无法在 QWIndow (Qt5) 中使用 OpenGL 启用深度测试

Question

我正在尝试使用QWindow在Qt 5.2中编写一个简单的OpenGL应用程序。我似乎无法进行深度测试。我已经大大简化了QWindow OpenGL的例子:我画了一个带彩色顶点的三角形，然后是一个带白色顶点的三角形。白色三角形具有较大的Z坐标，因此应该出现在彩色三角形的后面。它不是。

我显式地将QWindow的表面格式的深度缓冲区大小设置为24，但是当我检查QWindow::format()函数时，深度缓冲区大小为0。对于QGLFormat，我知道有一个setDepth()函数，您可以使用它来打开深度缓冲区，但在QSurfaceFormat中没有类似的功能。

我做错了什么?

我的代码…

testWindow.cpp:

#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QResizeEvent>
#include <QSurfaceFormat>
#include <QWidget>
#include <QWindow>
#include <QVBoxLayout>
#include "SphereWindow.h"
class GLDialog : public QDialog
{
public:
  GLDialog(QWidget *parent = 0, Qt::WindowFlags f = 0) : QDialog(parent, f)
  {
    QVBoxLayout *layout = new QVBoxLayout(this);
    QSurfaceFormat format;
    format.setSamples(16);
    format.setDepthBufferSize(24);
    qDebug() << "requested format:" << format;
    window = new SphereWindow;
    window->setFormat(format);
    qDebug() << "actual format:" << window->format();
    window->render();
    QWidget *glWidget = QWidget::createWindowContainer(window, this);
    layout->addWidget(glWidget);
  }
  ~GLDialog()
  {
    delete window;
  }
protected:
  void resizeEvent(QResizeEvent *event)
  {
    window->resize(event->size());
    window->render();
  }
private:
  SphereWindow *window;

};

int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  QDialog *dlg = new GLDialog;
  dlg->resize(640,480);
  dlg->show();
  return app.exec();
}

SphereWindow.h:

#include <QColor>
#include <QEvent>
#include <QExposeEvent>
#include <QOpenGLContext>
#include <QOpenGLFunctions>
#include <QOpenGLPaintDevice>
#include <QOpenGLShaderProgram>
#include <QPainter>
#include <QResizeEvent>
#include <QSize>
#include <QWindow>

class SphereWindow : public QWindow, protected QOpenGLFunctions
{
  Q_OBJECT
public:
  SphereWindow(QWindow * = 0);
  virtual ~SphereWindow();
  virtual void render();
  virtual void initialize();
public slots:
  void resizeViewport(const QSize &);
protected:
  virtual void resizeEvent(QResizeEvent *); 

private:
  bool _initialized;
  QOpenGLContext *_context;
  QOpenGLPaintDevice *_device;
  QOpenGLShaderProgram *_program;
  QColor _backgroundColour;
  GLuint _posAttr;
  GLuint _colAttr;
};

SphereWindow.cpp:

#include <QCoreApplication>
#include <QMatrix4x4>
#include <QOpenGLShader>
#include <QScreen>
#include <QSurfaceFormat>
#include <QDebug>
#include "SphereWindow.h"
SphereWindow::SphereWindow(QWindow *parent)
: QWindow(parent), 
_initialized(0), 
_program(0), 
_backgroundColour(Qt::black) 
{
  setSurfaceType(QWindow::OpenGLSurface);
  create();      
  _context = new QOpenGLContext(this);
  _context->setFormat(requestedFormat());
  _context->create();
}
SphereWindow::~SphereWindow()
{ }

