// license:GPL-2.0+
// copyright-holders:Kevin Thacker,Sandro Ronco
/***************************************************************************

  z88.c

  Functions to emulate the video hardware of the Cambridge Z88

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

#include "emu.h"
#include "includes/z88.h"


inline void z88_state::plot_pixel(bitmap_ind16 &bitmap, int x, int y, uint16_t color)
{
	if (x < Z88_SCREEN_WIDTH)
		bitmap.pix(y, x) = color;
}

// convert absolute offset into correct address to get data from
inline uint8_t* z88_state::convert_address(uint32_t offset)
{
	if (offset < 0x080000) // rom
		return m_bios + (offset & 0x7ffff);
	else if (offset < 0x100000) // slot0
		return m_ram_base + (offset & 0x7ffff);
	else if (offset < 0x200000) // slot1
		return m_carts[1]->get_cart_base() + (offset & 0xfffff);
	else if (offset < 0x300000) // slot2
		return m_carts[2]->get_cart_base() + (offset & 0xfffff);
	else if (offset < 0x400000) // slot3
		return m_carts[3]->get_cart_base() + (offset & 0xfffff);

	return nullptr;
}

/***************************************************************************
  Start the video hardware emulation.
***************************************************************************/

// Initialise the palette
void z88_state::z88_palette(palette_device &palette) const
{
	m_palette->set_pen_color(0, rgb_t(138, 146, 148));
	m_palette->set_pen_color(1, rgb_t(92,  83,  88));
	m_palette->set_pen_color(2, rgb_t(122, 126, 129));
}

/* temp - change to gfxelement structure */

void z88_state::vh_render_8x8(bitmap_ind16 &bitmap, int x, int y, uint16_t pen0, uint16_t pen1, uint8_t *gfx)
{
	for (int h = 0; h < 8; h++)
	{
		uint8_t data = gfx[h];

		for (int b = 0; b < 8; b++)
		{
			plot_pixel(bitmap, x + b, y + h, BIT(data, 7 - b) ? pen1 : pen0);
		}
	}
}

void z88_state::vh_render_6x8(bitmap_ind16 &bitmap, int x, int y, uint16_t pen0, uint16_t pen1, uint8_t *gfx)
{
	for (int h = 0; h < 8; h++)
	{
		uint8_t data = gfx[h] << 2;

		for (int b = 0; b < 6; b++)
		{
			plot_pixel(bitmap, x + 1 + b, y + h, BIT(data, 7 - b) ? pen1 : pen0);
		}
	}
}

void z88_state::vh_render_line(bitmap_ind16 &bitmap, int x, int y, uint16_t pen)
{
	for (int i = 0; i < 8; i++)
	{
		plot_pixel(bitmap, x + i, y + 7, pen);
	}
}

UPD65031_SCREEN_UPDATE(z88_state::lcd_update)
{
	if (sbf == 0)
	{
		// LCD disabled
		bitmap.fill(0);
	}
	else
	{
		uint8_t *vram = convert_address(sbf << 11);

		for (int y = 0; y < (Z88_SCREEN_HEIGHT >> 3); y++)
		{
			int x = 0, c = 0;

			while (x < Z88_SCREEN_WIDTH)
			{
				uint8_t byte0 = vram[(y * 0x100) + c];
				uint8_t byte1 = vram[(y * 0x100) + c + 1];

				// inverted graphics?
				uint16_t pen0 = 0;
				uint16_t pen1 = 0;
				if (byte1 & Z88_SCR_HW_REV)
					pen0 = (byte1 & Z88_SCR_HW_GRY) ? 2 : 1;
				else
					pen1 = (byte1 & Z88_SCR_HW_GRY) ? 2 : 1;

				if ((byte1 & Z88_SCR_HW_NULL) == Z88_SCR_HW_NULL)
				{
					// hidden
				}
				else if (!(byte1 & Z88_SCR_HW_HRS) || (((byte1 & Z88_SCR_HW_CURS) == Z88_SCR_HW_CURS)))
				{
					// low-res 6x8
					const uint16_t ch = (byte0 | (byte1 << 8)) & 0x1ff;

					uint8_t *char_gfx;
					if ((ch & 0x01c0) == 0x01c0)
						char_gfx = convert_address(lores0 << 9) + ((ch & 0x3f) << 3);
					else
						char_gfx = convert_address(lores1 << 12) + (ch << 3);

					// cursor flash
					if (flash && (byte1 & Z88_SCR_HW_CURS) == Z88_SCR_HW_CURS)
						vh_render_6x8(bitmap, x, y << 3, pen1, pen0, char_gfx);
					else
						vh_render_6x8(bitmap, x, y << 3, pen0, pen1, char_gfx);

					// underline?
					if (byte1 & Z88_SCR_HW_UND)
						vh_render_line(bitmap, x, y << 3, pen1);

					x += 6;
				}
				else if ((byte1 & Z88_SCR_HW_HRS) && !(byte1 & Z88_SCR_HW_REV))
				{
					// high-res 8x8
					const uint16_t ch = (byte0 | (byte1 << 8)) & 0x3ff;

					uint8_t *char_gfx;
					if (BIT(ch, 8))
						char_gfx = convert_address(hires1 << 11) + ((ch & 0xff) << 3);
					else
						char_gfx = convert_address(hires0 << 13) + ((ch & 0xff) << 3);

					// flash
					if ((byte1 & Z88_SCR_HW_FLS) && flash)
						pen0 = pen1 = 0;

					vh_render_8x8(bitmap, x, y << 3, pen0, pen1, char_gfx);

					x += 8;
				}

				// every char takes 2 bytes
				c += 2;
			}
		}
	}
}
