Why the center of the fir is not in the (0, 0) (not in the left bottom corner)

[8Observer8]

Hi,

Why the center of the fir is not in the (0, 0) (not in the left bottom corner)?

zip: https://discord.com/channels/457523061650882570/1247941120390991884/1247955899369132163

#include "opengl_widget.h"

OpenGLWidget::OpenGLWidget(QWidget *parent)
    : QOpenGLWidget(parent)
    , m_texture(QOpenGLTexture::Target::Target2D)
{
}

void OpenGLWidget::initializeGL()
{
    initializeOpenGLFunctions();

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    m_program.create();
    m_program.addShaderFromSourceFile(QOpenGLShader::ShaderTypeBit::Vertex,
        ":/assets/shaders/texture.vert");
    m_program.addShaderFromSourceFile(QOpenGLShader::ShaderTypeBit::Fragment,
        ":/assets/shaders/texture.frag");
    m_program.link();
    m_program.bind();

    float vertPositions[] = {
        -0.5f, -0.5f,
        0.5f, -0.5f,
        -0.5f, 0.5f,
        0.5f, 0.5f
    };
    m_vertPosBuffer.create();
    m_vertPosBuffer.bind();
    m_vertPosBuffer.allocate(vertPositions, sizeof(vertPositions));

    float texCoords[] = {
        0.f, 0.f,
        1.f, 0.f,
        0.f, 1.f,
        1.f, 1.f
    };
    m_texCoordBuffer.create();
    m_texCoordBuffer.bind();
    m_texCoordBuffer.allocate(texCoords, sizeof(texCoords));

    m_uMvpMatrixLocation = m_program.uniformLocation("uMvpMatrix");
    m_uSamplerLocation = m_program.uniformLocation("uSampler");

    m_program.setUniformValue(m_uSamplerLocation, 0);
    m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));

    QString texturePath(":/assets/textures/fir.png");
    m_texture.create();
    m_texture.setData(QImage(texturePath).mirrored());
    m_texture.setMinMagFilters(QOpenGLTexture::Filter::Linear,
        QOpenGLTexture::Filter::Linear);
    m_texture.setWrapMode(QOpenGLTexture::WrapMode::ClampToEdge);
}

void OpenGLWidget::resizeGL(int w, int h)
{
    int deviceW = w * devicePixelRatio();
    int deviceH = h * devicePixelRatio();
    float deviceAspect = deviceH / (float) deviceW;

    if (deviceAspect > m_worldAspect)
    {
        m_viewportWidth = deviceW;
        m_viewportHeight = (int) deviceW * m_worldAspect;
        m_viewportX = 0;
        m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
    }
    else
    {
        m_viewportWidth = (int) deviceH / m_worldAspect;
        m_viewportHeight = deviceH;
        m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
        m_viewportY = 0;
    }
    m_projMatrix.setToIdentity();
    m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
    m_projViewMatrix = m_projMatrix * m_viewMatrix;
}

void OpenGLWidget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glClearColor(0.2, 0.2, 0.2, 1);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glClearColor(153.f/255.f, 220.f/255.f, 236.f/255.f, 1.f);
    glEnable(GL_SCISSOR_TEST);
    glClear(GL_COLOR_BUFFER_BIT);
    glDisable(GL_SCISSOR_TEST);

    m_program.bind();
    m_texture.bind();

    m_program.setAttributeBuffer("aPosition", GL_FLOAT, 0, 2);
    m_program.enableAttributeArray("aPosition");

    m_program.setAttributeBuffer("aTexCoord", GL_FLOAT, 0, 2);
    m_program.enableAttributeArray("aTexCoord");

    m_modelMatrix.setToIdentity();
    m_modelMatrix.translate(QVector3D(0.f, 0.f, 0.f));
    m_modelMatrix.scale(QVector3D(78.6f, 100.f, 1.f));
    m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
    m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

The pivot point of the fir is in the center:

    float vertPositions[] = {
        -0.5f, -0.5f,
        0.5f, -0.5f,
        -0.5f, 0.5f,
        0.5f, 0.5f
    };