c - Opengl shapes not drawing in callback function -

in opengl program, want make screen turn red when user hits key. in my_keyboard function, have following:

void my_keyboard( unsigned char key, int x, int y ) {     int feedback_code=0;     if (key == 49) {         feedback_code=1;     }     if (feedback_code==1) {         flash_screen();     } 

my flash_screen method follows:

void screen_flash() {     float mat[16];     glgetfloatv(gl_modelview_matrix,mat);      glcolor3f(1.0f,0.0f,0.0f);      glbegin(gl_polygon);     glvertex2f(0.0f, 0.0f);     glvertex2f(0.0f, 640.0f);     glvertex2f(888.0f, 640.f);     glvertex2f(888.0f, 0.0f);     glend(); } 

by glgetfloatv call, know transformation matrix @ lower left corner should be, @ point (0,0). draw function should draw red square 888x640px, size of window. when run program , hit '1' key, however, don't shape! i've used breakpoints , determined glbegin-glend statements run, don't seem produce anything.

the other shapes have done in main display function, called before main_loop starts.

what doing wrong?

it's common newbie mistake. here's general rule: never make opengl drawing calls event handlers. never!

when want on screen happen in reaction input event, set flag variables, , signal redraw. in drawing function draw according signal.