include/vga.h

/*
 *  Copyright (C) 2002-2020  The DOSBox Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */


#ifndef DOSBOX_VGA_H
#define DOSBOX_VGA_H

#ifndef DOSBOX_DOSBOX_H
#include "dosbox.h"
#endif
#include <iostream>

#define VGA_LFB_MAPPED

#define S3_LFB_BASE_DEFAULT       0xE0000000u

class PageHandler;

enum VGAModes {
    M_CGA2,         // 0
    M_CGA4,
    M_EGA,
    M_VGA,
    M_LIN4,
    M_LIN8,         // 5
    M_LIN15,
    M_LIN16,
    M_LIN24,
    M_LIN32,
    M_TEXT,         // 10
    M_HERC_GFX,
    M_HERC_TEXT,
    M_CGA16,
    M_TANDY2,
    M_TANDY4,       // 15
    M_TANDY16,
    M_TANDY_TEXT,
    M_AMSTRAD,
    M_PC98,
    M_FM_TOWNS,     // 20 STUB
    M_PACKED4,
    M_ERROR,

    M_MAX
};

extern const char* const mode_texts[M_MAX];

enum VGA_Vsync {
        VS_Off,
        VS_On,
        VS_Force,
        VS_Host,
};

struct vsync_state {
        double period;
        bool manual;            // use manual vsync timing
        bool persistent;        // use persistent timer (to keep in sync even after internal mode switches)
        bool faithful;          // use faithful framerate adjustment
};

extern struct vsync_state vsync;
extern float uservsyncjolt;

#define CLK_25 25175u
#define CLK_28 28322u

#define MIN_VCO 180000u
#define MAX_VCO 360000u

#define S3_CLOCK_REF    14318u  /* KHz */
#define S3_CLOCK(_M,_N,_R)      ((S3_CLOCK_REF * (((Bitu)_M) + 2ul)) / ((((Bitu)_N) + 2ul) * ((Bitu)1ul << ((Bitu)_R))))
#define S3_MAX_CLOCK    150000u /* KHz */

#define S3_XGA_1024             0x00u
#define S3_XGA_1152             0x01u
#define S3_XGA_640              0x40u
#define S3_XGA_800              0x80u
#define S3_XGA_1280             0xc0u
#define S3_XGA_1600             0x81u
#define S3_XGA_WMASK    (S3_XGA_640|S3_XGA_800|S3_XGA_1024|S3_XGA_1152|S3_XGA_1280)

#define S3_XGA_8BPP  0x00u
#define S3_XGA_16BPP 0x10u
#define S3_XGA_32BPP 0x30u
#define S3_XGA_CMASK (S3_XGA_8BPP|S3_XGA_16BPP|S3_XGA_32BPP)

typedef struct {
        bool attrindex;
} VGA_Internal;

typedef struct {
/* Video drawing */
        Bitu display_start;
        Bitu real_start;
        bool retrace;                                   /* A retrace is active */
        Bitu scan_len;
        Bitu cursor_start;

/* Some other screen related variables */
        Bitu line_compare;
        bool chained;                                   /* Enable or Disabled Chain 4 Mode */
        bool compatible_chain4;

        /* Pixel Scrolling */
        Bit8u pel_panning;                              /* Amount of pixels to skip when starting horizontal line */
        Bit8u hlines_skip;
        Bit8u bytes_skip;
        Bit8u addr_shift;

/* Specific stuff memory write/read handling */
        
        Bit8u read_mode;
        Bit8u write_mode;
        Bit8u read_map_select;
        Bit8u color_dont_care;
        Bit8u color_compare;
        Bit8u data_rotate;
        Bit8u raster_op;

        Bit32u full_bit_mask;
        Bit32u full_map_mask;
        Bit32u full_not_map_mask;
        Bit32u full_set_reset;
        Bit32u full_not_enable_set_reset;
        Bit32u full_enable_set_reset;
        Bit32u full_enable_and_set_reset;
} VGA_Config;

typedef enum {
        DRAWLINE,
        EGALINE
} Drawmode;

