...

target_link_libraries(MyCPlusPlusActivity
     android
     native_app_glue
     EGL
     GLESv2
     GLESv1_CM
     log)

...

#include <GLES2/gl2.h>
#include <GLES/gl.h>

...

void MyGame::DrawGraphic_OpenGL()
{
     // green color
     glClearColor(0.72f, 0.87f, 0.55f, 1);
     glClear(GL_COLOR_BUFFER_BIT);

     // draw line
     XYZ points[] = {
               {0, -0.5, 0}, // point1
               {-1, 0.5, 0}, // point2
               {+1, 0.5, 0}, // point3
     };

     RGBA colors[] = {
               {0.0f, 0.0f, 1.0f, 1.0f}, // blue color for point1
               {1.0f, 0.0f, 0.0f, 1.0f}, // red color for point2
               {0.0f, 1.0f, 0.0f, 1.0f}, // green color for point3
     };
     glLineWidth(10);
     DrawGraphic_Primitive(points, colors, 3, GL_TRIANGLES);

     eglSwapBuffers(m_Display, m_Surface);
}

void MyGame::DrawGraphic_Primitive(XYZ* points, RGBA* colors, int count, int primitiveType)
{
     glVertexPointer(sizeof(points[0])/sizeof(GLfloat) /*=3 it is count of fields: x,y,z*/, GL_FLOAT, 0, points);

     glColorPointer(sizeof(colors[0])/sizeof(GLfloat) /*=4 it is count of fields: red,green,blue, alpha*/ , GL_FLOAT, 0, colors);

     glDrawArrays(primitiveType, 0 /*first index to draw*/, count /*count of points to draw*/);
}


bool MyGame::InitGraphic_OpenGL(ANativeWindow* pWindow)
{
     ...

     EGLint contextAttribs[] =
     {
          EGL_CONTEXT_CLIENT_VERSION, 2,
          EGL_CONTEXT_CLIENT_VERSION, 1,
     }

     ...

     // enable draw lines and colors
     glEnableClientState(GL_VERTEX_ARRAY);// allow to use glVertexPointer
     glEnableClientState(GL_COLOR_ARRAY); // allow to use glColorPointer

     return true;
}

...

include <android/input.h>
#include <android/asset_manager.h>
#include <EGL/egl.h>
#include <GLES/gl.h>

typedef struct
{
     GLfloat red; // [0...1]
     GLfloat green; // [0...1]
     GLfloat blue; // [0...1]
     GLfloat alpha; // [0...1]
} RGBA;

typedef struct
{
     GLfloat x;
     GLfloat y;
     GLfloat z;
} XYZ;

class MyGame
{
     ...

     // OpenGL
     public: void DrawGraphic_Primitive(XYZ* points, RGBA* colors, int count, int primitiveType);

     ...
}

     // draw line
     XYZ points[] = {
               {0, -0.5, 0}, // point1
               {-1, 0.5, 0}, // point2
               {+1, 0.5, 0}, // point3
     };

     RGBA colors[] = {
               {0.0f, 0.0f, 1.0f, 1.0f}, // blue color for point1
               {1.0f, 0.0f, 0.0f, 1.0f}, // red color for point2
               {0.0f, 1.0f, 0.0f, 1.0f}, // green color for point3
     };