From c2448c888126aa40991c96b875d955bb471ef6f0 Mon Sep 17 00:00:00 2001
From: Alibek Omarov <a1ba.omarov@gmail.com>
Date: Tue, 18 Nov 2025 13:26:01 +0500
Subject: [PATCH] engine: imagelib: allow specifiying index for empty pixels
 when processing luma texture

---
 engine/common/imagelib/imagelib.h  |  1 +
 engine/common/imagelib/img_main.c  |  1 +
 engine/common/imagelib/img_utils.c |  4 ++--
 engine/common/imagelib/img_wad.c   | 11 ++++++-----
 4 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/engine/common/imagelib/imagelib.h b/engine/common/imagelib/imagelib.h
index 3429c34f..d67fc6f6 100644
--- a/engine/common/imagelib/imagelib.h
+++ b/engine/common/imagelib/imagelib.h
@@ -85,6 +85,7 @@ typedef struct imglib_s
 	uint			*d_currentpal;	// installed version of internal palette
 	int			d_rendermode;	// palette rendermode
 	byte			*palette;		// palette pointer
+	int                     black_pixel;     // "free" index used for luma textures (0 for Quake as it's black, 255 for Half-Life as it's #0000FF)
 
 	// global parms
 	rgba_t			fogParams;	// some water textures has info about underwater fog
diff --git a/engine/common/imagelib/img_main.c b/engine/common/imagelib/img_main.c
index 49e74ff2..a7446cad 100644
--- a/engine/common/imagelib/img_main.c
+++ b/engine/common/imagelib/img_main.c
@@ -142,6 +142,7 @@ void Image_Reset( void )
 	image.fogParams[1] = 0;
 	image.fogParams[2] = 0;
 	image.fogParams[3] = 0;
+	image.black_pixel = 0;
 
 	// pointers will be saved with prevoius picture struct
 	// don't care about it
diff --git a/engine/common/imagelib/img_utils.c b/engine/common/imagelib/img_utils.c
index 9f63879a..72dd3b44 100644
--- a/engine/common/imagelib/img_utils.c
+++ b/engine/common/imagelib/img_utils.c
@@ -616,7 +616,7 @@ qboolean Image_Copy8bitRGBA( const byte *in, byte *out, int pixels )
 	if( image.flags & IMAGE_HAS_LUMA )
 	{
 		for( i = 0; i < image.width * image.height; i++ )
-			fin[i] = fin[i] < 224 ? fin[i] : 0;
+			fin[i] = fin[i] < 224 ? fin[i] : image.black_pixel;
 	}
 
 	// check for color
@@ -1204,7 +1204,7 @@ static byte *Image_MakeLuma( byte *fin, int width, int height, int type, int fla
 	case PF_INDEXED_32:
 		out = image.tempbuffer = Mem_Realloc( host.imagepool, image.tempbuffer, width * height );
 		for( i = 0; i < width * height; i++ )
-			*out++ = fin[i] >= 224 ? fin[i] : 0;
+			*out++ = fin[i] >= 224 ? fin[i] : image.black_pixel;
 		break;
 	default:
 		// another formats does ugly result :(
diff --git a/engine/common/imagelib/img_wad.c b/engine/common/imagelib/img_wad.c
index 3f0d5740..50425e78 100644
--- a/engine/common/imagelib/img_wad.c
+++ b/engine/common/imagelib/img_wad.c
@@ -430,7 +430,8 @@ qboolean Image_LoadMIP( const char *name, const byte *buffer, fs_offset_t filesi
 				{
 					if( fin[i] > 224 )
 					{
-						image.flags |= IMAGE_HAS_LUMA;
+						SetBits( image.flags, IMAGE_HAS_LUMA );
+						image.black_pixel = 0;
 						break;
 					}
 				}
@@ -464,15 +465,15 @@ qboolean Image_LoadMIP( const char *name, const byte *buffer, fs_offset_t filesi
 		hl_texture = false;
 
 		// check for luma and alpha pixels
-		if( !image.custom_palette )
+		// don't apply luma to water surfaces because they have no lightmap
+		if( !image.custom_palette && mip.name[0] != '*' && mip.name != '!' )
 		{
 			for( i = 0; i < image.width * image.height; i++ )
 			{
 				if( fin[i] > 224 && fin[i] != 255 )
 				{
-					// don't apply luma to water surfaces because they have no lightmap
-					if( mip.name[0] != '*' && mip.name[0] != '!' )
-						image.flags |= IMAGE_HAS_LUMA;
+					SetBits( image.flags, IMAGE_HAS_LUMA );
+					image.black_pixel = 0;
 					break;
 				}
 			}