typedef struct {
        bool resizing;
        Bitu width;
        Bitu height;
        Bitu blocks;
        Bitu address;
        Bitu panning;
        Bitu bytes_skip;
        Bit8u *linear_base;
        Bitu linear_mask;
    Bitu planar_mask;
        Bitu address_add;
        Bitu line_length;
        Bitu address_line_total;
        Bitu address_line;
        Bitu lines_total;
        Bitu vblank_skip;
        Bitu lines_done;
        Bitu split_line;
        Bitu byte_panning_shift;
    Bitu render_step,render_max;
        struct {
                double framestart;
                double vrstart, vrend;          // V-retrace
                double hrstart, hrend;          // H-retrace
                double hblkstart, hblkend;      // H-blanking
                double vblkstart, vblkend;      // V-Blanking
                double vdend, vtotal;
                double hdend, htotal;
                float singleline_delay;
        } delay;
        double screen_ratio;
        Bit8u font[516*1024]; /* enlarged to 516KB for PC-98 character font data (256*16) + (128*2*128*16) */
        Bit8u * font_tables[2];
        Bitu blinking;
        bool blink;
        bool char9dot;
        struct {
                Bitu address;
                Bit8u sline,eline;
                Bit8u count,delay;
                Bit8u enabled;
        } cursor;
        Drawmode mode;
        bool has_split;
        bool vret_triggered;
        bool vga_override;
        bool doublescan_set;
        bool doublescan_effect;
        bool char9_set;
        Bitu bpp;
        double clock;
        double oscclock;
        Bit8u cga_snow[80];                     // one bit per horizontal column where snow should occur

        /*Color and brightness for monochrome display*/
        Bit8u monochrome_pal;
        Bit8u monochrome_bright;
} VGA_Draw;

/* enable switch for the "alternative video system" */
extern bool vga_alt_new_mode;

/* NTS: Usage of this general struct will vary between the various video modes.
 *
 *      MDA/Hercules/CGA/PCjr/Tandy: Video hardware is based on the 6845 which
 *      counts horizontal AND vertical timing based on character cells. The
 *      fact that vertical timing is based on character cells is the reason
 *      why changing character cell height requires reprogramming the vertical
 *      timings. Most video modes are not entirely a multiple of the character
 *      cell height, which is why the 6845 has a "vertical adjust" to add to
 *      the total. For example, CGA produces a video signal with NTSC timing
 *      by programming enough character cells vertically with a vertical adjust
 *      to bring video output to the 262 scanlines required by one field of
 *      NTSC video, or 524 scanlines per frame. This isn't quite NTSC since
 *      CGA does not emit the half-a-scanline needed for interlaced (to produce
 *      262.5 lines per field or 525 scanlines per frame) but it happens to
 *      work with most TV sets (although incompatible with Happauge video
 *      capture cards).
 *
 *      Note that the CGA is not the only 80s hardware to emit non-interlaced
 *      NTSC, most video game consoles of the time period do as well. Your
 *      old Nintendo Entertainment System does it too.
 *
 *      Because of the character cell-based vertical timing, CGA emulation here
 *      will probably not rely so much on vert.total as it will on counting
 *      scan lines of the character cell.
 *
 *
 *      EGA/VGA/SVGA: Horizontal timing is based on character cells (which
 *      varies according to the mode and configuration). Vertical timing is
 *      based on scanlines, which is why it is easy to change character cell
 *      height without having to reprogram vertical timing.
 *
 *      Because of that, VGA emulation will count vertical timing entirely by
 *      vert.current and vert.total.
 *
 *
 *      MCGA: Not sure. This is weird hardware. Needs more study. It looks a
 *      lot like the marriage of CGA with a VGA DAC and a 256-color mode tied
 *      to 64KB of memory, and a CRTC that emulates a 6845 but generally ignores
 *      some horizontal and vertical values and hacks others and possibly
 *      carries video line doubling circuitry in order to produce 400-line video
 *      from 200-line video timings (except the 640x480 2-color mode).
 *
 *
 *      NEC PC-98: Two instances of this C++ class will be used in parallel,
 *      with the same dot clock, to emulate the text and graphics "layers" of
 *      PC-98 video. Both instances will generally have the same horizontal
 *      and vertical timing but they don't have to, in which case the VGA
 *      render code will generate the gibberish that would occur on real
 *      hardware when the two are not synchronized.
 */
typedef struct VGA_Experimental_Model_1_t {
    template <typename T> struct pix_char_t {
        T                       pixels;
        T                       chars;

        pix_char_t() { }
        pix_char_t(const T val) : pixels(val), chars(val) { }
    };

    template <typename T> struct start_end_t {
        T                       start;
        T                       end;

        start_end_t() { }
        start_end_t(const T val) : start(val), end(val) { }
        start_end_t(const unsigned int val) : start(val), end(val) { }
    };

