使用 QOpenGLWidget 进行屏幕外渲染的最简单方法
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【中文标题】使用 QOpenGLWidget 进行屏幕外渲染的最简单方法【英文标题】:Easiest way for offscreen rendering with QOpenGLWidget 【发布时间】:2015-07-09 16:53:10 【问题描述】:我有一个隐藏的 QOpenGLWidget(Qt 5.4.2,不是 QGLWidget),我想基本上不断地做 grab() 或 grabFramebuffer() 来获取它的内容(并将其写入磁盘)。小部件在可见时呈现良好,但在隐藏时不呈现。如果我先做一个 show() 然后再做一个 hide() 调用,它就可以工作。这看起来很奇怪,因为根据文档,QOpenGLWidget 确实在内部已经渲染到了帧缓冲区。实现此目的的最简单方法是什么(如果可能,无需创建另一个帧缓冲区)? 能够使用 QOpenGLWidget 作为其视口并在其中使用自定义 OpenGL 绘制的 QGraphicsItems 来捕获屏幕外 QGraphicsView 的奖励积分...
【问题讨论】:
【参考方案1】:更新 2:QOpenGLWidget 中的 corresponding bug 似乎在 Qt 5.10 中已修复,所以我建议再次使用该类。虽然您可能希望等待 this bug 也得到修复...更新 1:添加 3,使用自定义 QWindow 派生类的最佳解决方案
1 - QOpenGLWidget 如果隐藏的 QOpenGLWidget 确实分配了帧缓冲区(不确定是否发生这种情况),仍然无法手动绑定它,因为您无法获取缓冲区 id。此外,没有调用必要的函数 initializeGL()、resizeGL() 和paintGL,并且没有函数grab()、grabFramebuffer 和render() 正常工作。这是(imo)将小部件绘制到屏幕外的解决方法。在设置完所有必要的东西后直接调用paintGL:
class GLWidget: public QOpenGLWidget
public:
GLWidget(QWidget * parent = nullptr);
private:
bool m_isInitialized = false;
QOpenGLFramebufferObject m_fbo = nullptr;
;
void GLWidget::drawOffscreen()
//the context should be valid. make sure it is current for painting
makeCurrent();
if (!m_isInitialized)
initializeGL();
resizeGL(width(), height());
if (!m_fbo || m_fbo->width() != width() || m_fbo->height() != height())
//allocate additional? FBO for rendering or resize it if widget size changed
delete m_fbo;
QOpenGLFramebufferObjectFormat format;
format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
m_fbo = new QOpenGLFramebufferObject(width(), height(), format);
resizeGL(width(), height());
//#1 DOES NOT WORK: bind FBO and render() widget
m_fbo->bind();
QOpenGLPaintDevice fboPaintDev(width(), height());
QPainter painter(&fboPaintDev);
painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
render(&painter);
painter.end();
//You could now grab the content of the framebuffer we've rendered to
QImage image1 = m_fbo->toImage();
image1.save(QString("fb1.png"));
m_fbo->release();
//#1 --------------------------------------------------------------
//#2 WORKS: bind FBO and render stuff with paintGL() call
m_fbo->bind();
paintGL();
//You could now grab the content of the framebuffer we've rendered to
QImage image2 = m_fbo->toImage();
image2.save(QString("fb2.png"));
m_fbo->release();
//#2 --------------------------------------------------------------
//bind default framebuffer again. not sure if this necessary
//and isn't supposed to use defaultFramebuffer()...
m_fbo->bindDefault();
doneCurrent();
void GLWidget::paintGL()
//When doing mixed QPainter/OpenGL rendering make sure to use a QOpenGLPaintDevice, otherwise only OpenGL content is visible!
//I'm not sure why, because according to the docs (http://doc.qt.io/qt-5/topics-graphics.html) this is supposed to be the same...
QOpenGLPaintDevice fboPaintDev(width(), height());
QPainter painter(&fboPaintDev);
painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
//This is what you'd use (and what would work) if the widget was visible
//QPainter painter;
//painter.begin(this);
//now start OpenGL painting
painter.beginNativePainting();
glClearColor(0.5f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
...
painter.endNativePainting();
//draw non-OpenGL stuff with QPainter
painter.drawText(20, 40, "Foo");
...
painter.end();
2 - 带有 QOpenGLWidget 视口的 QGraphicsView 当您为它提供 QOpenGLPaintDevice 时,这里的 render() 会按预期工作:
MainWindow::MainWindow()
scene = new QGraphicsScene;
hiddenView = new QGraphicsView(scene);
hiddenGLWidget = new QOpenGLWidget;
hiddenView->setViewport(hiddenGLWidget);
//hiddenView->setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
//hiddenView->show();
void MainWindow::screenshot()
//try regular grab functions
QPixmap pixmap1 = hiddenView->grab(); //image with scrollbars, no OpenGL content
pixmap1.save("bla1.png");
QPixmap pixmap2 = hiddenGLWidget->grab(); //produces an empty image
pixmap2.save("bla2.png");
//try grabbing only the QOpenGLWidget framebuffer
QImage image1 = hiddenGLWidget->grabFramebuffer(); //null image
image1.save("bla3.png");
//WORKS: render via FBO
hiddenGLWidget->makeCurrent();
QOpenGLFramebufferObjectFormat format;
format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
QOpenGLFramebufferObject * fbo = new QOpenGLFramebufferObject(hiddenView->width(), hiddenView->height(), format);
fbo->bind();
QOpenGLPaintDevice fboPaintDev(hiddenView->width(), hiddenView->height());
QPainter painter(&fboPaintDev);
painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
hiddenView->render(&painter); //WORKS and captures mixed OpenGL and non-OpenGL QGraphicsitems
//hiddenView->repaint(); //does not work
//hiddenView->scene()->render(&painter); //does not work
//hiddenGLWidget->paintGL(); //might work. can not call, protected
//hiddenGLWidget->render(&painter); //does not work
//hiddenGLWidget->repaint(); //does not work
painter.end();
QImage image2 = fbo->toImage();
image2.save("bla4.png");
fbo->release();
delete fbo;
3 - 如何渲染到隐藏的 QOpenGLWidget 并从中抓取图像 更好的整体解决方案是使用具有 QSurface::OpenGLSurface 类型的自定义 QWindow。创建一个额外的 QOpenGLContext,一个额外的背景 QOpenGLFramebufferObject,你将绘制到,以及一个 QOpenGLShaderProgram 来将帧缓冲区 blit 到后台缓冲区。如果您想要多重采样,您可能还需要一个解析 QOpenGLFramebufferObject,将多重采样帧缓冲区转换为非多重采样帧缓冲区。 类接口可以类似于QOpenGLWidget(虚拟initializeGL()、resizeGL()、paintGL(),供用户使用)。重新实现 exposeEvent()、resizeEvent() 和 event()(您可能也需要重新实现 metric())。 一个半完整的实现:
标题:
#pragma once
#include <QtCore/QObject>
#include <QtGui/QScreen>
#include <QtGui/QWindow>
#include <QtGui/QPaintEvent>
#include <QtGui/QResizeEvent>
#include <QtGui/QOpenGLPaintDevice>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QOpenGLFunctions_3_0>
#include <QtGui/QOpenGLFramebufferObject>
#include <QtGui/QSurfaceFormat>
#include <QtWidgets/QWidget>
#include <atomic>
#include <mutex>
class MyGLWindow : public QWindow
Q_OBJECT
public:
/// @brief Constructor. Creates a render window.
