c - SDL - Why moving the mouse changes button state? -

i'm having problem simple directmedia layer library. following code draws block on screen when mouse button pressed:

sdl_event event; while(running){     while(sdl_pollevent(&event)){         while(event.button.state == sdl_pressed){              sdl_pollevent(&event);              //where draw                             boxrect.x = event.motion.x;             boxrect.y = event.motion.y;              //draw screen             sdl_fillrect(display,&boxrect,boxcolor);             sdl_flip(display);         }         // ...     }     // ... } 

it works fine until move mouse, why moving mouse makes event.button.state untrue?

how can work both simultaneously (i.e. keep drawing while button pressed)?

the problem code you're calling sdl_pollevent (documented here) twice. said in documentation:

if event not null, next event removed queue , stored in sdl_event structure pointed event.

rearranging code bit, getting rid of second sdl_pollevent, creating proper flow clicking, moving, releasing , extracting rendering input pumping should give this:

sdl_event event; while(running) {     while(sdl_pollevent(&event))     {         switch(event.type)         {             // handle drawing simple state machine:             case sdl_mousebuttondown:             {                 if(event.button.button == sdl_button_left)                 {                     if(statemachine == released)                     {                         // ... begin drawing                         statemachine = dragging                     }                 }                 break;             }             case sdl_mousemotion:             {                 if(statemachine == dragging)                 {                     // ... update extends of rect                 }             }             case sdl_mousebuttonup:             {                 if(event.button.button == sdl_button_left)                 {                     if(statemachine != released)                     {                         // ... finalize drawing... add rect list? flush it?                         statemachine = released;                     }                 }             }             case sdl_quit:             {                 running = false;                 break;             }         }     }      // outside of event pumping, update graphics     sdl_fillrect(display,&boxrect,boxcolor);     sdl_flip(display); }