c++ - 如何将QRect转换为OpenGL坐标？

Question

我有一个应用程序，其中需要将几个QOpenGLFramebufferObject放到较大的QOpenGLFramebufferObject上。为此，我认为可以使用Qt中的标准坐标将fbo粘贴到大型fbo上。 QOpenGLFramebufferObject::blitFramebuffer需要一个“源” rect和一个“目标” rect。例如，如果我的大型fbo是1000x1000，而较小的fbo是500x500。然后，我只需要执行以下操作:

auto sourceRect = QRect(0,0,500,500);
// i here would be the row of my grid of fbos
// j would be the column
for(int i =0; i < 2; i++){
    for(int j= 0; j < 2; j++){
            auto targetRect = QRect(i*500,j*500, 500, 500);
            // tileFbo are the small fbos
            QOpenGLFramebufferObject::blitFramebuffer(largeFbo,targetRect, tileFbo,sourceRect)
    }
}

但是，这似乎不起作用，因为QOpenGLFramebufferObject似乎使用OpenGL坐标。那么如何将QRect转换为使用OpenGL坐标呢？
这是一个示例，我在其中画了一条小fbo(500x500)的线，然后将小fbo画在大fbo(1000x1000)上。大fbo上的线似乎在左下角而不是左上角。

#include <QGuiApplication>
#include <QOffscreenSurface>
#include <QOpenGLFramebufferObject>
#include <QOpenGLContext>
#include <QPainter>
#include <QOpenGLPaintDevice>
#include <QDebug>

int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);
    QSurfaceFormat format;
    format.setSamples(8);
    QOffscreenSurface* surface = new QOffscreenSurface;
    surface->setFormat(format);
    surface->create();

    QOpenGLContext* context = new QOpenGLContext;
    if(!context->create()){
        qDebug() << "Failed to create context";
    }
    context->makeCurrent(surface);

    auto smallFbo = new QOpenGLFramebufferObject(QSize(500,500));
    auto largeFbo = new QOpenGLFramebufferObject(QSize(1000,1000));
    smallFbo->bind();
    QOpenGLPaintDevice paintDevice(smallFbo->size());
    QPainter painter(&paintDevice);
    painter.drawLine(QLine(0,0,400,400));
    smallFbo->release();
    // save small fbo to disk
    smallFbo->toImage().save("/home/Desktop/smallfbo.png");

    // blit the frame buffers
    QOpenGLFramebufferObject::blitFramebuffer(largeFbo, QRect(0,0,500,500), smallFbo, QRect(0,0,500,500));
    // save large fbo to disk
    largeFbo->toImage().save("/home/Desktop/largefbo.png");
    return 0;
}

Answer 1

据我了解，此功能是您需要的一切

QRect to_OpenGL_coordinates(const QRect& qt_coordinateRect, const QOpenGLFramebufferObject& fbo){
    return QRect(qt_coordinateRect.x(), fbo.height() - qt_coordinateRect.y(),
                 qt_coordinateRect.width(), qt_coordinateRect.height() * -1);
}

像这样使用

// blit the frame buffers
    QOpenGLFramebufferObject::blitFramebuffer(largeFbo, to_OpenGL_coordinates(QRect(0,0,500,500), *largeFbo),
                                              smallFbo, to_OpenGL_coordinates(QRect(0,0,500,500), *smallFbo));

结果是。