CSNG (File Format): Difference between revisions

CSNG (File Format) (view source)

Revision as of 20:30, 16 August 2018

400 bytes added , 16 August 2018

Fix pitch/mod encoding scheme

VisualWikitext

Anonymous user

imported>Jackoalan

@@ Line 163: / Line 163: @@
          next = streamIn.PeekU16()
          if next == 0:
+            # Automatically consume no-op and continue accumulating time value
              total += 0xffff
              streamIn.seekAhead(2)
@@ Line 169: / Line 170: @@
          return total
 </syntaxhighlight>
+=====No-Op Command=====
+When the two bytes following the delta-time are both zero, this is a no-op command.
+As mentioned before, no-ops are useful for accumulating delta times greater than 65535.
 =====Note Command=====
@@ Line 253: / Line 260: @@
 ====Continuous Pitch / Modulation Data====
-If the pitch or mod offsets in a region are non-zero, they point to a buffer of RLE-compressed
+If the pitch or mod offsets in a region are non-zero, they point to a buffer of
-(delta-tick, delta-value) pairs, decoding to signed 16-bit precision. The decoder must track
+(delta-tick, delta-value) pairs. The delta times are encoded as unsigned 7/15 bit values
-the absolute time and value, summing each consecutive update for the current time/values.
+and the delta values are signed 7/15-bit values. The values are promoted to 15-bit if they
+exceed their 7-bit range. In this case, the highest bit is set on the first byte in the pair
+(0x80). The decoder must track the absolute time and value, summing each consecutive update
+for the current time/values.
-The algorithm for this RLE is different than the delta-time one for commands. It may
+Similar to the command stream, when the delta time exceeds 15 bit range (>32767), extra pairs
-scale down to a single byte if able.
+with a value delta are inserted.
 <syntaxhighlight lang="python" line="1">
-def DecodeRLE(streamIn):
+def SignExtend7(value):
-     # high-bit shift-trigger RLE, limited to 2 bytes
+     return (value & 0x3f) - (value & 0x40)
-    term = streamIn.ReadU8()
-    total = term & 0x7f
+def SignExtend15(value):
-    if term & 0x80:
+     return (value & 0x3fff) - (value & 0x4000)
-        total = total * 256 + streamIn.ReadU8()
-     return total
-def DecodeContinuousRLE(streamIn, isValue):
+def DecodeSignedValue(streamIn):
-     total = 0
+     byte0 = streamIn.ReadU8()
-     while True:
+     if byte0 & 0x80:
-         # 1-2 byte RLE accumulated within continuable RLE
+         byte1 = streamIn.ReadU8()
-        term = DecodeRLE(streamIn)
+         return SignExtend15(byte1 | ((byte0 & 0x7f) << 8))
-         if term == 0x8000:
+    else:
-            total += 0xffff
+         return SignExtend7(byte0)
-            dummy = streamIn.ReadU8()
-            continue
-         total += term
-        # values are signed deltas;
+def DecodeUnsignedValue(streamIn):
-        # extending into the high-half of 15-bit precision
+    byte0 = streamIn.ReadU8()
-        if isValue:
+    if byte0 & 0x80:
-            if total >= 0x4000:
+        byte1 = streamIn.ReadU8()
-                return total - 0xffff
+        return byte1 | ((byte0 & 0x7f) << 8)
-            else:
+    else:
-                return total
+        return byte0
-         # times are always forward-deltas
+def DecodeDeltaPair(streamIn):
-         return total
+    ret = [0,0]
+    while ret[1] == 0:
+         ret[0] += DecodeUnsignedValue(streamIn)
+         ret[1] = DecodeSignedValue(streamIn)
+    return ret
 </syntaxhighlight>

CSNG (File Format): Difference between revisions

CSNG (File Format) (view source)

Revision as of 20:30, 16 August 2018

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