Sinclair ZX Spectrum patterns.

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• A Bounded Event Queue on Spectrum

  When three things happen before the game gets around to handling them, one event byte can only remember the last one.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• A Counted Text-entry Buffer on Spectrum

  Entering a player name needs more than appending characters.

  Sinclair ZX SpectrumInput · intermediateAssembly

• A Counted-Byte Adventure Parser

  Recognise two-word commands without changing the input buffer. Reusable Z80 code, checked vocabulary tables and a working keyboard caller.

  Sinclair ZX SpectrumInput · intermediateAssembly

• A game loop on the ROM clock

  Use the 48K ROM interrupt clock to accept one update at a time, including when game work takes longer.

  Sinclair ZX SpectrumFramework · beginnerAssembly

• A Saturating 16-bit Score on Spectrum

  A coin worth 300 points should still be worth 300 when the low byte fills up.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• A Streaming CRC-8 on Spectrum

  A saved score or a small asset can pick up an accidental changed byte.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• A Two-Word Adventure Parser

  Turn the player's words into commands your game can understand. A reusable, vocabulary-driven parser with a complete tiny adventure.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Accept a Stable Run of Input Samples in Spectrum BASIC

  Change a logical byte only after enough consecutive identical samples, retaining candidate and run history.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Accumulate a Capped Binary Score in Spectrum BASIC

  Add two-byte awards through a wide intermediate, distinguish an exact cap from clipping and preserve the award.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Action Cooldowns on Spectrum

  Keep an action timer advancing between requests, and spend its cooldown only when a requested resource is available.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Add and Remove Inventory Stacks on Spectrum

  Picking up a stack should either fit completely or leave the inventory as it was.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Add Signed Acceleration Without Wrapping in Spectrum BASIC

  Add a signed eight-point-eight velocity increment in a wider range, then clamp to an explicit symmetric limit before encoding the result.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Add Words with Saturation on Spectrum

  A large score or resource total should stop at its ceiling rather than wrap back to a small number.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Advance a Timed Animation on Spectrum

  A held pose and a running animation need different clocks.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Advance an Animation Timeline in Spectrum BASIC

  Return a frame index with configurable duration, looping and one-shot completion.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Aim a Projectile at a Target in Spectrum BASIC

  Compute a bounded two-component velocity towards a target with an explicit dominant-axis speed rule.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Aim a Projectile with Bounded Integer Speed on Spectrum

  A turret can fire towards the player without a trigonometry table or floating-point division.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Allocate Slots with a Bitset on Spectrum

  Eight occupied flags can fit in one byte when objects already live in fixed slots.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Allocate Slots with an Occupied Mask in Spectrum BASIC

  Reserve the lowest free slot and release an occupied slot using one retained eight-bit mask.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Apply Damage with Recovery Time in Spectrum BASIC

  Keep health above zero and give a hit a defined recovery interval, with explicit applied and killed results.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Approach a Target Without Overshoot on Spectrum

  An enemy can move towards a waypoint without orbiting it forever.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Attribute Clash

  The Spectrum stores one ink-and-paper colour per 8×8 cell, so pixels and colour live on different grids — the source of colour clash. Understanding it, and the design craft that turns the constraint into the platform's look.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Attribute Writing

  Write colours directly to attribute memory for fast, flicker-free graphics without touching pixel data.

  Sinclair ZX SpectrumRendering · beginnerAssembly

• AY Envelopes and Noise

  Let the AY shape a note's volume in hardware and add its noise channel — a decaying pluck from the envelope generator, an explosion from noise, each fired with a single register write.

  Sinclair ZX SpectrumAudio · intermediateAssembly

• AY Music

  Step a note pattern once per interrupt, handing each of the AY's three channels its note from a period table — a full three-voice tune that plays in the background while the game runs.

  Sinclair ZX SpectrumAudio · advancedAssembly

• AY Tone

  Play a tone on the 128K's AY-3-8912 sound chip — select a register through port $FFFD, write it through $BFFD, and the chip holds the note on its own while the CPU gets on with the game.

  Sinclair ZX SpectrumAudio · beginnerAssembly

• Beeper Music

  Play an actual melody on the Spectrum's one-bit speaker — a note table for pitch, a length per note — and coax two or more voices from that single bit with phase accumulators.