/// @param targetScreen Target screen.
/// this is because before the FBO and off-screen surface haven't been created.
/// By default this uses the QWindow::requestedFormat() for OpenGL context and off-screen surface.
explicit MyGLWindow(QScreen * targetScreen = nullptr);
/// @brief Constructor. Creates a render window.
/// @param parent Parent window.
/// this is because before the FBO and off-screen surface haven't been created.
/// By default this uses the QWindow::requestedFormat() for OpenGL context and off-screen surface.
explicit MyGLWindow(QWindow * parent);
/// @brief Destructor.
virtual ~MyGLWindow();
/// @brief Create a container widget for this window.
/// @param parent Parent widget.
/// @return Returns a container widget for the window.
QWidget * createWidget(QWidget * parent = nullptr);
/// @brief Check if the window is initialized and can be used for rendering.
/// @return Returns true if context, surface and FBO have been set up to start rendering.
bool isValid() const;
/// @brief Return the context used in this window.
/// @return The context used in this window or nullptr if it hasn't been created yet.
QOpenGLContext * context() const;
/// @brief Return the OpenGL function object that can be used the issue OpenGL commands.
/// @return The functions for the context or nullptr if it the context hasn't been created yet.
QOpenGLFunctions * functions() const;
/// @brief Return the OpenGL off-screen frame buffer object identifier.
/// @return The OpenGL off-screen frame buffer object identifier or 0 if no FBO has been created yet.
/// @note This changes on every resize!
GLuint framebufferObjectHandle() const;
/// @brief Return the OpenGL off-screen frame buffer object.
/// @return The OpenGL off-screen frame buffer object or nullptr if no FBO has been created yet.
/// @note This changes on every resize!
const QOpenGLFramebufferObject * getFramebufferObject() const;
/// @brief Return the OpenGL off-screen frame buffer object identifier.
/// @return The OpenGL off-screen frame buffer object identifier or 0 if no FBO has been created yet.
void bindFramebufferObject();
/// @brief Return the current contents of the FBO.
/// @return FBO content as 32bit QImage. You might need to swap RGBA to BGRA or vice-versa.
QImage grabFramebuffer();
/// @brief Makes the OpenGL context current for rendering.
/// @note Make sure to bindFramebufferObject() if you want to render to this widgets FBO.
void makeCurrent();
/// @brief Release the OpenGL context.
void doneCurrent();
/// @brief Copy content of framebuffer to back buffer and swap buffers if the surface is double-buffered.
/// If the surface is not double-buffered, the frame buffer content is blitted to the front buffer.
/// If the window is not exposed, only the OpenGL pipeline is glFlush()ed so the framebuffer can be read back.
void swapBuffers();
public slots:
/// @brief Lazy update routine like QWidget::update().
void update();
/// @brief Immediately render the widget contents to framebuffer.
void render();
signals:
/// @brief Emitted when swapBuffers() was called and bufferswapping is done.
void frameSwapped();
/// @brief Emitted after a resizeEvent().
void resized();
protected:
virtual void exposeEvent(QExposeEvent *e) override;
virtual void resizeEvent(QResizeEvent *e) override;
virtual bool event(QEvent *e) override;
// virtual int metric(QPaintDevice::PaintDeviceMetric metric) const override;
/// @brief Called exactly once when the window is first exposed OR render() is called when the widget is invisible.
/// @note After this the off-screen surface and FBO are available.
virtual void initializeGL() = 0;
/// @brief Called whenever the window size changes.
/// @param width New window width.
/// @param height New window height.
virtual void resizeGL(int width, int height) = 0;
/// @brief Called whenever the window needs to repaint itself. Override to draw OpenGL content.
/// When this function is called, the context is already current and the correct framebuffer is bound.
virtual void paintGL() = 0;
// /// @brief Called whenever the window needs to repaint itself. Override to draw QPainter content.
// /// @brief This is called AFTER paintGL()! Only needed when painting using a QPainter.
// virtual void paintEvent(QPainter & painter) = 0;
private:
Q_DISABLE_COPY(QGLWindow)
/// @brief Initialize the window.
void initializeInternal();
/// @brief Internal method that does the actual swap work, NOT using a mutex.
void swapBuffersInternal();
/// @brief Internal method that checks state and makes the context current, NOT using a mutex.
void makeCurrentInternal();
/// @brief Internal method to grab content of a specific framebuffer.
QImage grabFramebufferInternal(QOpenGLFramebufferObject * fbo);
/// @brief (Re-)allocate FBO and paint device if needed due to size changes etc.
void recreateFBOAndPaintDevice();
/// @brief False before the window was first exposed OR render() was called.
std::atomic_bool m_initialized;
/// @brief False before the overridden initializeGL() was first called.
bool m_initializedGL = false;
/// @brief True when currently a window update is pending.
std::atomic_bool m_updatePending;
/// @brief Mutex making sure not grabbing while drawing etc.
std::mutex m_mutex;
/// @brief OpenGL render context.
QOpenGLContext * m_context = nullptr;
/// @brief The OpenGL 2.1 / ES 2.0 function object that can be used the issue OpenGL commands.
QOpenGLFunctions * m_functions = nullptr;
/// @brief The OpenGL 3.0 function object that can be used the issue OpenGL commands.
QOpenGLFunctions_3_0 * m_functions_3_0 = nullptr;
/// @brief OpenGL paint device for painting with a QPainter.
QOpenGLPaintDevice * m_paintDevice = nullptr;
/// @brief Background FBO for off-screen rendering when the window is not exposed.
QOpenGLFramebufferObject * m_fbo = nullptr;
/// @brief Background FBO resolving a multi sampling frame buffer in m_fbo to a frame buffer
/// that can be grabbed to a QImage.
QOpenGLFramebufferObject * m_resolvedFbo = nullptr;
/// @brief Shader used for blitting m_fbo to screen if glBlitFrameBuffer is not available.
QOpenGLShaderProgram * m_blitShader;
;
来源:
#include "MyGLWindow.h"
#include <QtCore/QCoreApplication>
#include <QtGui/QPainter>
MyGLWindow::MyGLWindow(QScreen * targetScreen)
: QWindow(targetScreen)
//Set Qt::Widget flag to make sure the window resizes properly the first time
//when used as a widget via MyGLWindow::createWidget()!
setFlags(Qt::Widget);
setSurfaceType(QSurface::OpenGLSurface);
setFormat(QGLInfo::DefaultSurfaceFormat());
m_initialized = false;
m_updatePending = false;
create();
initializeInternal();
MyGLWindow::MyGLWindow(QWindow * parent)
: QWindow(parent)
//Set Qt::Widget flag to make sure the window resizes properly the first time
//when used as a widget via MyGLWindow::createWidget()!
setFlags(Qt::Widget);
setSurfaceType(QSurface::OpenGLSurface);
setFormat(QGLInfo::DefaultSurfaceFormat());
m_initialized = false;
m_updatePending = false;
create();
initializeInternal();
MyGLWindow::~MyGLWindow()
//to delete the FBOs we first need to make the context current
m_context->makeCurrent(this);
//destroy framebuffer objects
if (m_fbo)
m_fbo->release();
delete m_fbo;
m_fbo = nullptr;
if (m_resolvedFbo)
m_resolvedFbo->release();
delete m_resolvedFbo;
m_resolvedFbo = nullptr;
//destroy shader
delete m_blitShader;
m_blitShader = nullptr;
//free context
m_context->doneCurrent();
delete m_context;
m_context = nullptr;
//free paint device
delete m_paintDevice;
m_paintDevice = nullptr;
m_initialized = false;
m_updatePending = false;
QWidget * MyGLWindow::createWidget(QWidget * parent)
QWidget * container = QWidget::createWindowContainer(this, parent);
return container;
QOpenGLContext * MyGLWindow::context() const
return m_context;
QOpenGLFunctions * MyGLWindow::functions() const
return m_functions;
GLuint MyGLWindow::framebufferObjectHandle() const
return m_fbo ? m_fbo->handle() : 0;
const QOpenGLFramebufferObject * MyGLWindow::getFramebufferObject() const
return m_fbo;
void MyGLWindow::bindFramebufferObject()
if (m_fbo)
m_fbo->bind();
else
QOpenGLFramebufferObject::bindDefault();
bool MyGLWindow::isValid() const
return (m_initialized && m_context && m_fbo);
void MyGLWindow::makeCurrent()
makeCurrentInternal();
void MyGLWindow::makeCurrentInternal()
if (isValid())
m_context->makeCurrent(this);
else
throw("MyGLWindow::makeCurrent() - Window not yet properly initialized!");
void MyGLWindow::doneCurrent()
if (m_context)
m_context->doneCurrent();
QImage MyGLWindow::grabFramebuffer()
std::lock_guard<std::mutex> locker(m_mutex);
makeCurrentInternal();
//blit framebuffer to resolve framebuffer first if needed
if (m_fbo->format().samples() > 0)
//check if we have glFrameBufferBlit support. this is true for desktop OpenGL 3.0+, but not OpenGL ES 2.0
if (m_functions_3_0)
//only blit the color buffer attachment
m_functions_3_0->glBindFramebuffer(GL_READ_FRAMEBUFFER, m_fbo->handle());
m_functions_3_0->glBindFramebuffer(GL_DRAW_FRAMEBUFFER, m_resolvedFbo->handle());
m_functions_3_0->glBlitFramebuffer(0, 0, width(), height(), 0, 0, width(), height(),
GL_COLOR_BUFFER_BIT,
GL_NEAREST);
m_functions_3_0->glBindFramebuffer(GL_FRAMEBUFFER, 0);
else
//we must unbind the FBO here, so we can use its texture and bind the default back-buffer
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_resolvedFbo->handle());
//now use its texture for drawing in the shader
--> bind shader and draw textured quad here
//bind regular FBO again
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
//check if OpenGL errors happened
if (GLenum error = m_functions->glGetError() != GL_NO_ERROR)
qDebug() << "MyGLWindow::grabFramebuffer() - OpenGL error" << error;
//now grab from resolve FBO
return grabFramebufferInternal(m_resolvedFbo);
else
//no multi-sampling. grab directly from FBO
return grabFramebufferInternal(m_fbo);
QImage MyGLWindow::grabFramebufferInternal(QOpenGLFramebufferObject * fbo)
QImage image;
//bind framebuffer first
m_functions->glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo->handle());
if (m_functions_3_0)
m_functions_3_0->glReadBuffer(GL_COLOR_ATTACHMENT0);
GLenum internalFormat = fbo->format().internalTextureFormat();
