
        QPainter(this);
        painter.drawPixmap(0, 0, _foregroundPixmap->scaled(this->size()));
        // done, so switch back to culling the front face
        f->glCullFace(GL_BACK);
    }
}

问题是来自paintGL():的此代码

QPainter(this);

一旦创建了QPainter对象，我在函数前面进行的glScissor(...)调用就会被溢出，并进行某种glClearColor(...)调用(可能来自QPainter的构造函数(，将整个视口清除为我在glScissor(...)之后设置的背景色。然后像素图把我的斜面纹理画得很好。

我不希望QPainter超过我的剪刀。

我得到的最接近解释是两种QPainter方法，beginNativePainting()和endNativePainting()。根据文档，剪刀测试在这两者之间是禁用的，但在他们的例子中，他们重新启用了它。我尝试使用这个"原生绘画"代码，但我无法阻止QPainter的存在，因为它忽略了GL的剪刀测试并清除了我的整个视口。

为什么会发生这种情况，我该如何阻止这种情况

注意：这台工作电脑有网络策略，禁止我去imgur等娱乐网站上传"我想要的"one_answers"我得到的"图片，所以我必须通过文本进行支付。

Answer 1

为什么会发生这种情况

OpenGL上下文是一个共享资源，您必须与其他玩家共享它。

我该如何阻止这种情况？

你不能。只要做正确的事情，在右侧时刻设置视口、剪刀矩形和所有其他与绘图相关的状态：就在您要绘制依赖于这些设置的东西之前。不要在某个"初始化"或整形处理程序的某个位置之前(用计算机术语来说(设置它们。在绘图代码中，任何使用OpenGL调用的函数都会留下一些垃圾。