  Sinclair ZX SpectrumAudio · intermediateAssembly

• Bitmap Addressing

  Turn an (x, y) pixel into a Spectrum screen address — where consecutive lines are nowhere near each other in memory. The interleaved layout that every Spectrum drawing routine has to reckon with.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Bounded Signed Acceleration on Spectrum

  Gravity should keep adding speed until the chosen terminal velocity, not turn a fast fall into an upward launch when an integer overflows.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Buffer Turns Through a Grid on Spectrum

  A maze feels kinder when a turn pressed just before a junction happens as soon as the route opens.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Build Bounded Spatial Buckets on Spectrum

  Nearby objects are worth comparing; distant ones usually are not.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Camera Dead Zones on Spectrum

  A camera need not move every time the player takes a step.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Capture and Restore a Checked Checkpoint on Spectrum

  A restart point should restore a coherent snapshot, not whichever fields happened to be copied before a failed attempt.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Carry a Passenger with a Platform in Spectrum BASIC

  Apply signed platform movement to a supported passenger, with explicit position bounds and clipping feedback.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Carry a Supported Passenger on Spectrum

  A passenger should inherit a moving platform’s displacement without changing the platform’s own position.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Change Inventory Counts Atomically in Spectrum BASIC

  Add or remove a whole quantity from four fixed item categories, rejecting requests that exceed stock or capacity.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Character Printing

  Print ASCII characters to the screen using the ROM character set. Direct display file access for fast text rendering.

  Sinclair ZX SpectrumRendering · beginnerAssembly

• Check a Byte Stream with CRC-8 in Spectrum BASIC

  Retain an eight-bit remainder while feeding a message byte by byte, with two explicit polynomial choices and a clear reset boundary.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Choose a Bounded Text Line on Spectrum

  A dialogue box needs line breaks that fit its width without requiring a second copy of the text.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Choose a Winning Request in Spectrum BASIC

  Select the highest-priority request while keeping the first equal-priority winner and explicit batch ownership.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Choose an Eight-way Direction on Spectrum

  A character can face a target in eight directions without angles, trigonometry or a lookup table.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Choose from Weighted Outcomes on Spectrum

  A timid enemy might retreat often and attack rarely.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Choose Outcomes with Different Weights in Spectrum BASIC

  Map a caller-supplied bounded draw to one of eight weighted outcomes, skipping zero-weight entries.

  Sinclair ZX SpectrumAI · intermediateBASIC

• Choose the Highest-priority Request on Spectrum

  A pickup chime, a warning and an explosion may all request attention in one update.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Clip a Rectangle to a View in Spectrum BASIC

  Find the visible intersection of two half-open rectangles, separating an empty result from invalid reversed edges.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Clip a Rectangle to a Viewport on Spectrum

  A partly off-screen object should expose only the part that lies inside the viewport.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Clip Masked Sprites on the Spectrum

  A byte-aligned 16×16 sprite can cross any screen edge safely. Reusable signed clipping and masked drawing, with source cropping and a complete 48K tape example.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Commit a Crafting Recipe Atomically on Spectrum

  Do not take the player’s ingredients and only then discover there is nowhere to put the result.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Compact a Live Object Prefix on Spectrum

  A particle update can walk a dense live prefix instead of checking holes forever.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Compare Signed Byte Values on Spectrum

  A velocity of −1 must sort below zero even though its stored byte is 255.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Convert an Axis Sample to Intent in Spectrum BASIC

  Keep an inclusive quiet zone around a calibrated centre, then report direction and distance beyond it.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Count Active Play Ticks in Spectrum BASIC

  Keep a two-byte active counter, freeze it during pause and give reset explicit priority.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Count Active Play Time on Spectrum

  A pause screen should not quietly spend the player’s time allowance.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Craft Without Losing Ingredients in Spectrum BASIC

  Check two ingredient stocks and result capacity before applying an all-or-nothing crafting transaction.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Damage and Recovery on Spectrum

  Apply damage without byte underflow, give an entity time to recover and emit one fatal-hit event.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Debounce a Sampled Input Byte on Spectrum

  A noisy or bouncing input should settle before it changes the game’s logical state.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Decode a Small Run-length Block in Spectrum BASIC

  Expand count/value pairs into an eight-cell output with explicit input bounds, actual written length and useful partial-error results.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Decode Bounded Byte Deltas on Spectrum

