Controls with bitmaps - c

Question

How can I make a control using bitmaps which changes when I drag with the mouse (e.g. a rotating knob)? And this using the Win32 API?

Answer 1

Write code to recognize the WM_MOUSEWHEEL message in your control's window procedure.

Answer 2

The following is a typical loop you'll see in simple games. It's not good practice but a good basis to build upon:
while(!quit) {
while(evt = events_left_for_processing) {
react_to_event(evt);
}
draw_frame();
}
Pay special attention to the second "while", it is better to do it like this than to do an "if", you'll be able to process combined events more accurately.
After a while you may need time-based physics and it becomes more complicated (using accumulators).. A sample from a rather simple game I was writing:
/* Time-based animation loop.
* Accumulator idea picked from an article by Glenn Fiedler on gafferongames.com */
while(!done) {
/* Input */
while(SDL_PollEvent(&evt)) {
window_event(evt, &done);
}
/* Physics */
newTime = time();
deltaTime = newTime - currentTime;
if(deltaTime > 0.0f) {
currentTime = newTime;
accumulator += deltaTime;
while(accumulator >= dt) {
window_update(t, dt);
accumulator -= dt;
t += dt;
}
}
#ifdef FPS_CAPPED
drawTime = newTime - currentDrawTime;
/* Draw */
if(drawTime >= FPS_CAPPED) {
currentDrawTime = newTime;
#endif
window_draw();
SDL_GL_SwapBuffers();
#ifdef FPS_CAPPED
}
#endif
}
window_update etc are generalized functions (they execute a function in the game state, using function pointers).
In your case, the transformation of the square would be changed in the event handler, which catches mouse_move events and has a state for catching mouse_press/release events. In the update you would change the square's position/etc data. In the draw routine you would blit the square. (unless you use other frameworks like OpenGL which use matrix transforms in the render pipeline)