fixed half-tile shifting when teleporting between playfield borders

[rocksndiamonds.git] / src / game.c

diff --git a/src/game.c b/src/game.c
index 88fa0a6e3e19a3d80126795e35459f6d0f3d167e..94b74f786cdc2c7d211af21d484a3cec17a22eb0 100644 (file)
--- a/src/game.c
+++ b/src/game.c
@@ -5687,6 +5687,40 @@ static void DrawRelocateScreen(int old_x, int old_y, int x, int y,
     // make sure that shifted scroll position does not scroll beyond screen
     new_scroll_x = SCROLL_POSITION_X(shifted_scroll_x + MIDPOSX);
     new_scroll_y = SCROLL_POSITION_Y(shifted_scroll_y + MIDPOSY);
+
+    // special case for teleporting from one end of the playfield to the other
+    // (this kludge prevents the destination area to be shifted by half a tile
+    // against the source destination for even screen width or screen height;
+    // probably most useful when used with high "game.forced_scroll_delay_value"
+    // in combination with "game.forced_scroll_x" and "game.forced_scroll_y")
+    if (quick_relocation)
+    {
+      if (EVEN(SCR_FIELDX))
+      {
+       // relocate (teleport) between left and right border (half or full)
+       if (scroll_x == SBX_Left && new_scroll_x == SBX_Right - 1)
+         new_scroll_x = SBX_Right;
+       else if (scroll_x == SBX_Left + 1 && new_scroll_x == SBX_Right)
+         new_scroll_x = SBX_Right - 1;
+       else if (scroll_x == SBX_Right && new_scroll_x == SBX_Left + 1)
+         new_scroll_x = SBX_Left;
+       else if (scroll_x == SBX_Right - 1 && new_scroll_x == SBX_Left)
+         new_scroll_x = SBX_Left + 1;
+      }
+
+      if (EVEN(SCR_FIELDY))
+      {
+       // relocate (teleport) between top and bottom border (half or full)
+       if (scroll_y == SBY_Upper && new_scroll_y == SBY_Lower - 1)
+         new_scroll_y = SBY_Lower;
+       else if (scroll_y == SBY_Upper + 1 && new_scroll_y == SBY_Lower)
+         new_scroll_y = SBY_Lower - 1;
+       else if (scroll_y == SBY_Lower && new_scroll_y == SBY_Upper + 1)
+         new_scroll_y = SBY_Upper;
+       else if (scroll_y == SBY_Lower - 1 && new_scroll_y == SBY_Upper)
+         new_scroll_y = SBY_Upper + 1;
+      }
+    }
   }
 
   if (quick_relocation)