    /* pixel 0 is start of display area.
     * next scanline starts when current == total before drawing next pixel.
     */
    struct general_dim {
        // CRTC counter address (H) / CRTC counter address at start of line (V)
        unsigned int                                crtc_addr = 0;

        // CRTC counter address to add per character clock (H) / per scan line (V)
        unsigned int                                crtc_addr_add = 0;

        // current position in pixels within scan line (H) / number of scan line (V)
        pix_char_t<unsigned int>                    current = 0;

        // total pixels in scan line (H) / total scan lines (V)
        pix_char_t<unsigned int>                    total = 0;

        // first pixel (H) / scan line (V) that active display STARTs, ENDs (start == 0 usually)
        start_end_t< pix_char_t<unsigned int> >     active = 0;

        // first pixel (H) / scan line (V) that blanking BEGINs, ENDs
        start_end_t< pix_char_t<unsigned int> >     blank = 0;

        // first pixel (H) / scan line (V) that retrace BEGINs, ENDs
        start_end_t< pix_char_t<unsigned int> >     retrace = 0;

        // largest horizontal active.end value during the entire frame (H) for demos like DoWhackaDo.
        // largest vertical active.end value during the entire frame (V).
        // reset to active.end at start of active display. (H/V)
        pix_char_t<unsigned int>                    active_max = 0;

        // start of scan line (H) / frame (V) PIC full index time
        pic_tickindex_t                             time_begin = 0;

        // length of scan line (H) / length of frame (V)
        pic_tickindex_t                             time_duration = 0;

        // current pixel position (H) / scan line (V) within character cell
        unsigned char                               current_char_pixel = 0;

        // width (H) / scan lines (V) of a character cell
        unsigned char                               char_pixels = 0;

        // bit mask for character row compare
        unsigned char                               char_pixel_mask = 0;

        bool                                        blank_enable = false;           // blank enable
        bool                                        display_enable = false;         // display enable (active area)
        bool                                        retrace_enable = false;         // retrace enable
    };

    // NTS: If start < end, cell starts with enable = false. at start of line,
    //      toggle enable (true) when line == start, then toggle enable (false) when
    //      line == end, then draw.
    //
    //      If start >= end, cell starts with enable = true, at start of line,
    //      toggle enable (false) when line == start, then toggle enable (true) when
    //      line == end, then draw.

    bool                        cursor_enable = false;  // if set, show cursor

    unsigned char               cursor_start = 0;       // cursor starts on this line (toggle cursor enable)
    unsigned char               cursor_end = 0;         // cursor stops on this line (first line to toggle again to disable)

    unsigned int                crtc_cursor_addr = 0;   // crtc address to display cursor at

    unsigned int                crtc_mask = 0;      // draw from memory ((addr & mask) + add)
    unsigned int                crtc_add = 0;       // NTS: For best results crtc_add should only change bits that are masked off

    inline unsigned int crtc_addr_fetch(void) const {
        return (horz.crtc_addr & crtc_mask) + crtc_add;
    }

    inline unsigned int crtc_addr_fetch_and_advance(void) {
        const unsigned int ret = crtc_addr_fetch();
        horz.crtc_addr += horz.crtc_addr_add;
        return ret;
    }

    unsigned int                raster_scanline = 0;    // actual scan line out to display

    unsigned char               doublescan_count = 0;   // VGA doublescan counter
    unsigned char               doublescan_max = 0;     // Advance scanline at this count

    // NTS: horz.char_pixels == 8 for CGA/MDA/etc and EGA/VGA text, but EGA/VGA can select 9 pixels/char.
    //      VGA 320x200x256-color mode will have 4 pixels/char. A hacked version of 320x200x256-color mode
    //      in which the 8BIT bit is cleared (which makes it a sort of 640x200x256-color-ish mode that
    //      reveals the intermediate register states normally hidden) will have 8 pixels/char.
    //
    //      MCGA 320x200x256-color will have horz.char_pixels == 8. A register dump from real hardware shows
    //      that Mode 13 has the same horizontal timings as every other mode (as if 320x200 CGA graphics!).
    //      This is very different from VGA where 320x200x256 is programmed as if a 640x200 graphics mode.
    //
    //      PC-98 will render as if horz.char_pixels == 8 on the text layer. It may set horz.char_pixels == 16
    //      on some text cells if the hardware is to render a double-wide character. The graphics layer is
    //      generally programmed into WORDs mode which means horz.char_pixels == 16 at all times. If it is
    //      ever programmed into byte mode then it will set horz.char_pixels == 8.

