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

  video.c

  Functions to emulate the video hardware of the machine.

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

#include "emu.h"
#include "includes/gaplus.h"


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

  Convert the color PROMs.

  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 )
{
	const UINT8 *color_prom = machine.root_device().memregion("proms")->base();
	int i;

	/* allocate the colortable */
	machine.colortable = colortable_alloc(machine, 256);

	for (i = 0;i < 256;i++)
	{
		int bit0,bit1,bit2,bit3,r,g,b;

		/* red component */
		bit0 = (color_prom[i] >> 0) & 0x01;
		bit1 = (color_prom[i] >> 1) & 0x01;
		bit2 = (color_prom[i] >> 2) & 0x01;
		bit3 = (color_prom[i] >> 3) & 0x01;
		r = 0x0e * bit0 + 0x1f * bit1 + 0x43 * bit2 + 0x8f * bit3;
		/* green component */
		bit0 = (color_prom[i + 0x100] >> 0) & 0x01;
		bit1 = (color_prom[i + 0x100] >> 1) & 0x01;
		bit2 = (color_prom[i + 0x100] >> 2) & 0x01;
		bit3 = (color_prom[i + 0x100] >> 3) & 0x01;
		g = 0x0e * bit0 + 0x1f * bit1 + 0x43 * bit2 + 0x8f * bit3;
		/* blue component */
		bit0 = (color_prom[i + 0x200] >> 0) & 0x01;
		bit1 = (color_prom[i + 0x200] >> 1) & 0x01;
		bit2 = (color_prom[i + 0x200] >> 2) & 0x01;
		bit3 = (color_prom[i + 0x200] >> 3) & 0x01;
		b = 0x0e * bit0 + 0x1f * bit1 + 0x43 * bit2 + 0x8f * bit3;

		colortable_palette_set_color(machine.colortable,i,MAKE_RGB(r,g,b));
	}

	color_prom += 0x300;
	/* color_prom now points to the beginning of the lookup table */

	/* characters use colors 0xf0-0xff */
	for (i = 0;i < machine.gfx[0]->total_colors * machine.gfx[0]->color_granularity;i++)
		colortable_entry_set_value(machine.colortable, machine.gfx[0]->color_base + i, 0xf0 + (*color_prom++ & 0x0f));

	/* sprites */
	for (i = 0;i < machine.gfx[1]->total_colors * machine.gfx[1]->color_granularity;i++)
	{
		colortable_entry_set_value(machine.colortable, machine.gfx[1]->color_base + i, (color_prom[0] & 0x0f) + ((color_prom[0x200] & 0x0f) << 4));
		color_prom++;
	}
}



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

  Callbacks for the TileMap code

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

/* convert from 32x32 to 36x28 */
static TILEMAP_MAPPER( tilemap_scan )
{
	int offs;

	row += 2;
	col -= 2;
	if (col & 0x20)
		offs = row + ((col & 0x1f) << 5);
	else
		offs = col + (row << 5);

	return offs;
}

static TILE_GET_INFO( get_tile_info )
{
	gaplus_state *state = machine.driver_data<gaplus_state>();
	UINT8 attr = state->m_videoram[tile_index + 0x400];
	tileinfo.category = (attr & 0x40) >> 6;
	tileinfo.group = attr & 0x3f;
	SET_TILE_INFO(
			0,
			state->m_videoram[tile_index] + ((attr & 0x80) << 1),
			attr & 0x3f,
			0);
}



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

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

static void starfield_init(running_machine &machine)
{
	gaplus_state *state = machine.driver_data<gaplus_state>();
	struct star *stars = state->m_stars;
	int generator = 0;
	int x,y;
	int set = 0;

	int width = machine.primary_screen->width();
	int height = machine.primary_screen->height();

	state->m_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 && state->m_total_stars < MAX_STARS ) {
					stars[state->m_total_stars].x = x;
					stars[state->m_total_stars].y = y;
					stars[state->m_total_stars].col = color;
					stars[state->m_total_stars].set = set++;

					if ( set == 3 )
						set = 0;

					state->m_total_stars++;
				}
			}
		}
	}
}



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

  Start the video hardware emulation.

