Category Archives: Programming languages

Multiple views with OsgQtQuick

I wrote a sample application using OsgQtQuick that shows the Earth in two views:

with the following QML, that I copied from OsgQtQuick samples:

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A sample C++ code demonstrating why int is not atomic

The code below demonstrates why it is not guaranteed that 4-byte value being written by another thread is read either as original or final, but it can be read “partially written”:

static constexpr int offset=2;
alignas(64) char vars[64+4-offset];
static volatile unsigned * const p = reinterpret_cast<unsigned *>(&vars[64-offset]);

unsigned getVar()
{
    return *p;
}

void loop()
{
    while(true)
    {
        *p = -1;
        *p = 0;
    }
}

#include <thread>
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <map>

int main()
{
    std::thread thread(loop);
    std::map<unsigned,int> xs;
    for(int i=0;i<10000000;++i)
    {
        const auto x=getVar();
        ++xs[x];
    }
    for(const auto& x : xs)
        std::cout << std::setfill('0') << std::setw(8) << std::hex << x.first << ": " << std::dec << x.second << " times\n";
    std::exit(0); // exit, killing the thread without abnormal termination via std::terminate
}

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Qt Quick Controls 2 does not support TableView

The information provided below is outdated. QT 5.13 supports SplitView and TableView but without TableHeader yet. Probably TableHeader can be implemented with the overlays.

Qt Quick Controls 2 does not support TableView and looks like they are not going to support it, some notable missing features from Qt Quick Controls 1 also are Action, SplitView and TreeView, so the following QML code would not work:

TableView {

    TableViewColumn {
        role: "time"
        title: qsTr("date/time:")
        width: parent.width - 30
    }

    TableViewColumn {
        role: "score"
        title: qsTr("result:")
        width: 30
    }

    model: boardModel.list

    ScrollIndicator.vertical: ScrollIndicator { }
}

But there is a solution with ListView, so there can be something like this:

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Numeric promotions and conversions in C++

In the following C++ code the values of ‘z’ and ‘n’ are undefined, because they are the result of an operation with signed integer arithmetic overflow (‘x’ and ‘y’ are first implicitly converted to signed int). The value of ‘w’ is implementation defined, because it is the result of a conversion:

#include <iostream>
#include <bitset>

int main(int argc, char *argv[])
{
    unsigned short x = 65535, y = x;
    unsigned short z = x * y;
    unsigned int n = x * y;
    std::cerr << "z = " << std::bitset<16>(z) << ", n = " << std::bitset<32>(n) << ", sizeof(int) = " << sizeof(int) << std::endl;

    short w = 0x80000000;
    
    return 0;
}

see Numeric conversions section of Implicit conversions article.

Comparison of std::mutex and std::atomic performance

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";
}

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Detecting memory leaks of C++ application in Ubuntu

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)

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QML DropShadow is very slow

QML DropShadow is an interesting effect that acts in a very simple way. It works fine in my application and produces the following result:

QML DropShadow is very slow

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:

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Lines 3D application structure (Windows Store version)

Lines 3D game is a UWP application based on “XAML App for OpenGL ES (Universal Windows)VS2015 project template (written in C++/VS2015 using OpenGL ES 2.0 and elements of OpenGL 3.0). You can install Lines 3D  from Windows Store and play for free, or at least see the game screenshots.

Main components

Game logic and OpenGL rendering engine in Lines 3D are cross-platform. Their code uses STL, OpenGL and abstract C++ interfaces for doing the following tasks:

  • Loading sounds from wav files and playing them with different speed and volume.
  • Loading textures from PNG images (this code uses Windows API, but probably it can be made cross-platform).
  • Logging game events, such as “game over” to the Windows Store. They used to collect statistics on what game levels the users play and what score they get. The possible application crashes (unhandled exceptions and memory failures) and internal errors (like file not found, etc.) are also logged to the Windows Store.
  • Accessing application installation path and application data path in the file system.

All the graphic controls, including the main windows, application bar (main menu), dialogs, message boxes and advertising are written using XAML and Windows-specific code.

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Drawing a transparent image with OpenGL ES in a UWP XAML app

In my previous post Testing XAML App for OpenGL ES on Windows 10 Mobile Device I described the changes I made to UWP application based on “XAML App for OpenGL ES (Universal Windows)” template to demonstrate some strange effect related to the transparency of the image drawn with OpenGL ES in SwapChainPanel. But I did yet another experiment with this application and got some beautiful pictures that demonstrate what happens if I make the scene completely transparent with the following code:

void SimpleRenderer::Draw()
{
    glEnable(GL_DEPTH_TEST);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    ...
}

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Testing XAML App for OpenGL ES on Windows 10 Mobile Device

Today I played a bit with a UWP application based on “XAML App for OpenGL ES (Universal Windows)” template and realized that there is some specific bug probably related to the interaction between SwapChainPanel and OpenGL surface. First, I made the cube transparent by changing two lines of code in the vertex shader:

const std::string vs = STRING
(
    uniform mat4 uModelMatrix;
    uniform mat4 uViewMatrix;
    uniform mat4 uProjMatrix;
    attribute vec4 aPosition;
    attribute vec3 aColor;
    varying vec4 vColor;
    void main()
    {
        gl_Position = uProjMatrix * uViewMatrix * uModelMatrix * aPosition;
        vColor = vec4(aColor, 0.1);
    }
);

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