    struct dotclock_t {
        double                  rate_invmult = 0;
        double                  rate_mult = 0;
        double                  rate = 0;
        pic_tickindex_t         base = 0;
        signed long long        ticks = 0;
        signed long long        ticks_prev = 0;

        void reset(const pic_tickindex_t now) {
            ticks = ticks_prev = 0;
            base = now;
        }

        // do not call unless all ticks processed
        void set_rate(const double new_rate,const pic_tickindex_t now) {
            if (rate != new_rate) {
                update(now);
                rebase();

                if ((rate <= 0) || (fabs(now - base) > (0.5 * rate_invmult)))
                    base = now;

                if (new_rate > 0) {
                    rate_invmult = 1000 / new_rate; /* Hz -> ms */
                    rate_mult = new_rate / 1000; /* ms -> Hz */
                    rate = new_rate;
                }
                else {
                    rate_invmult = 0;
                    rate_mult = 0;
                    rate = 0;
                }

                update(now);
                ticks_prev = ticks;
            }
        }

        inline pic_tickindex_t ticks2pic_relative(const signed long long t,const pic_tickindex_t now) const {
            return (t * rate_invmult) + (base - now);/* group float operations to maintain precision */
        }

        inline pic_tickindex_t ticks2pic(const signed long long t) const {
            return (t * rate_invmult) + base;
        }

        inline signed long long pic2ticks(const pic_tickindex_t now) const {
            /* typecasting rounds down to 0 apparently. floor() is slower. */
            return (signed long long)((now - base) * rate_mult);
        }

        // inline and minimal for performance!
        inline void update(const pic_tickindex_t now) {
            /* NTS: now = PIC_FullIndex() which is time in ms (1/1000 of a sec) */
            ticks = pic2ticks(now);
        }

        // retrival of tick count and reset of counter
        inline signed long long delta_peek(void) const {
            return ticks - ticks_prev;
        }

        inline signed long long delta_get(void) {
            signed long long ret = delta_peek();
            ticks_prev = ticks;
            return ret;
        }

        // rebase of the counter.
        // call this every so often (but not too often) in order to prevent floating point
        // precision loss over time as the numbers get larger and larger.
        void rebase(void) {
            if (rate_mult > 0) {
                base += ticks * rate_invmult;
                ticks = ticks_prev = 0;
            }
        }
    };

    /* integer fraction.
     * If you need more precision (4.1:3 instead of 4:3) just scale up the values (4.1:3 -> 41:30) */
    struct int_fraction_t {
        unsigned int            numerator = 0;
        unsigned int            denominator = 0;

        int_fraction_t() { }
        int_fraction_t(const unsigned int n,const unsigned int d) : numerator(n), denominator(d) { }
    };

    /* 2D display dimensions */
    struct dimensions_t {
        unsigned int            width = 0;
        unsigned int            height = 0;

        dimensions_t() { }
        dimensions_t(const unsigned int w,const unsigned int h) : width(w), height(h) { }
    };

    /* 2D coordinate */
    struct int_point2d_t {
        int                     x = 0;
        int                     y = 0;

        int_point2d_t() { }
        int_point2d_t(const int nx,const int ny) : x(nx), y(ny) { }
    };

    // use the dot clock to map advancement of emulator time to dot clock ticks.
    // apply the dot clock ticks against the horizontal and vertical current position
    // to emulate the raster of the video output over time.
    //
    // if anything changes dot clock rate, process all ticks and advance hardware
    // state, then set the rate and process all dot clock ticks after that point
    // at the new rate.

    dotclock_t                  dotclock;
    general_dim                 horz,vert;

    // monitor emulation
    dimensions_t                monitor_display;                // image sent to GFX (may include overscan, blanking, etc)
    int_point2d_t               monitor_start_point;            // pixel(x)/scanline(y) counter of the CRTC that is start of line(x)/frame(y)
    int_fraction_t              monitor_aspect_ratio = {4,3};   // display aspect ratio of the video frame

    // The GFX/scaler system will be sent a frame of dimensions monitor_display.
    // The start of the frame will happen when the CRTC pixel count matches the monitor_start_point.
    // monitor_start_point will be set to 0,0 if DOSBox-X is set only to show active area.
    // it will be set to match on the first clock/scanline of the non-blanking area (overscan), upper left corner if set to do so.
    // it will be set to some point of the blanking area if asked to do so to approximate how a VGA monitor centers the image.
    // finally, a debug mode will be offered to show the ENTIRE frame (htotal/vtotal) with markings for retrace if wanted by the user.

