官方Qt opengl示例有一个错误，即当您经常调整Threaded QOpenGLWidget example top level窗口的大小（拖动窗口）时，它会崩溃，产生Cannot make QOpenGLContext current in a different thread。我试过Qt 5.7和Qt 5.8。它们都包含相同的问题。
可以找到示例：Qt\Qt5.8.0\Examples\Qt-5.8\opengl\threadedqopenglwidget
以下是代码：
glwidget.h
#ifndef GLWIDGET_H
#define GLWIDGET_H
#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QOpenGLShaderProgram>
#include <QOpenGLBuffer>
#include <QVector3D>
#include <QMatrix4x4>
#include <QThread>
#include <QMutex>
#include <QWaitCondition>
#include <QElapsedTimer>
class GLWidget;
class Renderer : public QObject, protected QOpenGLFunctions
{
Q_OBJECT
public:
Renderer(GLWidget *w);
void lockRenderer() { m_renderMutex.lock(); }
void unlockRenderer() { m_renderMutex.unlock(); }
QMutex *grabMutex() { return &m_grabMutex; }
QWaitCondition *grabCond() { return &m_grabCond; }
void prepareExit() { m_exiting = true; m_grabCond.wakeAll(); }
signals:
void contextWanted();
public slots:
void render();
private:
void paintQtLogo();
void createGeometry();
void quad(qreal x1, qreal y1, qreal x2, qreal y2, qreal x3, qreal y3, qreal x4, qreal y4);
void extrude(qreal x1, qreal y1, qreal x2, qreal y2);
bool m_inited;
qreal m_fAngle;
qreal m_fScale;
QVector<QVector3D> vertices;
QVector<QVector3D> normals;
QOpenGLShaderProgram program;
QOpenGLBuffer vbo;
int vertexAttr;
int normalAttr;
int matrixUniform;
GLWidget *m_glwidget;
QMutex m_renderMutex;
QElapsedTimer m_elapsed;
QMutex m_grabMutex;
QWaitCondition m_grabCond;
bool m_exiting;
};
class GLWidget : public QOpenGLWidget
{
Q_OBJECT
public:
explicit GLWidget(QWidget *parent = 0);
~GLWidget();
protected:
void paintEvent(QPaintEvent *) override { }
signals:
void renderRequested();
public slots:
void grabContext();
private slots:
void onAboutToCompose();
void onFrameSwapped();
void onAboutToResize();
void onResized();
private:
QThread *m_thread;
Renderer *m_renderer;
};
#endif
glwidget.cpp
#include "glwidget.h"
#include <math.h>
#include <QGuiApplication>
GLWidget::GLWidget(QWidget *parent)
: QOpenGLWidget(parent)
{
setMinimumSize(300, 250);
connect(this, &QOpenGLWidget::aboutToCompose, this, &GLWidget::onAboutToCompose);
connect(this, &QOpenGLWidget::frameSwapped, this, &GLWidget::onFrameSwapped);
connect(this, &QOpenGLWidget::aboutToResize, this, &GLWidget::onAboutToResize);
connect(this, &QOpenGLWidget::resized, this, &GLWidget::onResized);
m_thread = new QThread;
m_renderer = new Renderer(this);
m_renderer->moveToThread(m_thread);
connect(m_thread, &QThread::finished, m_renderer, &QObject::deleteLater);
connect(this, &GLWidget::renderRequested, m_renderer, &Renderer::render);
connect(m_renderer, &Renderer::contextWanted, this, &GLWidget::grabContext);
m_thread->start();
}
GLWidget::~GLWidget()
{
m_renderer->prepareExit();
m_thread->quit();
m_thread->wait();
delete m_thread;
}
void GLWidget::onAboutToCompose()
{
// We are on the gui thread here. Composition is about to
// begin. Wait until the render thread finishes.
m_renderer->lockRenderer();
}
void GLWidget::onFrameSwapped()
{
m_renderer->unlockRenderer();
// Assuming a blocking swap, our animation is driven purely by the
// vsync in this example.
