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# basic arcade game timing problem

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my game right now has a main loop like this:


do
{
//check input functions//

//update player position//

//update computer logic (moveX, moveY)//

//update computer position (xPos+=moveX, etc.//

//clear screen//

//draw background//

//draw player//

//draw computer//

//flip screen//

} while(!gameOver);


Where in all that do i put in something to control speed? How can i do this? (I''ve never made a large arcade type game before, so I''ve never really faced this problem)

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Id put the delay after the Flip screen.

How ?
Well you could try a usleep(41);
but I''d have a look at http://nehe.gamedev.net/tutorials/lesson.asp?l=21

It has a nice and easy timer.
the line that dose it is:
while(TimerGetTime()

Hope that helps.

It is a good day to code.

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i''ll give you another alternative:

i''ll have a global variable that controls the speed of sprites. this variable will be fps dependent. so if the fps goes big, it will be big, if fps goes small, it will be small also.

  float g_speedcontrol;// assuming that 60.0 is the normal speedg_speedcontrol = fps / 60.0f;sprite.speed = 5.0f / g_speedcontrol; sprite.xpos += speed;

i''ve tested this and the movement of the sprites is pretty much the same when the game is running at 300fps or 60fps.
however, beware, it will go off limits when fps is very small (1 or 2 fps). if fps = 1, g_speedcontrol = 1/60 -> speed = 50*60; that''s too fast. to solve this, i''ll put an if statement to limit g_speedcontrol to a certain boundary.

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ok so my speeds were real low (originally pixel by pixel so they were like 10) and I got the following suggestion:

xPos += (((SDL_GetTicks()-last_time)/1000.0)*xVel);

but b/c of my speeds being low it was real slow so instead of multipling each speed by about 200 (which i found gave me a desired speed) i did this:

xPos += (((SDL_GetTicks()-last_time)/1000.0)*xVel*200);

which i later simplified to this:

xPos += (((SDL_GetTicks()-last_time)/50.0)*xVel);

is this a decent solution?

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The calculation is being done everytime you want to add move your object. When I did this, I found a bug. We''re dealing with floating point variables, so I got this round-off bugs. When I ran my game, and I''m not moving my object but the fps changing, the object moves by itself. So, I fixed it by doing the calculation on the speed (xVel) and then do the movement as usual:

xVel = (SDL_GetTicks()-last_time)/50.0f;
xpos += xVel;

I think this is more reliable, but if you find your way works better, do it so.

The hardest part of a project is to finish it as planned.
-Albert Tedja-

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