commit 692ac0da8f8300c6a61f49cf7d51f7f448ec7b7c
Author:     jens <jens.se@icloud.com>
AuthorDate: Sat Aug 22 09:39:03 2026 +0200
Commit:     jens <jens.se@icloud.com>
CommitDate: Sat Aug 22 09:39:03 2026 +0200

    Fix sky texture offset from the larger screen buffer

    skytexturemid (r_sky.c) was computed as SCREENHEIGHT/2*FRACUNIT, but
    SCREENHEIGHT is no longer the same as the resolution the game's fixed-
    point math was calibrated for (see i_video.h) - it's real screen
    pixels, twice ORIGHEIGHT.

    The sky column drawer (r_plane.c) computes
    dc_texturemid + (dc_yl - centery) * dc_iscale. dc_iscale is already
    scaled down in proportion to the larger real view (see pspriteiscale
    in r_main.c), which exactly cancels (dc_yl - centery) being scaled up
    by that same amount - so this additive base term needs to stay in
    original vanilla-sized terms too. Using SCREENHEIGHT there added an
    extra, unwanted offset to every sky column, which - since sky sampling
    wraps at the texture's actual height - showed up as the sky shifting
    down and seaming/duplicating partway down the screen instead of
    wrapping cleanly at the top.

    Changed to ORIGHEIGHT/2*FRACUNIT (the original vanilla constant,
    100*FRACUNIT). Verified in E1M1 with noclip: the sky now renders as a
    single coherent mountain skyline with no visible seam.

    Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
---
 src/doom/r_sky.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/doom/r_sky.c b/src/doom/r_sky.c
index bcd5a75b..709bc9cd 100644
--- a/src/doom/r_sky.c
+++ b/src/doom/r_sky.c
@@ -28,6 +28,8 @@
 // Needed for Flat retrieval.
 #include "r_data.h"

+// Needed for ORIGHEIGHT.
+#include "i_video.h"

 #include "r_sky.h"

@@ -47,6 +49,15 @@ int			skytexturemid;
 void R_InitSkyMap (void)
 {
   // skyflatnum = R_FlatNumForName ( SKYFLATNAME );
-    skytexturemid = SCREENHEIGHT/2*FRACUNIT;
+    // Deliberately ORIGHEIGHT, not SCREENHEIGHT (see i_video.h for why
+    // they differ now): the column drawer computes
+    // dc_texturemid + (dc_yl - centery) * dc_iscale, and dc_iscale is
+    // already scaled down in proportion to the real view being bigger
+    // (see pspriteiscale in r_main.c), which cancels out (dc_yl -
+    // centery) being scaled up by that same real view size - so this
+    // additive base term needs to stay in the original vanilla-sized
+    // terms too, or every sky column ends up offset by the difference,
+    // wrapping (and so visibly seaming/duplicating) at the wrong row.
+    skytexturemid = ORIGHEIGHT/2*FRACUNIT;
 }