Rate top gamesVolleyring by Nick Shcherbyna
About
| EXTREME-256 BASIC game for MSX |
| |
| (c) 2021 Nick Shcherbyna (Lviv, Ukraine) [email protected] |
+------------------------------------------------------------------------------+
| Instructions / |
|-------------- |
| |
| Hedgehogs cannot play volleyball because their spines might pierce the ball. |
| Instead they choose volleyring - essentially the same game, but using a ring |
| from Sonic's universe. The rules are simple: send a ring to opponent's side, |
| don't touch the net or ground. Hedgehog have to jump to strike the ring, but |
| three consecutive contacts with it is a fault. Match is played to 15 points. |
| |
| Left player is Sonic the Hedgehog, right player is Shadow the Hedgehog. Both |
| are controlled by players using joysticks or cursor keys. Press [ 1 ] in the |
| main menu to choose Sonic's controls, press [ 2 ] to pick Shadow's controls. |
| Press [ S ] to start match. Note that there is an easter egg in the game! |
| |
| The game is written in MSX BASIC, and can run even on MSX1. For crazy action |
| pick MSX Turbo R. If you do not have real hardware, use emulator like WebMSX |
| (https://webmsx.org/). |
| |
| General tips: |
| For single-player action choose the same controls for Sonic and Shadow. Then |
| you will control both hedgehogs simultaneously. Playing with someone else is |
| likely more enjoyable, but this mode is good for practice. |
| |
| WebMSX tips: |
| Copy BASIC source to clipboard, then press [ Alt ]-[ V ] and [ Ctrl ]-[ V ], |
| after that press [ F5 ] to run the game. |
| Press [ Alt ]-[ T ] to change the CPU frequency (and game speed). |
| Press [ Alt ]-[ K ] several times to activate double joysticks emulation via |
| keyboard. Note that the first joystick is mapped to cursor keys, and the 2nd |
| one is mapped to [ F ] (left), [ T ] (jump), and [ H ] (right). |
| |
| Alternatively, one can run game from disk, either automatically or manually: |
| LOAD "VOLLEY10.BAS",R |
| |
+------------------------------------------------------------------------------+
| Disk Contents / |
|--------------- |
| |
| AUTOEXEC.BAS - Autoloader |
| VOLLEY10.SC2 - Splash screen |
| README.TXT - This document |
| VOLLEY10.BAS - 10-Liner game |
| |
+------------------------------------------------------------------------------+
| Source Code Explained / |
|----------------------- |
| |
| Variables: |
| (U, Y + W) - Sonic's coordinates. Y is constant, W becomes negative on jump, |
| otherwise 0. |
| (X, Y + Z) - Shadow's coordinates, like above. |
| (P, Q) - Ring coordinates. |
| (R, S) - Ring speed vector. Mirrored on screen bounds, updated when hedgehog |
| strikes the ring in jump. V is used to simulate physics - every 128 |
| steps |R| is decreasing, and every 8 steps S is increasing. |
| N - Number of consecutive contacts. Reset to 0 when the ring passes the net. |
| T - Temporary variable, mostly used for joystick and keyboard readings. |
| M(2) - Array of scores per player. |
| K(2) - Array of controls per player (i.e., STICK() arguments). |
| A(3) - Array of control names (cursor keys, joystick 1/2). |
| |
| Functions: |
| FNM(V) - Mirroring bits in byte V. Used to generate Shadow's sprite from |
| Sonic in three steps (C code): |
| V = ((V >> 1) & 0x55) | ((V & 0x55) << 1); // 1) Swap bits |
| V = ((V >> 2) & 0x33) | ((V & 0x33) << 2); // 2) Swap pairs |
| V = ((V >> 4) & 0x0F) | ((V & 0x0F) << 4); // 3) Swap nibbles |
| FNR(V,S,M) - Helper function for FNM(V), performs single step from above. |
| FNK(J) - Wrapper for STICK() for player J. |
| FNJ(J) - Helper for jumps. Assumes T is STICK() reading. Argument is W or Z, |
| for Sonic or Shadow. Returns -1 if stick is up and jump is allowed, |
| 0 otherwise. |
| |
| Tricks: |
| As already stated above, Shadow's sprite is mirrored from Sonic. Also, first |
| ten scanlines of two Sonic's sprites are similar, so there is no 2nd copy. |
| Ring is generated from its quarter by mirroring horizontally and vertically. |
| Net is created using STRING$(), as the same pattern for all scanlines. |
| Many IF statements are replaced by math, since MSX BASIC represents FALSE as |
| 0, and TRUE as -1. An example of this technique is changing ring vector when |
| it touches screen bounds: R=R*SGN(1+2*(P<1ORP>239)). The result of SGN is -1 |
| for bounds, 1 otherwise. |
| |
| Lines: |
| 0 Initialize graphics screen, define integer and string variable prefixes to |
| save on % and $, prepare control names, draw grass and sun. |
| 1 Define helper functions, define the ring sprite, prepare hedgehog sprites. |
| 2 Define hedgehog sprites, define and draw the net. |
| 3 Initialize core variables, draw checkered ground, finish grass, play intro |
| music. |
| 4 Display game title, copyright, and main menu. Keyboard handling for menu. |
| 5 Control handling and sprite moving for Sonic, then do the same for Shadow. |
| Move the ring by the current speed vector. |
| 6 Reset the consecutive contacts counter if needed. Handle Sonic's strike. |
| 7 Handle Shadow's strike. |
| 8 Simulate ring physics. Check for all faults, update score and variables if |
| needed. Otherwise flip the speed vector, if the ring hits screen bounds. |
| 9 Subroutine that shows score and checks for victory. If so, puts the winner |
| name and restarts the game. |
| |
+------------------------------------------------------------------------------+
| Acknowledgements / |
|------------------ |
| |
| Thanks to my son Dan for the game idea, ad picture and sprites. |
| Thanks to SEGA for Sonic and Shadow hedgehog characters. |
| Thanks to Microsoft and ASCII Corp. for MSX BASIC and machines. |
| Thanks to Arcade Voleyball authors for some inspiration. |
| |
+------------------------------------------------------------------------------+