src/doom/r_draw.c

//
// Copyright(C) 1993-1996 Id Software, Inc.
// Copyright(C) 2005-2014 Simon Howard
//
// 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.
//
// DESCRIPTION:
//	The actual span/column drawing functions.
//	Here find the main potential for optimization,
//	 e.g. inline assembly, different algorithms.
//


#include "doomdef.h"
#include "deh_main.h"

#include "i_system.h"
#include "z_zone.h"
#include "w_wad.h"

#include "r_local.h"

// Needs access to LFB (guess what).
#include "v_video.h"
#include "v_trans.h"

// State.
#include "doomstat.h"


// ?
//#define MAXWIDTH			1120
//#define MAXHEIGHT			832

// status bar height at bottom of screen
#define SBARHEIGHT		(32 << crispy->hires)

//
// All drawing to the view buffer is accomplished in this file.
// The other refresh files only know about ccordinates,
//  not the architecture of the frame buffer.
// Conveniently, the frame buffer is a linear one,
//  and we need only the base address,
//  and the total size == width*height*depth/8.,
//


byte*		viewimage;
int		viewwidth;
int		scaledviewwidth;
int		viewheight;
int		viewwindowx;
int		viewwindowy;
pixel_t*		ylookup[MAXHEIGHT];
int		columnofs[MAXWIDTH];

// Color tables for different players,
//  translate a limited part to another
//  (color ramps used for  suit colors).
//
byte		translations[3][256];

// Backing buffer containing the bezel drawn around the screen and
// surrounding background.

static pixel_t *background_buffer = NULL;


//
// R_DrawColumn
// Source is the top of the column to scale.
//
lighttable_t*		dc_colormap[2]; // [crispy] brightmaps
int			dc_x;
int			dc_yl;
int			dc_yh;
fixed_t			dc_iscale;
fixed_t			dc_texturemid;
int			dc_texheight; // [crispy] Tutti-Frutti fix

// first pixel in a column (possibly virtual)
byte*			dc_source;

// just for profiling
int			dccount;

//
// A column is a vertical slice/span from a wall texture that,
//  given the DOOM style restrictions on the view orientation,
//  will always have constant z depth.
// Thus a special case loop for very fast rendering can
//  be used. It has also been used with Wolfenstein 3D.
//
// [crispy] replace R_DrawColumn() with Lee Killough's implementation
// found in MBF to fix Tutti-Frutti, taken from mbfsrc/R_DRAW.C:99-1979

void R_DrawColumn (void)
{
    int			count;
    pixel_t*		dest;
    fixed_t		frac;
    fixed_t		fracstep;
    int			heightmask = dc_texheight - 1;

    count = dc_yh - dc_yl;

    // Zero length, column does not exceed a pixel.
    if (count < 0)
	return;

#ifdef RANGECHECK
    if ((unsigned)dc_x >= SCREENWIDTH
	|| dc_yl < 0
	|| dc_yh >= SCREENHEIGHT)
	I_Error ("R_DrawColumn: %i to %i at %i", dc_yl, dc_yh, dc_x);
#endif

    // Framebuffer destination address.
    // Use ylookup LUT to avoid multiply with ScreenWidth.
    // Use columnofs LUT for subwindows?
    dest = ylookup[dc_yl] + columnofs[flipviewwidth[dc_x]];

    // Determine scaling,
    //  which is the only mapping to be done.
    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    // Inner loop that does the actual texture mapping,
    //  e.g. a DDA-lile scaling.
    // This is as fast as it gets.

  // heightmask is the Tutti-Frutti fix -- killough
  if (dc_texheight & heightmask) // not a power of 2 -- killough
  {
    heightmask++;
    heightmask <<= FRACBITS;

    if (frac < 0)
	while ((frac += heightmask) < 0);
    else
	while (frac >= heightmask)
	    frac -= heightmask;

    do
    {
	// [crispy] brightmaps
	const byte source = dc_source[frac>>FRACBITS];
	*dest = dc_colormap[dc_brightmap[source]][source];

	dest += SCREENWIDTH;
	if ((frac += fracstep) >= heightmask)
	    frac -= heightmask;
    } while (count--);
  }
  else // texture height is a power of 2 -- killough
  {
    do
    {
	// Re-map color indices from wall texture column
	//  using a lighting/special effects LUT.
	// [crispy] brightmaps
	const byte source = dc_source[(frac>>FRACBITS)&heightmask];
	*dest = dc_colormap[dc_brightmap[source]][source];

	dest += SCREENWIDTH;
	frac += fracstep;

