throttle.c

/*
Copyright 2015 by Joseph Forgione
This file is part of VCC (Virtual Color Computer).

    VCC (Virtual Color Computer) is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    VCC (Virtual Color Computer) is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with VCC (Virtual Color Computer).  If not, see <http://www.gnu.org/licenses/>.
*/

#include <windows.h>
#include "throttle.h"
#include "audio.h"
#include "defines.h"
#include "vcc.h"

static _LARGE_INTEGER StartTime,EndTime,OneFrame,CurrentTime,SleepRes,TargetTime,OneMs;
static _LARGE_INTEGER MasterClock,Now;
static unsigned char FrameSkip=0;
static float fMasterClock=0;

void CalibrateThrottle(void)
{
	timeBeginPeriod(1);	//Needed to get max resolution from the timer normally its 10Ms
	QueryPerformanceFrequency(&MasterClock);
	OneFrame.QuadPart=MasterClock.QuadPart/(TARGETFRAMERATE);
	OneMs.QuadPart=MasterClock.QuadPart/1000;
	fMasterClock=(float)MasterClock.QuadPart;
}


void StartRender(void)
{
	QueryPerformanceCounter(&StartTime);
	return;
}

void EndRender(unsigned char Skip)
{
	FrameSkip=Skip;
	TargetTime.QuadPart=( StartTime.QuadPart+(OneFrame.QuadPart*FrameSkip));
	return;
}

void FrameWait(void)
{
	QueryPerformanceCounter(&CurrentTime);
	while ( (TargetTime.QuadPart-CurrentTime.QuadPart)> (OneMs.QuadPart*2))	//If we have more that 2Ms till the end of the frame
	{
		Sleep(1);	//Give about 1Ms back to the system
		QueryPerformanceCounter(&CurrentTime);	//And check again
	}

	if (GetSoundStatus())	//Lean on the sound card a bit for timing
	{
		PurgeAuxBuffer();
		if (FrameSkip==1)
		{
			if (GetFreeBlockCount()>AUDIOBUFFERS/2)		//Dont let the buffer get lest that half full
				return;
			while (GetFreeBlockCount() < 1);	// Dont let it fill up either
		}

	}
	while ( CurrentTime.QuadPart< TargetTime.QuadPart)	//Poll Untill frame end.
		QueryPerformanceCounter(&CurrentTime);

	return;
}

float CalculateFPS(void) //Done at end of render;
{

	static unsigned short FrameCount=0;
	static float fps=0,fNow=0,fLast=0;

	if (++FrameCount!=FRAMEINTERVAL)
		return(fps);

	QueryPerformanceCounter(&Now);
	fNow=(float)Now.QuadPart;
	fps=(fNow-fLast)/fMasterClock;
	fLast=fNow;
	FrameCount=0;
	fps= FRAMEINTERVAL/fps;
	return(fps);
}