  A path or table whose values change slowly can be stored as a starting value followed by small signed differences.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Decode Bounded RLE Data on Spectrum

  Repeated tiles or pixels can be stored as a count followed by a value.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Defer Object Changes Until After Traversal on Spectrum

  Spawning or deleting objects during a traversal can accidentally update a new object twice or skip a neighbour.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Detect a Button Chord Once on Spectrum

  Holding two buttons together should trigger one action, not one action every frame.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Detect a Whole Button Chord Once in Spectrum BASIC

  Require a set of held buttons, exclude forbidden buttons and report a rising edge for the complete chord.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Divide a Word by a Byte on Spectrum

  A quotient without its remainder throws useful information away.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Divide Ticks Without Losing the Remainder on Spectrum

  Thirty updates from fifty display ticks should be spaced out, not rounded down to zero.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Draw Bitmap Text on Spectrum 48K

  Reusable fixed-width characters and counted strings at any pixel position, with explicit clipping, font ownership and drawing costs.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Draw Every Item Before Repeating the Bag in Spectrum BASIC

  Select and remove an item from a bounded bag, with explicit reset and caller-owned random indices.

  Sinclair ZX SpectrumAI · intermediateBASIC

• Draw Lines, Circles and Ellipses on Spectrum 48K

  Reusable clipped integer geometry, span-filled curves and explicit endpoint ownership for Spectrum 48K.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Draw Objects in Stable Depth Order in Spectrum BASIC

  Sort object indices by depth without moving the objects, keeping equal-depth objects in their original order.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Draw Pixels and Boxes in ZX Spectrum BASIC

  Reusable set/clear pixels, filled boxes and outlines, with machine-specific coordinate conversion.

  Sinclair ZX SpectrumRendering · beginnerBASIC

• Draw Pixels, Spans and Boxes on Spectrum 48K

  Callable set, clear, XOR, read, span and rectangle routines for Spectrum 48K, with explicit bounds and byte ownership.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Draw Without Repeating from a Bag on Spectrum

  Random pieces can arrive in long droughts.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Edit a Counted Text Buffer in Spectrum BASIC

  Append a checked character, erase safely and clear a fixed eight-slot buffer while keeping live length separate from capacity.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Encode a Small Run-length Block in Spectrum BASIC

  Group up to eight byte values into count/value pairs, checking complete output capacity before changing any encoded byte.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Encode a Small Run-length Block on Spectrum

  Repeated map values can take less room as a count and a value—but only if the output buffer is big enough.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Enter and Leave a Ladder on Spectrum

  Climbing should suspend gravity, but jumping away must hand movement back to the ordinary player controller.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Face a Target in Eight Directions in Spectrum BASIC

  Choose a discrete facing from two positions using signed displacement and a deliberate 2:1 sector rule.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Fill a Connected Grid Region on Spectrum

  A paint fill can also discover a connected room or reveal matching puzzle cells.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Filter Collision Pairs by Layer on Spectrum

  A projectile can cross its owner without hitting them, while still hitting an opponent in the same patch of screen.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Filter Collision Pairs by Policy in Spectrum BASIC

  Require mutual group acceptance, then classify an accepted pair as a sensor or solid before geometry testing.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Find a Grid Path and Reachable Cells in Spectrum BASIC

  Return shortest four-neighbour distances, parents and a first step from a bounded tile map.

  Sinclair ZX SpectrumAI · intermediateBASIC

• Find a Value in a Small Dictionary in Spectrum BASIC

  Search eight byte-key/value pairs, preserving the dictionary and returning the first match with separate found and validity flags.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Find an Integer Square Root on Spectrum

  Sometimes the useful answer is the whole-number distance, with no floating point in sight.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Find the First Step Along a Shortest Grid Path on Spectrum

  An enemy can walk around a wall without pretending that moving towards the player is already pathfinding.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Follow an Ordered Waypoint Route in Spectrum BASIC

  Move through four ordered positions, retaining the route cursor and choosing a loop or a finished one-shot.

