mirror of
https://github.com/imjasonh/nescript
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43 lines
1.5 KiB
Text
43 lines
1.5 KiB
Text
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// Per-frame pitch envelope on a pulse SFX. The user authors the
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// `pitch:` array as one byte per frame (matching the per-frame
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// `volume:` array) and the runtime audio tick walks both pointers
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// in lockstep, writing pitch to `$4002` and volume to `$4000` on
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// every NMI. The result is a frequency-sweeping "siren" tone — the
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// classic latch-once pulse SFX driver couldn't model this at all.
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//
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// Per-frame pitch is opt-in: if the `pitch:` array has a single
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// value (or repeats one byte) the compiler emits the byte-identical
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// pre-pitch-envelope sequence and no extra blob, so existing
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// programs that just want a static pitch keep working unchanged.
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// See `runtime/gen_audio_tick` for the gated extension.
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//
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// Build: cargo run -- build examples/sfx_pitch_envelope.ne
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game "SFX Pitch Envelope" {
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mapper: NROM
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}
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// 16-frame pitch sweep from $40 down to $20 paired with a slow
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// volume ramp. Both arrays are the same length so the runtime's
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// lockstep walker handles the simplest possible case.
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sfx Siren {
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duty: 2
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pitch: [0x40, 0x3D, 0x3A, 0x37, 0x34, 0x31, 0x2E, 0x2B, 0x28, 0x26, 0x24, 0x22, 0x21, 0x20, 0x20, 0x20]
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volume: [15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
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}
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var tick: u8 = 0
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on frame {
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// Re-trigger the sfx every 60 frames so the siren restarts
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// whenever the previous pass mutes itself, giving the
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// emulator harness a stable pattern to capture.
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tick += 1
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if tick == 60 {
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tick = 0
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play Siren
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}
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}
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start Main
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