Multi-platform OpenGL ES1.1 problem

JayKim

I have trouble in developing a multi-platform application featuring 2d line graphics using QT.
The codes below show a triangle in Windows and Linux but nothing in Android.

OGL.pro

QT += core gui widgets

CONFIG += c++11

SOURCES += glwidget.cpp main.cpp

HEADERS += glwidget.h

win32:LIBS += -lopengl32
android:LIBS += -lGLESv1_CM

main.cpp

#include <QApplication>
#include <QMainWindow>
#include "glwidget.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
    w.resize(512,512);
    GLWidget g(&w);
    g.resize(w.width(),w.height());
    w.show();
    return a.exec();
}

glwidget.h

#pragma once
#include <QOpenGLWidget>
#include <QOpenGLFunctions>

class GLWidget : public QOpenGLWidget, protected QOpenGLFunctions
{
    Q_OBJECT

public:
    GLWidget(QWidget *parent = nullptr);

protected:
    void initializeGL() override;
    void resizeGL(int w, int h) override;
    void paintGL() override;

    int m_w, m_h;
};

glwidget.cpp

#include "glwidget.h"

#if defined(__ANDROID__)
#   include <GLES/gl.h>
#   define glOrtho glOrthox
#elif defined(__linux__)
#   include <GL/gl.h>
#else
#   include <gl/GL.h>
#endif

GLWidget::GLWidget(QWidget *parent) : QOpenGLWidget(parent)
{
}

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

    glClearColor(0.f,0.f,.5f,1.f);
}

void GLWidget::resizeGL(int w, int h)
{
    glViewport(0, 0, m_w = w, m_h = h);
}

void GLWidget::paintGL()
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, m_w, m_h, 0, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glClear(GL_COLOR_BUFFER_BIT);

    glColor4f(1.f,1.f,1.f,.1f);
    glLineWidth(1.f);

    glEnableClientState(GL_VERTEX_ARRAY);
    float vertex[] = {100.f, 100.f, 300.f, 400.f, 400.f, 300.f, 100.f, 100.f};
    glVertexPointer(2, GL_FLOAT, 0, vertex);
    glDrawArrays(GL_LINE_STRIP, 0, 4);
    glDisableClientState(GL_VERTEX_ARRAY);
}

Windows/Linux(Ubuntu) build runs properly but Android(Samsung galaxy note 20) build does not draw lines at all as below. My project uses a dedicated native c++ library(based on OpenGL ES 1.1) to deal with some complicated vector data. I found that the codes in paintGL() works also properly when they're compiled as JNI libary and called by Java application using Android Studio.

Thank you in advance.

Result of Windows build
Result of Android build