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

  vidhrdw.c

  Functions to emulate the video hardware of the machine.

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

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


unsigned char *ambush_scrollram;
unsigned char *ambush_colorbank;


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

  Convert the color PROMs into a more useable format.

  I'm not sure about the resistor value, I'm using the Galaxian ones.

***************************************************************************/
PALETTE_INIT( ambush )
{
	int i;

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

		/* red component */
		bit0 = (color_prom[i] >> 0) & 0x01;
		bit1 = (color_prom[i] >> 1) & 0x01;
		bit2 = (color_prom[i] >> 2) & 0x01;
		r = 0x21 * bit0 + 0x47 * bit1 + 0x97 * bit2;
		/* green component */
		bit0 = (color_prom[i] >> 3) & 0x01;
		bit1 = (color_prom[i] >> 4) & 0x01;
		bit2 = (color_prom[i] >> 5) & 0x01;
		g = 0x21 * bit0 + 0x47 * bit1 + 0x97 * bit2;
		/* blue component */
		bit0 = 0;
		bit1 = (color_prom[i] >> 6) & 0x01;
		bit2 = (color_prom[i] >> 7) & 0x01;
		b = 0x21 * bit0 + 0x47 * bit1 + 0x97 * bit2;

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


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

  Draw the game screen in the given mame_bitmap.
  Do NOT call osd_update_display() from this function, it will be called by
  the main emulation engine.

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

static void draw_chars(struct mame_bitmap *bitmap, int priority)
{
	int offs, transparency;


	transparency = (priority == 0) ? TRANSPARENCY_NONE : TRANSPARENCY_PEN;

	for (offs = 0; offs < videoram_size; offs++)
	{
		int code,sx,sy,col;
		UINT8 scroll;


		sy = (offs / 32);
		sx = (offs % 32);

		col = colorram[((sy & 0x1c) << 3) + sx];

		if ((col & 0x10) != priority)  continue;

		scroll = ~ambush_scrollram[sx];

		code = videoram[offs] | ((col & 0x60) << 3);

		if (flip_screen)
		{
			sx = 31 - sx;
			sy = 31 - sy;
			scroll = ~scroll - 1;
		}

		drawgfx(bitmap,Machine->gfx[0],
				code,
				(col & 0x0f) | ((*ambush_colorbank & 0x03) << 4),
				flip_screen,flip_screen,
				8*sx, (8*sy + scroll) & 0xff,
				&Machine->visible_area,transparency,0);
	}
}


VIDEO_UPDATE( ambush )
{
	int offs;


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


	/* Draw the background priority characters */
	draw_chars(bitmap, 0x00);


	/* Draw the sprites. */
	for (offs = spriteram_size - 4;offs >= 0;offs -= 4)
	{
		int code,col,sx,sy,flipx,flipy,gfx;


		sy = spriteram[offs + 0];
		sx = spriteram[offs + 3];

		if ( (sy == 0) ||
			 (sy == 0xff) ||
			((sx <  0x40) && (  spriteram[offs + 2] & 0x10)) ||
			((sx >= 0xc0) && (!(spriteram[offs + 2] & 0x10))))  continue;  /* prevent wraparound */


		code = (spriteram[offs + 1] & 0x3f) | ((spriteram[offs + 2] & 0x60) << 1);

		if (spriteram[offs + 2] & 0x80)
		{
			/* 16x16 sprites */
			gfx = 1;

			if (!flip_screen)
			{
				sy = 240 - sy;
			}
			else
			{
				sx = 240 - sx;
			}
		}
		else
		{
			/* 8x8 sprites */
			gfx = 0;
			code <<= 2;

			if (!flip_screen)
			{
				sy = 248 - sy;
			}
			else
			{
				sx = 248 - sx;
			}
		}

		col   = spriteram[offs + 2] & 0x0f;
		flipx = spriteram[offs + 1] & 0x40;
		flipy = spriteram[offs + 1] & 0x80;

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

		drawgfx(bitmap,Machine->gfx[gfx],
				code, col | ((*ambush_colorbank & 0x03) << 4),
				flipx, flipy,
				sx,sy,
				&Machine->visible_area,TRANSPARENCY_PEN,0);
	}


	/* Draw the foreground priority characters */
	draw_chars(bitmap, 0x10);
}
