/***************************************************************************

  vidhrdw.c

  Functions to emulate the video hardware of the machine.

***************************************************************************/

#include "driver.h"
#include "vidhrdw/generic.h"

/***************************************************************************

  Convert the color PROMs into a more useable format.

  The palette PROMs are connected to the RGB output this way:

  bit 3 -- 220 ohm resistor  -- RED/GREEN/BLUE
        -- 470 ohm resistor  -- RED/GREEN/BLUE
        -- 1  kohm resistor  -- RED/GREEN/BLUE
  bit 0 -- 2.2kohm resistor  -- RED/GREEN/BLUE

***************************************************************************/
PALETTE_INIT( gaplus )
{
	int i;
	#define TOTAL_COLORS(gfxn) (Machine->gfx[gfxn]->total_colors * Machine->gfx[gfxn]->color_granularity)
	#define COLOR(gfxn,offs) (colortable[Machine->drv->gfxdecodeinfo[gfxn].color_codes_start + offs])


	for (i = 0;i < Machine->drv->total_colors;i++)
	{
		int bit0,bit1,bit2,bit3,r,g,b;


		/* red component */
		bit0 = (color_prom[0] >> 0) & 0x01;
		bit1 = (color_prom[0] >> 1) & 0x01;
		bit2 = (color_prom[0] >> 2) & 0x01;
		bit3 = (color_prom[0] >> 3) & 0x01;
		r = 0x0e * bit0 + 0x1f * bit1 + 0x43 * bit2 + 0x8f * bit3;
		/* green component */
		bit0 = (color_prom[Machine->drv->total_colors] >> 0) & 0x01;
		bit1 = (color_prom[Machine->drv->total_colors] >> 1) & 0x01;
		bit2 = (color_prom[Machine->drv->total_colors] >> 2) & 0x01;
		bit3 = (color_prom[Machine->drv->total_colors] >> 3) & 0x01;
		g = 0x0e * bit0 + 0x1f * bit1 + 0x43 * bit2 + 0x8f * bit3;
		/* blue component */
		bit0 = (color_prom[2*Machine->drv->total_colors] >> 0) & 0x01;
		bit1 = (color_prom[2*Machine->drv->total_colors] >> 1) & 0x01;
		bit2 = (color_prom[2*Machine->drv->total_colors] >> 2) & 0x01;
		bit3 = (color_prom[2*Machine->drv->total_colors] >> 3) & 0x01;
		b = 0x0e * bit0 + 0x1f * bit1 + 0x43 * bit2 + 0x8f * bit3;

		palette_set_color(i,r,g,b);
		color_prom++;
	}

	color_prom += 2*Machine->drv->total_colors;
	/* color_prom now points to the beginning of the lookup table */


	/* characters use colors 240-255 */
	for (i = 0;i < TOTAL_COLORS(0);i++)
		COLOR(0,i) = 240 + (*(color_prom++) & 0x0f);

	/* sprites */
	for (i = 0;i < TOTAL_COLORS(2);i++)
	{
		COLOR(2,i) = (color_prom[0] & 0x0f) + ((color_prom[TOTAL_COLORS(2)] & 0x0f) << 4);
		color_prom++;
	}
}

/***************************************************************************
	Starfield information
	There's 3 sets of stars planes at different speeds.

	a000 ---> (bit 0 = 1) enable starfield.
	  		  (bit 0 = 0) disable starfield.
	a001 ---> starfield plane 0 control
	a002 ---> starfield plane 1 control
	a003 ---> starfield plane 2 control
***************************************************************************/

#define MAX_STARS			250

/* starfield speed constants (bigger = faster) */
#define SPEED_1 0.5
#define SPEED_2 1.0
#define SPEED_3 2.0

struct star {
	float x,y;
	int col,set;
};
static struct star stars[MAX_STARS];

static unsigned char gaplus_starfield_control[4];
static int total_stars;

static void starfield_init( void ) {

	int generator = 0;
	int x,y;
	int set = 0;
	int width, height;

	width = Machine->drv->screen_width;
	height = Machine->drv->screen_height;

	total_stars = 0;

