From 3faf5afa3aec40b5df9f334d915430631a740f7b Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@zdoom.fake>
Date: Tue, 26 Apr 2016 21:49:30 +0200
Subject: [PATCH] - re-added software translucency splitting for old hardware.

---
 src/gl/scene/gl_drawinfo.cpp | 43 ++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

diff --git a/src/gl/scene/gl_drawinfo.cpp b/src/gl/scene/gl_drawinfo.cpp
index c9cdf094d..8bfa3df4e 100644
--- a/src/gl/scene/gl_drawinfo.cpp
+++ b/src/gl/scene/gl_drawinfo.cpp
@@ -319,8 +319,29 @@ void GLDrawList::SortWallIntoPlane(SortNode * head,SortNode * sort)
 		// Bad things will happen if the memory must be reallocated!
 		GLWall w = *ws;
 		AddWall(&w);
+	
+		// Splitting is done in the shader with clip planes, if available
+		if (gl.glslversion < 1.3f)
+		{
+			GLWall * ws1;
+			ws1=&walls[walls.Size()-1];
+			ws=&walls[drawitems[sort->itemindex].index];	// may have been reallocated!
+			float newtexv = ws->uplft.v + ((ws->lolft.v - ws->uplft.v) / (ws->zbottom[0] - ws->ztop[0])) * (fh->z - ws->ztop[0]);
 
-		// Splitting is done in the shader with clip planes.
+			// I make the very big assumption here that translucent walls in sloped sectors
+			// and 3D-floors never coexist in the same level. If that were the case this
+			// code would become extremely more complicated.
+			if (!ceiling)
+			{
+				ws->ztop[1] = ws1->zbottom[1] = ws->ztop[0] = ws1->zbottom[0] = fh->z;
+				ws->uprgt.v = ws1->lorgt.v = ws->uplft.v = ws1->lolft.v = newtexv;
+			}
+			else
+			{
+				ws1->ztop[1] = ws->zbottom[1] = ws1->ztop[0] = ws->zbottom[0] = fh->z;
+				ws1->uplft.v = ws->lolft.v = ws1->uprgt.v = ws->lorgt.v=newtexv;
+			}
+		}
 
 		SortNode * sort2 = SortNodes.GetNew();
 		memset(sort2, 0, sizeof(SortNode));
@@ -357,8 +378,26 @@ void GLDrawList::SortSpriteIntoPlane(SortNode * head,SortNode * sort)
 		// We have to split this sprite
 		GLSprite s=*ss;
 		AddSprite(&s);	// add a copy to avoid reallocation issues.
+	
+		// Splitting is done in the shader with clip planes, if available
+		if (gl.glslversion < 1.3f)
+		{
+			GLSprite * ss1;
+			ss1=&sprites[sprites.Size()-1];
+			ss=&sprites[drawitems[sort->itemindex].index];	// may have been reallocated!
+			float newtexv=ss->vt + ((ss->vb-ss->vt)/(ss->z2-ss->z1))*(fh->z-ss->z1);
 
-		// Splitting is done in the shader with clip planes.
+			if (!ceiling)
+			{
+				ss->z1=ss1->z2=fh->z;
+				ss->vt=ss1->vb=newtexv;
+			}
+			else
+			{
+				ss1->z1=ss->z2=fh->z;
+				ss1->vt=ss->vb=newtexv;
+			}
+		}
 
 		SortNode * sort2=SortNodes.GetNew();
 		memset(sort2,0,sizeof(SortNode));