/******************************************************************
 * Created: Josep Valls 20080211
 * Simple shell for CMPS105/Winter2008
 * Code for limited devices and practice direct memory access and volatile registers
 * Features: This code is a modified version to show how the blinking effect is properly handled
 ******************************************************************/


//general
typedef unsigned short u16;
typedef unsigned char u8;

//the vertical line being draw, volatile as changed outside of code
#define VBLANK_CNT	*(volatile unsigned short*)0x4000006
//this controls vid mode, bkgs, objs etc
#define REG_DISPCNT *(unsigned short*)0x4000000
//controls which buffer is active in mode 4/5
#define BACKBUFFER	0x10


//globals
	// create a pointer to the video buffer
	unsigned short* videoBuffer = (unsigned short*)0x6000000;
	unsigned short* videoBuffer1 = (unsigned short*)0x6000000;
    unsigned short* videoBuffer2 = (unsigned short*)0x600A000;


	// create a pointer to the palette
	unsigned short* videoPalette = (unsigned short*)0x5000000;

//16 bit RGB function
#define RGB16(r,g,b)  ((r)+(g<<5)+(b<<10))

//will wait for screen redraw without interrupts
void WaitVBlank(void){
	while (VBLANK_CNT<160) {};	//do nothing untill vblank has completed
}
//this swaps the locations of the current display and current writing location
void SwapBuffer(void)
{
	if (REG_DISPCNT&BACKBUFFER)		//backbuffer is being displayed so swap
	{
		REG_DISPCNT &= ~BACKBUFFER;	//make display show the frontbuffer (remove backbuffer using it's bitwise compliement)
		videoBuffer=(unsigned short*)videoBuffer2;	//make backbuffer the one we draw to
	}
	else		//frontbuffer is being displayed so swap
	{
		REG_DISPCNT|=BACKBUFFER;	//make display show the backbuffer (add backbuffer)
		videoBuffer=(unsigned short*)videoBuffer1;	//make frontbuffer the one we draw to
	}
}


//prototypes
int changePalette(int);
void drawSomething(void);
void moveBuffer(void);

// entry point to program
int main(void)
{
	// switch to video mode 4 (240x160 8-bit)
	*(unsigned long*)0x4000000 = (0x4 | 0x400);
	
    //initialization
   	u16 x,y;
   	u8 pal;

	//set a palette
	changePalette(0);
	
    //Adds some spice for the effects
    for (x=0;x<120*160;x++) videoBuffer[rand() % (120*160)]=rand()%0xFF;	
    for (x=0;x<6;x++) {
        moveBuffer();
        SwapBuffer();
    }
	int currentPalette=31;
	
	// continuous loop
	while(1) {
        WaitVBlank();

        currentPalette=changePalette(currentPalette);
    }

	return 0; // end program
}

//Sets a palette with a gradient
int changePalette(int p){
    u16 x;
    p++;
	for(x=0;x<256;x++){
	   videoPalette[x]=RGB16(31-(int)x*31/256,abs(p-31),(int)x*31/256);
    }
    if (p==62) p=0;
    return p;
}
//Just plots a dot (two actually in mode 4) in the first line
void drawSomething(void){
    videoBuffer[rand() % 120]=rand()%0xFF;
}
//This function is supposed to be processor intensive
//Will average some points and move those down, from one buffer to the other
void moveBuffer(void){
    unsigned short* bFrom;
    unsigned short* bTo;
    u16 x,y,y2;
    u8 pixel1,pixel2,pixel0,pixel3;
   	if (REG_DISPCNT&BACKBUFFER){
   	    bFrom=(unsigned short*)videoBuffer2;
   	    bTo=(unsigned short*)videoBuffer1;
    }else{
   	    bFrom=(unsigned short*)videoBuffer1;
   	    bTo=(unsigned short*)videoBuffer2;
    }
    for (y=0;y<160;y++){
	   for (x=0;x<120;x++){
	       pixel1=bFrom[y*120+x]&0x00FF;
	       pixel2=(bFrom[y*120+x]&0xFF00)>>8;
	
	       pixel0=bFrom[(y*120+x)-1]&0x00FF;
	       pixel3=(bFrom[(y*120+x)+1]&0xFF00)>>8;

	       pixel1=(pixel1*3+pixel0+pixel2)/5;
	       pixel2=(pixel2*3+pixel1+pixel3)/5;

	       if(y==159) y2=0; else y2=y;
	       bTo[y2*120+x+120]=pixel1|(pixel2<<8);
        }
    }
    //for (x=0;x<120*159;x++)
        //bTo[x+120]=bFrom[x];
}