    // Pointers to draw from. This represents CRTC character clock 0.
    Bit8u*                      draw_base = NULL;

    template <typename T> inline const T* drawptr(const size_t offset) const {
        return (const T*)draw_base + offset; /* equiv T* ptr = (T*)draw_base; return &ptr[offset]; */
    }

    template <typename T> inline T* drawptr_rw(const size_t offset) const {
        return (T*)draw_base + offset; /* equiv T* ptr = (T*)draw_base; return &ptr[offset]; */
    }
} VGA_Draw_2;

typedef struct {
        Bit8u curmode;
        Bit16u originx, originy;
        Bit8u fstackpos, bstackpos;
        Bit8u forestack[4];
        Bit8u backstack[4];
        Bit16u startaddr;
        Bit8u posx, posy;
        Bit8u mc[64][64];
} VGA_HWCURSOR;

typedef struct {
        Bit8u reg_lock1;
        Bit8u reg_lock2;
        Bit8u reg_31;
        Bit8u reg_35;
        Bit8u reg_36; // RAM size
        Bit8u reg_3a; // 4/8/doublepixel bit in there
        Bit8u reg_40; // 8415/A functionality register
        Bit8u reg_41; // BIOS flags 
        Bit8u reg_42; // CR42 Mode Control
        Bit8u reg_43;
        Bit8u reg_45; // Hardware graphics cursor
        Bit8u reg_50;
        Bit8u reg_51;
        Bit8u reg_52;
        Bit8u reg_55;
        Bit8u reg_58;
        Bit8u reg_6b; // LFB BIOS scratchpad
        Bit8u ex_hor_overflow;
        Bit8u ex_ver_overflow;
        Bit16u la_window;
        Bit8u misc_control_2;
        Bit8u ext_mem_ctrl;
        Bitu xga_screen_width;
        VGAModes xga_color_mode;
        struct {
                Bit8u r;
                Bit8u n;
                Bit8u m;
        } clk[4],mclk;
        struct {
                Bit8u lock;
                Bit8u cmd;
        } pll;
        VGA_HWCURSOR hgc;
} VGA_S3;

typedef struct {
        Bit8u mode_control;
        Bit8u enable_bits;
        bool blend;
} VGA_HERC;

typedef struct {
        Bit32u mask_plane;
        Bit8u write_plane;
        Bit8u read_plane;
        Bit8u border_color;
} VGA_AMSTRAD;

typedef struct {
        Bit8u index;
        Bit8u htotal;
        Bit8u hdend;
        Bit8u hsyncp;
        Bit8u hsyncw;
        Bit8u vtotal;
        Bit8u vdend;
        Bit8u vadjust;
        Bit8u vsyncp;
        Bit8u vsyncw;
        Bit8u max_scanline;
        Bit16u lightpen;
        bool lightpen_triggered;
        Bit8u cursor_start;
        Bit8u cursor_end;
    Bit8u mcga_mode_control;
} VGA_OTHER;

typedef struct {
        Bit8u pcjr_flipflop;
        Bit8u mode_control;
        Bit8u color_select;
        Bit8u disp_bank;
        Bit8u reg_index;
        Bit8u gfx_control;
        Bit8u palette_mask;
        Bit8u extended_ram;
        Bit8u border_color;
        Bit8u line_mask, line_shift;
        Bit8u draw_bank, mem_bank;
        Bit8u *draw_base, *mem_base;
        Bitu addr_mask;
} VGA_TANDY;

typedef struct {
        Bit8u index;
        Bit8u reset;
        Bit8u clocking_mode;
        Bit8u map_mask;
        Bit8u character_map_select;
        Bit8u memory_mode;
} VGA_Seq;

typedef struct {
        Bit8u palette[16];
        Bit8u mode_control;
        Bit8u horizontal_pel_panning;
        Bit8u overscan_color;
        Bit8u color_plane_enable;
        Bit8u color_select;
        Bit8u index;
        Bit8u disabled; // Used for disabling the screen.
                                        // Bit0: screen disabled by attribute controller index
                                        // Bit1: screen disabled by sequencer index 1 bit 5
                                        // These are put together in one variable for performance reasons:
                                        // the line drawing function is called maybe 60*480=28800 times/s,
                                        // and we only need to check one variable for zero this way.
} VGA_Attr;

