从上下文共享 QOpenGLWidget 崩溃

Question

我有两个 QOpenGLWidgets(view1, view2) 作为顶级小部件中的子项。 Qt 文档说 'When multiple QOpenGLWidgets are added as children to the same top-level widget, their contexts will share with each other'。因此，view1 和 view2 共享 OpenGL 上下文。我试图渲染在 view1 的上下文中初始化的相同场景，并且应用程序在 view2 的 paintGL() 中崩溃。我做错了什么？

这是简化的代码：

#include <QtGui/QtGui>
#include <QtWidgets/QOpenGLWidget>
#include <QtWidgets/QApplication>
#include <QtWidgets/QHBoxLayout>

static const char *vertexShaderSource =
    "attribute vec4 posAttr;\n"
    "void main() {\n"
    "   gl_Position = posAttr;\n"
    "}\n";

static const char *fragmentShaderSource =
    "void main() {\n"
    "   gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
    "}\n";

QOpenGLShaderProgram *program = nullptr;
QOpenGLBuffer arrayBuf;
int posAttr = -1;

class View3D : public QOpenGLWidget {
public:
    View3D()
    {
        setMinimumSize(300, 200);
    }
private:
    auto initializeGL() -> void override
    {
        if (program)
            return;

        program = new QOpenGLShaderProgram(this);
        program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
        program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
        program->link();
        posAttr = program->attributeLocation("posAttr");

        program->bind();

        GLfloat vertices[] = {
            0.0f, 0.707f, 0.f,
            -0.5f, -0.5f, 0.f,
            0.5f, -0.5f, 0.f,
        };

        arrayBuf.create();
        arrayBuf.bind();
        arrayBuf.allocate(vertices, sizeof(vertices));

        program->enableAttributeArray(posAttr);
        program->setAttributeBuffer(posAttr, GL_FLOAT, 0, 3, 0);

        program->release();
    }

    auto paintGL() -> void override
    {
        auto f = context()->functions();

        const auto dpr = devicePixelRatio();
        f->glViewport(0, 0, width() * dpr, height() * dpr);

        f->glClear(GL_COLOR_BUFFER_BIT);

        program->bind();
        arrayBuf.bind();

        program->enableAttributeArray(posAttr);
        f->glDrawArrays(GL_TRIANGLES, 0, 3);
        program->disableAttributeArray(posAttr);

        arrayBuf.release();
        program->release();
    }

};

auto main(int argc, char **argv) -> int
{
    QApplication app{argc, argv};

    QWidget w;
    auto hbox = new QHBoxLayout{&w};
    hbox->addWidget(new View3D); // view1
    hbox->addWidget(new View3D); // view2
    w.show();

    return app.exec();
}

Answer 1

似乎不应在上下文之间共享顶点状态，即使这些上下文是共享的。

这是固定版本：

#include <QtGui/QtGui>
#include <QtWidgets/QOpenGLWidget>
#include <QtWidgets/QApplication>
#include <QtWidgets/QHBoxLayout>

static const char *vertexShaderSource =
    "attribute vec4 posAttr;\n"
    "void main() {\n"
    "   gl_Position = posAttr;\n"
    "}\n";

static const char *fragmentShaderSource =
    "void main() {\n"
    "   gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
    "}\n";

QOpenGLBuffer *arrayBuf = nullptr;
QOpenGLShaderProgram *program = nullptr;

class View3D : public QOpenGLWidget {
public:
    View3D()
    {
        setMinimumSize(300, 200);
    }
private:
    int posAttr = -1;
    auto initializeGL() -> void override
    {
        if (!arrayBuf) {
            arrayBuf = new QOpenGLBuffer;
            arrayBuf->create();
            arrayBuf->bind();
            GLfloat vertices[] = {
                0.0f, 0.707f, 0.f,
                -0.5f, -0.5f, 0.f,
                0.5f, -0.5f, 0.f,
            };
            arrayBuf->allocate(vertices, sizeof(vertices));
        }

        if (!program) {
            program = new QOpenGLShaderProgram(this);
            program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
            program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
            program->link();
        }

        posAttr = program->attributeLocation("posAttr");
        program->bind();
        arrayBuf->bind();
        program->enableAttributeArray(posAttr);
        program->setAttributeBuffer(posAttr, GL_FLOAT, 0, 3, 0);
        program->release();
    }

    auto paintGL() -> void override
    {
        auto f = context()->functions();

        const auto dpr = devicePixelRatio();
        f->glViewport(0, 0, width() * dpr, height() * dpr);

        f->glClear(GL_COLOR_BUFFER_BIT);

        program->bind();
        arrayBuf->bind();

        program->enableAttributeArray(posAttr);
        f->glDrawArrays(GL_TRIANGLES, 0, 3);
        program->disableAttributeArray(posAttr);

        arrayBuf->release();
        program->release();
    }

};

auto main(int argc, char **argv) -> int
{
    QApplication app{argc, argv};

    QWidget w;
    auto hbox = new QHBoxLayout{&w};
    hbox->addWidget(new View3D); // view1
    hbox->addWidget(new View3D); // view2
    w.show();

    return app.exec();
}

据观察，共享顶点属性状态也会导致问题。我知道我不能通过 OpenGL 规范共享 VAO，但我从未在这里明确使用 VAO。

我不确定这是否被规范禁止或驱动程序错误。但是，至少在 NVidia 驱动程序上，很明显您不应该在任何情况下共享顶点属性状态，包括共享上下文。

从上下文共享 QOpenGLWidget 崩溃

crash from context shared QOpenGLWidget

c++

qt

opengl

openglcontext

qopenglwidget