Sonic 1-squared

Sonic 1-squared is an enhanced version of the original Sonic the Hedgehog game engine. Various changes are planned to make editing the game easier.

Features

• The player's Chaos Emerald count is stored as a bitfield instead of a list. It's a longword, so there can be up to 32 Emeralds.
• LoadPerZone subroutine consolidates all pointers and parameters for zones and acts. This simplifies the process of adding levels. (incomplete)
• LoadPerCharacter subroutine does the same for the Sonic object, palette and life icon, allowing for extra characters.
• LoadPerDemo loads the level number, demo data, character and start position for all demos, including those during the credits.
• Rewritten level select routine to be more customisable. It now uses standard ASCII, and supports multiple columns (which are automatically generated based on the lines-per-column setting).
• The hidden Japanese credits, "try again" and "end" screens have been given their own gamemodes, which are accessible through the level select.
• The HUD has new debug features, including a CPU cycle usage indicator (displayed as two arrows on the left side of the screen - red for VBlank overflow and yellow for overall usage), sprite counter ($50 is max) and camera x/y position.
• 6 button support. v_joypad_hold_actual_xyz contains the status of the X/Y/Z/Mode buttons.

Graphics

• SlowPLC subroutine loads Kosinski-compressed graphics over several frames.
• UncPLC subroutine load uncompressed graphics at any time. This complements SlowPLC by loading graphics during a level. Both this and SlowPLC use the DMA queue.
• DMA queue system for loading uncompressed graphics.
• Animated level graphics use a script instead of being hard-coded. The exception is Marble Zone's magma, which works somewhat differently to other animations.
• Palette cycling uses a script.
• Water palettes are generated in-game by the WaterFilter subroutine, instead of being hardcoded.
• Fading to black/white is controlled by a brightness variable, and no longer requires a "next" palette. This simplifies loading new palettes.
• Sprites can be hidden with the variables v_spritemask_height and v_spritemask_pos.
• Sonic's sprites are loaded from a PNG spritesheet using HiveMap.

Objects

• Modified the way animation works to save 2 bytes in RAM per object. The high bit of ost_anim now serves as an update flag instead of ost_anim_restart.
• Object scratch RAM is assigned automatically with rsobj macro. If you attempt to use more RAM than is available ($40 bytes), assembly will fail.
• ost_id is now a longword pointer instead of a single byte (as is the case in Sonic 3 & Knuckles). This allows for unlimited object types, and slightly improves performance.
• ost_frame extended to a word (ost_frame_hi), allowing objects to have up to 8,192 distinct frames of animation.
• ost_displaywidth extended to a word (ost_displaywidth_hi), allowing for objects wider than 256px to remain visible when partially off screen.
• ost_width and ost_height extended to words (ost_width_hi and ost_height_hi).
• Sprite mappings use 6 bytes per piece instead of 5, and the piece count is a word instead of a byte. This ensures the data is always aligned to even.
• ost_parent contains the parent object's OST address (shortened to a word), if the saveparent was useded when the child object was created. getparent will set the parent object as a1. Calling DeleteFamily will delete an object as well as any objects which have it set as their parent.
• ost_linked is similar to ost_parent. getlinked will set the linked object as a1. DeleteFamily won't delete linked objects.
• ost_col_width and ost_col_height set an object's hitbox for ReactToItem instead of using a table.
• ost_col_width_extra and ost_col_height_extra (bytes) set a secondary hitbox for enemies with spikes (e.g. Yadrin) in the top left corner of the standard hitbox. Setting either value as negative moves the hitbox to the opposite corner. Unlike usual width and height settings, the value is for the diameter of the hitbox, not just the radius.
• ost_status now includes status_pointy_bit for spikes and similar objects. It causes a different sound to play when Sonic is harmed by the object.
• ost_subsprite contains the address of a subsprite table. Subsprites are additional sprite pieces that are not part of the object's mappings. Call FindFreeSub to assign a subsprite table to the current object, and getsubsprite to set that table as a2. Subsprites use the same format as sprite mappings, except the VRAM setting is absolute instead of relative to ost_tile.
• ost_priority is now a word that points to the sprite queue directly, which slightly improves performance.
• Monitor icons load only as needed, allowing for up to 256 unique monitor types (with a maximum of 8 loaded at any one time).
• Monitors can be broken from below if they are already on the ground.
• Each title card has its own PLC, so only letters that are used need to be loaded. Title cards are automatically centered by the autocard macro. Title card mappings are also automated, and can use sprite mappings more efficiently by joining two letters together as a single sprite.
• GHZ/SLZ loops use an object instead of being hard-coded. The object reads Sonic's position within the loop and updates the level layout accordingly.
• Pushable blocks can be moved by standing on top of them and pushing against a wall. The player can use this to retrieve a block if it's stuck next to a wall.
• Debug mode has been rewritten with more features, including info overlays for Sonic and the nearest object (similar to those in the Sonic Physics Guide). The controls are as follows:
  • B - Toggle between Sonic and object.
  • C (as object) - Place an object.
  • Hold A (as object) - Select an object with left/right. The previous and next objects are now visible. Toggle x/yflip with down/up respectively.
  • X - Target overlay to current nearest object. This is not automatically updated until the targeted object despawns.
  • Y - Toggle between displaying x/y position, x/y speed and angle/routine numbers.
  • Z - Toggle between displaying actual width/height and hitbox width/height.
  • Mode - Toggle hide all overlays. Overlays use approximately 5% of available CPU cycles, so hiding them provides a more accurate reading of CPU usage.

Sonic

• Sonic ducks when down is pressed if he's moving slowly.

Bugfixes

• Spikes no longer kill Sonic immediately after losing rings. Add $80 to the subtype to restore the original lethal behaviour.
• Sonic's mirrored sprites are no longer misaligned by 1 pixel. This was most obvious when pushing a wall to the left.
• Scrolling to the left is limited to 16 pixels per frame, as it previously was only when scrolling right.
• Sonic is no longer killed by the screen not scrolling down fast enough. This was a problem on the S-tunnels in Green Hill Zone.

Credits

• flamewing for mdcomp.
• vladikcomper for the advanced error handler.
• Devon for the optimised CalcAngle routine.
• OrionNavattan for various optimisations.
• Brainulator for some display bugfixes.