  Sinclair ZX SpectrumAI · intermediateBASIC

• Format a 16-bit Decimal Number on Spectrum

  A binary score is good for adding points.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Format a Byte as Hexadecimal on Spectrum

  Two hexadecimal digits are a compact way to show a byte in a debugger, password or diagnostic panel.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Fractional Position Updates on Spectrum

  A quarter-pixel step should eventually move the sprite a whole pixel.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Game States and Restart on Spectrum

  Separate title, play, pause and game over, preserve a paused session and reset a new one exactly once.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Gate a Dialogue Choice with Flags on Spectrum

  A dialogue option can depend on what the player knows and change what happens next.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Give a Spectrum BASIC turn a deadline

  Keep untimed play valid, then add a reusable FRAMES countdown with an explicit input and expiry policy.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Give a Spectrum Z80 turn a deadline

  Keep untimed play valid, then add a reusable FRAMES countdown with an explicit input and expiry policy.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Give Ready Jobs a Fair Turn in Spectrum BASIC

  Select one of eight ready slots from a retained rotating start position, wrapping fairly and leaving work execution to the caller.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Grid Movement with Bounds

  Move an entity on a grid with boundary checking. Prevents moving outside the play area.

  Sinclair ZX SpectrumPhysics · beginnerAssembly

• Group Nearby Objects into Fixed Buckets in Spectrum BASIC

  Store up to four object IDs in each of four spatial buckets, with explicit capacity overflow and read-only queries.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Insert a Score and Keep Ties Stable in Spectrum BASIC

  Maintain four descending byte scores with associated tags, retaining existing equal scores first and rejecting an invalid table without changing it.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Insert into a High-score Table on Spectrum

  A score table needs a clear answer for ties, a full table and the player who just misses the cut.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Interpolate Between Byte Endpoints on Spectrum

  A menu panel or camera can move towards an endpoint without a different hand-written position for every frame.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Jump Buffering and Coyote Time on Spectrum

  Press Jump just before landing and it is frustrating when the press disappears.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Keep a Bounded Cell-edit Undo Log on Spectrum

  Undo should restore the previous cell value, including when the same cell was edited twice.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Keep a Menu Selection Visible on Spectrum

  A list can hold more choices than the screen has rows while its cursor still stays in view.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Keep a Small Position History on Spectrum

  A trailing companion needs where the leader was, not another guess at where it might be going.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Keep a Stable Interaction Focus on Spectrum

  A prompt should not flicker between two nearby objects whenever their distances differ by one pixel.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Keep a Stable Priority Event Queue on Spectrum

  An urgent event may need service before an older routine event, while equal priorities should remain fair.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Keep a Turn Until the Route Opens in Spectrum BASIC

  Retain a requested turn, try it before the current direction and move at most one checked grid cell per service.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keep an Effect on a Timer in Spectrum BASIC

  Track a finite duration and pulse interval, including a possible pulse on the final active tick.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keep Camera Shake Alive Across Updates in Spectrum BASIC

  Produce bounded signed camera offsets for a retained lifetime, without modifying the world position.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Keep Camera Shake out of World State on Spectrum

  An impact can shake the view without moving the player, the level or the collision geometry.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Keep Fractional Tick Credit in Spectrum BASIC

  Emit a chosen numerator of events per denominator calls without discarding the remainder.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keep Fractions Between Position Updates in Spectrum BASIC

  Add a signed eight-point-eight displacement to a retained position, preserving sub-unit motion and making wrapping explicit.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Keep Interaction Focus Stable in Spectrum BASIC

  Choose an eligible nearby target while retaining the current one within an explicit distance margin.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keep Object References with Their Lifetimes in Spectrum BASIC

  Allocate, query and release four stable slots while rejecting references to an earlier generation of a slot.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keep Starts and Resumes Separate in Spectrum BASIC

  Separate fresh sessions, held-button edges and pause/resume transitions with explicit caller-owned progress.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keep the Camera Quiet Until Needed in Spectrum BASIC

  Retain a world-space camera, move only beyond a screen-relative quiet zone and clamp the result to valid scrolling bounds.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Keep Track of Cells That Need Redrawing in Spectrum BASIC

  Mark, inspect and consume pending cell updates without losing repeated marks or crossing the two-byte boundary.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Keep Travel Remaining After a Bounce in Spectrum BASIC

  Move within inclusive axis bounds while consuming the whole requested distance, retaining direction and counting repeated reflections.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Keep Urgent Events in a Stable Queue in Spectrum BASIC

  Queue four event/priority pairs, service the highest priority first and preserve insertion order for equal priorities.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Keyboard Reading

  Read the ZX Spectrum keyboard matrix by polling I/O ports. Simple, efficient, and no ROM routines required.

