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https://github.com/alttiri/demo-image-viewer-qt
Demonstration only image viewer made with Qt6
https://github.com/alttiri/demo-image-viewer-qt
demo image-viewer qt-widgets qt6
Last synced: about 2 months ago
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Demonstration only image viewer made with Qt6
- Host: GitHub
- URL: https://github.com/alttiri/demo-image-viewer-qt
- Owner: AlttiRi
- License: gpl-3.0
- Created: 2022-01-29T16:38:58.000Z (almost 3 years ago)
- Default Branch: master
- Last Pushed: 2023-06-07T08:10:33.000Z (over 1 year ago)
- Last Synced: 2024-10-15T01:07:23.766Z (3 months ago)
- Topics: demo, image-viewer, qt-widgets, qt6
- Language: C++
- Homepage:
- Size: 53.7 KB
- Stars: 2
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: license
Awesome Lists containing this project
README
# demo-image-viewer
It's a **demonstration** only image viewer made with Qt6.
[The binaries are available](https://github.com/AlttiRi/demo-image-viewer/releases).
---
## Features
- Opens an image in a time independent of the count of images in a directory where it is located.
- Handles the images of the directory in a separated thread with `QtConcurrent::run`.
- The directory parsing is fast. It does not use `QFileInfo` in `std::sort`, but a custom struct.
- Handles the directory only once, until it is changed. (For example, drag'n'dropping a file from the same directory does not trigger the directory parsing, since it's not needed to do, just find the file by name in the list structure.)
- Decodes 8.3 file names to long file names with Win API (`GetLongPathNameW`). An 8.3 can be faced on a user input of a file with long path (260+ chars) from disc C from Windows Explorer:
on Drag'n'Drop and when a user opens an image with a double click (the image path is passed as a command line argument to the program.)
- Opens images with a long path starts with [`\\?\`](https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#win32-file-namespaces) ([`\\?\UNC\`](https://web.archive.org/web/1/https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation)).
- Preloades the adjacent images in a separate thread.
- Sorts by mtime, btime, size.
- Updates the image position (in the title) on the sorting change.
- Lists hidden files (`QDir::Hidden`).
- All long time taking operations log the execution time in the console with `qDebug()`.
---
Here is the example of the console log, after the program is started (~70 ms):
The speed results for 350 KB image with a directory with 30000+ files (Run it with Qt Creator to look at the `qDebug()` logs):
- _[timer][displayImage]_: **84 ms** — time to display the image.
**At this moment the image is visible.**
That is performed in a background thread:
- _[timer][entryInfoList]_: **143 ms** — time to get the list with QFileInfo of all files (31973) in the directory
- _[timer][filterBySupportedExts]_: **6 ms** — time filter that list to exclude the unsupported files
- _[filterBySupportedExts] fileInfoList.size_: **31973**
- _[filterBySupportedExts] fileInfoListFiltered.size_: **30006**
- _[timer][initFileEntryList]_: **200 ms** — time to create a list of data structure with all necessary information for all filtered files (30006)
- _[timer][initFileList]_: **352 ms** — the **total time** of the work with directory files ~(143 + 6 + 200)
- _[timer][sortByMtime]_: **6 ms** — to sort all files by mtime
---
Note: Do **NOT** use code that calls methods of `QFileInfo` in `std::sort`. **It's incredibly slow.**
That is up to **600 times slower**
```c++
std::sort(fileEntryList.begin(), fileEntryList.end(),
[](const FileEntry& a, const FileEntry& b) {
return a.fileInfo.lastModified() < b.fileInfo.lastModified();
}
);
```
than that
```c++
std::sort(fileEntryList.begin(), fileEntryList.end(),
[](const FileEntry& a, const FileEntry& b) {
return a.mtime < b.mtime;
}
);
```
**3200-3600 ms** vs **6 ms**.
So, store all required fields of `QFileInfo` in your own data struct.
Try by yourself (uncomment the line 307 and comment lines 298-304): https://github.com/AlttiRi/demo-image-viewer/blob/ad9ac9b1c9d78244462064983e676542700e96d9/core.h#L296-L311