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

VIDEO_START( gaplus )
{
	gaplus_state *state = machine.driver_data<gaplus_state>();
	state->m_bg_tilemap = tilemap_create(machine, get_tile_info,tilemap_scan,8,8,36,28);

	colortable_configure_tilemap_groups(machine.colortable, state->m_bg_tilemap, machine.gfx[0], 0xff);

	starfield_init(machine);
}



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

  Memory handlers

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

READ8_MEMBER(gaplus_state::gaplus_videoram_r)
{
	return m_videoram[offset];
}

WRITE8_MEMBER(gaplus_state::gaplus_videoram_w)
{
	m_videoram[offset] = data;
	m_bg_tilemap->mark_tile_dirty(offset & 0x3ff);
}

WRITE8_MEMBER(gaplus_state::gaplus_starfield_control_w)
{
	offset &= 3;
	m_starfield_control[offset] = data;
}



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

    Display Refresh

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

static void starfield_render(running_machine &machine, bitmap_ind16 &bitmap)
{
	gaplus_state *state = machine.driver_data<gaplus_state>();
	struct star *stars = state->m_stars;
	int i;

	int width = machine.primary_screen->width();
	int height = machine.primary_screen->height();

	/* check if we're running */
	if ( ( state->m_starfield_control[0] & 1 ) == 0 )
		return;

	/* draw the starfields */
	for ( i = 0; i < state->m_total_stars; i++ )
	{
		int x, y;

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

		if ( x >=0 && x < width && y >= 0 && y < height )
		{
			bitmap.pix16(y, x) = stars[i].col;
		}
	}
}

static void draw_sprites(running_machine &machine, bitmap_ind16 &bitmap, const rectangle &cliprect )
{
	gaplus_state *state = machine.driver_data<gaplus_state>();
	UINT8 *spriteram = state->m_spriteram + 0x780;
	UINT8 *spriteram_2 = spriteram + 0x800;
	UINT8 *spriteram_3 = spriteram_2 + 0x800;
	int offs;

	for (offs = 0;offs < 0x80;offs += 2)
	{
		/* is it on? */
		if ((spriteram_3[offs+1] & 2) == 0)
		{
			static const int gfx_offs[2][2] =
			{
				{ 0, 1 },
				{ 2, 3 }
			};
			int sprite = spriteram[offs] | ((spriteram_3[offs] & 0x40) << 2);
			int color = spriteram[offs+1] & 0x3f;
			int sx = spriteram_2[offs+1] + 0x100 * (spriteram_3[offs+1] & 1) - 71;
			int sy = 256 - spriteram_2[offs] - 8;
			int flipx = (spriteram_3[offs] & 0x01);
			int flipy = (spriteram_3[offs] & 0x02) >> 1;
			int sizex = (spriteram_3[offs] & 0x08) >> 3;
			int sizey = (spriteram_3[offs] & 0x20) >> 5;
			int duplicate = spriteram_3[offs] & 0x80;
			int x,y;

			if (state->flip_screen())
			{
				flipx ^= 1;
				flipy ^= 1;
			}

			sy -= 16 * sizey;
			sy = (sy & 0xff) - 32;	// fix wraparound

			for (y = 0;y <= sizey;y++)
			{
				for (x = 0;x <= sizex;x++)
				{
					drawgfx_transmask(bitmap,cliprect,machine.gfx[1],
						sprite + (duplicate ? 0 : (gfx_offs[y ^ (sizey * flipy)][x ^ (sizex * flipx)])),
						color,
						flipx,flipy,
						sx + 16*x,sy + 16*y,
						colortable_get_transpen_mask(machine.colortable, machine.gfx[1], color, 0xff));
				}
			}
		}
	}
}

SCREEN_UPDATE_IND16( gaplus )
{
	gaplus_state *state = screen.machine().driver_data<gaplus_state>();
	/* flip screen control is embedded in RAM */
	state->flip_screen_set(state->m_spriteram[0x1f7f-0x800] & 1);

	bitmap.fill(0, cliprect);

	starfield_render(screen.machine(), bitmap);

	/* draw the low priority characters */
	state->m_bg_tilemap->draw(bitmap, cliprect, 0,0);

	draw_sprites(screen.machine(), bitmap, cliprect);

	/* draw the high priority characters */
	/* (I don't know if this feature is used by Gaplus, but it's shown in the schematics) */
	state->m_bg_tilemap->draw(bitmap, cliprect, 1,0);
	return 0;
}


SCREEN_VBLANK( gaplus )	/* update starfields */
{
	// falling edge
	if (!vblank_on)
	{
		gaplus_state *state = screen.machine().driver_data<gaplus_state>();
		struct star *stars = state->m_stars;
		int i;

		int width = screen.machine().primary_screen->width();
		int height = screen.machine().primary_screen->height();

		/* check if we're running */
		if ( ( state->m_starfield_control[0] & 1 ) == 0 )
			return;

		/* update the starfields */
		for ( i = 0; i < state->m_total_stars; i++ ) {
			switch( state->m_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 );
		}
	}
}
