diff --git a/src/gl/renderer/gl_postprocess.cpp b/src/gl/renderer/gl_postprocess.cpp
index 827dd7da2..acc0a08b4 100644
--- a/src/gl/renderer/gl_postprocess.cpp
+++ b/src/gl/renderer/gl_postprocess.cpp
@@ -612,9 +612,9 @@ void FGLRenderer::CreateTonemapPalette()
 				{
 					PalEntry color = GPalette.BaseColors[(uint8_t)PTM_BestColor((uint32_t *)GPalette.BaseColors, (r << 2) | (r >> 4), (g << 2) | (g >> 4), (b << 2) | (b >> 4), 0, 256)];
 					int index = ((r * 64 + g) * 64 + b) * 4;
-					lut[index] = color.r;
+					lut[index] = color.b;
 					lut[index + 1] = color.g;
-					lut[index + 2] = color.b;
+					lut[index + 2] = color.r;
 					lut[index + 3] = 255;
 				}
 			}
diff --git a/src/swrenderer/r_swcanvas.cpp b/src/swrenderer/r_swcanvas.cpp
index 087d0ca87..88c0a6b29 100644
--- a/src/swrenderer/r_swcanvas.cpp
+++ b/src/swrenderer/r_swcanvas.cpp
@@ -271,8 +271,8 @@ void SWCanvas::FillSimplePoly(DCanvas *canvas, FTexture *tex, FVector2 *points,
 
 	viewport->RenderTarget->Lock(true);
 
-	scalex /= tex->Scale.X;
-	scaley /= tex->Scale.Y;
+	scalex = tex->Scale.X / scalex;
+	scaley = tex->Scale.Y / scaley;
 
 	// Use the CRT's functions here.
 	cosrot = cos(rotation.Radians());
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index 5b4d1438f..ee113676b 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -103,34 +103,29 @@ vec4 getTexel(vec2 st)
 //===========================================================================
 float R_DoomLightingEquation(float light)
 {
-	// Calculated from r_visibility. It differs between walls, floor and sprites.
+	// globVis = WallVisibility / r_viewwindow.FocalTangent / 32.0
 	//
-	// Wall: globVis = r_WallVisibility
-	// Floor: r_FloorVisibility / abs(plane.Zat0 - ViewPos.Z)
-	// Sprite: same as wall
-	// All are calculated in R_SetVisibility and seem to be decided by the
-	// aspect ratio amongst other things.
-	//
-	// 1706 is the value for walls on 1080p 16:9 displays.
-	float globVis = 1706.0;
+	// WallVisibility is calculated in LightVisibility::SetVisibility
+	// 1706 is the default value for WallVisibility on 1080p 16:9 displays.
+	float globVis = 1706.0 / 1.3333333333333333 / 32.0;
 
-	/* L is the integer light level used in the game */
+	// L is the integer light level used in the game
 	float L = light * 255.0;
 
-	/* z is the depth in view/eye space, positive going into the screen */
+	// z is the depth in view/eye space, positive going into the screen
 	float z = pixelpos.w;
 
-	/* The zdoom light equation */
-	float vis = globVis / z;
-	float shade = 64.0 - (L + 12.0) * 32.0/128.0;
+	// The zdoom light equation
+	float vis = min(globVis / z, 24.0 / 32.0);
+	float shade = 2.0 - (L + 12.0) / 128.0;
 	float lightscale;
 	if (uPalLightLevels != 0)
-		lightscale = clamp(float(int(shade - min(24.0, vis))) / 32.0, 0.0, 31.0/32.0);
+		lightscale = float(-int(-(shade - vis) * 32.0)) / 32.0;
 	else
-		lightscale = clamp((shade - min(24.0, vis)) / 32.0, 0.0, 31.0/32.0);
+		lightscale = shade - vis;
 
 	// Result is the normalized colormap index (0 bright .. 1 dark)
-	return lightscale;
+	return clamp(lightscale, 0.0, 31.0 / 32.0);
 }
 
 //===========================================================================
diff --git a/wadsrc/static/zscript/base.txt b/wadsrc/static/zscript/base.txt
index d6f7f318e..726e46fcc 100644
--- a/wadsrc/static/zscript/base.txt
+++ b/wadsrc/static/zscript/base.txt
@@ -449,7 +449,7 @@ struct DropItem native
 	native readonly DropItem Next;
 	native readonly name Name;
 	native readonly int Probability;
-	native int Amount;
+	native readonly int Amount;
 }
 
 class SpotState : Object native
diff --git a/wadsrc/static/zscript/doom/bossbrain.txt b/wadsrc/static/zscript/doom/bossbrain.txt
index 5b87182c9..fadc280e3 100644
--- a/wadsrc/static/zscript/doom/bossbrain.txt
+++ b/wadsrc/static/zscript/doom/bossbrain.txt
@@ -318,11 +318,12 @@ extend class Actor
 			{
 				if (di.Name != 'None')
 				{
-					if (di.Amount < 0)
+					int amt = di.Amount;
+					if (amt < 0)
 					{
-						di.Amount = 1; // default value is -1, we need a positive value.
+						amt = 1; // default value is -1, we need a positive value.
 					}
-					n += di.Amount; // this is how we can weight the list.
+					n += amt; // this is how we can weight the list.
 				}
 			}
 			di = drop;
@@ -331,7 +332,12 @@ extend class Actor
 			{
 				if (di.Name != 'none')
 				{
-					n -= di.Amount; // logically, none of the -1 values have survived by now.
+					int amt = di.Amount;
+					if (amt < 0)
+					{
+						amt = 1;
+					}
+					n -= amt;
 				}
 				if ((di.Next != null) && (n >= 0))
 				{
diff --git a/wadsrc/static/zscript/shared/randomspawner.txt b/wadsrc/static/zscript/shared/randomspawner.txt
index b6e28cc37..7488fdd4d 100644
--- a/wadsrc/static/zscript/shared/randomspawner.txt
+++ b/wadsrc/static/zscript/shared/randomspawner.txt
@@ -48,8 +48,9 @@ class RandomSpawner : Actor
 				{
 					if (!nomonsters || !IsMonster(di))
 					{
-						if (di.Amount < 0) di.Amount = 1; // default value is -1, we need a positive value.
-						n += di.Amount; // this is how we can weight the list.
+						int amt = di.Amount;
+						if (amt < 0) amt = 1; // default value is -1, we need a positive value.
+						n += amt; // this is how we can weight the list.
 					}
 					di = di.Next;
 				}
@@ -69,7 +70,9 @@ class RandomSpawner : Actor
 				if (di.Name != 'None' &&
 					(!nomonsters || !IsMonster(di)))
 				{
-					n -= di.Amount;
+					int amt = di.Amount;
+					if (amt < 0) amt = 1;
+					n -= amt;
 					if ((di.Next != null) && (n > -1))
 						di = di.Next;
 					else