QPixmap运行在我的glScissor（...）设置上

Question

如果这不确切，我道歉。我尽力将代码从一台计算机手动复制到另一台计算机，而目标计算机没有编译器（不要问）。

标头文件

#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QPainter对象，我在函数中先前调用的glScissor(...)调用就会被调用，并且会进行某种glClearColor(...)调用（可能来自QPainter的构造函数）将整个视口清除为我在glScissor(...)之后设置的背景颜色。然后pixmap绘制我的斜面纹理就好了。

我不希望QPainter超越我的剪刀。

我最接近解释的是two QPainter methods，beginNativePainting()和endNativePainting()。根据文档，剪刀测试在这两者之间被禁用，但在他们的示例中，他们重新启用它。我试过用这个＆＃34;本土绘画＆＃34;代码，但我无法阻止QPainter的存在而忽略了GL的剪刀和清除我的整个视口。

为什么会发生这种情况？如何阻止这种情况？

注意：这台工作计算机有网络政策，以防止我去imgur等娱乐网站上传＆＃34;我想要的＆＃34;和＆＃34;我得到的＆＃34;图片，所以我必须使用文字。

Answer 1

  

为什么会发生这种情况

OpenGL上下文是共享资源，您必须与其他玩家共享。

  

我该怎么做呢？

你不能。只需做正确的事情并在右侧时刻设置视口，剪刀矩形和所有其他绘图相关状态：就在您要绘制依赖于这些设置的东西之前。不要将它们（在计算机术语中）设置为永久性的，在某些地方进行初始化＆＃34;初始化＆＃34;或重塑处理程序。并且可以预期，在绘图代码中，您调用的任何使用OpenGL的函数都会留下一些垃圾。