c++ - opengl draw in 2D coordinates instead of vertex coordinate system -

how can draw in 2d coordinates instead of vertex coordinate system, =>

drawpoint(50 , 100 ,  0.01f); 

this code , background texture , point

static void draw(void) {     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);     double w = glutget( glut_window_width ) / 300.0;     double h = glutget( glut_window_height ) / 300.0;     glmatrixmode(gl_projection);     glloadidentity();     glmatrixmode(gl_modelview);     glloadidentity();      glortho( -1 * w/2, 1 * w/2, -1 * h/2, 1 * h/2, w/2, -h/2);     glbegin(gl_polygon);     gltexcoord2f(0.0f, 0.0f); glvertex3f(-w/2.f, -h/2.f,  0.0f);     gltexcoord2f(1.0f, 0.0f); glvertex3f( w/2.f, -h/2.f,  0.0f);     gltexcoord2f(1.0f, 1.0f); glvertex3f( w/2.f,  h/2.f,  0.0f);     gltexcoord2f(0.0f, 1.0f); glvertex3f(-w/2.f,  h/2.f,  0.0f);     glend();    drawpoint(50 , 100 ,  0.01f);   glutswapbuffers(); } 

the function drawpoint => draws circles

void drawpoint(glfloat x, glfloat y, glfloat radius){     gldisable(gl_lighting);     gldisable(gl_texture_2d);     int i;     int triangleamount = 20; //# of triangles used draw circle      //glfloat radius = 0.8f; //radius     glfloat twicepi = 2.0f * 3.1415;      glbegin(gl_triangle_fan);     glcolor3f(1.0, 0.0, 0.0);         glvertex2f(x, y); // center of circle         for(i = 0; <= triangleamount;i++) {             glvertex2f(                     x + (radius * cos(i *  twicepi / triangleamount)),                 y + (radius * sin(i * twicepi / triangleamount))             );         }     glend();     glenable(gl_lighting);     glenable(gl_texture_2d); } 

so don't know if have change drawpoint function.

update : main source

 glutinitdisplaymode(glut_double | glut_rgb);     glutinit(&argc, argv);     glutinitwindowsize(widthx, heighty);     glutcreatewindow("prg");     glutreshapefunc(resize);     glutdisplayfunc(draw);     glutkeyboardfunc(keypressed);     glutkeyboardupfunc(keyup);     texture[0] = soil_load_ogl_texture      (         "img.jpg",         soil_load_auto,         soil_create_new_id,         soil_flag_invert_y | soil_flag_ntsc_safe_rgb | soil_flag_compress_to_dxt     );     glbindtexture(gl_texture_2d, texture[0]);     glenable(gl_texture_2d);     glclearcolor(0.0f, 0.0f, 0.0f, 0.5f);     glenable(gl_point_smooth);     glhint(gl_point_smooth_hint, gl_nicest);     glhint(gl_perspective_correction_hint, gl_nicest);     glutmainloop(); 

update 2 :

if in way impossible, there method transform x , y vector ?, example :

drawpoint(vectconvert(50),vectconvert(100),0.01f);

i not sure if right answer. edited code, try this:

static void draw(void) {     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);       // divided window width , height 300 seems wrong     double w = glutget( glut_window_width );     double h = glutget( glut_window_height );      glmatrixmode(gl_projection);     glloadidentity();     glmatrixmode(gl_modelview);     glloadidentity();      // create ortho 2d     // last 2 parameters near , far planes     // since using 2d should keep them @ 0.0 , 1.0     glortho( -1 * w/2.0, 1 * w/2.0, -1 * h/2.0, 1 * h/2.0, 0.0f, 1.0f);     // mirror y axis      glscalef(1, -1, 1);     // coordinate system starts @ center of window     // need move left top corner     gltranslatef(-(w/2.0f), -(h/2.0f), 0.0f);      texture[0] = soil_load_ogl_texture // load image file directly new opengl texture     (         "img.jpg",         soil_load_auto,         soil_create_new_id,         soil_flag_invert_y | soil_flag_ntsc_safe_rgb | soil_flag_compress_to_dxt     );      glbindtexture(gl_texture_2d, texture[0]);     glbegin(gl_polygon);     // need mirror y coordinates texture     gltexcoord2f(0.0f, 1.0f); glvertex3f(0.0f , 0.0f, 0.0f);     gltexcoord2f(1.0f, 1.0f); glvertex3f(w    , 0.0f, 0.0f);     gltexcoord2f(1.0f, 0.0f); glvertex3f(w    , h   , 0.0f);     gltexcoord2f(0.0f, 0.0f); glvertex3f(0.0f , h   , 0.0f);     glend();     drawpoint(50 , 100 ,  0.01f);     glutswapbuffers(); } 

also, not load texture file every frame. overkill gpu.