DEV Community: QienWang

Qt -- QDir 过滤出jpg文件并保存在QFileInfoList中

QienWang — Mon, 12 May 2025 13:24:18 +0000

    QDir dir("/path/to/your/directory");、
    QFileInfoList fileList = dir.entryInfoList(QStringList{"*.jpg", "*.JPG"}, QDir::Files);

Qt -- 通过 Qt xml 读取 VOC2012 数据集xml标注文件中的目标名称和包含框

QienWang — Mon, 12 May 2025 10:25:55 +0000

在.pro文件中添加以下内容

QT += xml

实现 -- 以单个文件作为示例

#include "mainwindow.h"
#include <QApplication>

void parseXml(const QString & filePath);

int main(int argc, char * argv[])
{
    QApplication a(argc, argv);
    // MainWindow w;
    // w.show();

    QString xmlPath = ".../VOC2012_train_val/Annotations/2012_002880.xml";
    parseXml(xmlPath);

    return a.exec();
}

#include <QFile>
#include <QDomDocument>
#include <QDomElement>
#include <QDomNode>
void parseXml(const QString & filePath)
{
    QFile file(filePath);
    if (!file.open(QIODevice::ReadOnly))
    {
        qDebug() << "Failed to open file:" << filePath;
        return;
    }

    QDomDocument document;
    if (!document.setContent(&file))
    {
        qDebug() << "Failed to parse XML file.";
        return;
    }

    QDomElement root = document.documentElement();
    QDomNodeList objects = root.elementsByTagName("object");

    for (int i = 0; i < objects.size(); ++i)
    {
        QDomElement object = objects.at(i).toElement();

        // 获取物体名称
        QDomElement nameElement = object.elementsByTagName("name").at(0).toElement();
        QString name = nameElement.text();
        qDebug() << "Object Name:" << name;

        // 获取包含框信息
        QDomElement bndboxElement = object.elementsByTagName("bndbox").at(0).toElement();
        QDomElement xminElement = bndboxElement.elementsByTagName("xmin").at(0).toElement();
        QDomElement yminElement = bndboxElement.elementsByTagName("ymin").at(0).toElement();
        QDomElement xmaxElement = bndboxElement.elementsByTagName("xmax").at(0).toElement();
        QDomElement ymaxElement = bndboxElement.elementsByTagName("ymax").at(0).toElement();

        int xmin = xminElement.text().toInt();
        int ymin = yminElement.text().toInt();
        int xmax = xmaxElement.text().toInt();
        int ymax = ymaxElement.text().toInt();

        qDebug() << "Bounding Box:" << xmin << ymin << xmax << ymax;
    }
}

Qt -- Quick3D加载外部模型文件 - 即载入.obj等模型文件到Qt项目中

QienWang — Mon, 14 Apr 2025 10:23:28 +0000

转换 qt命令行工具: balsam C:\Users\Administrator\Desktop\FreeCAD\test.obj -o c:\model 将会生成Test.qml文件和meshs文件夹.
导入将test.obj生成的所有文件放入项目目录meshes/test/文件夹下, 之后导入这个文件夹 import "./meshes/test/"
使用模型在项目的View3D { } 中直接使用Test.qml作为组件即可 Test { }

Softmax Derivation: A Step-by-Step Approach

QienWang — Fri, 10 May 2024 03:39:17 +0000

f(x1, x2, ..., xn) = (e^x1 / Σ(e^xj), e^x2 / Σ(e^xj), ..., e^xn / Σ(e^xj)) (j = 1 to n)
where f[xi] = e^xi / Σ(e^xj) 

Let's begin!

∂f/∂xi = (d(e^x1 / Σ(e^xj))/dxi, d(e^x2 / Σ(e^xj))/dxi, ..., d(e^xi/ Σ(e^xj))/dxi, ..., d(e^xn / Σ(e^xj))/dxi)
(j = 1 to n)
∂f/∂xi = (-e^x1 * e^xi / (Σ(e^xj))^2, -e^x2 * e^xi / (Σ(e^xj))^2, ..., e^xi(Σ(e^xj) - e^xi) / (Σ(e^xj))^2, ...,
-e^xn * e^xi / (Σ(e^xj))^2) (j = 1 to n) 

When k=i,
(∂f/∂xi)[k] = e^xi * (Σ(e^xj) - e^xi) / (Σ(e^xj))^2 (j = 1 to n)
(∂f/∂xi)[k] = (e^xi / Σ(e^xj) * ((Σ(e^xj) - e^xi) / Σ(e^xj)) (j = 1 to n)
(∂f/∂xi)[k] = f[xi] * (1 - f[xi]) (j = 1 to n) 

When k≠i,
(∂f/∂xi)[k] = -e^xk * e^xi / (Σ(e^xj))^2 (j = 1 to n)
(∂f/∂xi)[k] = (-e^xk / Σ(e^xj)) * (e^xi / Σ(e^xj)) (j = 1 to n)
(∂f/∂xi)[k] = -f[xk] * f[xi] (j = 1 to n) 

In summary,
(∂f/∂xi)[k] = f[xi] * (1 - f[xi]) (j = 1 to n, k=i)
(∂f/∂xi)[k] = -f[xk] * f[xi] (j = 1 to n, k≠i)

Qt -- QTreeWidget Tree Traversal

QienWang — Mon, 18 Dec 2023 08:16:37 +0000

Need to use QTreeWidgetItemIterator class：

//Each item in a tree, checking the text in the first column 
//against a user-specified search string.
QTreeWidgetItemIterator it(treeWidget);
while (*it) {
    if ((*it)->text(0) == itemText)
        (*it)->setSelected(true);
    ++it;
}

Note: The above code is excerpted from Qt documentation.