Fix dragon random movement and 1.x slime speeds.

docs/changelog.txt

@@ -275,6 +275,8 @@ USERS
   FWRITE_APPEND) is now stored in save files. This fixes a bug
   where the output file would be reopened in the wrong mode (ab)
   when reloading a saved game.
++ Fixed dragon random movement behavior. A compatibility check
+  has been added for 2.80 to 2.92 non-random dragon movement.
 + save_slots is now enabled by default for consoles. (Spectere)
 + editor_show_thing_toggles is now enabled by default.
 - board_editor_hide_help and robot_editor_hide_help are no

src/game_update_board.c

@@ -31,6 +31,7 @@
 #include "idarray.h"
 #include "idput.h"
 #include "robot.h"
+#include "world.h"
 #include "util.h"
 
 #include "audio/sfx.h"
@@ -468,7 +469,6 @@ void update_board(context *ctx)
           }
           break;
         }
-        // Cw/Ccw
 
         case CW_ROTATE:
         case CCW_ROTATE:
@@ -787,21 +787,25 @@ void update_board(context *ctx)
         {
           if(!slow_down)
           {
-            // This is pretty weird, but I have to go by the ASM for now
             int spread_speed = current_param & 0x03;
-            int current_cycle = (current_param &  0x3C) >> 2;
-
-            spread_speed |= spread_speed << 1;
+            int current_cycle = (current_param & 0x3C) >> 2;
+
+            // This was changed from speed*5 some time between 2.04 and 2.07.
+            // Despite MegaZeux 2.x having changed the speed setting range
+            // from 1-4 to 1-8, this setting has always been two bits.
+            // BUG: The newer behavior seems to be a broken attempt at speed*3.
+            if(mzx_world->version >= V251)
+              spread_speed |= spread_speed << 1;
+            else
+              spread_speed |= spread_speed << 2;
 
             if(spread_speed == current_cycle)
             {
               int new_x, new_y;
               current_color = level_color[level_offset];
               // Clear cycle
-              // BUG: This leaves the lowest cycle count bit set, which can't
-              // be fixed right now (compatibility). Seems like Alexis planned
-              // to extend the speed range in 2.00 but didn't fully implement
-              // it; the param dialog has the "wrong" bound too...
+              // BUG: This leaves the lowest cycle count bit set.
+              // This bug exists even in MegaZeux 1.x.
               current_param &= 0xC7;
 
               // Put slimes all around
@@ -838,6 +842,7 @@ void update_board(context *ctx)
             else
             {
               // Increase cycle
+              // BUG: corrupting overflow.
               level_param[level_offset] = current_param + 4;
             }
           }
@@ -951,6 +956,9 @@ void update_board(context *ctx)
               level_param[level_offset] = current_param & 0xE7;
 
               // One out of 8 moves is random
+              // This was broken in the port for a long time.
+              if(mzx_world->version < VERSION_PORT || mzx_world->version >= V293)
+                rval = Random(8);
 
               if(!(rval & 0x07))
               {
@@ -1496,7 +1504,7 @@ void update_board(context *ctx)
                 level_param[level_offset] = 0x20;
               }
 
-              level_id[level_offset] = 38;
+              level_id[level_offset] = (char)EXPLOSION;
               play_sfx(mzx_world, SFX_EXPLOSION);
             }
             else

src/legacy_rasm.c

@@ -2968,10 +2968,10 @@ boolean legacy_convert_v1_program(char **_dest, int *_dest_len,
     if(!dest)
       return false;
 
+    dest[0] = 0xff;
+    dest[1] = 0;
     *_dest = dest;
     *_dest_len = 2;
-    *_dest[0] = 0xff;
-    *_dest[1] = 0;
     *_cur_prog_line = 0;
     return true;
   }

testworlds/1.00/008 slimeblob.txt

@@ -0,0 +1,3 @@
+Title: Slime Spread Speed Test
+Author: Alice Rowan
+Desc: Test MegaZeux 1.x slime spread speeds 1-4 and '5-8', including bugs.

testworlds/2.51/013 slimeblob.txt

@@ -0,0 +1,3 @@
+Title: Slime Spread Speed Test
+Author: Alice Rowan
+Desc: Test MegaZeux 2.x slime spread speeds 1-4 and '5-8', including bugs. This test does NOT work prior to 2.07, as older versions use 1.x slime speeds.