    } while (count--);
  }
}


// UNUSED.
// Loop unrolled.
#if 0
void R_DrawColumn (void)
{
    int			count;
    byte*		source;
    byte*		dest;
    byte*		colormap;

    unsigned		frac;
    unsigned		fracstep;
    unsigned		fracstep2;
    unsigned		fracstep3;
    unsigned		fracstep4;

    count = dc_yh - dc_yl + 1;

    source = dc_source;
    colormap = dc_colormap;
    dest = ylookup[dc_yl] + columnofs[dc_x];

    fracstep = dc_iscale<<9;
    frac = (dc_texturemid + (dc_yl-centery)*dc_iscale)<<9;

    fracstep2 = fracstep+fracstep;
    fracstep3 = fracstep2+fracstep;
    fracstep4 = fracstep3+fracstep;

    while (count >= 8)
    {
	dest[0] = colormap[source[frac>>25]];
	dest[SCREENWIDTH] = colormap[source[(frac+fracstep)>>25]];
	dest[SCREENWIDTH*2] = colormap[source[(frac+fracstep2)>>25]];
	dest[SCREENWIDTH*3] = colormap[source[(frac+fracstep3)>>25]];

	frac += fracstep4;

	dest[SCREENWIDTH*4] = colormap[source[frac>>25]];
	dest[SCREENWIDTH*5] = colormap[source[(frac+fracstep)>>25]];
	dest[SCREENWIDTH*6] = colormap[source[(frac+fracstep2)>>25]];
	dest[SCREENWIDTH*7] = colormap[source[(frac+fracstep3)>>25]];

	frac += fracstep4;
	dest += SCREENWIDTH*8;
	count -= 8;
    }

    while (count > 0)
    {
	*dest = colormap[source[frac>>25]];
	dest += SCREENWIDTH;
	frac += fracstep;
	count--;
    }
}
#endif


void R_DrawColumnLow (void)
{
    int			count;
    pixel_t*		dest;
    pixel_t*		dest2;
    fixed_t		frac;
    fixed_t		fracstep;
    int                 x;
    int			heightmask = dc_texheight - 1;

    count = dc_yh - dc_yl;

    // Zero length.
    if (count < 0)
	return;

#ifdef RANGECHECK
    if ((unsigned)dc_x >= SCREENWIDTH
	|| dc_yl < 0
	|| dc_yh >= SCREENHEIGHT)
    {

	I_Error ("R_DrawColumn: %i to %i at %i", dc_yl, dc_yh, dc_x);
    }
    //	dccount++;
#endif
    // Blocky mode, need to multiply by 2.
    x = dc_x << 1;

    dest = ylookup[dc_yl] + columnofs[flipviewwidth[x]];
    dest2 = ylookup[dc_yl] + columnofs[flipviewwidth[x+1]];

    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

  // heightmask is the Tutti-Frutti fix -- killough
  if (dc_texheight & heightmask) // not a power of 2 -- killough
  {
    heightmask++;
    heightmask <<= FRACBITS;

    if (frac < 0)
	while ((frac += heightmask) < 0);
    else
	while (frac >= heightmask)
	    frac -= heightmask;

    do
    {
	// [crispy] brightmaps
	const byte source = dc_source[frac>>FRACBITS];
	*dest2 = *dest = dc_colormap[dc_brightmap[source]][source];

	dest += SCREENWIDTH;
	dest2 += SCREENWIDTH;

	if ((frac += fracstep) >= heightmask)
	    frac -= heightmask;
    } while (count--);
  }
  else // texture height is a power of 2 -- killough
  {
    do
    {
	// Hack. Does not work corretly.
	// [crispy] brightmaps
	const byte source = dc_source[(frac>>FRACBITS)&heightmask];
	*dest2 = *dest = dc_colormap[dc_brightmap[source]][source];
	dest += SCREENWIDTH;
	dest2 += SCREENWIDTH;

	frac += fracstep;