  Sinclair ZX SpectrumInput · beginnerAssembly

• Land on a One-way Platform on Spectrum

  A fast-falling character can cross a thin platform between two updates without ever having its feet exactly on the top.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Land While Crossing a One-way Platform in Spectrum BASIC

  Compare old and proposed feet against a platform top, using widened horizontal spans and a deliberate drop-through flag.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Limit Hits to an Attack Window in Spectrum BASIC

  Accept each target once during a chosen attack interval, retaining a hit set across updates.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Limit Hits to an Attack Window on Spectrum

  A sword can overlap the same enemy for several frames without dealing damage on every frame.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Look Up a Bounded Byte Dictionary on Spectrum

  An item code, tile identifier or command token often needs a small associated value.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Look Up a Small Slope Surface in Spectrum BASIC

  Query an eight-column height profile, mirror it without copying data and reject a surface that would exceed the byte coordinate range.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Look Up Tile Properties on Spectrum

  The picture number in a map does not automatically tell you whether a tile is solid, harmful or climbable.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Manhattan Distance on Spectrum

  On a four-way grid, distance is the horizontal gap plus the vertical gap.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Masked Sprites

  The Spectrum has no hardware sprites, so a moving object is drawn by hand — AND a mask to punch a hole in the background, OR the image into it — with pre-shifted copies for pixel-accurate, fast movement.

  Sinclair ZX SpectrumRendering · advancedAssembly

• Measure, Align and Wrap Text on Spectrum 48K

  Measure and align labels, choose character or word wrapping, and give narrow letters less room with proportional text.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Menu Key Repeat on Spectrum

  A menu should move once when you press Down, pause briefly, then scroll while you hold it.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Mirror an Eight-bit Bitmap Row on Spectrum

  A stored row of pixels can face the other way without keeping a second copy of the artwork.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Move, collect and respond on the ZX Spectrum

  Combine input, bounded movement, box collision, drawing and sound in a small program you can take apart.

  Sinclair ZX SpectrumFramework · beginnerAssembly

• Multiply Two Bytes into a Word on Spectrum

  A small machine still needs products larger than one byte: an area, a score multiplier or a scaled distance.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Numeric Display

  Convert a number (0-99) to two ASCII digits and print them. Essential for scores and counters.

  Sinclair ZX SpectrumRendering · beginnerAssembly

• Offer Dialogue Choices with Quest Flags in Spectrum BASIC

  Test quest conditions before accepting a choice, then apply its changes once.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Pack Live Objects and Keep Their Order in Spectrum BASIC

  Compact paired flag/payload arrays in place, clearing vacated entries while preserving unused capacity.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Parse a Bounded Decimal Number on Spectrum

  A score name box and a numeric prompt need different input rules.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Parse Two Hexadecimal Digits on Spectrum

  A short hexadecimal input still needs validation before it becomes an address, colour or seed.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Patrol Between Two Endpoints on Spectrum

  A guard walks to the end of a corridor, turns and comes back.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Pick the Nearest Active Target in Spectrum BASIC

  Choose among four active candidates using Manhattan distance, preserving the first slot on ties and retaining the ninth distance bit.

  Sinclair ZX SpectrumAI · intermediateBASIC

• Place Spectrum Sprites at Pixel Positions

  Select one of eight prepared masks, keep signed pixel positions correct at the left edge, and draw the visible three-byte footprint.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Print a Bounded Text Region in ZX Spectrum BASIC

  Print a map slice with a complete bounds and tile-ID preflight before any output.

  Sinclair ZX SpectrumRendering · beginnerBASIC

• Profile a Routine

  Find where a Spectrum routine spends its time, change one thing, and measure the saving against the extra code.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Progress Bar (BASIC)

  Horizontal progress bar coloured like a gauge — red when low, yellow in the middle, green when high. Useful for fuel, health or time left.

