The basic commands for using apitrace with an OpenGL application are:
apitrace trace --api=gl MyApp qapitrace MyApp.trace apitrace dump --blobs MyApp.trace
The last command generates blobs that can be inspected with the following command, for example:
tail -c $((12*10)) ~/repos/MyApp/build/blob_call2325.bin | xxd -g1
Or by writing a simple C++ program that converts them into CVS format:
The following C++ code compares the performance of std::atomic and std::mutex:
#include <atomic>
#include <mutex>
#include <iostream>
#include <chrono>
#include <thread>
const size_t size = 100000000;
std::mutex mutex;
bool var = false;
typedef std::chrono::high_resolution_clock Clock;
void testA()
{
std::atomic<bool> sync(true);
const auto start_time = Clock::now();
for (size_t counter = 0; counter < size; counter++)
{
var = sync.load();
//sync.store(true);
//sync.exchange(true);
}
const auto end_time = Clock::now();
std::cout << 1e-6*std::chrono::duration_cast<std::chrono::microseconds>(end_time - start_time).count() << " s\n";
}
All the following commands assumes we saved MySQL root password into MROOTPASS variable:
export MROOTPASS=<mysql root password>
The most straight forward method to backup all the MySQL databases and all the website files (PHP scripts, images, etc..) stored in the /home directory is the following:
mysqldump --all-databases -u root -p$MROOTPASS | gzip > all-databases-$(date '+%Y-%m-%d_%H-%M-%S').sql.gz tar -cvzf home.tar.gz /home
If we backup some individual database (probably not as root) and change its user while restoring it, it might make a sense to remove DEFINER from the output script:
sed -e 's/DEFINER=[^*]*\*/\*/'
The following commands restore all the websites from the archives:
gunzip -c all-databases-2017-05-23_15-31-00.sql.gz | mysql -u root -p$MROOTPASS cd / sudo tar -xvzf home.tar.gz
After migration from MySQL version 14.14 Distrib 5.5.54 to 14.14 Distrib 5.7.18 (I do not know what is the difference between them) I got the following error: “ERROR 1805 (HY000) at line 1: Column count of mysql.user is wrong. Expected 45, found 42. The table is probably corrupted” while trying to drop some user, and fixed it by running:
mysql_upgrade -u root -p$MROOTPASS service mysql restart
The following bash script renames all the files matching src_name.* with dst_name.*:
src_name=$1 dst_name=$2 unset $1 cp $src_name.* ~/temp/ cd ~/temp/ rename "s/$src_name\.([a-z]+)/$dst_name\.\$1/" * cd - mv ~/temp/$dst_name.* .
If you have some files like src1.h and src1.cpp, you can save this script into dupsource.sh file, for example, and then rename those files with src2.h and src2.cpp using the following command:
dupsource.sh src1 src2
The script requires ~/temp directory to exist and be writable.
If QAudioDecoder does not decode mp3, reporting a format error (GStreamer; Unable to start decoding process), the following package can help:
On Ubuntu:
apt-get install gstreamer0.10-fluendo-mp3
On CentOS:
yum -y install http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-5.el7.nux.noarch.rpm
yum install gstreamer{,1}-plugins-ugly
Install sox tool with mp3 support:
apt-get install sox apt-get install libsox-fmt-mp3 sox file.mp3 file.wav
Basically that is all, but if you need to check resulting wav file parameters like channels, sample rate, precision, duration, bit rate, etc…, use soxi command:
(more…)
First, I tried Valgrind tool using the following command:
valgrind --tool=memcheck --leak-check=yes ./app
With some large QT application started for some short period I got the following output:
==7090== HEAP SUMMARY:
==7090== in use at exit: 5,623,365 bytes in 36,268 blocks
==7090== total heap usage: 32,454,680 allocs, 32,418,412 frees, 12,822,939,874 bytes allocated
…………………………..
==7090== LEAK SUMMARY:
==7090== definitely lost: 20,163 bytes in 74 blocks
==7090== indirectly lost: 60,053 bytes in 1,273 blocks
==7090== possibly lost: 396,167 bytes in 2,169 blocks
==7090== still reachable: 4,834,822 bytes in 31,576 blocks
==7090== suppressed: 0 bytes in 0 blocks
==7090== Reachable blocks (those to which a pointer was found) are not shown.
==7090== To see them, rerun with: –leak-check=full –show-leak-kinds=all
==7090==
==7090== For counts of detected and suppressed errors, rerun with: -v
==7090== Use –track-origins=yes to see where uninitialised values come from
==7090== ERROR SUMMARY: 20905 errors from 1583 contexts (suppressed: 15 from 2)
Below I provided parameters of three Android phones I tested my Lines game with:
| Android Version | Screen Resolution | Pixel Ratio | DPI | Screen Size |
|---|---|---|---|---|
| 4.4? | 320×496 (480×744/706) | 1.5 | 156.89 | 52×80 mm |
| 4.4? | 360×592 (540×888/850) | 1.5 | 160.19 | 57×94 mm |
| 6.0 | 360×592 (720×1184/1136) | 2.0 | 160.19 | ~68×123 mm |
| N/A | 800×1232 | 1.0 | 188.3295 | 108×166 mm |
Screen Resolution column contains the information in the following format: <logical resolution> (<physical resolution>/<physical height available for applications in portrait orientation>.
DPIs with ‘~’ sign are measured manually because QT (or some Android API) provides incorrect Screen Size.
QML DropShadow is an interesting effect that acts in a very simple way. It works fine in my application and produces the following result:
The only disadvantage of DropShadow effect is that is slows down my application from 60 FPS to 30 FPS on Android Phone. The following code demonstrates how I use it with StackView:
Lines 3D is a fun logical game with different difficulty levels. While “Beginner” level is an easy to play relaxing game, the “Professional” and “Expert” levels are good exercises for your brain where you can apply your knowledge in the area of the probability theory. There is also some specific “Baby” level for babies, allowing them to move balls and do not worry about the result.
For IT professionals, there is auto-play mode for testing the application performance and stability. To start Lines 3D game in auto-play mode first install Lines 3D game from Windows Store, start it and select the following game options:
