Add cv_debugrender_contrast, adjusts contrast of level geometry

debugrender_contrast -1.0 to 1.0, default 0.0 (no change).
Higher values add more contrast (darkens the level), lower
values add less (brighten). Does not affect thing drawing.
Software mode only.

Adds r_debug.cpp

src/CMakeLists.txt

@@ -64,6 +64,7 @@ add_executable(SRB2SDL2 MACOSX_BUNDLE WIN32
 	tables.c
 	r_bsp.c
 	r_data.c
+	r_debug.cpp
 	r_draw.c
 	r_fps.c
 	r_main.c

src/r_debug.cpp

@@ -0,0 +1,38 @@
+// RING RACERS
+//-----------------------------------------------------------------------------
+// Copyright (C) 2023 by James Robert Roman.
+//
+// This program is free software distributed under the
+// terms of the GNU General Public License, version 2.
+// See the 'LICENSE' file for more details.
+//-----------------------------------------------------------------------------
+/// \file  r_debug.cpp
+/// \brief Software renderer debugging
+
+#include <algorithm> // std::clamp
+
+#include "cxxutil.hpp"
+
+#include "command.h"
+#include "m_fixed.h"
+#include "r_main.h"
+
+namespace
+{
+
+CV_PossibleValue_t contrast_cons_t[] = {{-FRACUNIT, "MIN"}, {FRACUNIT, "MAX"}, {}};
+
+}; // namespace
+
+consvar_t cv_debugrender_contrast =
+	CVAR_INIT("debugrender_contrast", "0.0", CV_CHEAT | CV_FLOAT, contrast_cons_t, nullptr);
+
+INT32 R_AdjustLightLevel(INT32 light)
+{
+	constexpr fixed_t kRange = (LIGHTLEVELS - 1) * FRACUNIT;
+	const fixed_t adjust = FixedMul(cv_debugrender_contrast.value, kRange);
+
+	light = std::clamp((light * FRACUNIT) - adjust, 0, kRange);
+
+	return light / FRACUNIT;
+}

src/r_main.c

@@ -1656,4 +1656,8 @@ void R_RegisterEngineStuff(void)
 	CV_RegisterVar(&cv_fpscap);
 
 	CV_RegisterVar(&cv_drawpickups);
+
+	// debugging
+
+	CV_RegisterVar(&cv_debugrender_contrast);
 }

src/r_main.h

@@ -123,6 +123,13 @@ extern consvar_t cv_skybox;
 extern consvar_t cv_tailspickup;
 extern consvar_t cv_drawpickups;
 
+// debugging
+
+INT32 R_AdjustLightLevel(INT32 light);
+
+extern consvar_t
+	cv_debugrender_contrast;
+
 // Called by startup code.
 void R_Init(void);
 

src/r_plane.c

@@ -1030,6 +1030,8 @@ void R_DrawSinglePlane(visplane_t *pl)
 	if (light < 0)
 		light = 0;
 
+	light = R_AdjustLightLevel(light);
+
 	if (pl->slope)
 	{
 		mapfunc = R_MapTiltedPlane;

src/r_segs.c

@@ -298,6 +298,8 @@ void R_RenderMaskedSegRange(drawseg_t *ds, INT32 x1, INT32 x2)
 		else if (P_ApplyLightOffset(lightnum))
 			lightnum += curline->lightOffset;
 
+		lightnum = R_AdjustLightLevel(lightnum);
+
 		if (lightnum < 0)
 			walllights = scalelight[0];
 		else if (lightnum >= LIGHTLEVELS)
@@ -413,12 +415,14 @@ void R_RenderMaskedSegRange(drawseg_t *ds, INT32 x1, INT32 x2)
 						if ((rlight->flags & FOF_NOSHADE))
 							continue;
 
-						if (rlight->lightnum < 0)
+						lightnum = R_AdjustLightLevel(rlight->lightnum);
+
+						if (lightnum < 0)
 							xwalllights = scalelight[0];
-						else if (rlight->lightnum >= LIGHTLEVELS)
+						else if (lightnum >= LIGHTLEVELS)
 							xwalllights = scalelight[LIGHTLEVELS-1];
 						else
-							xwalllights = scalelight[rlight->lightnum];
+							xwalllights = scalelight[lightnum];
 
 						pindex = FixedMul(spryscale, LIGHTRESOLUTIONFIX)>>LIGHTSCALESHIFT;
 
@@ -789,6 +793,8 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 		else if (P_ApplyLightOffset(lightnum))
 			lightnum += curline->lightOffset;
 
+		lightnum = R_AdjustLightLevel(lightnum);
+
 		if (lightnum < 0)
 			walllights = scalelight[0];
 		else if (lightnum >= LIGHTLEVELS)
@@ -963,7 +969,7 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 					lighteffect = !(dc_lightlist[i].flags & FOF_NOSHADE);
 					if (lighteffect)
 					{
-						lightnum = rlight->lightnum;
+						lightnum = R_AdjustLightLevel(rlight->lightnum);
 
 						if (lightnum < 0)
 							xwalllights = scalelight[0];
@@ -1379,6 +1385,8 @@ static void R_RenderSegLoop (void)
 				else if (P_ApplyLightOffset(lightnum))
 					lightnum += curline->lightOffset;
 
+				lightnum = R_AdjustLightLevel(lightnum);
+
 				if (lightnum < 0)
 					xwalllights = scalelight[0];
 				else if (lightnum >= LIGHTLEVELS)
@@ -2425,6 +2433,8 @@ void R_StoreWallRange(INT32 start, INT32 stop)
 		if (P_ApplyLightOffset(lightnum))
 			lightnum += curline->lightOffset;
 
+		lightnum = R_AdjustLightLevel(lightnum);
+
 		if (lightnum < 0)
 			walllights = scalelight[0];
 		else if (lightnum >= LIGHTLEVELS)