typedef struct {
        Bit8u horizontal_total;
        Bit8u horizontal_display_end;
        Bit8u start_horizontal_blanking;
        Bit8u end_horizontal_blanking;
        Bit8u start_horizontal_retrace;
        Bit8u end_horizontal_retrace;
        Bit8u vertical_total;
        Bit8u overflow;
        Bit8u preset_row_scan;
        Bit8u maximum_scan_line;
        Bit8u cursor_start;
        Bit8u cursor_end;
        Bit8u start_address_high;
        Bit8u start_address_low;
        Bit8u cursor_location_high;
        Bit8u cursor_location_low;
        Bit8u vertical_retrace_start;
        Bit8u vertical_retrace_end;
        Bit8u vertical_display_end;
        Bit8u offset;
        Bit8u underline_location;
        Bit8u start_vertical_blanking;
        Bit8u end_vertical_blanking;
        Bit8u mode_control;
        Bit8u line_compare;

        Bit8u index;
        bool read_only;
} VGA_Crtc;

typedef struct {
        Bit8u index;
        Bit8u set_reset;
        Bit8u enable_set_reset;
        Bit8u color_compare;
        Bit8u data_rotate;
        Bit8u read_map_select;
        Bit8u mode;
        Bit8u miscellaneous;
        Bit8u color_dont_care;
        Bit8u bit_mask;
} VGA_Gfx;

typedef struct  {
        Bit8u red;
        Bit8u green;
        Bit8u blue;
} RGBEntry;

typedef struct {
        Bit8u bits;                                             /* DAC bits, usually 6 or 8 */
        Bit8u pel_mask;
        Bit8u pel_index;        
        Bit8u state;
        Bit8u write_index;
        Bit8u read_index;
        Bitu first_changed;
        Bit8u combine[16];
        RGBEntry rgb[0x100];
        Bit16u xlat16[256];
        Bit32u xlat32[256];
        Bit8u hidac_counter;
        Bit8u reg02;
} VGA_Dac;

typedef struct {
        Bitu    readStart, writeStart;
        Bitu    bankMask;
        Bitu    bank_read_full;
        Bitu    bank_write_full;
        Bit8u   bank_read;
        Bit8u   bank_write;
        Bitu    bank_size;
} VGA_SVGA;

typedef union CGA_Latch {
        Bit16u d;
    Bit8u b[2] = {};

    CGA_Latch() { }
    CGA_Latch(const Bit16u raw) : d(raw) { }
} CGA_Latch;

typedef union VGA_Latch {
        Bit32u d;
    Bit8u b[4] = {};

    VGA_Latch() { }
    VGA_Latch(const Bit32u raw) : d(raw) { }
} VGA_Latch;

typedef struct VGA_Memory_t {
        Bit8u*      linear = NULL;
        Bit8u*      linear_orgptr = NULL;

    uint32_t    memsize = 0;
    uint32_t    memmask = 0;
    uint32_t    memmask_crtc = 0;       // in CRTC-visible units (depends on byte/word/dword mode)
} VGA_Memory;

typedef struct {
        Bit32u page;
        Bit32u addr;
        Bit32u mask;
        PageHandler *handler;
} VGA_LFB;

static const size_t VGA_Draw_2_elem = 2;

typedef struct VGA_Type_t {
    VGAModes mode = {};                              /* The mode the vga system is in */
    VGAModes lastmode = {};
    Bit8u misc_output = 0;
    VGA_Draw_2 draw_2[VGA_Draw_2_elem];         /* new parallel video emulation. PC-98 mode will use both, all others only the first. */
    VGA_Draw draw = {};
    VGA_Config config = {};
    VGA_Internal internal = {};
    /* Internal module groups */
    VGA_Seq seq = {};
    VGA_Attr attr = {};
    VGA_Crtc crtc = {};
    VGA_Gfx gfx = {};
    VGA_Dac dac = {};
    VGA_Latch latch;
    VGA_S3 s3 = {};
    VGA_SVGA svga = {};
    VGA_HERC herc = {};
    VGA_TANDY tandy = {};
    VGA_AMSTRAD amstrad = {};
    VGA_OTHER other = {};
    VGA_Memory mem;
    VGA_LFB lfb = {};
} VGA_Type;


/* Hercules Palette function */
void Herc_Palette(void);

/* CGA Mono Palette function */
void Mono_CGA_Palette(void);

/* Functions for different resolutions */
void VGA_SetMode(VGAModes mode);
void VGA_DetermineMode(void);
void VGA_SetupHandlers(void);
void VGA_StartResize(Bitu delay=50);
void VGA_SetupDrawing(Bitu val);
void VGA_CheckScanLength(void);
void VGA_ChangedBank(void);