    } while (count--);
  }
}


//
// Spectre/Invisibility.
//
#define FUZZTABLE		50
#define FUZZOFF	(1)


int	fuzzoffset[FUZZTABLE] =
{
    FUZZOFF,-FUZZOFF,FUZZOFF,-FUZZOFF,FUZZOFF,FUZZOFF,-FUZZOFF,
    FUZZOFF,FUZZOFF,-FUZZOFF,FUZZOFF,FUZZOFF,FUZZOFF,-FUZZOFF,
    FUZZOFF,FUZZOFF,FUZZOFF,-FUZZOFF,-FUZZOFF,-FUZZOFF,-FUZZOFF,
    FUZZOFF,-FUZZOFF,-FUZZOFF,FUZZOFF,FUZZOFF,FUZZOFF,FUZZOFF,-FUZZOFF,
    FUZZOFF,-FUZZOFF,FUZZOFF,FUZZOFF,-FUZZOFF,-FUZZOFF,FUZZOFF,
    FUZZOFF,-FUZZOFF,-FUZZOFF,-FUZZOFF,-FUZZOFF,FUZZOFF,FUZZOFF,
    FUZZOFF,FUZZOFF,-FUZZOFF,FUZZOFF,FUZZOFF,-FUZZOFF,FUZZOFF
};

int	fuzzpos = 0;

// [crispy] draw fuzz effect independent of rendering frame rate
static int fuzzpos_tic;
void R_SetFuzzPosTic (void)
{
	// [crispy] prevent the animation from remaining static
	if (fuzzpos == fuzzpos_tic)
	{
		fuzzpos = (fuzzpos + 1) % FUZZTABLE;
	}
	fuzzpos_tic = fuzzpos;
}
void R_SetFuzzPosDraw (void)
{
	fuzzpos = fuzzpos_tic;
}

//
// Framebuffer postprocessing.
// Creates a fuzzy image by copying pixels
//  from adjacent ones to left and right.
// Used with an all black colormap, this
//  could create the SHADOW effect,
//  i.e. spectres and invisible players.
//
void R_DrawFuzzColumn (void)
{
    int			count;
    pixel_t*		dest;
    fixed_t		frac;
    fixed_t		fracstep;
    boolean		cutoff = false;

    // Adjust borders. Low...
    if (!dc_yl)
	dc_yl = 1;

    // .. and high.
    if (dc_yh == viewheight-1)
    {
	dc_yh = viewheight - 2;
	cutoff = true;
    }

    count = dc_yh - dc_yl;

    // Zero length.
    if (count < 0)
	return;

#ifdef RANGECHECK
    if ((unsigned)dc_x >= SCREENWIDTH
	|| dc_yl < 0 || dc_yh >= SCREENHEIGHT)
    {
	I_Error ("R_DrawFuzzColumn: %i to %i at %i",
		 dc_yl, dc_yh, dc_x);
    }
#endif

    dest = ylookup[dc_yl] + columnofs[flipviewwidth[dc_x]];

    // Looks familiar.
    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    // Looks like an attempt at dithering,
    //  using the colormap #6 (of 0-31, a bit
    //  brighter than average).
    do
    {
	// Lookup framebuffer, and retrieve
	//  a pixel that is either one column
	//  left or right of the current one.
	// Add index from colormap to index.
#ifndef CRISPY_TRUECOLOR
	*dest = colormaps[6*256+dest[SCREENWIDTH*fuzzoffset[fuzzpos]]];
#else
	*dest = I_BlendDark(dest[SCREENWIDTH*fuzzoffset[fuzzpos]], 0xD3);
#endif

	// Clamp table lookup index.
	if (++fuzzpos == FUZZTABLE)
	    fuzzpos = 0;

	dest += SCREENWIDTH;

	frac += fracstep;
    } while (count--);

    // [crispy] if the line at the bottom had to be cut off,
    // draw one extra line using only pixels of that line and the one above
    if (cutoff)
    {
#ifndef CRISPY_TRUECOLOR
	*dest = colormaps[6*256+dest[SCREENWIDTH*(fuzzoffset[fuzzpos]-FUZZOFF)/2]];
#else
	*dest = I_BlendDark(dest[SCREENWIDTH*(fuzzoffset[fuzzpos]-FUZZOFF)/2], 0xD3);
#endif
    }
}

// low detail mode version

void R_DrawFuzzColumnLow (void)
{
    int			count;
    pixel_t*		dest;
    pixel_t*		dest2;
    fixed_t		frac;
    fixed_t		fracstep;
    int x;
    boolean		cutoff = false;

    // Adjust borders. Low...
    if (!dc_yl)
	dc_yl = 1;

    // .. and high.
    if (dc_yh == viewheight-1)
    {
	dc_yh = viewheight - 2;
	cutoff = true;
    }

    count = dc_yh - dc_yl;

    // Zero length.
    if (count < 0)
	return;

    // low detail mode, need to multiply by 2

    x = dc_x << 1;