bool hasAlpha = internalFormat == GL_RGBA || internalFormat == GL_BGRA || internalFormat == GL_RGBA8;
if (internalFormat == GL_BGRA)
image = QImage(fbo->size(), hasAlpha ? QImage::Format_ARGB32 : QImage::Format_RGB32);
m_functions->glReadPixels(0, 0, fbo->size().width(), fbo->size().height(), GL_BGRA, GL_UNSIGNED_BYTE, image.bits());
else if (internalFormat == GL_RGBA || internalFormat == GL_RGBA8)
image = QImage(fbo->size(), hasAlpha ? QImage::Format_RGBA8888 : QImage::Format_RGBX8888);
m_functions->glReadPixels(0, 0, fbo->size().width(), fbo->size().height(), GL_RGBA, GL_UNSIGNED_BYTE, image.bits());
else
qDebug() << "MyGLWindow::grabFramebuffer() - Unsupported framebuffer format" << internalFormat << "!";
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
return image.mirrored();
void MyGLWindow::swapBuffers()
swapBuffersInternal();
emit frameSwapped();
void MyGLWindow::swapBuffersInternal()
if (isExposed() && isVisible())
//blit framebuffer to back buffer
m_context->makeCurrent(this);
//make sure all paint operation have been processed
m_functions->glFlush();
//check if we have glFrameBufferBlit support. this is true for desktop OpenGL 3.0+, but not OpenGL ES 2.0
if (m_functions_3_0)
//if our framebuffer has multi-sampling, the resolve should be done automagically
m_functions_3_0->glBindFramebuffer(GL_READ_FRAMEBUFFER, m_fbo->handle());
m_functions_3_0->glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
//blit all buffers including depth buffer for further rendering
m_functions_3_0->glBlitFramebuffer(0, 0, width(), height(), 0, 0, width(), height(),
GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT,
GL_NEAREST);
m_functions_3_0->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
else
//we must unbind the FBO here, so we can use its texture and bind the default back-buffer
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, 0);
//now use its texture for drawing in the shader
--> bind shader and draw textured quad here
//bind regular FBO again
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
//check if OpenGL errors happened
if (GLenum error = m_functions->glGetError() != GL_NO_ERROR)
qDebug() << "MyGLWindow::swapBuffersInternal() - OpenGL error" << error;
//now swap back buffer to front buffer
m_context->swapBuffers(this);
else
//not visible. only flush the pipeline so we can possibly grab the FBO later
m_context->makeCurrent(this);
m_functions->glFlush();
void MyGLWindow::recreateFBOAndPaintDevice()
const QSize deviceSize = size() * devicePixelRatio();
if (m_context && (m_fbo == nullptr || m_fbo->size() != deviceSize))
m_context->makeCurrent(this);
//free old FBOs
if (m_fbo)
m_fbo->release();
delete m_fbo;
m_fbo = nullptr;
if (m_resolvedFbo)
m_resolvedFbo->release();
delete m_resolvedFbo;
m_resolvedFbo = nullptr;
//create new frame buffer
QOpenGLFramebufferObjectFormat format = QGLInfo::DefaultFramebufferFormat();
format.setSamples(QGLInfo::HasMultisamplingSupport(m_context) ? 4 : 0);
m_fbo = new QOpenGLFramebufferObject(deviceSize, format);
if (!m_fbo->isValid())
throw("MyGLWindow::recreateFbo() - Failed to create background FBO!");
//clear framebuffer
m_fbo->bind();
m_functions->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
m_fbo->release();
//if multi sampling is requested and supported we need a resolve FBO
if (format.samples() > 0)
//create resolve framebuffer with only a color attachment
format.setAttachment(QOpenGLFramebufferObject::NoAttachment);
format.setSamples(0);
m_resolvedFbo = new QOpenGLFramebufferObject(deviceSize, format);
if (!m_resolvedFbo->isValid())
throw("MyGLWindow::recreateFbo() - Failed to create resolve FBO!");
//clear resolve framebuffer
m_resolvedFbo->bind();
m_functions->glClear(GL_COLOR_BUFFER_BIT);
m_resolvedFbo->release();
//create paint device for painting with QPainter if needed
if (!m_paintDevice)
m_paintDevice = new QOpenGLPaintDevice;
//update paint device size if needed
if (m_paintDevice->size() != deviceSize)
m_paintDevice->setDevicePixelRatio(devicePixelRatio());
m_paintDevice->setSize(deviceSize);
void MyGLWindow::initializeInternal()
if (!m_initialized.exchange(true))
//create OpenGL context. we set the format requested by the user (default: QWindow::requestedFormat())
m_context = new QOpenGLContext(this);
m_context->setFormat(format());
if (m_context->create())
m_context->makeCurrent(this);
//initialize the OpenGL 2.1 / ES 2.0 functions for this object
m_functions = m_context->functions();
m_functions->initializeOpenGLFunctions();
//try initializing the OpenGL 3.0 functions for this object
m_functions_3_0 = m_context->versionFunctions<QOpenGLFunctions_3_0>();
if (m_functions_3_0)
m_functions_3_0->initializeOpenGLFunctions();
else
//if we do not have OpenGL 3.0 functions, glBlitFrameBuffer is not available, so we must do the blit
//using a shader and the framebuffer texture, so we need to create the shader here...