	/* precalculate the star background */
	/* this comes from the Galaxian hardware, Gaplus is probably different */

	for ( y = 0;y < height; y++ ) {
		for ( x = width*2 - 1; x >= 0; x--) {
			int bit1,bit2;

			generator <<= 1;
			bit1 = (~generator >> 17) & 1;
			bit2 = (generator >> 5) & 1;

			if (bit1 ^ bit2) generator |= 1;

			if ( ((~generator >> 16) & 1) && (generator & 0xff) == 0xff) {
				int color;

				color = (~(generator >> 8)) & 0x3f;
				if ( color && total_stars < MAX_STARS ) {
					stars[total_stars].x = x;
					stars[total_stars].y = y;
					stars[total_stars].col = Machine->pens[color];
					stars[total_stars].set = set++;

					if ( set == 3 )
						set = 0;

					total_stars++;
				}
			}
		}
	}
}

void gaplus_starfield_update( void ) {
	int i;
	int width, height;

	width = Machine->drv->screen_width;
	height = Machine->drv->screen_height;

	/* check if we're running */
	if ( ( gaplus_starfield_control[0] & 1 ) == 0 )
		return;

	/* update the starfields */
	for ( i = 0; i < total_stars; i++ ) {
		switch( gaplus_starfield_control[stars[i].set + 1] ) {
			case 0x87:
				/* stand still */
			break;

			case 0x86:
				/* scroll down (speed 1) */
				stars[i].x += SPEED_1;
			break;

			case 0x85:
				/* scroll down (speed 2) */
				stars[i].x += SPEED_2;
			break;

			case 0x06:
				/* scroll down (speed 3) */
				stars[i].x += SPEED_3;
			break;

			case 0x80:
				/* scroll up (speed 1) */
				stars[i].x -= SPEED_1;
			break;

			case 0x82:
				/* scroll up (speed 2) */
				stars[i].x -= SPEED_2;
			break;

			case 0x81:
				/* scroll up (speed 3) */
				stars[i].x -= SPEED_3;
			break;

			case 0x9f:
				/* scroll left (speed 2) */
				stars[i].y += SPEED_2;
			break;

			case 0xaf:
				/* scroll left (speed 1) */
				stars[i].y += SPEED_1;
			break;
		}

		/* wrap */
		if ( stars[i].x < 0 )
			stars[i].x = ( float )( width*2 ) + stars[i].x;

		if ( stars[i].x >= ( float )( width*2 ) )
			stars[i].x -= ( float )( width*2 );

		if ( stars[i].y < 0 )
			stars[i].y = ( float )( height ) + stars[i].y;

		if ( stars[i].y >= ( float )( height ) )
			stars[i].y -= ( float )( height );
	}
}

static void starfield_render( struct mame_bitmap *bitmap ) {

	int i;
	int width, height;

	width = Machine->drv->screen_width;
	height = Machine->drv->screen_height;

	/* check if we're running */
	if ( ( gaplus_starfield_control[0] & 1 ) == 0 )
		return;

	/* draw the starfields */
	for ( i = 0; i < total_stars; i++ )
	{
		int x, y;

		x = stars[i].x;
		y = stars[i].y;

		if ( x >=0 && x < width && y >= 0 && y < height )
		{
			plot_pixel(bitmap, x, y, stars[i].col);
		}
	}
}

WRITE_HANDLER( gaplus_starfield_control_w ) {
	gaplus_starfield_control[offset] = data;
}

extern unsigned char *gaplus_sharedram;

VIDEO_START( gaplus ) {

	/* set up spriteram area */
	spriteram_size = 0x80;
	spriteram = &gaplus_sharedram[0x780];
	spriteram_2 = &gaplus_sharedram[0x780+0x800];
	spriteram_3 = &gaplus_sharedram[0x780+0x800+0x800];

	starfield_init();

	return video_start_generic();
}

/***************************************************************************

	Display Refresh

***************************************************************************/

static void gaplus_draw_sprites(struct mame_bitmap *bitmap){
	int offs;