#ifdef RANGECHECK
    if ((unsigned)x >= SCREENWIDTH
	|| dc_yl < 0 || dc_yh >= SCREENHEIGHT)
    {
	I_Error ("R_DrawFuzzColumn: %i to %i at %i",
		 dc_yl, dc_yh, dc_x);
    }
#endif

    dest = ylookup[dc_yl] + columnofs[flipviewwidth[x]];
    dest2 = ylookup[dc_yl] + columnofs[flipviewwidth[x+1]];

    // Looks familiar.
    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    // Looks like an attempt at dithering,
    //  using the colormap #6 (of 0-31, a bit
    //  brighter than average).
    do
    {
	// Lookup framebuffer, and retrieve
	//  a pixel that is either one column
	//  left or right of the current one.
	// Add index from colormap to index.
#ifndef CRISPY_TRUECOLOR
	*dest = colormaps[6*256+dest[SCREENWIDTH*fuzzoffset[fuzzpos]]];
	*dest2 = colormaps[6*256+dest2[SCREENWIDTH*fuzzoffset[fuzzpos]]];
#else
	*dest = I_BlendDark(dest[SCREENWIDTH*fuzzoffset[fuzzpos]], 0xD3);
	*dest2 = I_BlendDark(dest2[SCREENWIDTH*fuzzoffset[fuzzpos]], 0xD3);
#endif

	// Clamp table lookup index.
	if (++fuzzpos == FUZZTABLE)
	    fuzzpos = 0;

	dest += SCREENWIDTH;
	dest2 += SCREENWIDTH;

	frac += fracstep;
    } while (count--);

    // [crispy] if the line at the bottom had to be cut off,
    // draw one extra line using only pixels of that line and the one above
    if (cutoff)
    {
#ifndef CRISPY_TRUECOLOR
	*dest = colormaps[6*256+dest[SCREENWIDTH*(fuzzoffset[fuzzpos]-FUZZOFF)/2]];
	*dest2 = colormaps[6*256+dest2[SCREENWIDTH*(fuzzoffset[fuzzpos]-FUZZOFF)/2]];
#else
	*dest = I_BlendDark(dest[SCREENWIDTH*(fuzzoffset[fuzzpos]-FUZZOFF)/2], 0xD3);
	*dest2 = I_BlendDark(dest2[SCREENWIDTH*(fuzzoffset[fuzzpos]-FUZZOFF)/2], 0xD3);
#endif
    }
}


//
// R_DrawTranslatedColumn
// Used to draw player sprites
//  with the green colorramp mapped to others.
// Could be used with different translation
//  tables, e.g. the lighter colored version
//  of the BaronOfHell, the HellKnight, uses
//  identical sprites, kinda brightened up.
//
byte*	dc_translation;
byte*	translationtables;

void R_DrawTranslatedColumn (void)
{
    int			count;
    pixel_t*		dest;
    fixed_t		frac;
    fixed_t		fracstep;

    count = dc_yh - dc_yl;
    if (count < 0)
	return;

#ifdef RANGECHECK
    if ((unsigned)dc_x >= SCREENWIDTH
	|| dc_yl < 0
	|| dc_yh >= SCREENHEIGHT)
    {
	I_Error ( "R_DrawColumn: %i to %i at %i",
		  dc_yl, dc_yh, dc_x);
    }

#endif


    dest = ylookup[dc_yl] + columnofs[flipviewwidth[dc_x]];

    // Looks familiar.
    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    // Here we do an additional index re-mapping.
    do
    {
	// Translation tables are used
	//  to map certain colorramps to other ones,
	//  used with PLAY sprites.
	// Thus the "green" ramp of the player 0 sprite
	//  is mapped to gray, red, black/indigo.
	*dest = dc_colormap[0][dc_translation[dc_source[frac>>FRACBITS]]];
	dest += SCREENWIDTH;

	frac += fracstep;
    } while (count--);
}

void R_DrawTranslatedColumnLow (void)
{
    int			count;
    pixel_t*		dest;
    pixel_t*		dest2;
    fixed_t		frac;
    fixed_t		fracstep;
    int                 x;

    count = dc_yh - dc_yl;
    if (count < 0)
	return;

    // low detail, need to scale by 2
    x = dc_x << 1;

#ifdef RANGECHECK
    if ((unsigned)x >= SCREENWIDTH
	|| dc_yl < 0
	|| dc_yh >= SCREENHEIGHT)
    {
	I_Error ( "R_DrawColumn: %i to %i at %i",
		  dc_yl, dc_yh, x);
    }

#endif


    dest = ylookup[dc_yl] + columnofs[flipviewwidth[x]];
    dest2 = ylookup[dc_yl] + columnofs[flipviewwidth[x+1]];

