From d586d774cfb0b5149894f3dd8251fbf3ddb51422 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Thu, 22 Mar 2018 20:42:17 +0100
Subject: [PATCH] - adjusted GL renderer to the new rules for alpha textures.
 This means that the translation fallback is only needed for the legacy
 renderer now. Modern GL can use the regular texture and will apply a
 grayscale mapping instead of merely using the red channel.

---
 src/gl/renderer/gl_2ddrawer.cpp    |  5 +++--
 src/gl/renderer/gl_renderstate.h   | 11 +++--------
 src/textures/textures.h            |  1 +
 wadsrc/static/shaders/glsl/main.fp |  3 ++-
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/src/gl/renderer/gl_2ddrawer.cpp b/src/gl/renderer/gl_2ddrawer.cpp
index cda4ea374..9c89c6f60 100644
--- a/src/gl/renderer/gl_2ddrawer.cpp
+++ b/src/gl/renderer/gl_2ddrawer.cpp
@@ -91,7 +91,9 @@ void F2DDrawer::AddTexture(FTexture *img, DrawParms &parms)
 
 	if (!img->bHasCanvas)
 	{
-		if (!parms.alphaChannel)
+		dg.mAlphaTexture = !!(parms.style.Flags & STYLEF_RedIsAlpha);
+
+		if (!dg.mAlphaTexture)
 		{
 			if (parms.remap != NULL && !parms.remap->Inactive)
 			{
@@ -99,7 +101,6 @@ void F2DDrawer::AddTexture(FTexture *img, DrawParms &parms)
 				if (pal) dg.mTranslation = -pal->GetIndex();
 			}
 		}
-		dg.mAlphaTexture = !!(parms.style.Flags & STYLEF_RedIsAlpha);
 		u1 = gltex->GetUL();
 		v1 = gltex->GetVT();
 		u2 = gltex->GetUR();
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index 09888db5c..4e844c979 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -144,14 +144,9 @@ public:
 
 	void SetMaterial(FMaterial *mat, int clampmode, int translation, int overrideshader, bool alphatexture)
 	{
-		// textures without their own palette are a special case for use as an alpha texture:
-		// They use the color index directly as an alpha value instead of using the palette's red.
-		// To handle this case, we need to set a special translation for such textures.
-		// Without shaders this translation must be applied to any texture.
-		if (alphatexture)
-		{
-			if (mat->tex->UseBasePalette() || gl.legacyMode) translation = TRANSLATION(TRANSLATION_Standard, 8);
-		}
+		// alpha textures need special treatment in the legacy renderer because withouz shaders they need a different texture.
+		if (alphatexture &&  gl.legacyMode) translation = TRANSLATION(TRANSLATION_Standard, 8);
+		
 		if (mat->tex->bHasCanvas)
 		{
 			mTempTM = TM_OPAQUE;
diff --git a/src/textures/textures.h b/src/textures/textures.h
index 0c175f328..c0a1e9dcf 100644
--- a/src/textures/textures.h
+++ b/src/textures/textures.h
@@ -211,6 +211,7 @@ public:
 		TEX_Flat,
 		TEX_Sprite,
 		TEX_WallPatch,
+		TEX_Build,		// no longer used but needs to remain for ZScript
 		TEX_SkinSprite,
 		TEX_Decal,
 		TEX_MiscPatch,
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index 444a9811f..2ff3ef483 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -64,7 +64,8 @@ vec4 getTexel(vec2 st)
 			break;
 			
 		case 4:	// TM_REDTOALPHA
-			texel = vec4(1.0, 1.0, 1.0, texel.r*texel.a);
+			float gray = (texel.r * 0.3 + texel.g * 0.56 + texel.b * 0.14);	
+			texel = vec4(1.0, 1.0, 1.0, gray*texel.a);
 			break;
 			
 		case 5:	// TM_CLAMPY