--> allocate m_blitShader, a simple shader for drawing a textured quad
--> build quad geometry, VBO, whatever
//now we have a context, create the FBO
recreateFBOAndPaintDevice();
else
m_initialized = false;
delete m_context;
m_context = nullptr;
throw("Failed to create OpenGL context!");
void MyGLWindow::update()
//only queue an update if there's not already an update pending
if (!m_updatePending.exchange(true))
QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
void MyGLWindow::render()
std::lock_guard<std::mutex> locker(m_mutex);
//check if we need to initialize stuff
initializeInternal();
//check if we need to call the user initialization
if (!m_initializedGL)
m_initializedGL = true;
initializeGL();
//make context current and bind framebuffer
makeCurrent();
bindFramebufferObject();
//call user paint function
paintGL();
doneCurrent();
//mark that we're done with updating
m_updatePending = false;
void MyGLWindow::exposeEvent(QExposeEvent * e)
//call base implementation
QWindow::exposeEvent(e);
//render window content if window is exposed
if (isExposed()/* && isVisible()*/)
render();
void MyGLWindow::resizeEvent(QResizeEvent *e)
//call base implementation
QWindow::resizeEvent(e);
m_mutex.lock();
//make context current first
makeCurrent();
//update FBO and paint device
recreateFBOAndPaintDevice();
m_mutex.unlock();
//call user-defined resize method
resizeGL(e->size().width(), e->size().height());
emit resized();
bool MyGLWindow::event(QEvent *event)
switch (event->type())
case QEvent::UpdateLater:
update();
return true;
case QEvent::UpdateRequest:
render();
return true;
default:
return QWindow::event(event);
【讨论】:
我知道这是一篇旧文章,但我正在尝试了解它是如何工作的,据我从发布的代码中可以看出,方法 drawOffscreen 不包含在类原型中,实际上从未包含叫?你能帮忙吗? The "bug" is fixed in Qt 5.10 now,所以我会走 QOpenGLWidget 路线并忽略 #1 和 #2。如果您想滚动自己的窗口/小部件,请使用 #3 或查看 Nikita Feodonits 的答案。 问题: 1. 如果我使用#1,我是否需要运行 QApplication 或 QGuiApplication 或者如果没有这些,它是否真的会按需绘制? 2. 如果我只使用原生 gl 函数,我必须在 paintGL 中使用 QPainter 吗? @Geronimo:首先:使用已修复错误的 Qt 版本!如果你不能: 1. 很可能。 2. 不,你为什么要这样做。 如果想用 PySide2 选择选项 2,不要尝试实现它。 PySide2 缺少 QOpenGLPaintDevice:bugreports.qt.io/browse/PYSIDE-1090 只有 PySide6 暴露了它。【参考方案2】:对于屏幕外渲染,我们也可以使用QOffscreenSurface。
这是基于 Bim 的 MyGLWindow 的工作类(并非所有都经过测试):
标头OpenGlOffscreenSurface.h
:
#ifndef OPENGLOFFSCREENSURFACE_H
#define OPENGLOFFSCREENSURFACE_H
#pragma once
#include <QtCore/QObject>
#include <QtGui/QScreen>
#include <QtGui/QOffscreenSurface>
#include <QtGui/QPaintEvent>
#include <QtGui/QResizeEvent>
#include <QtGui/QOpenGLPaintDevice>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QOpenGLFunctions_3_0>
#include <QtGui/QOpenGLFramebufferObject>
#include <QtGui/QSurfaceFormat>
#include <QtWidgets/QWidget>
#include <QOpenGLShaderProgram>
#include <atomic>
#include <mutex>
class OpenGlOffscreenSurface
: public QOffscreenSurface
Q_OBJECT
public:
/// @brief Constructor. Creates a render window.
/// @param targetScreen Target screen.
/// @param size Initial size of a surface buffer.
/// this is because before the FBO and off-screen surface haven't been created.
/// By default this uses the QWindow::requestedFormat() for OpenGL context and off-screen
/// surface.
explicit OpenGlOffscreenSurface(
QScreen* targetScreen = nullptr,
const QSize& size = QSize (1, 1));
/// @brief Destructor.
virtual ~OpenGlOffscreenSurface();
/// @brief Check if the window is initialized and can be used for rendering.
/// @return Returns true if context, surface and FBO have been set up to start rendering.
bool isValid() const;
/// @brief Return the context used in this window.
/// @return The context used in this window or nullptr if it hasn't been created yet.
QOpenGLContext* context() const;
/// @brief Return the OpenGL function object that can be used the issue OpenGL commands.
/// @return The functions for the context or nullptr if it the context hasn't been created yet.
QOpenGLFunctions* functions() const;
/// @brief Return the OpenGL off-screen frame buffer object identifier.
/// @return The OpenGL off-screen frame buffer object identifier or 0 if no FBO has been created
/// yet.
/// @note This changes on every resize!
GLuint framebufferObjectHandle() const;
/// @brief Return the OpenGL off-screen frame buffer object.
/// @return The OpenGL off-screen frame buffer object or nullptr if no FBO has been created yet.
/// @note This changes on every resize!
const QOpenGLFramebufferObject* getFramebufferObject() const;
/// @brief Return the QPaintDevice for paint into it.
QPaintDevice* getPaintDevice() const;
/// @brief Return the OpenGL off-screen frame buffer object identifier.
/// @return The OpenGL off-screen frame buffer object identifier or 0 if no FBO has been created
/// yet.
void bindFramebufferObject();
/// @brief Return the current contents of the FBO.
/// @return FBO content as 32bit QImage. You might need to swap RGBA to BGRA or vice-versa.
QImage grabFramebuffer();
/// @brief Makes the OpenGL context current for rendering.
/// @note Make sure to bindFramebufferObject() if you want to render to this widgets FBO.
void makeCurrent();
/// @brief Release the OpenGL context.
void doneCurrent();
/// @brief Copy content of framebuffer to back buffer and swap buffers if the surface is
/// double-buffered.
/// If the surface is not double-buffered, the frame buffer content is blitted to the front
/// buffer.
/// If the window is not exposed, only the OpenGL pipeline is glFlush()ed so the framebuffer can
/// be read back.
void swapBuffers();
/// @brief Use bufferSize() instead size() for get a size of a surface buffer. We can't override size() as it is not virtual.
QSize bufferSize() const;
/// @brief Resize surface buffer to newSize.
void resize(const QSize& newSize);
/// @brief Resize surface buffer to size with width w and height h.
/// @param w Width.
/// @param h Height.
void resize(int w, int h);
public slots:
/// @brief Lazy update routine like QWidget::update().
void update();
/// @brief Immediately render the widget contents to framebuffer.
void render();
signals:
/// @brief Emitted when swapBuffers() was called and bufferswapping is done.
void frameSwapped();
/// @brief Emitted after a resizeEvent().
void resized();
protected:
virtual void exposeEvent(QExposeEvent* e);
virtual void resizeEvent(QResizeEvent* e);
virtual bool event(QEvent* e) override;
// virtual int metric(QPaintDevice::PaintDeviceMetric metric) const override;
/// @brief Called exactly once when the window is first exposed OR render() is called when the
/// widget is invisible.
/// @note After this the off-screen surface and FBO are available.
virtual void initializeGL() = 0;
/// @brief Called whenever the window size changes.
/// @param width New window width.
/// @param height New window height.
virtual void resizeGL(
int width,
int height) = 0;
/// @brief Called whenever the window needs to repaint itself. Override to draw OpenGL content.
/// When this function is called, the context is already current and the correct framebuffer is
/// bound.
virtual void paintGL() = 0;
// /// @brief Called whenever the window needs to repaint itself. Override to draw QPainter
// content.
// /// @brief This is called AFTER paintGL()! Only needed when painting using a QPainter.