/* Some DAC/Attribute functions */
void VGA_DAC_CombineColor(Bit8u attr,Bit8u pal);
void VGA_DAC_SetEntry(Bitu entry,Bit8u red,Bit8u green,Bit8u blue);
void VGA_ATTR_SetPalette(Bit8u index,Bit8u val);

typedef enum {CGA, EGA, MONO} EGAMonitorMode;

typedef enum {AC_4x4, AC_low4/*4low*/} ACPalRemapMode;

extern unsigned char VGA_AC_remap;

void VGA_ATTR_SetEGAMonitorPalette(EGAMonitorMode m);

/* The VGA Subfunction startups */
void VGA_SetupAttr(void);
void VGA_SetupMemory(void);
void VGA_SetupDAC(void);
void VGA_SetupMisc(void);
void VGA_SetupGFX(void);
void VGA_SetupSEQ(void);
void VGA_SetupOther(void);
void VGA_SetupXGA(void);

/* Some Support Functions */
void VGA_SetClock(Bitu which,Bitu target);
void VGA_StartUpdateLFB(void);
void VGA_SetBlinking(Bitu enabled);
void VGA_SetCGA2Table(Bit8u val0,Bit8u val1);
void VGA_SetCGA4Table(Bit8u val0,Bit8u val1,Bit8u val2,Bit8u val3);
void VGA_ActivateHardwareCursor(void);
void VGA_KillDrawing(void);

void VGA_SetOverride(bool vga_override);

extern VGA_Type vga;

/* Support for modular SVGA implementation */
/* Video mode extra data to be passed to FinishSetMode_SVGA().
   This structure will be in flux until all drivers (including S3)
   are properly separated. Right now it contains only three overflow
   fields in S3 format and relies on drivers re-interpreting those.
   For reference:
   ver_overflow:X|line_comp10|X|vretrace10|X|vbstart10|vdispend10|vtotal10
   hor_overflow:X|X|X|hretrace8|X|hblank8|hdispend8|htotal8
   offset is not currently used by drivers (useful only for S3 itself)
   It also contains basic int10 mode data - number, vtotal, htotal
   */
typedef struct {
        Bit8u ver_overflow;
        Bit8u hor_overflow;
        Bitu offset;
        Bitu modeNo;
        Bitu htotal;
        Bitu vtotal;
} VGA_ModeExtraData;

// Vector function prototypes
typedef void (*tWritePort)(Bitu reg,Bitu val,Bitu iolen);
typedef Bitu (*tReadPort)(Bitu reg,Bitu iolen);
typedef void (*tFinishSetMode)(Bitu crtc_base, VGA_ModeExtraData* modeData);
typedef void (*tDetermineMode)();
typedef void (*tSetClock)(Bitu which,Bitu target);
typedef Bitu (*tGetClock)();
typedef bool (*tHWCursorActive)();
typedef bool (*tAcceptsMode)(Bitu modeNo);
typedef void (*tSetupDAC)();
typedef void (*tINT10Extensions)();

struct SVGA_Driver {
        tWritePort write_p3d5;
        tReadPort read_p3d5;
        tWritePort write_p3c5;
        tReadPort read_p3c5;
        tWritePort write_p3c0;
        tReadPort read_p3c1;
        tWritePort write_p3cf;
        tReadPort read_p3cf;

        tFinishSetMode set_video_mode;
        tDetermineMode determine_mode;
        tSetClock set_clock;
        tGetClock get_clock;
        tHWCursorActive hardware_cursor_active;
        tAcceptsMode accepts_mode;
        tSetupDAC setup_dac;
        tINT10Extensions int10_extensions;
};

extern SVGA_Driver svga;
extern int enableCGASnow;

void SVGA_Setup_S3Trio(void);
void SVGA_Setup_TsengET4K(void);
void SVGA_Setup_TsengET3K(void);
void SVGA_Setup_ParadisePVGA1A(void);
void SVGA_Setup_Driver(void);