    // Looks familiar.
    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    // Here we do an additional index re-mapping.
    do
    {
	// Translation tables are used
	//  to map certain colorramps to other ones,
	//  used with PLAY sprites.
	// Thus the "green" ramp of the player 0 sprite
	//  is mapped to gray, red, black/indigo.
	*dest = dc_colormap[0][dc_translation[dc_source[frac>>FRACBITS]]];
	*dest2 = dc_colormap[0][dc_translation[dc_source[frac>>FRACBITS]]];
	dest += SCREENWIDTH;
	dest2 += SCREENWIDTH;

	frac += fracstep;
    } while (count--);
}

void R_DrawTLColumn (void)
{
    int			count;
    pixel_t*		dest;
    fixed_t		frac;
    fixed_t		fracstep;

    count = dc_yh - dc_yl;
    if (count < 0)
	return;

#ifdef RANGECHECK
    if ((unsigned)dc_x >= SCREENWIDTH
	|| dc_yl < 0
	|| dc_yh >= SCREENHEIGHT)
    {
	I_Error ( "R_DrawColumn: %i to %i at %i",
		  dc_yl, dc_yh, dc_x);
    }
#endif

    dest = ylookup[dc_yl] + columnofs[flipviewwidth[dc_x]];

    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    do
    {
#ifndef CRISPY_TRUECOLOR
        // actual translucency map lookup taken from boom202s/R_DRAW.C:255
        *dest = tranmap[(*dest<<8)+dc_colormap[0][dc_source[frac>>FRACBITS]]];
#else
        const pixel_t destrgb = dc_colormap[0][dc_source[frac>>FRACBITS]];
        *dest = blendfunc(*dest, destrgb);
#endif
	dest += SCREENWIDTH;

	frac += fracstep;
    } while (count--);
}

// [crispy] draw translucent column, low-resolution version
void R_DrawTLColumnLow (void)
{
    int			count;
    pixel_t*		dest;
    pixel_t*		dest2;
    fixed_t		frac;
    fixed_t		fracstep;
    int                 x;

    count = dc_yh - dc_yl;
    if (count < 0)
	return;

    x = dc_x << 1;

#ifdef RANGECHECK
    if ((unsigned)x >= SCREENWIDTH
	|| dc_yl < 0
	|| dc_yh >= SCREENHEIGHT)
    {
	I_Error ( "R_DrawColumn: %i to %i at %i",
		  dc_yl, dc_yh, x);
    }
#endif

    dest = ylookup[dc_yl] + columnofs[flipviewwidth[x]];
    dest2 = ylookup[dc_yl] + columnofs[flipviewwidth[x+1]];

    fracstep = dc_iscale;
    frac = dc_texturemid + (dc_yl-centery)*fracstep;

    do
    {
#ifndef CRISPY_TRUECOLOR
	*dest = tranmap[(*dest<<8)+dc_colormap[0][dc_source[frac>>FRACBITS]]];
	*dest2 = tranmap[(*dest2<<8)+dc_colormap[0][dc_source[frac>>FRACBITS]]];
#else
	const pixel_t destrgb = dc_colormap[0][dc_source[frac>>FRACBITS]];
	*dest = blendfunc(*dest, destrgb);
	*dest2 = blendfunc(*dest2, destrgb);
#endif
	dest += SCREENWIDTH;
	dest2 += SCREENWIDTH;

	frac += fracstep;
    } while (count--);
}

//
// R_InitTranslationTables
// Creates the translation tables to map
//  the green color ramp to gray, brown, red.
// Assumes a given structure of the PLAYPAL.
// Could be read from a lump instead.
//
void R_InitTranslationTables (void)
{
    int		i;

    translationtables = Z_Malloc (256*3, PU_STATIC, 0);

    // translate just the 16 green colors
    for (i=0 ; i<256 ; i++)
    {
	if (i >= 0x70 && i<= 0x7f)
	{
	    // map green ramp to gray, brown, red
	    translationtables[i] = 0x60 + (i&0xf);
	    translationtables [i+256] = 0x40 + (i&0xf);
	    translationtables [i+512] = 0x20 + (i&0xf);
	}
	else
	{
	    // Keep all other colors as is.
	    translationtables[i] = translationtables[i+256]
		= translationtables[i+512] = i;
	}
    }
}