emit renderRequested();
}
void GLWidget::onAboutToResize()
{
m_renderer->lockRenderer();
}
void GLWidget::onResized()
{
m_renderer->unlockRenderer();
}
void GLWidget::grabContext()
{
m_renderer->lockRenderer();
QMutexLocker lock(m_renderer->grabMutex());
context()->moveToThread(m_thread);
m_renderer->grabCond()->wakeAll();
m_renderer->unlockRenderer();
}
Renderer::Renderer(GLWidget *w)
: m_inited(false),
m_glwidget(w),
m_exiting(false)
{
}
void Renderer::paintQtLogo()
{
vbo.bind();
program.setAttributeBuffer(vertexAttr, GL_FLOAT, 0, 3);
program.setAttributeBuffer(normalAttr, GL_FLOAT, vertices.count() * 3 * sizeof(GLfloat), 3);
vbo.release();
program.enableAttributeArray(vertexAttr);
program.enableAttributeArray(normalAttr);
glDrawArrays(GL_TRIANGLES, 0, vertices.size());
program.disableAttributeArray(normalAttr);
program.disableAttributeArray(vertexAttr);
}
// Some OpenGL implementations have serious issues with compiling and linking
// shaders on multiple threads concurrently. Avoid this.
Q_GLOBAL_STATIC(QMutex, initMutex)
void Renderer::render()
{
if (m_exiting)
return;
QOpenGLContext *ctx = m_glwidget->context();
if (!ctx) // QOpenGLWidget not yet initialized
return;
// Grab the context.
m_grabMutex.lock();
emit contextWanted();
m_grabCond.wait(&m_grabMutex);
QMutexLocker lock(&m_renderMutex);
m_grabMutex.unlock();
if (m_exiting)
return;
Q_ASSERT(ctx->thread() == QThread::currentThread());
// Make the context (and an offscreen surface) current for this thread. The
// QOpenGLWidget's fbo is bound in the context.
m_glwidget->makeCurrent();
if (!m_inited) {
m_inited = true;
initializeOpenGLFunctions();
QMutexLocker initLock(initMutex());
QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
const char *vsrc =
"attribute highp vec4 vertex;\n"
"attribute mediump vec3 normal;\n"
"uniform mediump mat4 matrix;\n"
"varying mediump vec4 color;\n"
"void main(void)\n"
"{\n"
" vec3 toLight = normalize(vec3(0.0, 0.3, 1.0));\n"
" float angle = max(dot(normal, toLight), 0.0);\n"
" vec3 col = vec3(0.40, 1.0, 0.0);\n"
" color = vec4(col * 0.2 + col * 0.8 * angle, 1.0);\n"
" color = clamp(color, 0.0, 1.0);\n"
" gl_Position = matrix * vertex;\n"
"}\n";
vshader->compileSourceCode(vsrc);
QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
const char *fsrc =
"varying mediump vec4 color;\n"
"void main(void)\n"
"{\n"
" gl_FragColor = color;\n"
"}\n";
fshader->compileSourceCode(fsrc);
program.addShader(vshader);
program.addShader(fshader);
program.link();
vertexAttr = program.attributeLocation("vertex");
normalAttr = program.attributeLocation("normal");
matrixUniform = program.uniformLocation("matrix");
m_fAngle = 0;
m_fScale = 1;
createGeometry();
vbo.create();
vbo.bind();
const int verticesSize = vertices.count() * 3 * sizeof(GLfloat);
vbo.allocate(verticesSize * 2);
vbo.write(0, vertices.constData(), verticesSize);
vbo.write(verticesSize, normals.constData(), verticesSize);
m_elapsed.start();
}
//qDebug("%p elapsed %lld", QThread::currentThread(), m_elapsed.restart());
glClearColor(0.1f, 0.2f, 0.2f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glFrontFace(GL_CW);
glCullFace(GL_FRONT);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
QMatrix4x4 modelview;
modelview.rotate(m_fAngle, 0.0f, 1.0f, 0.0f);
modelview.rotate(m_fAngle, 1.0f, 0.0f, 0.0f);
modelview.rotate(m_fAngle, 0.0f, 0.0f, 1.0f);
modelview.scale(m_fScale);
modelview.translate(0.0f, -0.2f, 0.0f);
program.bind();
program.setUniformValue(matrixUniform, modelview);
paintQtLogo();
program.release();
glDisable(GL_DEPTH_TEST);
glDisable(GL_CULL_FACE);
m_fAngle += 1.0f;
// Make no context current on this thread and move the QOpenGLWidget's
// context back to the gui thread.
m_glwidget->doneCurrent();
ctx->moveToThread(qGuiApp->thread());
// Schedule composition. Note that this will use QueuedConnection, meaning
// that update() will be invoked on the gui thread.