// virtual void paintEvent(QPainter & painter) = 0;
private:
Q_DISABLE_COPY(OpenGlOffscreenSurface)
/// @brief Initialize the window.
void initializeInternal();
/// @brief Internal method that does the actual swap work, NOT using a mutex.
void swapBuffersInternal();
/// @brief Internal method that checks state and makes the context current, NOT using a mutex.
void makeCurrentInternal();
/// @brief Internal method to grab content of a specific framebuffer.
QImage grabFramebufferInternal(QOpenGLFramebufferObject* fbo);
/// @brief (Re-)allocate FBO and paint device if needed due to size changes etc.
void recreateFBOAndPaintDevice();
/// @brief False before the window was first exposed OR render() was called.
std::atomic_bool m_initialized;
/// @brief False before the overridden initializeGL() was first called.
bool m_initializedGL = false;
/// @brief True when currently a window update is pending.
std::atomic_bool m_updatePending;
/// @brief Mutex making sure not grabbing while drawing etc.
std::mutex m_mutex;
/// @brief OpenGL render context.
QOpenGLContext* m_context = nullptr;
/// @brief The OpenGL 2.1 / ES 2.0 function object that can be used the issue OpenGL commands.
QOpenGLFunctions* m_functions = nullptr;
/// @brief The OpenGL 3.0 function object that can be used the issue OpenGL commands.
QOpenGLFunctions_3_0* m_functions_3_0 = nullptr;
/// @brief OpenGL paint device for painting with a QPainter.
QOpenGLPaintDevice* m_paintDevice = nullptr;
/// @brief Background FBO for off-screen rendering when the window is not exposed.
QOpenGLFramebufferObject* m_fbo = nullptr;
/// @brief Background FBO resolving a multi sampling frame buffer in m_fbo to a frame buffer
/// that can be grabbed to a QImage.
QOpenGLFramebufferObject* m_resolvedFbo = nullptr;
/// @brief Shader used for blitting m_fbo to screen if glBlitFrameBuffer is not available.
QOpenGLShaderProgram* m_blitShader;
QSize m_size;
;
#endif // OPENGLOFFSCREENSURFACE_H
来源OpenGlOffscreenSurface.cpp
:
#include "OpenGlOffscreenSurface.h"
#include <QtCore/QCoreApplication>
#include <QtGui/QPainter>
OpenGlOffscreenSurface::OpenGlOffscreenSurface(
QScreen* targetScreen,
const QSize& size)
: QOffscreenSurface(targetScreen)
, m_size(size)
setFormat(QSurfaceFormat::defaultFormat());
m_initialized = false;
m_updatePending = false;
create(); // Some platforms require this function to be called on the main (GUI) thread
initializeInternal();
OpenGlOffscreenSurface::~OpenGlOffscreenSurface()
// to delete the FBOs we first need to make the context current
m_context->makeCurrent(this);
// destroy framebuffer objects
if (m_fbo)
m_fbo->release();
delete m_fbo;
m_fbo = nullptr;
if (m_resolvedFbo)
m_resolvedFbo->release();
delete m_resolvedFbo;
m_resolvedFbo = nullptr;
// destroy shader
delete m_blitShader;
m_blitShader = nullptr;
// free context
m_context->doneCurrent();
delete m_context;
m_context = nullptr;
// free paint device
delete m_paintDevice;
m_paintDevice = nullptr;
m_initialized = false;
m_updatePending = false;
destroy();
QOpenGLContext* OpenGlOffscreenSurface::context() const
return (m_context);
QOpenGLFunctions* OpenGlOffscreenSurface::functions() const
return (m_functions);
GLuint OpenGlOffscreenSurface::framebufferObjectHandle() const
return (m_fbo ? m_fbo->handle() : 0);
const QOpenGLFramebufferObject* OpenGlOffscreenSurface::getFramebufferObject() const
return (m_fbo);
QPaintDevice* OpenGlOffscreenSurface::getPaintDevice() const
return (m_paintDevice);
void OpenGlOffscreenSurface::bindFramebufferObject()
if (m_fbo)
m_fbo->bind();
else
QOpenGLFramebufferObject::bindDefault();
bool OpenGlOffscreenSurface::isValid() const
return (m_initialized && m_context && m_fbo);
void OpenGlOffscreenSurface::makeCurrent()
makeCurrentInternal();
void OpenGlOffscreenSurface::makeCurrentInternal()
if (isValid())
m_context->makeCurrent(this);
else
throw ("OpenGlOffscreenSurface::makeCurrent() - Window not yet properly initialized!");
void OpenGlOffscreenSurface::doneCurrent()
if (m_context)
m_context->doneCurrent();
QImage OpenGlOffscreenSurface::grabFramebuffer()
std::lock_guard <std::mutex> locker(m_mutex);
makeCurrentInternal();
// blit framebuffer to resolve framebuffer first if needed
if (m_fbo->format().samples() > 0)
// check if we have glFrameBufferBlit support. this is true for desktop OpenGL 3.0+, but not
// OpenGL ES 2.0
if (m_functions_3_0)
// only blit the color buffer attachment
m_functions_3_0->glBindFramebuffer(GL_READ_FRAMEBUFFER, m_fbo->handle());
m_functions_3_0->glBindFramebuffer(GL_DRAW_FRAMEBUFFER, m_resolvedFbo->handle());
m_functions_3_0->glBlitFramebuffer(0, 0, bufferSize().width(),
bufferSize().height(), 0, 0, bufferSize().width(),
bufferSize().height(), GL_COLOR_BUFFER_BIT, GL_NEAREST);
m_functions_3_0->glBindFramebuffer(GL_FRAMEBUFFER, 0);
else
// we must unbind the FBO here, so we can use its texture and bind the default
// back-buffer
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_resolvedFbo->handle());
// now use its texture for drawing in the shader
// --> bind shader and draw textured quad here
// bind regular FBO again
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
// check if OpenGL errors happened
if (GLenum error = m_functions->glGetError() != GL_NO_ERROR)
qDebug() << "OpenGlOffscreenSurface::grabFramebuffer() - OpenGL error" << error;
// now grab from resolve FBO
return (grabFramebufferInternal(m_resolvedFbo));
else
// no multi-sampling. grab directly from FBO