//
// R_DrawSpan
// With DOOM style restrictions on view orientation,
//  the floors and ceilings consist of horizontal slices
//  or spans with constant z depth.
// However, rotation around the world z axis is possible,
//  thus this mapping, while simpler and faster than
//  perspective correct texture mapping, has to traverse
//  the texture at an angle in all but a few cases.
// In consequence, flats are not stored by column (like walls),
//  and the inner loop has to step in texture space u and v.
//
int			ds_y;
int			ds_x1;
int			ds_x2;

lighttable_t*		ds_colormap[2];
byte*			ds_brightmap;

fixed_t			ds_xfrac;
fixed_t			ds_yfrac;
fixed_t			ds_xstep;
fixed_t			ds_ystep;

// start of a 64*64 tile image
byte*			ds_source;

// just for profiling
int			dscount;


//
// Draws the actual span.
void R_DrawSpan (void)
{
//  unsigned int position, step;
    pixel_t *dest;
    int count;
    int spot;
    unsigned int xtemp, ytemp;

#ifdef RANGECHECK
    if (ds_x2 < ds_x1
	|| ds_x1<0
	|| ds_x2>=SCREENWIDTH
	|| (unsigned)ds_y>SCREENHEIGHT)
    {
	I_Error( "R_DrawSpan: %i to %i at %i",
		 ds_x1,ds_x2,ds_y);
    }
//	dscount++;
#endif

    // Pack position and step variables into a single 32-bit integer,
    // with x in the top 16 bits and y in the bottom 16 bits.  For
    // each 16-bit part, the top 6 bits are the integer part and the
    // bottom 10 bits are the fractional part of the pixel position.

/*
    position = ((ds_xfrac << 10) & 0xffff0000)
             | ((ds_yfrac >> 6)  & 0x0000ffff);
    step = ((ds_xstep << 10) & 0xffff0000)
         | ((ds_ystep >> 6)  & 0x0000ffff);
*/

//  dest = ylookup[ds_y] + columnofs[ds_x1];

    // We do not check for zero spans here?
    count = ds_x2 - ds_x1;

    do
    {
	byte source;
	// Calculate current texture index in u,v.
        // [crispy] fix flats getting more distorted the closer they are to the right
        ytemp = (ds_yfrac >> 10) & 0x0fc0;
        xtemp = (ds_xfrac >> 16) & 0x3f;
        spot = xtemp | ytemp;

	// Lookup pixel from flat texture tile,
	//  re-index using light/colormap.
	source = ds_source[spot];
	dest = ylookup[ds_y] + columnofs[flipviewwidth[ds_x1++]];
	*dest = ds_colormap[ds_brightmap[source]][source];

//      position += step;
        ds_xfrac += ds_xstep;
        ds_yfrac += ds_ystep;

    } while (count--);
}


// UNUSED.
// Loop unrolled by 4.
#if 0
void R_DrawSpan (void)
{
    unsigned	position, step;

    byte*	source;
    byte*	colormap;
    pixel_t*	dest;

    unsigned	count;
    usingned	spot;
    unsigned	value;
    unsigned	temp;
    unsigned	xtemp;
    unsigned	ytemp;

    position = ((ds_xfrac<<10)&0xffff0000) | ((ds_yfrac>>6)&0xffff);
    step = ((ds_xstep<<10)&0xffff0000) | ((ds_ystep>>6)&0xffff);

    source = ds_source;
    colormap = ds_colormap;
    dest = ylookup[ds_y] + columnofs[ds_x1];
    count = ds_x2 - ds_x1 + 1;

    while (count >= 4)
    {
	ytemp = position>>4;
	ytemp = ytemp & 4032;
	xtemp = position>>26;
	spot = xtemp | ytemp;
	position += step;
	dest[0] = colormap[source[spot]];

	ytemp = position>>4;
	ytemp = ytemp & 4032;
	xtemp = position>>26;
	spot = xtemp | ytemp;
	position += step;
	dest[1] = colormap[source[spot]];

	ytemp = position>>4;
	ytemp = ytemp & 4032;
	xtemp = position>>26;
	spot = xtemp | ytemp;
	position += step;
	dest[2] = colormap[source[spot]];

	ytemp = position>>4;
	ytemp = ytemp & 4032;
	xtemp = position>>26;
	spot = xtemp | ytemp;
	position += step;
	dest[3] = colormap[source[spot]];

	count -= 4;
	dest += 4;
    }
    while (count > 0)
    {
	ytemp = position>>4;
	ytemp = ytemp & 4032;
	xtemp = position>>26;
	spot = xtemp | ytemp;
	position += step;
	*dest++ = colormap[source[spot]];
	count--;
    }
}
#endif