void SphereWindow::resizeEvent(QResizeEvent *event)
{
  resizeViewport(event->size());
}
void SphereWindow::resizeViewport(const QSize &size)
{
  int width = size.width();
  int height = size.height();
  int side = qMin(width, height);
  int hoffset = (int)((width - side) / 2.0 + 0.5);
  int voffset = (int)((height - side) / 2.0 + 0.5);
  glViewport(hoffset, voffset, side, side);
}
void SphereWindow::render()
{
  if (! _initialized)
    initialize();
  if (! isExposed()) return;
  glEnable(GL_DEPTH_TEST);
  _context->makeCurrent(this);
  glClearColor(_backgroundColour.redF(), _backgroundColour.greenF(), _backgroundColour.blueF(), 1.0);
  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
  _program->bind();
    GLfloat vertices[] = {
        -0.75f, 0.75f, 0.0f,
        -0.75f, -0.75f, 0.0f,
        0.75f, -0.75f, 0.0f,
        0.75f, 0.75f, 0.5f,
        0.75f, -0.75f, 0.5f,
        -0.75f, -0.75f, 0.5f,
    };
    GLfloat colors[] = {
        1.0f, 0.0f, 0.0f,
        0.0f, 1.0f, 0.0f,
        0.0f, 0.0f, 1.0f,
        1.0f, 1.0f, 1.0f,
        1.0f, 1.0f, 1.0f,
        1.0f, 1.0f, 1.0f,
    };
    glVertexAttribPointer(_posAttr, 3, GL_FLOAT, GL_FALSE, 0, vertices);
    glVertexAttribPointer(_colAttr, 3, GL_FLOAT, GL_FALSE, 0, colors);
    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glDrawArrays(GL_TRIANGLES, 0, 6);
    glDisableVertexAttribArray(1);
    glDisableVertexAttribArray(0);   
    _program->release();
    _context->swapBuffers(this);
    _context->doneCurrent();
}
static const char *vertexShaderSource =
    "attribute highp vec4 posAttr;n"
    "attribute lowp vec4 colAttr;n"
    "varying lowp vec4 col;n"
    "void main() {n"
    "   col = colAttr;n"
    "   gl_Position = posAttr;n"
    "}n";
static const char *fragmentShaderSource =
    "varying lowp vec4 col;n"
    "void main() {n"
    "   gl_FragColor = col;n"
    "}n";

void SphereWindow::initialize()
{
  _context->makeCurrent(this);
  _program = new QOpenGLShaderProgram(this);
  _program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
  _program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
  _program->link();
  _program->bind();
  _posAttr = _program->attributeLocation("posAttr");
  _colAttr = _program->attributeLocation("colAttr");
  _program->release();

  initializeOpenGLFunctions();
}

testqwindow.pro:

######################################################################
# Automatically generated by qmake (3.0) Sat May 3 05:01:55 2014
######################################################################
TEMPLATE = app
TARGET = testqwindow
INCLUDEPATH += .
QT += widgets
CONFIG += debug
# Input
HEADERS += SphereWindow.h
SOURCES += SphereWindow.cpp testWindow.cpp

Answer 1

问题是这样的:我在调用我的SphereWindow构造函数后设置了表面格式，但创建了一个QOpenGLContext并在构造函数中设置了它的格式。结果是上下文没有得到深度缓冲区。我已经将QOpenGLContext::setFormat()和QOpenGLContext::create()的调用移动到我的SphereWindow::initialize()函数，现在深度缓冲正在为我工作。

SphereWindow::SphereWindow(QWindow *parent)
: QWindow(parent), 
_initialized(0), 
_program(0), 
_backgroundColour(Qt::black) 
{
  setSurfaceType(QWindow::OpenGLSurface);
  create();
  qDebug() << "format:" << format();

  _context = new QOpenGLContext(this);
  /* Move these lines into initialize() */
//   _context->setFormat(requestedFormat());
//   _context->create();
}
...
void SphereWindow::initialize()
{
  _context->setFormat(requestedFormat());
  _context->create();
  _context->makeCurrent(this);
  _program = new QOpenGLShaderProgram(this);
  _program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
  _program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
  _program->link();
  _program->bind();
  _posAttr = _program->attributeLocation("posAttr");
  _colAttr = _program->attributeLocation("colAttr");
  _program->release();

  initializeOpenGLFunctions();
}

正如我在上面的评论中提到的，我在基于qglwidget的设置中有几乎相同的代码，深度缓冲"开箱即用"。我猜QGLWidget(或QGLFormat?)必须有一个深度缓冲区在默认情况下打开，和QWindow(或QSurfaceFormat?)没有。