Serious problems getting LockFPS to work.

[savage]

Latest version of sdlticks...

[pascal]
interface

uses
sdl;

type
TSDLTicks = class
private
FStartTime : UInt32;
FTicksPerSecond : UInt32;
FElapsedLastTime : UInt32;
FFPSLastTime : UInt32;
FLockFPSLastTime : UInt32;
public
constructor Create;
destructor Destroy; override; // destructor

{************************************************* ****************************
Init
If the hi-res timer is present, the tick rate is stored and the function
returns true. Otherwise, the function returns false, and the timer should
not be used.
************************************************** ***************************}
function Init : boolean;

{************************************************* **************************
GetGetElapsedSeconds
Returns the Elapsed time, since the function was last called.
************************************************** *************************}
function GetElapsedSeconds : Single;

{************************************************* **************************
GetFPS
Returns the average frames per second.
If this is not called every frame, the client should track the number
of frames itself, and reset the value after this is called.
************************************************** *************************}
function GetFPS : single;

{************************************************* **************************
LockFPS
Used to lock the frame rate to a set amount. This will block until enough
time has passed to ensure that the fps won't go over the requested amount.
Note that this can only keep the fps from going above the specified level;
it can still drop below it. It is assumed that if used, this function will
be called every frame. The value returned is the instantaneous fps, which
will be less than or equal to the targetFPS.
************************************************** *************************}
procedure LockFPS( targetFPS : Byte );
end;

implementation

{ TSDLTicks }
constructor TSDLTicks.Create;
begin
inherited;
FTicksPerSecond := 1000;
end;

destructor TSDLTicks.Destroy;
begin
inherited;
end;

function TSDLTicks.GetElapsedSeconds : Single;
var
currentTime : Cardinal;
begin
currentTime := SDL_GetTicks;

result := ( currentTime - FElapsedLastTime ) / FTicksPerSecond;

// reset the timer
FElapsedLastTime := currentTime;
end;

function TSDLTicks.GetFPS : Single;
var
currentTime, FrameTime : UInt32;
fps : single;
begin
currentTime := SDL_GetTicks;

FrameTime := ( currentTime - FFPSLastTime );

if FrameTime = 0 then
FrameTime := 1;

fps := FTicksPerSecond / FrameTime;

// reset the timer
FFPSLastTime := currentTime;
result := fps;
end;

function TSDLTicks.Init : boolean;
begin
FStartTime := SDL_GetTicks;
FElapsedLastTime := FStartTime;
FFPSLastTime := FStartTime;
FLockFPSLastTime := FStartTime;
result := true;
end;

procedure TSDLTicks.LockFPS( targetFPS : Byte );
var
currentTime : UInt32;
targetTime : single;
begin
if ( targetFPS = 0 ) then
targetFPS := 1;

targetTime := FTicksPerSecond / targetFPS;

// delay to maintain a constant frame rate
repeat
currentTime := SDL_GetTicks;
until ( ( currentTime - FLockFPSLastTime ) > targetTime );

// reset the timer
FLockFPSLastTime := currentTime;
end;
[/pascal]

[jasonf]

Dom, Both GetFPS and LockFPS modify the s_LastTime variable. This means that you can't use them together. You can either view the FPS or Lock the FPS. I don't know if this is a design feature but I was hoping to use them both.. first of all as a test that LockFPS was working and to see when the FPS went really low.


In my game the process is...

[pascal]Loop

Reset the counters

Do some Stuff... some rendering etc

Draw the FPS using GetFPS

Lock the FPS to a specific value

Until Quitting[/pascal]

At the moment, as it stands, GetFPS is resetting the counter before LockFPS has a chance to limit the FPS.

They either need to use 2 variables or there has to be an reset function which is called before anything happens.

[savage]

That's my design flaw, as I was only thinking about using them independently. I'll add fix later tonight, or you can submit a patch .

[jasonf]

Well, I believe that the GetFPS should be a non-destructive reporting function only...

Successive calls to GetFPS should return the same value (well, pretty similar anyway)

Successive calls to LockFPS should not. So it might be OK for LockFPS to modify the start time but not GetFPS.

I'll take a look at this code tonight.

[savage]

I've edited the previous sdlticks.pas post. Testing shows that they all work independently now.

[jasonf]

Sweet

[jasonf]

Sweet as a honey coated lollypop brought with lottery winnings.

It works a treat. the frame rate is nicely balanced at 30fps. Gonna try it on the wife's laptop, I want to see what the performance difference is..

Before my optimisations, I was getting a logic time of 9 now I get 4.. She was getting 4...

Should be smooth

[savage]

This version of sdlticks.pas has not been checked into CVS.