QPixmap跑过我的glScissor(.)设置

Question

如果这不准确我很抱歉。我正在尽我所能从一台计算机复制代码到另一台计算机，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()**:** 的代码

QPainter(this);

一旦创建了一个QPainter对象，我在函数中前面所做的glScissor(...)调用就会溢出，并且会发出某种glClearColor(...)调用(可能来自QPainter的构造函数)，将整个视图清除到我在glScissor(...)之后设置的背景色。然后像素地图画我的斜面纹理很好。

我不想QPainter超过我的剪刀。

我最接近的解释是两种QPainter方法，beginNativePainting()和endNativePainting()。根据文档，剪刀测试在这两者之间是禁用的，但在它们的示例中，它们会重新启用它。我试着使用这个“本地绘画”代码，但我无法阻止QPainter的存在，即忽略GL的剪裁和清除我的整个视图。

，为什么会发生这种事，我怎样才能阻止它？

注意:这台工作电脑有网络政策来阻止我去像imgur这样的娱乐网站上传“我想要什么”和“我得到什么”的图片，所以我必须用文本来做。

Answer 1

为什么会发生这种事

OpenGL上下文是一个共享资源，您必须与其他参与者共享它。

我该怎么阻止这一切？

你不能。只要做正确的事情，并设置视口，剪刀矩形和所有其他绘图相关的状态在正确的时刻:就在你要画的东西依赖于这些设置。不要在此之前，在某个“初始化”或重塑处理程序的某个地方设置它们的时间(以计算机术语表示)。而且，在绘制代码时，使用OpenGL调用的任何函数都会留下一些垃圾。