	for (offs = 0; offs < spriteram_size; offs += 2){
        if ((spriteram_3[offs+1] & 2) == 0){
			int number = spriteram[offs]+4*(spriteram_3[offs] & 0x40);
			int color = spriteram[offs+1] & 0x3f;
            int sx = (spriteram_2[offs+1]-71) + 0x100*(spriteram_3[offs+1] & 1);
			int sy = ( Machine->drv->screen_height ) - spriteram_2[offs]-24;
			int flipy = spriteram_3[offs] & 2;
			int flipx = spriteram_3[offs] & 1;
			int width, height;

			if (number >= 128*3) continue;

			if (flip_screen)
			{
				flipx = !flipx;
				flipy = !flipy;
			}

			if ((spriteram_3[offs] & 0xa8) == 0xa0){ /* draw the sprite twice in a row */
                    drawgfx(bitmap,Machine->gfx[2+(number >> 7)],
								number,color,flipx,flipy,sx,sy,
								&Machine->visible_area,TRANSPARENCY_COLOR,255);
					drawgfx(bitmap,Machine->gfx[2+(number >> 7)],
								number,color,flipx,flipy,sx,sy+16,
								&Machine->visible_area,TRANSPARENCY_COLOR,255);
			}
			else{
				switch (spriteram_3[offs] & 0x28){
					case 0x28:	/* 2x both ways */
						width = height = 2; number &= (~3); break;
					case 0x20:	/* 2x vertical */
						width = 1; height = 2; number &= (~2); break;
					case 0x08:	/* 2x horizontal */
						width = 2; height = 1; number &= (~1); sy += 16; break;
					default:	/* normal sprite */
						width = height = 1; sy += 16; break;
				}
				{
					static int x_offset[2] = { 0x00, 0x01 };
					static int y_offset[2] = { 0x00, 0x02 };
					int x,y, ex, ey;

					for( y=0; y < height; y++ ){
						for( x=0; x < width; x++ ){
							ex = flipx ? (width-1-x) : x;
							ey = flipy ? (height-1-y) : y;

							drawgfx(bitmap,Machine->gfx[2+(number >> 7)],
								(number)+x_offset[ex]+y_offset[ey],
								color,
								flipx, flipy,
								sx+x*16,sy+y*16,
								&Machine->visible_area,
								TRANSPARENCY_COLOR,255);
						}
					}
				}
			}
		}
	}
}

VIDEO_UPDATE( gaplus )
{
	int offs;

	fillbitmap( bitmap, Machine->pens[0], &Machine->visible_area );

	starfield_render( bitmap );

	/* colorram layout: */
	/* bit 7 = bank */
	/* bit 6 = not used? */
	/* bit 5-0 = color */


	/* for every character in the Video RAM, check if it has been modified */
	/* since last time and update it accordingly. */
	for (offs = videoram_size - 1;offs >= 0;offs--)
	{
        int sx,sy,mx,my, bank;

        /* Even if Gaplus screen is 28x36, the memory layout is 32x32. We therefore
        have to convert the memory coordinates into screen coordinates.
        Note that 32*32 = 1024, while 28*36 = 1008: therefore 16 bytes of Video RAM
        don't map to a screen position. We don't check that here, however: range
        checking is performed by drawgfx(). */

        mx = offs / 32;
		my = offs % 32;

        if (mx <= 1)        /* bottom screen characters */
		{
			sx = 29 - my;
			sy = mx + 34;
		}
        else if (mx >= 30)  /* top screen characters */
		{
			sx = 29 - my;
			sy = mx - 30;
		}
        else                /* middle screen characters */
		{
			sx = 29 - mx;
			sy = my + 2;
		}

		if (flip_screen)
		{
			sx = 27 - sx;
			sy = 35 - sy;
		}

		sx = ( ( Machine->drv->screen_height - 1 ) / 8 ) - sx;

		bank = ( colorram[offs] & 0x80 ) ? 1 : 0;

        drawgfx(bitmap,Machine->gfx[bank],
                videoram[offs],
                colorram[offs] & 0x3f,
                flip_screen,flip_screen,8*sy,8*sx,
                &Machine->visible_area,TRANSPARENCY_PEN,0);
	}

	gaplus_draw_sprites(bitmap);
}