//
// Again..
//
void R_DrawSpanLow (void)
{
//  unsigned int position, step;
    unsigned int xtemp, ytemp;
    pixel_t *dest;
    int count;
    int spot;

#ifdef RANGECHECK
    if (ds_x2 < ds_x1
	|| ds_x1<0
	|| ds_x2>=SCREENWIDTH
	|| (unsigned)ds_y>SCREENHEIGHT)
    {
	I_Error( "R_DrawSpan: %i to %i at %i",
		 ds_x1,ds_x2,ds_y);
    }
//	dscount++;
#endif

/*
    position = ((ds_xfrac << 10) & 0xffff0000)
             | ((ds_yfrac >> 6)  & 0x0000ffff);
    step = ((ds_xstep << 10) & 0xffff0000)
         | ((ds_ystep >> 6)  & 0x0000ffff);
*/

    count = (ds_x2 - ds_x1);

    // Blocky mode, need to multiply by 2.
    ds_x1 <<= 1;
    ds_x2 <<= 1;

//  dest = ylookup[ds_y] + columnofs[ds_x1];

    do
    {
	byte source;
	// Calculate current texture index in u,v.
        // [crispy] fix flats getting more distorted the closer they are to the right
        ytemp = (ds_yfrac >> 10) & 0x0fc0;
        xtemp = (ds_xfrac >> 16) & 0x3f;
        spot = xtemp | ytemp;

	// Lowres/blocky mode does it twice,
	//  while scale is adjusted appropriately.
	source = ds_source[spot];
	dest = ylookup[ds_y] + columnofs[flipviewwidth[ds_x1++]];
	*dest = ds_colormap[ds_brightmap[source]][source];
	dest = ylookup[ds_y] + columnofs[flipviewwidth[ds_x1++]];
	*dest = ds_colormap[ds_brightmap[source]][source];

//	position += step;
	ds_xfrac += ds_xstep;
	ds_yfrac += ds_ystep;


    } while (count--);
}

//
// R_InitBuffer
// Creats lookup tables that avoid
//  multiplies and other hazzles
//  for getting the framebuffer address
//  of a pixel to draw.
//
void
R_InitBuffer
( int		width,
  int		height )
{
    int		i;

    // Handle resize,
    //  e.g. smaller view windows
    //  with border and/or status bar.
    viewwindowx = (SCREENWIDTH-width) >> 1;

    // Column offset. For windows.
    for (i=0 ; i<width ; i++)
	columnofs[i] = viewwindowx + i;

    // Samw with base row offset.
    if (width == SCREENWIDTH)
	viewwindowy = 0;
    else
	viewwindowy = (SCREENHEIGHT-SBARHEIGHT-height) >> 1;

    // Preclaculate all row offsets.
    for (i=0 ; i<height ; i++)
	ylookup[i] = I_VideoBuffer + (i+viewwindowy)*SCREENWIDTH;
}


//
// R_FillBackScreen
// Fills the back screen with a pattern
//  for variable screen sizes
// Also draws a beveled edge.
//
void R_FillBackScreen (void)
{
    byte*	src;
    pixel_t*	dest;
    int		x;
    int		y;
    patch_t*	patch;

    // DOOM border patch.
    const char *name1 = DEH_String("FLOOR7_2");

    // DOOM II border patch.
    const char *name2 = DEH_String("GRNROCK");

    const char *name;

    // If we are running full screen, there is no need to do any of this,
    // and the background buffer can be freed if it was previously in use.

    if (scaledviewwidth == SCREENWIDTH)
    {
        if (background_buffer != NULL)
        {
            Z_Free(background_buffer);
            background_buffer = NULL;
        }

	return;
    }

    // Allocate the background buffer if necessary

    if (background_buffer == NULL)
    {
        background_buffer = Z_Malloc(MAXWIDTH * (MAXHEIGHT - SBARHEIGHT) * sizeof(*background_buffer),
                                     PU_STATIC, NULL);
    }

    if (gamemode == commercial)
	name = name2;
    else
	name = name1;

    src = W_CacheLumpName(name, PU_CACHE);
    dest = background_buffer;

    for (y=0 ; y<SCREENHEIGHT-SBARHEIGHT ; y++)
    {
#ifndef CRISPY_TRUECOLOR
	for (x=0 ; x<SCREENWIDTH/64 ; x++)
	{
	    memcpy (dest, src+((y&63)<<6), 64);
	    dest += 64;
	}

	if (SCREENWIDTH&63)
	{
	    memcpy (dest, src+((y&63)<<6), SCREENWIDTH&63);
	    dest += (SCREENWIDTH&63);
	}
#else
	for (x=0 ; x<SCREENWIDTH ; x++)
	{
		*dest++ = colormaps[src[((y&63)<<6) + (x&63)]];
	}
#endif
    }

    // Draw screen and bezel; this is done to a separate screen buffer.

