[fpc-pascal]CD-Rom handling

ddt at headrush.co.za ddt at headrush.co.za
Sun Sep 8 18:46:43 CEST 2002

I am currently creating a simple simulation game that is highly dependant  
on my abillity to know which frame is currently being played on an audio 
I am using the SDL cdrom API to do all my CD-Rom stuff (it makes sense 
since it is an SDL game) 
My game needs to be able to jump to frames on the CD relative to the frame 
currently being played (if your wondering I am trying to create a 
simulation of hip-hop style record scratching). 
SDL_CD's cur_frame function doesn't work because it is track relative(I 
have to work as if there is ONLY frames) 
I have tried to handle it by using SDL_Getticks, the idea being that if I 
know the ticks value of the last scratch and the tick value of the current 
scratch I can work out how many frames has played since then (there is 
exactly 75 frames per seccond or 3 frames for every 4 ticks) but this 
refuses to work (I am not sure why). 
Part of the problem appears to be that I the scratches can be either 
forward or backward, but the ticks are allways forward.  
The system emulates a scratch with a mouse drag, if the mouse X is 
increased during the drag then it will scratch forward when the button is 
released, if it decreases it scratches backward. 
Here is the relevant code as it is right now, any help fixing it would be 
greatly appreciated. The current bug is that even when you scratch 
backward, last almost always is higher than when you last scratched (which 
means you don't go back) this code is executed when the mousebutton is 
{Begin Code snippet} 
If (EX > SX)  then Dir := FWD else {EX/SX - Start/End X value of the mouse 
 Dir := BWD; {BWD/FWD is constants declared for readabillity} 
time2 := SDL_Getticks; 
time1 := time2 - time1; 
Last := last +  (time1 div 4) * 3; 
Ammount := ABS(EX - SX) * 10; 
If Dir = FWD then 
Last := Last + Ammount else 
Last := Last - Ammount; 
{Skip to last, last is supposed to be the correct new spot after the 
scratch, the seccond number is how many  to
stop before the next scratch} 
time1 := SDL_Getticks; 
writeln(last);  {This is here for debugging purposses} 
{END code snippet} 
PS. I am using Daniel Moisette's h2pas headers for SDL. 
A.J. Venter 

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