return (grabFramebufferInternal(m_fbo));
// OpenGlOffscreenSurface::grabFramebuffer
QImage OpenGlOffscreenSurface::grabFramebufferInternal(QOpenGLFramebufferObject* fbo)
QImage image;
// bind framebuffer first
m_functions->glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo->handle());
if (m_functions_3_0)
m_functions_3_0->glReadBuffer(GL_COLOR_ATTACHMENT0);
GLenum internalFormat = fbo->format().internalTextureFormat();
bool hasAlpha = internalFormat == GL_RGBA || internalFormat == GL_BGRA
|| internalFormat == GL_RGBA8;
if (internalFormat == GL_BGRA)
image = QImage(fbo->size(), hasAlpha ? QImage::Format_ARGB32 : QImage::Format_RGB32);
m_functions->glReadPixels(0, 0, fbo->size().width(),
fbo->size().height(), GL_BGRA, GL_UNSIGNED_BYTE, image.bits());
else if ((internalFormat == GL_RGBA) || (internalFormat == GL_RGBA8))
image = QImage(fbo->size(), hasAlpha ? QImage::Format_RGBA8888 : QImage::Format_RGBX8888);
m_functions->glReadPixels(0, 0, fbo->size().width(),
fbo->size().height(), GL_RGBA, GL_UNSIGNED_BYTE, image.bits());
else
qDebug() << "OpenGlOffscreenSurface::grabFramebuffer() - Unsupported framebuffer format"
<< internalFormat << "!";
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
return (image.mirrored());
// OpenGlOffscreenSurface::grabFramebufferInternal
void OpenGlOffscreenSurface::swapBuffers()
swapBuffersInternal();
emit frameSwapped();
void OpenGlOffscreenSurface::swapBuffersInternal()
// blit framebuffer to back buffer
m_context->makeCurrent(this);
// make sure all paint operation have been processed
m_functions->glFlush();
// check if we have glFrameBufferBlit support. this is true for desktop OpenGL 3.0+, but not
// OpenGL ES 2.0
if (m_functions_3_0)
// if our framebuffer has multi-sampling, the resolve should be done automagically
m_functions_3_0->glBindFramebuffer(GL_READ_FRAMEBUFFER, m_fbo->handle());
m_functions_3_0->glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
// blit all buffers including depth buffer for further rendering
m_functions_3_0->glBlitFramebuffer(0, 0, bufferSize().width(),
bufferSize().height(), 0, 0, bufferSize().width(),
bufferSize().height(), GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT,
GL_NEAREST);
m_functions_3_0->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
else
// we must unbind the FBO here, so we can use its texture and bind the default back-buffer
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, 0);
// now use its texture for drawing in the shader
// --> bind shader and draw textured quad here
// bind regular FBO again
m_functions->glBindFramebuffer(GL_FRAMEBUFFER, m_fbo->handle());
// check if OpenGL errors happened
if (GLenum error = m_functions->glGetError() != GL_NO_ERROR)
qDebug() << "OpenGlOffscreenSurface::swapBuffersInternal() - OpenGL error" << error;
// now swap back buffer to front buffer
m_context->swapBuffers(this);
// OpenGlOffscreenSurface::swapBuffersInternal
void OpenGlOffscreenSurface::recreateFBOAndPaintDevice()
if (m_context && ((m_fbo == nullptr) || (m_fbo->size() != bufferSize())))
m_context->makeCurrent(this);
// free old FBOs
if (m_fbo)
m_fbo->release();
delete m_fbo;
m_fbo = nullptr;
if (m_resolvedFbo)
m_resolvedFbo->release();
delete m_resolvedFbo;
m_resolvedFbo = nullptr;
// create new frame buffer
// QOpenGLFramebufferObjectFormat format = QGLInfo::DefaultFramebufferFormat();
// format.setSamples(QGLInfo::HasMultisamplingSupport(m_context) ? 4 : 0);
QOpenGLFramebufferObjectFormat format;
format.setSamples(0);
m_fbo = new QOpenGLFramebufferObject(bufferSize(), format);
if (!m_fbo->isValid())
throw ("OpenGlOffscreenSurface::recreateFbo() - Failed to create background FBO!");
// clear framebuffer
m_fbo->bind();
m_functions->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
m_fbo->release();
// if multi sampling is requested and supported we need a resolve FBO
if (format.samples() > 0)
// create resolve framebuffer with only a color attachment
format.setAttachment(QOpenGLFramebufferObject::NoAttachment);
format.setSamples(0);
m_resolvedFbo = new QOpenGLFramebufferObject(bufferSize(), format);
if (!m_resolvedFbo->isValid())
throw ("OpenGlOffscreenSurface::recreateFbo() - Failed to create resolve FBO!");
// clear resolve framebuffer
m_resolvedFbo->bind();
m_functions->glClear(GL_COLOR_BUFFER_BIT);
m_resolvedFbo->release();
// create paint device for painting with QPainter if needed
if (!m_paintDevice)
m_paintDevice = new QOpenGLPaintDevice;
// update paint device size if needed
if (m_paintDevice->size() != bufferSize())
m_paintDevice->setSize(bufferSize());
// OpenGlOffscreenSurface::recreateFBOAndPaintDevice
void OpenGlOffscreenSurface::initializeInternal()
if (!m_initialized.exchange(true))
// create OpenGL context. we set the format requested by the user (default:
// QWindow::requestedFormat())
m_context = new QOpenGLContext(this);
m_context->setFormat(format());
if (m_context->create())
m_context->makeCurrent(this);
// initialize the OpenGL 2.1 / ES 2.0 functions for this object
m_functions = m_context->functions();
m_functions->initializeOpenGLFunctions();
// try initializing the OpenGL 3.0 functions for this object
m_functions_3_0 = m_context->versionFunctions <QOpenGLFunctions_3_0>();
if (m_functions_3_0)
m_functions_3_0->initializeOpenGLFunctions();
else
// if we do not have OpenGL 3.0 functions, glBlitFrameBuffer is not available, so we
// must do the blit
// using a shader and the framebuffer texture, so we need to create the shader
// here...