    V_UseBuffer(background_buffer);

    patch = W_CacheLumpName(DEH_String("brdr_t"),PU_CACHE);

    for (x=0 ; x<(scaledviewwidth >> crispy->hires) ; x+=8)
	V_DrawPatch((viewwindowx >> crispy->hires)+x-WIDESCREENDELTA, (viewwindowy >> crispy->hires)-8, patch);
    patch = W_CacheLumpName(DEH_String("brdr_b"),PU_CACHE);

    for (x=0 ; x<(scaledviewwidth >> crispy->hires) ; x+=8)
	V_DrawPatch((viewwindowx >> crispy->hires)+x-WIDESCREENDELTA, (viewwindowy >> crispy->hires)+(viewheight >> crispy->hires), patch);
    patch = W_CacheLumpName(DEH_String("brdr_l"),PU_CACHE);

    for (y=0 ; y<(viewheight >> crispy->hires) ; y+=8)
	V_DrawPatch((viewwindowx >> crispy->hires)-8-WIDESCREENDELTA, (viewwindowy >> crispy->hires)+y, patch);
    patch = W_CacheLumpName(DEH_String("brdr_r"),PU_CACHE);

    for (y=0 ; y<(viewheight >> crispy->hires) ; y+=8)
	V_DrawPatch((viewwindowx >> crispy->hires)+(scaledviewwidth >> crispy->hires)-WIDESCREENDELTA, (viewwindowy >> crispy->hires)+y, patch);

    // Draw beveled edge.
    V_DrawPatch((viewwindowx >> crispy->hires)-8-WIDESCREENDELTA,
                (viewwindowy >> crispy->hires)-8,
                W_CacheLumpName(DEH_String("brdr_tl"),PU_CACHE));

    V_DrawPatch((viewwindowx >> crispy->hires)+(scaledviewwidth >> crispy->hires)-WIDESCREENDELTA,
                (viewwindowy >> crispy->hires)-8,
                W_CacheLumpName(DEH_String("brdr_tr"),PU_CACHE));

    V_DrawPatch((viewwindowx >> crispy->hires)-8-WIDESCREENDELTA,
                (viewwindowy >> crispy->hires)+(viewheight >> crispy->hires),
                W_CacheLumpName(DEH_String("brdr_bl"),PU_CACHE));

    V_DrawPatch((viewwindowx >> crispy->hires)+(scaledviewwidth >> crispy->hires)-WIDESCREENDELTA,
                (viewwindowy >> crispy->hires)+(viewheight >> crispy->hires),
                W_CacheLumpName(DEH_String("brdr_br"),PU_CACHE));

    V_RestoreBuffer();
}


//
// Copy a screen buffer.
//
void
R_VideoErase
( unsigned	ofs,
  int		count )
{
  // LFB copy.
  // This might not be a good idea if memcpy
  //  is not optiomal, e.g. byte by byte on
  //  a 32bit CPU, as GNU GCC/Linux libc did
  //  at one point.

    if (background_buffer != NULL)
    {
        memcpy(I_VideoBuffer + ofs, background_buffer + ofs, count * sizeof(*I_VideoBuffer));
    }
}


//
// R_DrawViewBorder
// Draws the border around the view
//  for different size windows?
//
void R_DrawViewBorder (void)
{
    int		top;
    int		side;
    int		ofs;
    int		i;

    if (scaledviewwidth == SCREENWIDTH)
	return;

    top = ((SCREENHEIGHT-SBARHEIGHT)-viewheight)/2;
    side = (SCREENWIDTH-scaledviewwidth)/2;

    // copy top and one line of left side
    R_VideoErase (0, top*SCREENWIDTH+side);

    // copy one line of right side and bottom
    ofs = (viewheight+top)*SCREENWIDTH-side;
    R_VideoErase (ofs, top*SCREENWIDTH+side);

    // copy sides using wraparound
    ofs = top*SCREENWIDTH + SCREENWIDTH-side;
    side <<= 1;

    for (i=1 ; i<viewheight ; i++)
    {
	R_VideoErase (ofs, side);
	ofs += SCREENWIDTH;
    }

    // ?
    V_MarkRect (0,0,SCREENWIDTH, SCREENHEIGHT-SBARHEIGHT);
}