ngs2: size 16-bit PCM blocks in Ngs2CalcWaveformBlock (The Binding of Isaac: Repentance) (#1968)

Ngs2CalcWaveformBlock returned NGS2_ERROR_UNKNOWN_WAVEFORM_FORMAT with a
zeroed block for 16-bit PCM (0x12). The Binding of Isaac: Repentance
(PPSA03311) ignores the error and queues the zeroed blocks, which the
sampler skips, so the game had no audio at all. PCM frames have a fixed
size, so the block now starts at sample_pos frames and spans num_samples
frames.

Fixes #667

Co-authored-by: gl-ungus <notasecondemail63@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/libs/ngs2.cpp

@@ -2210,6 +2210,11 @@ int KYTY_SYSV_ABI Ngs2CalcWaveformBlock(const Ngs2WaveformFormat* format, uint32
 		                       : ((skip + num_samples + frame_samples - 1) / frame_samples) *
 		                             codec.superframeSize;
 		block->num_skip_samples = num_samples == 0 ? 0 : static_cast<uint32_t>(skip);
+	} else if (format->waveform_type == 0x12) {
+		// 16-bit PCM has fixed-size frames, so the block starts exactly at the sample.
+		const uint64_t frame_size = uint64_t(format->num_channels) * sizeof(int16_t);
+		block->data_offset        = uint64_t(sample_pos) * frame_size;
+		block->data_size          = uint64_t(num_samples) * frame_size;
 	} else {
 		return NGS2_ERROR_UNKNOWN_WAVEFORM_FORMAT;
 	}

tests/Ngs2SamplerTests.cpp

@@ -651,6 +651,11 @@ void TestWaveformBlockGeometry() {
 	Check(Ngs2CalcWaveformBlock(&format, 0, 0, &block) == OK && block.data_size == 0 &&
 	          block.num_samples == 0,
 	      "empty ATRAC9 block acquired encoded data");
+	const Ngs2WaveformFormat pcm {0x12, 2, 48000};
+	Check(Ngs2CalcWaveformBlock(&pcm, 4096, 4096, &block) == OK &&
+	          block.data_offset == 16384 && block.data_size == 16384 &&
+	          block.num_skip_samples == 0 && block.num_samples == 4096,
+	      "PCM block calculation omitted the sample frames");
 	Fixture f(24000);
 	const int16_t silence = 0;
 	f.Queue(&silence, 0, 0, UINT32_MAX);