November 12, 2009

- Improved sky stretching a bit: It now only stretches the sky as tall as it
  needs to be: 228 pixels, not 256. It no longer stretches horizontally,
  either.
  
  The reason it stretches to 228 and not 200 pixels is because Doom shifted
  its sky texture down 28 pixels. By stretching to 228 pixels, we can keep
  the sky tiled at the same height on the horizon. Skies 200 pixels tall
  (or more) will continue to tile at the center of the screen when looking
  directly ahead.


SVN r1976 (trunk)

docs/rh-log.txt

@@ -1,4 +1,13 @@
 November 12, 2009
+- Improved sky stretching a bit: It now only stretches the sky as tall as it
+  needs to be: 228 pixels, not 256. It no longer stretches horizontally,
+  either.
+  
+  The reason it stretches to 228 and not 200 pixels is because Doom shifted
+  its sky texture down 28 pixels. By stretching to 228 pixels, we can keep
+  the sky tiled at the same height on the horizon. Skies 200 pixels tall
+  (or more) will continue to tile at the center of the screen when looking
+  directly ahead.
 - Cleaned up win32/i_system.cpp.
 - Put back the previous event-driven ticker, except now the timer isn't
   started until the first time it is needed.

src/r_plane.cpp

@@ -823,7 +823,7 @@ static void R_DrawSky (visplane_t *pl)
  	if (pl->minx > pl->maxx)
 		return;
 
-	dc_iscale = skyiscale >> skystretch;
+	dc_iscale = skyiscale;
 
 	clearbuf (swall+pl->minx, pl->maxx-pl->minx+1, dc_iscale<<2);
 
@@ -864,7 +864,7 @@ static void R_DrawSky (visplane_t *pl)
 	}
 	else
 	{ // The texture does not tile nicely
-		frontyScale = DivScale16 (skyscale << skystretch, frontyScale);
+		frontyScale = DivScale16 (skyscale, frontyScale);
 		frontiScale = DivScale32 (1, frontyScale);
 		R_DrawSkyStriped (pl);
 	}
@@ -1328,9 +1328,9 @@ void R_DrawSkyPlane (visplane_t *pl)
 			skyflip = l->args[2] ? 0u : ~0u;
 
 			frontcyl = MAX(frontskytex->GetWidth(), frontskytex->xScale >> (16 - 10));
-			if (skystretch && frontskytex->GetScaledWidth() < 512)
+			if (skystretch)
 			{
-				frontcyl >>= 1;
+				skymid = Scale(skymid, frontskytex->GetScaledHeight(), SKYSTRETCH_HEIGHT);
 			}
 		}
 	}

src/r_sky.cpp

@@ -43,9 +43,8 @@ FTextureID	skyflatnum;
 FTextureID	sky1texture,	sky2texture;
 fixed_t		skytexturemid;
 fixed_t		skyscale;
-int			skystretch;
-fixed_t		skyheight;					
 fixed_t		skyiscale;
+bool		skystretch;
 
 fixed_t		sky1cyl,		sky2cyl;
 double		sky1pos,		sky2pos;
@@ -68,7 +67,7 @@ extern fixed_t freelookviewheight;
 
 void R_InitSkyMap ()
 {
-	fixed_t fskyheight;
+	int skyheight;
 	FTexture *skytex1, *skytex2;
 
 	skytex1 = TexMan[sky1texture];
@@ -83,27 +82,30 @@ void R_InitSkyMap ()
 		sky2texture = sky1texture;
 	}
 
-	fskyheight = skytex1->GetHeight() << FRACBITS;
-	if (skytex1->GetScaledHeight() <= 128)
+	// Skies between [128,200) are stretched to 200 pixels. Shorter skies do
+	// not stretch because it is assumed they are meant to tile, and taller
+	// skies do not stretch because they provide enough information for no
+	// repetition when looking all the way up.
+	skyheight = skytex1->GetScaledHeight();
+	if (skyheight < 200)
 	{
-		skytexturemid = r_Yaspect/2*FRACUNIT;
 		skystretch = (r_stretchsky
+					  && skyheight >= 128
 					  && level.IsFreelookAllowed()
 					  && !(level.flags & LEVEL_FORCENOSKYSTRETCH)) ? 1 : 0;
+		// The sky is shifted down from center so that it is entirely visible
+		// when looking straight ahead.
+		skytexturemid = -28*FRACUNIT;
 	}
 	else
 	{
-		skytexturemid = 199 * skytex1->yScale;
-		skystretch = 0;
-		// At heights above 600 pixels, the sky is drawn slightly too low.
-		if (SCREENHEIGHT > 600)
-		{
-			skytexturemid += FRACUNIT;
-		}
+		// The sky is directly centered so that it is entirely visible when
+		// looking fully up.
+		skytexturemid = 0;
+		skystretch = false;
 	}
-	skyheight = fskyheight << skystretch;
 
-	if (viewwidth && viewheight)
+	if (viewwidth != 0 && viewheight != 0)
 	{
 		skyiscale = (r_Yaspect*FRACUNIT) / ((freelookviewheight * viewwidth) / viewwidth);
 		skyscale = (((freelookviewheight * viewwidth) / viewwidth) << FRACBITS) /
@@ -113,26 +115,18 @@ void R_InitSkyMap ()
 		skyscale = Scale (skyscale, 2048, FieldOfView);
 	}
 
+	if (skystretch)
+	{
+		skyscale = Scale(skyscale, SKYSTRETCH_HEIGHT, skyheight);
+		skyiscale = Scale(skyiscale, skyheight, SKYSTRETCH_HEIGHT);
+		skytexturemid = Scale(skytexturemid, skyheight, SKYSTRETCH_HEIGHT);
+	}
+
 	// The standard Doom sky texture is 256 pixels wide, repeated 4 times over 360 degrees,
 	// giving a total sky width of 1024 pixels. So if the sky texture is no wider than 1024,
 	// we map it to a cylinder with circumfrence 1024. For larger ones, we use the width of
 	// the texture as the cylinder's circumfrence.
 	sky1cyl = MAX(skytex1->GetWidth(), skytex1->xScale >> (16 - 10));
 	sky2cyl = MAX(skytex2->GetWidth(), skytex2->xScale >> (16 - 10));
-
-	// If we are stretching short skies, we also stretch them horizontally by halving the
-	// circumfrence of the sky cylinder, unless the texture is 512 or more pixels wide,
-	// in which case we only stretch it vertically.
-	if (skystretch)
-	{
-		if (skytex1->GetScaledWidth() < 512)
-		{
-			sky1cyl >>= 1;
-		}
-		if (skytex2->GetScaledWidth() < 512)
-		{
-			sky2cyl >>= 1;
-		}
-	}
 }
 

src/r_sky.h

@@ -30,10 +30,11 @@ extern fixed_t		sky1cyl,		sky2cyl;
 extern FTextureID	sky1texture,	sky2texture;
 extern double		sky1pos,		sky2pos;
 extern fixed_t	skytexturemid;
-extern int		skystretch;
 extern fixed_t	skyiscale;
 extern fixed_t	skyscale;
-extern fixed_t	skyheight;
+extern bool		skystretch;
+
+#define SKYSTRETCH_HEIGHT 228
 
 // Called whenever the sky changes.
 void R_InitSkyMap		();