  Sinclair ZX SpectrumRendering · beginnerBASIC

• Project a World Point into the View in Spectrum BASIC

  Convert byte-pair world coordinates to visible screen positions without dropping high bytes or wrapping negative differences.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Project World Points into a Viewport on Spectrum

  A world can be larger than the screen even when the drawing routine expects byte-sized screen coordinates.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Propose a Push from a Moving Solid in Spectrum BASIC

  Detect a one-dimensional moving solid crossing an actor and propose a safe displacement or an explicit blocked result.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Push a Block Atomically on Spectrum

  A crate should move with the player only when the space beyond it is free.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Push a Crate After Checking the Whole Move in Spectrum BASIC

  Check the adjacent cell and the space beyond a crate before changing the player or map.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Push an Actor with a Moving Solid on Spectrum

  A moving wall should carry an actor ahead of its leading face, or report that the actor cannot fit.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Query a Byte Map on ZX Spectrum

  Read and change map cells, look up tile properties and convert world positions with reusable Z80 code and an explicit memory contract.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Query a Small Slope Height Profile on Spectrum

  A sloping tile needs a surface at each horizontal position, not one flat collision edge.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Query a Thin Grid Sight Line in Spectrum BASIC

  Visit the cells along an integer line and stop at the first blocking cell.

  Sinclair ZX SpectrumAI · intermediateBASIC

• Query and Change a Tile Map in ZX Spectrum BASIC

  Keep room data separate from its picture, with checked reads, edits, properties and world-to-cell conversion.

  Sinclair ZX SpectrumRendering · beginnerBASIC

• Quest and Inventory Flags on Spectrum

  A key collected, a door unlocked, a conversation finished: eight yes/no facts fit in one byte.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Queue Game Events in Spectrum BASIC

  Store byte-valued game requests in a bounded FIFO, with explicit full/empty results and validated wrap-around.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Read and Edit Packed Four-bit Cells in Spectrum BASIC

  Store two logical cells per numeric byte value and update either half without damaging its neighbour.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Read and Update Packed Four-bit Cells on Spectrum

  Sixteen tile values do not need sixteen whole bytes when each value fits in four bits.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Read and Write Hexadecimal Bytes in Spectrum BASIC

  Format one byte as two ASCII digits and parse two checked digits back into a byte.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Read Bits from a Bounded Data Block on Spectrum

  Packed flags and small fields can share a byte, provided the reader knows exactly how many bits remain.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Read Bits from a Small Data Block in Spectrum BASIC

  Extract up to eight bits at a time from a four-byte block, keeping a cursor and rejecting a field that would cross the end.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Read Decimal Digits with Bounds in Spectrum BASIC

  Accept one ASCII digit at a time while retaining the valid prefix, rejecting other characters and refusing values above 255.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Rebuild Byte Values from Deltas in Spectrum BASIC

  Expand up to eight signed byte differences from an explicit base, wrapping modulo 256 and preserving output when input is invalid.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Recognise a Short Input Sequence on Spectrum

  A sequence is about order.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Recognise an Overlapping Input Sequence in Spectrum BASIC

  Remember a short ordered prefix, pulse on a match and retain the useful suffix for overlapping matches.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Rectangle Overlap

  Reuse a checked half-open rectangle test, understand touching edges and diagnose the equality mistake.

  Sinclair ZX SpectrumPhysics · beginnerAssembly

• Rectangle Overlap

  Reuse a checked half-open rectangle test, understand touching edges and diagnose the equality mistake.

  Sinclair ZX SpectrumPhysics · beginnerBASIC

• Reflect a Surface-normal Speed with Restitution on Spectrum

  A bounce can lose speed along a wall’s normal while keeping its sideways motion.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Reflect Movement at Axis Bounds on Spectrum

  A fast ball should use the distance left after a bounce rather than sticking to the wall.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Reflect Speed with a Material Coefficient in Spectrum BASIC

  Scale a normal-speed magnitude by quarter-step restitution, reverse its direction and preserve its tangential component.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Reject Stale Object Handles on Spectrum

  A reused pool slot should not let an old reference suddenly name a different enemy.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Remember an Unordered Contact Pair in Spectrum BASIC

  Remember which pairs have already been considered during one traversal, without treating reversed IDs as a new pair.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Remember Contact Pairs for a Step on Spectrum

  The same contact can appear in both objects’ candidate lists.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Remember Jump Presses for a Short Window in Spectrum BASIC

  Retain separate jump-buffer and coyote timers, grant a jump only when they overlap and consume permission after the pulse.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Remember Previous Positions in a Ring in Spectrum BASIC