// --> allocate m_blitShader, a simple shader for drawing a textured quad
// --> build quad geometry, VBO, whatever
// now we have a context, create the FBO
recreateFBOAndPaintDevice();
else
m_initialized = false;
delete m_context;
m_context = nullptr;
throw ("Failed to create OpenGL context!");
// OpenGlOffscreenSurface::initializeInternal
void OpenGlOffscreenSurface::update()
// only queue an update if there's not already an update pending
if (!m_updatePending.exchange(true))
QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
void OpenGlOffscreenSurface::render()
std::lock_guard <std::mutex> locker(m_mutex);
// check if we need to initialize stuff
initializeInternal();
// check if we need to call the user initialization
// makeCurrent(); // TODO: may be makeCurrent() must be here, as noted for QOpenGLWidget.initializeGL()
if (!m_initializedGL)
m_initializedGL = true;
initializeGL();
// make context current and bind framebuffer
makeCurrent();
bindFramebufferObject();
// call user paint function
paintGL();
doneCurrent();
// mark that we're done with updating
m_updatePending = false;
// OpenGlOffscreenSurface::render
void OpenGlOffscreenSurface::exposeEvent(QExposeEvent* e)
// render window content if window is exposed
render();
// OpenGlOffscreenSurface::exposeEvent
void OpenGlOffscreenSurface::resizeEvent(QResizeEvent* e)
// call base implementation
resize(e->size());
emit resized();
void OpenGlOffscreenSurface::resize(const QSize& newSize)
m_mutex.lock();
// make context current first
makeCurrent();
m_size = QSize(newSize);
// update FBO and paint device
recreateFBOAndPaintDevice();
m_mutex.unlock();
// call user-defined resize method
resizeGL(bufferSize().width(), bufferSize().height());
// OpenGlOffscreenSurface::resize
void OpenGlOffscreenSurface::resize(
int w,
int h)
resize(QSize(w, h));
bool OpenGlOffscreenSurface::event(QEvent* event)
switch (event->type())
case QEvent::UpdateLater:
update();
return (true);
case QEvent::UpdateRequest:
render();
return (true);
default:
return (false);
// switch
// OpenGlOffscreenSurface::event
QSize OpenGlOffscreenSurface::bufferSize() const
return (m_size);
使用OpenGlOffscreenSurface
:
标头ExamplePaintSurface.h
:
#ifndef EXAMPLEPAINTSURFACE_H
#define EXAMPLEPAINTSURFACE_H
#include "OpenGlOffscreenSurface.h"
class ExamplePaintSurface
: public OpenGlOffscreenSurface
public:
explicit ExamplePaintSurface(
QScreen* targetScreen = nullptr,
const QSize& size = QSize (1, 1));
virtual ~ExamplePaintSurface() override;
protected:
virtual void initializeGL() override;
virtual void resizeGL(
int width,
int height) override;
virtual void paintGL() override;
;
#endif // EXAMPLEPAINTSURFACE_H
来源ExamplePaintSurface.cpp
:
#include "ExamplePaintSurface.h"
#include <QPainter>
ExamplePaintSurface::ExamplePaintSurface(
QScreen* targetScreen,
const QSize& size)
: OpenGlOffscreenSurface(targetScreen, size)
ExamplePaintSurface::~ExamplePaintSurface()
void ExamplePaintSurface::initializeGL()
void ExamplePaintSurface::resizeGL(int width, int height)
void ExamplePaintSurface::paintGL()
QPainter painter(getPaintDevice());
painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
painter.drawText(20, 40, "Test"); // <-- drawing here
painter.end();
来源main.cpp
:
#include <QApplication>
#include "ExamplePaintSurface.h"
int main(int argc, char *argv[])
QApplication a(argc, argv);
ExamplePaintSurface paintSurface;
paintSurface.resize(300, 200);
paintSurface.render();
QImage image = paintSurface.grabFramebuffer();
image.save(QString("image.png"));
return a.exec();
带有QOffscreenSurface 的部分示例来自here:
#include <QGuiApplication>
#include <QSurfaceFormat>
#include <QOpenGlContext>
#include <QOffscreenSurface>
#include <QOpenGLFunctions_4_3_Core>
#include <QDebug>
int main(int argc, char* argv[])
QGuiApplication a(argc, argv);
QSurfaceFormat surfaceFormat;
surfaceFormat.setMajorVersion(4);
surfaceFormat.setMinorVersion(3);
QOpenGLContext openGLContext;
openGLContext.setFormat(surfaceFormat);
openGLContext.create();
if(!openGLContext.isValid()) return -1;
QOffscreenSurface surface;
surface.setFormat(surfaceFormat);
surface.create();
if(!surface.isValid()) return -2;
openGLContext.makeCurrent(&surface);
QOpenGLFunctions_4_3_Core f;
if(!f.initializeOpenGLFunctions()) return -3;
qDebug() << QString::fromLatin1((const char*)f.glGetString(GL_VERSION));
return 0;
here 对此表示怀疑:
对于离屏渲染,尝试渲染成 QOpenGLFramebufferObject,可以是converted into a
QImage
,又可以很容易地保存到磁盘。但是,您仍然需要一个要渲染的表面(根据需要
QOpenGLContext::makeCurrent()
),所以你唯一的选择是 确实使用QWindow
或QGLWidget
来获得这样的表面。在 Qt 5.1 中,将会有一个新的类叫做 QOffscreenSurface, 这可能最适合您的用例。你会用
QOffscreenSurface
为您的OpenGL context 获取表面,然后使用QOpenGLFramebufferObject
,然后拨打QOpenGLFramebufferObject::toImage()
访问 像素。
【讨论】:
非常感谢您的评论!很棒的资源,但是我确实有一个奇怪的问题...我使用过这个类,但是我没有创建新的上下文,而是从 QOpenGLWindow 传递了现有的上下文,它渲染得很好,但是我注意到在捕获缓冲区时,它捕获了旧的 QOpenGLWindow缓冲第一。我必须捕获缓冲区 2x 才能获得第二个 - offscreensurface 被绘制到...任何想法我错过了什么信号/轻推?我尝试在drawwing之前/之后/中间调用swapBuffer(),但到目前为止没有运气。感觉有一些信号延迟...以上是关于使用 QOpenGLWidget 进行屏幕外渲染的最简单方法的主要内容,如果未能解决你的问题,请参考以下文章