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[SDL] WarpMouse kinda buggy


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#1 oddant   Members   -  Reputation: 100

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Posted 23 February 2012 - 10:09 AM

Hello y'all,

first of all, I'd like to say I'm glad third places like gamedev stand on the web, i'm new on here then I hope I'll make a good impression and won't be so dreadful with this trouble...

here's the situation:

I try to emalute physical attraction, I'm moving the mouse in the screen and as I goes closer from a specific element (e.g. planet or atom) the cursor comes faster until it touches it.

I'm not here to find the function or some equations (I got them) but because I can't figure out how to manage the cursor moving.

I can't simply use SDL_warpMouse( x, y ) because actually this method generates events and cause the program being crazy!

I just need some leading into the documentation because I don't know how I can handle this problem.

to simplify the problem,
let say I want to move the cursor 1px to the right every 0.2s, let see the code :

Uint32 mousex, mousey;

int running = 1;
while (running) {

	 SDL_PollEvent(&Event);

	 switch (event.type) {

	 case SDL_MOUSEMOTION:
	 	 {
	 	 	 mousex = event.motion.x;
	 	 	 mousey = event.motion.y;
	 	 }
	 	 break;

	 }

	 // drawings
	
	 mousex += 1;
	 SDL_warpMouse( mousex, mousey ); // <-- this function seems so inappropriate
	 SDL_Delay( 200 );
}


thanks for your help my friends

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#2 SimonForsman   Crossbones+   -  Reputation: 5468

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Posted 23 February 2012 - 11:54 AM

You could simply separate the mouse position from the "cursor" you display, if you hide the cursor and grab input (SDL_ShowCursor(0); and SDL_WM_GrabInput(SDL_GRAB_ON);) then you will recieve relative motion events even if the cursor is at the edge of the screen, then you use those relative events rather than the absolute cursor position to move your cursor (Which you can then also apply things like gravity to)

So something like

int running = 1;
unsigned int currentTime,oldTime;
oldTime = SDL_GetTicks;
currentTime = oldTime;
while (running) {

		 while (SDL_PollEvent(&event)) { //While loop to process all pending events to prevent the event queue from filling up
		 		switch (event.type) {

			 		case SDL_MOUSEMOTION:
					 cursor.addVelocity(event.motion.xrel,event,motion.yrel);
		 			break;
			  }
		 }
		 currentTime = SDL_GetTicks();
		 if (currentTime-oldTime>10) { //10ms have passed, time to update (updating once every 200ms will be choppy really)
			 //pseudo code incoming (This will not compile)
			for each object:obj that can attract the cursor do {
				Vector2f dir = GetDistanceVector(obj,cursor);
				float distancesq = dir.length()*dir.length();
				Vector2f normDir = dir.normalize();
			  
				cursor.addVelocity(normDir.x*obj.gravity/distancesq , normDir.y*obj.gravity/distancesq);
			}
			cursor.x+=cursor.xvel*0.01f; //positions have to be stored as floats so that we can move partial pixels aswell, we can round them off to even pixels when rendering
			cursor.y+=cursor.yvel*0.01f;
			//end of pseudo code
		 }
		 //Draw everything here.
}

I don't suffer from insanity, I'm enjoying every minute of it.
The voices in my head may not be real, but they have some good ideas!

#3 oddant   Members   -  Reputation: 100

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Posted 24 February 2012 - 08:49 AM

Thanks for your answer,
Well I wasn't looping the queue, that is why I got some unexpected results.
Thanks for the comment at the top of the main loop, it seems to work like a charm now. Posted Image




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