  Append positions without shifting the buffer, then query a sample by its age, including after wraparound.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Remember Which Cells Need Redrawing on Spectrum

  Changing one cell should not force a whole board to be redrawn.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Repeat a Held Menu Control in Spectrum BASIC

  Pulse on a new hold, wait a configurable delay, then repeat at a separate cadence until release.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Repeat a Small Random Sequence in Spectrum BASIC

  Seed and restore a portable eight-bit LFSR, expose corrupted zero state and keep random-call order explicit.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Report Trigger Enter, Stay and Exit Events on Spectrum

  Standing in a doorway should not count as entering it on every update.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Report Trigger Entry, Stay and Exit in Spectrum BASIC

  Turn an eight-bit overlap snapshot into separate entered, stayed and exited masks while retaining the previous snapshot.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Resolve Held Input to Four Directions in Spectrum BASIC

  Cancel opposed directions, then use retained axis preference to choose a single direction from a diagonal.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Resolve Input to Four Directions on Spectrum

  A maze character needs one direction even when the player holds a diagonal.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Resource Counters on Spectrum

  An empty magazine should refuse a shot, not turn into 255 rounds.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Retain Climbing State on a Ladder in Spectrum BASIC

  Enter, retain and leave a bounded ladder mode with explicit gravity and jump-release outputs.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Reusable Object Slots on Spectrum

  Claim and release fixed game-object slots, handle exhaustion, and expire objects without moving their neighbours.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Reuse Object Slots in Spectrum BASIC

  Allocate, release and age reusable object slots, with explicit full-pool results and caller-owned payloads.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Reveal Counted Text Over Time on Spectrum

  A line of dialogue can appear a character at a time, with a button to show the rest immediately.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Run a Timed Wave of Events in Spectrum BASIC

  Emit up to four event IDs with explicit quiet-call delays, retaining the cursor and emitting at most one event per call.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Save and Restore a Small Game State in Spectrum BASIC

  Capture three byte-valued fields in RAM and validate the complete stored record before restoring any live field.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Save and Restore Software Sprite Backgrounds

  Keep a separate packed background for each Spectrum object, then restore overlaps in reverse order. Reusable rectangle helpers and a complete masked-sprite tape caller.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Screen Frame (BASIC)

  Draw a 1-cell border around the play area with title and footer bars. The standard game screen layout.

  Sinclair ZX SpectrumFramework · beginnerBASIC

• Seeded Random Numbers on ZX Spectrum

  Reusable seed and next routines, repeatable draws, state replay and a visible zero-state trap.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Select Ready Work with Round-robin Fairness on Spectrum

  Background jobs should each get a turn when the game can afford only one piece of work this tick.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Select the Nearest Active Target on Spectrum

  An enemy or homing projectile needs a target-selection rule that stays predictable when candidates tie.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Sequence Counted Notes and Rests on Spectrum

  A short tune needs a clock and a sequence of notes, not a fresh sound effect every frame.

  Sinclair ZX SpectrumAudio · intermediateAssembly

• Service a Logical Attack–Decay–Sustain–Release Envelope on Spectrum

  A sound can swell, settle and fade instead of switching between full volume and silence.

  Sinclair ZX SpectrumAudio · intermediateAssembly

• Service a Small Spawn Timeline on Spectrum

  A wave can have deliberate pauses without burying every spawn in the main loop.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Service a Timed Status Effect on Spectrum

  A poison effect needs a duration and a pulse interval, not a fresh timer every time the actor is updated.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Service an Action Cooldown in Spectrum BASIC

  Keep time moving between requests, then grant an action only when the cooldown and caller-supplied availability allow it.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Seven-Segment Digits (BASIC)

  Draw large seven-segment display digits using PLOT/DRAW. Cell-aligned with 1px outline. 10 DATA strings define all digits 0-9.

  Sinclair ZX SpectrumRendering · beginnerBASIC

• Shape a Logical Sound Envelope in Spectrum BASIC

  Service attack, decay, sustain and release as bounded logical control levels with retained gate-edge history.

  Sinclair ZX SpectrumAudio · intermediateBASIC

• Software Scrolling a Bitmap Band

  Move a Spectrum playfield one pixel at a time, supplying the newly exposed edge yourself. Reusable Z80 code and a running tiled-band caller.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Sort a Small Draw Order Stably on Spectrum

  When two sprites have the same depth, their order should not flicker from frame to frame.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Sound Beep

  Make a fixed beep, a rising or falling effect, and a short click with separate pitch and length controls.