QMetaObject::invokeMethod(m_glwidget, "update");
}
void Renderer::createGeometry()
{
vertices.clear();
normals.clear();
qreal x1 = +0.06f;
qreal y1 = -0.14f;
qreal x2 = +0.14f;
qreal y2 = -0.06f;
qreal x3 = +0.08f;
qreal y3 = +0.00f;
qreal x4 = +0.30f;
qreal y4 = +0.22f;
quad(x1, y1, x2, y2, y2, x2, y1, x1);
quad(x3, y3, x4, y4, y4, x4, y3, x3);
extrude(x1, y1, x2, y2);
extrude(x2, y2, y2, x2);
extrude(y2, x2, y1, x1);
extrude(y1, x1, x1, y1);
extrude(x3, y3, x4, y4);
extrude(x4, y4, y4, x4);
extrude(y4, x4, y3, x3);
const qreal Pi = 3.14159f;
const int NumSectors = 100;
for (int i = 0; i < NumSectors; ++i) {
qreal angle1 = (i * 2 * Pi) / NumSectors;
qreal x5 = 0.30 * sin(angle1);
qreal y5 = 0.30 * cos(angle1);
qreal x6 = 0.20 * sin(angle1);
qreal y6 = 0.20 * cos(angle1);
qreal angle2 = ((i + 1) * 2 * Pi) / NumSectors;
qreal x7 = 0.20 * sin(angle2);
qreal y7 = 0.20 * cos(angle2);
qreal x8 = 0.30 * sin(angle2);
qreal y8 = 0.30 * cos(angle2);
quad(x5, y5, x6, y6, x7, y7, x8, y8);
extrude(x6, y6, x7, y7);
extrude(x8, y8, x5, y5);
}
for (int i = 0;i < vertices.size();i++)
vertices[i] *= 2.0f;
}
void Renderer::quad(qreal x1, qreal y1, qreal x2, qreal y2, qreal x3, qreal y3, qreal x4, qreal y4)
{
vertices << QVector3D(x1, y1, -0.05f);
vertices << QVector3D(x2, y2, -0.05f);
vertices << QVector3D(x4, y4, -0.05f);
vertices << QVector3D(x3, y3, -0.05f);
vertices << QVector3D(x4, y4, -0.05f);
vertices << QVector3D(x2, y2, -0.05f);
QVector3D n = QVector3D::normal
(QVector3D(x2 - x1, y2 - y1, 0.0f), QVector3D(x4 - x1, y4 - y1, 0.0f));
normals << n;
normals << n;
normals << n;
normals << n;
normals << n;
normals << n;
vertices << QVector3D(x4, y4, 0.05f);
vertices << QVector3D(x2, y2, 0.05f);
vertices << QVector3D(x1, y1, 0.05f);
vertices << QVector3D(x2, y2, 0.05f);
vertices << QVector3D(x4, y4, 0.05f);
vertices << QVector3D(x3, y3, 0.05f);
n = QVector3D::normal
(QVector3D(x2 - x4, y2 - y4, 0.0f), QVector3D(x1 - x4, y1 - y4, 0.0f));
normals << n;
normals << n;
normals << n;
normals << n;
normals << n;
normals << n;
}
void Renderer::extrude(qreal x1, qreal y1, qreal x2, qreal y2)
{
vertices << QVector3D(x1, y1, +0.05f);
vertices << QVector3D(x2, y2, +0.05f);
vertices << QVector3D(x1, y1, -0.05f);
vertices << QVector3D(x2, y2, -0.05f);
vertices << QVector3D(x1, y1, -0.05f);
vertices << QVector3D(x2, y2, +0.05f);
QVector3D n = QVector3D::normal
(QVector3D(x2 - x1, y2 - y1, 0.0f), QVector3D(0.0f, 0.0f, -0.1f));
normals << n;
normals << n;
normals << n;
normals << n;
normals << n;
normals << n;
}
在过于频繁地调整窗口小部件时，grabContext调用似乎无法正确锁定上下文。
答案 0 :(得分：-1)
我在调整大小之前通过处理事件修复了崩溃：
void GLWidget::onAboutToResize()
{
// process events before resizing to avoid crash "Cannot make QOpenGLContext current in a different thread"
QCoreApplication::processEvents();
m_renderer->lockRenderer();
}
我不相信这是最好的解决方案，但我希望它有所帮助。