Merge branch 'hannushadow' into 'master'

Hannu's dropshadow hack

See merge request KartKrew/Kart!527

src/r_draw.h

@@ -180,6 +180,7 @@ void R_DrawViewBorder(void);
 void R_DrawColumn_8(void);
 void R_DrawShadeColumn_8(void);
 void R_DrawTranslucentColumn_8(void);
+void R_DrawDropShadowColumn_8(void);
 void R_DrawTranslatedColumn_8(void);
 void R_DrawTranslatedTranslucentColumn_8(void);
 void R_Draw2sMultiPatchColumn_8(void);

src/r_draw8.c

@@ -566,6 +566,39 @@ void R_DrawTranslucentColumn_8(void)
 	}
 }
 
+// Hack: A cut-down copy of R_DrawTranslucentColumn_8 that does not read texture
+// data since something about calculating the texture reading address for drop shadows is broken.
+// dc_texturemid and dc_iscale get wrong values for drop shadows, however those are not strictly
+// needed for the current design of the shadows, so this function bypasses the issue
+// by not using those variables at all.
+void R_DrawDropShadowColumn_8(void)
+{
+	register INT32 count;
+	register UINT8 *dest;
+
+	count = dc_yh - dc_yl + 1;
+
+	if (count <= 0) // Zero length, column does not exceed a pixel.
+		return;
+
+	dest = &topleft[dc_yl*vid.width + dc_x];
+
+	{
+#define DSCOLOR 15 // palette index for the color of the shadow
+		register const UINT8 *transmap_offset = dc_transmap + (dc_colormap[DSCOLOR] << 8);
+#undef DSCOLOR
+		while ((count -= 2) >= 0)
+		{
+			*dest = *(transmap_offset + (*dest));
+			dest += vid.width;
+			*dest = *(transmap_offset + (*dest));
+			dest += vid.width;
+		}
+		if (count & 1)
+			*dest = *(transmap_offset + (*dest));
+	}
+}
+
 /**	\brief The R_DrawTranslatedTranslucentColumn_8 function
 	Spiffy function. Not only does it colormap a sprite, but does translucency as well.
 	Uber-kudos to Cyan Helkaraxe

src/r_things.c

@@ -836,7 +836,15 @@ static void R_DrawVisSprite(vissprite_t *vis)
 	dc_fullbright = colormaps;
 	dc_translation = R_GetSpriteTranslation(vis);
 
-	if (R_SpriteIsFlashing(vis)) // Bosses "flash"
+	// Hack: Use a special column function for drop shadows that bypasses
+	// invalid memory access crashes caused by R_ProjectDropShadow putting wrong values
+	// in dc_texturemid and dc_iscale when the shadow is sloped.
+	if (vis->cut & SC_SHADOW)
+	{
+		R_SetColumnFunc(COLDRAWFUNC_DROPSHADOW, false);
+		dc_transmap = vis->transmap;
+	}
+	else if (R_SpriteIsFlashing(vis)) // Bosses "flash"
 		R_SetColumnFunc(COLDRAWFUNC_TRANS, false); // translate certain pixels to white
 	else if (vis->mobj->color && vis->transmap) // Color mapping
 	{

src/screen.c

@@ -133,6 +133,7 @@ void SCR_SetDrawFuncs(void)
 		colfuncs[COLDRAWFUNC_TWOSMULTIPATCH] = R_Draw2sMultiPatchColumn_8;
 		colfuncs[COLDRAWFUNC_TWOSMULTIPATCHTRANS] = R_Draw2sMultiPatchTranslucentColumn_8;
 		colfuncs[COLDRAWFUNC_FOG] = R_DrawFogColumn_8;
+		colfuncs[COLDRAWFUNC_DROPSHADOW] = R_DrawDropShadowColumn_8;
 
 		spanfuncs[SPANDRAWFUNC_TRANS] = R_DrawTranslucentSpan_8;
 		spanfuncs[SPANDRAWFUNC_TILTED] = R_DrawTiltedSpan_8;

src/screen.h

@@ -131,6 +131,7 @@ enum
 	COLDRAWFUNC_TWOSMULTIPATCH,
 	COLDRAWFUNC_TWOSMULTIPATCHTRANS,
 	COLDRAWFUNC_FOG,
+	COLDRAWFUNC_DROPSHADOW,
 
 	COLDRAWFUNC_MAX
 };