Come usare
- Copia il comando e controlla il pacchetto prima di installarlo nel tuo ambiente agente.
- Controlla strumenti, credenziali e ambienti richiesti nel documento originale.
- Descrivi input e risultato desiderato; confronta l’output con le fonti.
npx skills add https://github.com/ewrogers/sgdk-skills --skill sgdk-mathPrima di iniziare
- L’installazione non include abbonamenti, quote API o accesso ai file.
- Stelle e installazioni indicano attività, non un test indipendente di qualità o sicurezza.
Contenuto dal repository con titoli, esempi, codice, tabelle, link e immagini preservati.
SGDK Math
Choose the coordinate range, smallest useful fraction and largest intermediate before choosing a type. A wider storage type does not automatically mean a more accurate or safer multiply/divide implementation.
Choose the right reference
- Numbers and arithmetic: SGDK's actual formats,
conversions, rounding, overflow and multiply/divide limits.
- Motion and effects: degrees, vectors, aiming,
diagonal movement, squared distances, interpolation and bounded tables.
- Math Lab: a runnable perspective starfield and
orbit/figure-eight/spiral formations, with controls and a playtest checklist.
Use ewrogers/sgdk:latest and check its inc/maths.h, inc/types.h and src/maths.c before using an unfamiliar helper. These references were checked against SGDK 2.11. In particular, current F16_sin/F16_cos take degrees; deprecated sinFix16 uses a different angle convention.
Make the calculation safe
Keep world positions separate from screen coordinates. Prefer fix32 or integer world positions when a level exceeds fix16's range. Use small fix16 offsets and velocities where they fit. Convert at explicit boundaries; do not cast between fixed-point formats as though their scales were identical.
Widen before subtracting or multiplying. Establish a valid divisor and bound the quotient before division. Avoid signed overflow, shifting negative signed values in your own C and assuming that a wrapped result will be useful. SGDK's helpers have implementation-specific limits too; follow the reference rather than replacing them with floating point or an untested fast-math trick.
For a new effect, test known points, negative inputs, near-zero divisors, maximum supported coordinates and a full angle cycle. Compare with an independent higher-precision oracle within a stated tolerance. Execute the actual target SDK routines when host arithmetic cannot establish their behavior.
Keep repeated work small
Cache a shared sine or reciprocal table when the memory tradeoff is worthwhile. Bound the angle/depth index before looking it up. Prefer squared-distance tests to square roots when only a threshold matters. Do not replace an exact hit test with SGDK's approximate distance without allowing for its error.
Use a consistent simulation clock and cache input once per display frame. Separate simulation coordinates from rendering so a PAL display or a missed frame does not silently change the units of velocity. Measure optimized ROMs; a successful build or smooth host animation does not establish a 68000 budget.