// Amount of video memory required for a mode, implemented in int10_modes.cpp
Bitu VideoModeMemSize(Bitu mode);

extern Bit32u ExpandTable[256];
extern Bit32u FillTable[16];
extern Bit32u CGA_2_Table[16];
extern Bit32u CGA_4_Table[256];
extern Bit32u CGA_4_HiRes_Table[256];
extern Bit32u CGA_16_Table[256];
extern Bit32u TXT_Font_Table[16];
extern Bit32u TXT_FG_Table[16];
extern Bit32u TXT_BG_Table[16];
extern Bit32u Expand16Table[4][16];
extern Bit32u Expand16BigTable[0x10000];

void VGA_DAC_UpdateColorPalette();

extern uint32_t GFX_Rmask;
extern unsigned char GFX_Rshift;

extern uint32_t GFX_Gmask;
extern unsigned char GFX_Gshift;

extern uint32_t GFX_Bmask;
extern unsigned char GFX_Bshift;

extern uint32_t GFX_Amask;
extern unsigned char GFX_Ashift;

extern unsigned char GFX_bpp;

/* current dosplay page (controlled by A4h) */
extern unsigned char *pc98_pgraph_current_display_page;
/* current CPU page (controlled by A6h) */
extern unsigned char *pc98_pgraph_current_cpu_page;

/* functions to help cleanup memory map access instead of hardcoding offsets.
 * your C++ compiler should be smart enough to inline these into the body of this function. */

/* TODO: Changes to memory layout relative to vga.mem.linear:
 *
 *       Text to take 0x00000-0x03FFF instead of 0x00000-0x07FFF.
 *
 *       Graphics to start at 0x04000
 *
 *       Each bitplane will be 64KB (0x10000) bytes long, and the page flip bit in 0xA6
 *       will select which 32KB half within the 64KB block to use, or if another bit is
 *       set as documented in Undocumented PC-98, the full 64KB block.
 *
 *       The 512KB + 32KB will be reduced slightly to 512KB + 16KB to match the layout.
 *
 *       The bitplane layout change will permit emulating an 8 bitplane 256-color mode
 *       suggested by Yksoft1 that early PC-9821 systems supported and that the 256-color
 *       driver shipped with Windows 3.1 (for PC-98) uses. Based on Windows 3.1 behavior
 *       that also means the linear framebuffer at 0xF00000 must also change in planar
 *       mode to spread all 8 bits across the planes on write and gather all 8 bits
 *       on read. As far as I can tell the Windows 3.1 256-color driver uses planar
 *       and EGC functions as it would in 16-color mode, but draws bitmaps using the
 *       LFB. The picture is wrong EXCEPT when Windows icons and bitmaps are drawn.
 *
 *       256-color packed mode will be retained as direct LFB mapping from the start of
 *       graphics RAM.
 *
 *       On a real PC-9821 laptop, contents accessible to the CPU noticeably shift order
 *       and position when you switch on/off 256-color packed mode, suggesting that the
 *       planar mode is simply reordered memory access in hardware OR that 256-color
 *       mode is "chained" (much like 256-color packed mode on IBM VGA hardware) across
 *       bitplanes. */

#define PC98_VRAM_TEXT_OFFSET           ( 0x00000u )        /* 16KB memory (8KB text + 8KB attributes) */
#define PC98_VRAM_GRAPHICS_OFFSET       ( 0x04000u )        /* where graphics memory begins */

#define PC98_VRAM_BITPLANE_SIZE         ( 0x10000u )        /* one bitplane */

#define PC98_VRAM_PAGEFLIP_SIZE         ( 0x08000u )        /* add this amount for the second page in 8/16/256-color planar mode */
#define PC98_VRAM_PAGEFLIP256_SIZE      ( 0x40000u )        /* add this amount for the second page in 256-color packed mode */

#define PC98_VRAM_256BANK_SIZE          ( 0x08000u )        /* window/bank size (256-color packed) */

extern uint32_t pc98_pegc_banks[2];

static inline unsigned char *pc98_vram_text(void) {
    return vga.mem.linear + PC98_VRAM_TEXT_OFFSET;
}

/* return value is relative to current CPU page or current display page ptr */
static inline constexpr unsigned int pc98_pgram_bitplane_offset(const unsigned int b) {
    /* WARNING: b is not range checked for performance! Do not call with b >= 8 if memsize = 512KB or b >= 4 if memsize >= 256KB */
    return (b * PC98_VRAM_BITPLANE_SIZE);
}

static inline unsigned char *pc98_vram_256bank_from_window(const unsigned int b) {
    /* WARNING: b is not range checked for performance! Do not call with b >= 2 */
    return vga.mem.linear + PC98_VRAM_GRAPHICS_OFFSET + pc98_pegc_banks[b];
}

#define VRAM98_TEXT         ( pc98_vram_text() )

#endif