Add 1 pixel tall and wide texture support to the renderer

- These require manual detection and overriding of the scaling factors to
  0, because a right shift of (32-0) bits wraps around to 0 and results in
  no shift at all rather than leaving the register zeroed out.

src/asm_ia32/tmap2.asm

@@ -198,7 +198,10 @@ SetTiltedSpanSize:
 	mov	[y8+2],cl
 	mov	[y9+2],cl
 	mov	[y10+2],cl
+	cmp	eax,0		; if x bits is 0, mask must be 0 too.
+	jz	.notted
 	not	eax
+.notted:
 	pop	ecx
 	
 	mov	[m1+2],eax

src/r_plane.cpp

@@ -221,10 +221,26 @@ void R_MapPlane (int y, int x1)
 
 	distance = planeheight * yslope[y];
 
+	if (ds_xbits != 0)
+	{
 		ds_xstep = xs_ToFixed(32 - ds_xbits, distance * xstepscale);
-	ds_ystep = xs_ToFixed(32-ds_ybits, distance * ystepscale);
 		ds_xfrac = xs_ToFixed(32 - ds_xbits, distance * basexfrac) + pviewx;
+	}
+	else
+	{
+		ds_xstep = 0;
+		ds_xfrac = 0;
+	}
+	if (ds_ybits != 0)
+	{
+		ds_ystep = xs_ToFixed(32 - ds_ybits, distance * ystepscale);
 		ds_yfrac = xs_ToFixed(32 - ds_ybits, distance * baseyfrac) + pviewy;
+	}
+	else
+	{
+		ds_ystep = 0;
+		ds_yfrac = 0;
+	}
 
 	if (plane_shade)
 	{
@@ -1888,6 +1904,15 @@ void R_DrawTiltedPlane (visplane_t *pl, double _xscale, double _yscale, fixed_t
 		}
 	}
 
+	// Hack in support for 1 x Z and Z x 1 texture sizes
+	if (ds_ybits == 0)
+	{
+		plane_sv[2] = plane_sv[1] = plane_sv[0] = 0;
+	}
+	if (ds_xbits = 0)
+	{
+		plane_su[2] = plane_su[1] = plane_su[0] = 0;
+	}
 #if defined(X86_ASM)
 	if (ds_source != ds_curtiltedsource)
 		R_SetTiltedSpanSource_ASM (ds_source);

src/r_segs.cpp

@@ -1104,6 +1104,12 @@ void wallscan (int x1, int x2, short *uwal, short *dwal, float *swal, fixed_t *l
 
 	rw_pic->GetHeight();	// Make sure texture size is loaded
 	fracbits = 32 - rw_pic->HeightBits;
+	if (fracbits == 32)
+	{ // Hack for one pixel tall textures
+		fracbits = 0;
+		yrepeat = 0;
+		dc_texturemid = 0;
+	}
 	setupvline(fracbits);
 	xoffset = rw_offset;
 	basecolormapdata = basecolormap->Maps;
@@ -1456,6 +1462,12 @@ void maskwallscan (int x1, int x2, short *uwal, short *dwal, float *swal, fixed_
 
 	rw_pic->GetHeight();	// Make sure texture size is loaded
 	fracbits = 32- rw_pic->HeightBits;
+	if (fracbits == 32)
+	{ // Hack for one pixel tall textures
+		fracbits = 0;
+		yrepeat = 0;
+		dc_texturemid = 0;
+	}
 	setupmvline(fracbits);
 	xoffset = rw_offset;
 	basecolormapdata = basecolormap->Maps;
@@ -1631,6 +1643,12 @@ void transmaskwallscan (int x1, int x2, short *uwal, short *dwal, float *swal, f
 
 	rw_pic->GetHeight();	// Make sure texture size is loaded
 	fracbits = 32 - rw_pic->HeightBits;
+	if (fracbits == 32)
+	{ // Hack for one pixel tall textures
+		fracbits = 0;
+		yrepeat = 0;
+		dc_texturemid = 0;
+	}
 	setuptmvline(fracbits);
 	xoffset = rw_offset;
 	basecolormapdata = basecolormap->Maps;

src/textures/texture.cpp

@@ -210,8 +210,9 @@ void FTexture::CalcBitSize ()
 	}
 	WidthMask = (1 << WidthBits) - 1;
 
-	// The minimum height is 2, because we cannot shift right 32 bits.
-	for (i = 1; (1 << i) < Height; ++i)
+	// <hr>The minimum height is 2, because we cannot shift right 32 bits.</hr>
+	// Scratch that. Somebody actually made a 1x1 texture, so now we have to handle it.
+	for (i = 0; (1 << i) < Height; ++i)
 	{ }
 
 	HeightBits = i;