From 3a7532fd9bd702858431d8ecaffaf6cbab93bc1c Mon Sep 17 00:00:00 2001
From: Magnus Norddahl <dpjudas@users.noreply.github.com>
Date: Sun, 6 Nov 2016 11:39:28 +0100
Subject: [PATCH] Improve flat mipmap selection

---
 src/r_draw.cpp      |  1 +
 src/r_draw.h        |  1 +
 src/r_draw_rgba.cpp | 17 ++++++-----------
 src/r_plane.cpp     | 10 ++++++++++
 4 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/src/r_draw.cpp b/src/r_draw.cpp
index 0ff047238..bd53889a1 100644
--- a/src/r_draw.cpp
+++ b/src/r_draw.cpp
@@ -1046,6 +1046,7 @@ dsfixed_t 				ds_xstep;
 dsfixed_t 				ds_ystep;
 int						ds_xbits;
 int						ds_ybits;
+double					ds_lod;
 
 // start of a floor/ceiling tile image 
 const BYTE*				ds_source;
diff --git a/src/r_draw.h b/src/r_draw.h
index 005897de6..196e26bea 100644
--- a/src/r_draw.h
+++ b/src/r_draw.h
@@ -316,6 +316,7 @@ extern "C" dsfixed_t		ds_ystep;
 extern "C" int				ds_xbits;
 extern "C" int				ds_ybits;
 extern "C" fixed_t			ds_alpha;
+extern "C" double			ds_lod;
 
 // start of a 64*64 tile image
 extern "C" const BYTE*		ds_source;
diff --git a/src/r_draw_rgba.cpp b/src/r_draw_rgba.cpp
index 34c79b3aa..a649572cc 100644
--- a/src/r_draw_rgba.cpp
+++ b/src/r_draw_rgba.cpp
@@ -97,7 +97,7 @@ public:
 		args.flags = 0;
 		if (ds_shade_constants.simple_shade)
 			args.flags |= DrawSpanArgs::simple_shade;
-		if (!sampler_setup(args.source, args.xbits, args.ybits, args.xstep, args.ystep, ds_source_mipmapped))
+		if (!sampler_setup(args.source, args.xbits, args.ybits, ds_source_mipmapped))
 			args.flags |= DrawSpanArgs::nearest_filter;
 	}
 
@@ -117,18 +117,13 @@ protected:
 	DrawSpanArgs args;
 
 private:
-	inline static bool sampler_setup(const uint32_t * &source, int &xbits, int &ybits, fixed_t xstep, fixed_t ystep, bool mipmapped)
+	inline static bool sampler_setup(const uint32_t * &source, int &xbits, int &ybits, bool mipmapped)
 	{
-		// Is this a magfilter or minfilter?
-		fixed_t xmagnitude = abs(xstep) >> (32 - xbits - FRACBITS);
-		fixed_t ymagnitude = abs(ystep) >> (32 - ybits - FRACBITS);
-		fixed_t magnitude = (xmagnitude + ymagnitude) * 2 + (1 << (FRACBITS - 1));
-		bool magnifying = (magnitude >> FRACBITS == 0);
-
+		bool magnifying = ds_lod < 0.0f;
 		if (r_mipmap && mipmapped)
 		{
-			int level = magnitude >> (FRACBITS + 1);
-			while (level != 0)
+			int level = (int)ds_lod;
+			while (level > 0)
 			{
 				if (xbits <= 2 || ybits <= 2)
 					break;
@@ -136,7 +131,7 @@ private:
 				source += (1 << (xbits)) * (1 << (ybits));
 				xbits -= 1;
 				ybits -= 1;
-				level >>= 1;
+				level--;
 			}
 		}
 
diff --git a/src/r_plane.cpp b/src/r_plane.cpp
index 21cea7bcf..96225729b 100644
--- a/src/r_plane.cpp
+++ b/src/r_plane.cpp
@@ -245,6 +245,16 @@ void R_MapPlane (int y, int x1)
 		ds_yfrac = 0;
 	}
 
+	if (r_swtruecolor)
+	{
+		double distance2 = planeheight * yslope[(y + 1 < viewheight) ? y + 1 : y - 1];
+		double xmagnitude = fabs(ystepscale * (distance2 - distance) * FocalLengthX);
+		double ymagnitude = fabs(xstepscale * (distance2 - distance) * FocalLengthX);
+		double magnitude = MAX(ymagnitude, xmagnitude);
+		double min_lod = -1000.0;
+		ds_lod = MAX(log2(magnitude) + r_lod_bias, min_lod);
+	}
+
 	if (plane_shade)
 	{
 		// Determine lighting based on the span's distance from the viewer.