  Sinclair ZX SpectrumAudio · beginnerAssembly

• Spend and Refill a Resource in Spectrum BASIC

  Reject unaffordable spending atomically, but accept a refill and cap it deliberately at 255.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• State Machine Loop

  Organise game flow with distinct states (title, playing, game over). Clean separation of game phases.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Step Each Packed Colour Channel in Spectrum BASIC

  Unpack logical RGB332, move each channel by one towards its target and repack without cross-channel carry.

  Sinclair ZX SpectrumRendering · intermediateBASIC

• Step Towards a Packed Colour on Spectrum

  A fade can approach its target one channel step at a time instead of treating a packed colour as a single number.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Stop Fast Motion at a Wall Face in Spectrum BASIC

  Sweep one interval towards a requested endpoint, returning first contact instead of letting a fast step pass through a wall.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Sweep an Interval Along One Axis on Spectrum

  A fast object can cross a wall between frames even when neither endpoint overlaps it.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Test a Point Against a Circle in Spectrum BASIC

  Check an inclusive circular boundary without a square root, preserving full coordinate differences and enough arithmetic range for squared distances.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Test a Point Against a Circle on Spectrum

  A round pickup should not become a square just because a box test was convenient.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Test Opaque Pixels in Two Small Masks in Spectrum BASIC

  Align two eight-by-eight opaque masks, then return the first overlapping row rather than treating overlapping boxes as a pixel hit.

  Sinclair ZX SpectrumPhysics · intermediateBASIC

• Test Sight Along a Grid Row or Column on Spectrum

  A sentry looking down a corridor must stop at the first wall.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Test Two Small Opaque Pixel Masks on Spectrum

  Two sprite boxes can overlap while their visible shapes still miss each other.

  Sinclair ZX SpectrumPhysics · intermediateAssembly

• Text Utilities (BASIC)

  Centre text on any row and clear rows — two tiny subroutines used in every BASIC game.

  Sinclair ZX SpectrumFramework · beginnerBASIC

• Trace a Thin Grid Line of Sight on Spectrum

  A guard looking across a room needs more than a same-row check.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Transfer Inventory Stacks Atomically on Spectrum

  Moving arrows from a chest to a pack should never remove more than the pack can hold.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Transpose an Eight-by-eight Bitmap on Spectrum

  Turning rows into columns is the building block behind rotating small glyphs and adapting bitmap layouts.

  Sinclair ZX SpectrumRendering · intermediateAssembly

• Turn a Score into Five Digits in Spectrum BASIC

  Convert an unsigned 16-bit value into exactly five ASCII character codes, preserving its two input bytes and making leading-zero policy explicit.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Turn an Analogue Axis into Intent on Spectrum

  A joystick that rests a little off-centre should not make the player creep across the screen.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Undo Edits to a Small Board in Spectrum BASIC

  Record each cell’s previous value before editing it, then restore edits in reverse order with a four-entry log.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Validate a Save Before Replacing Live State on Spectrum

  A damaged save should leave the current game alone rather than half-replacing it with invalid state.

  Sinclair ZX SpectrumFramework · intermediateAssembly

• Walk an Ordered Waypoint Route on Spectrum

  A guard should reach a waypoint before choosing the next, even when one movement step would overshoot it.

  Sinclair ZX SpectrumAI · intermediateAssembly

• Wrap and Skip Menu Options in Spectrum BASIC

  Move a bounded selection in either direction, wrap at the ends and skip options that are currently disabled.

  Sinclair ZX SpectrumInput · intermediateBASIC

• Wrap and Skip Menu Options on Spectrum

  A menu should wrap cleanly at either end and skip options the player cannot choose.

  Sinclair ZX SpectrumInput · intermediateAssembly

• Write Bits into a Small Data Block in Spectrum BASIC

  Pack the low bits of a value into a four-byte block while preserving neighbouring bits and rejecting incomplete writes.

  Sinclair ZX SpectrumFramework · intermediateBASIC

• Write Packed Bits with Bounds on Spectrum

  Flags and short fields can share a compact record without overwriting their neighbours.

  Sinclair ZX SpectrumFramework · intermediateAssembly