Fix inaccurate method for computing the fumenOffset values for the initial measures (#28)

- Before: 'OFFSET' = 2nd measure fumenOffset
- After: ('OFFSET'-Full measure duration) = 1st measure fumenOffset

Both methods will produce the same results if no #MEASURE/#BPMCHANGE
commands are present in the first two measures. However, if these
commands ARE present, then you will get wildly different results.

This change doesn't affect 4/6 tests, but for 2/6 tests there were
#MEASURE/#BPMCHANGE commands. For these songs, I had erroneously "fixed"
the OFFSET values, when they were correct all along. So, I reverted them
back to their original values.

Fixes #25.

src/tja2fumen/converters.py

@@ -159,7 +159,8 @@ def convertTJAToFumen(tja):
             measureRatio = 1.0 if measureTJA['subdivisions'] == 0.0 else (measureLength / measureTJA['subdivisions'])
             # - measureDurationBase: The "base" measure duration, computed using a single BPM value.
             # - measureDuration: The actual measure duration, which may be adjusted if there is a mid-measure BPM change.
-            measureDurationBase = measureDuration = (4 * 60_000 * measureSize * measureRatio / measureTJA['bpm'])
+            measureDurationFullMeasure = 4 * 60_000 / measureTJA['bpm']
+            measureDurationBase = measureDuration = (measureDurationFullMeasure * measureSize * measureRatio)
             # The following adjustment accounts for BPM changes. (!!! Discovered by tana :3 !!!)
             if idx_m != len(branch)-1:
                 measureTJANext = branch[idx_m + 1]
@@ -168,12 +169,9 @@ def convertTJAToFumen(tja):
 
             # Compute the millisecond offset for each measure
             if idx_m == 0:
-                pass  # NB: Pass for now, since we need the 2nd measure's duration to compute the 1st measure's offset
+                tjaOffset = float(tja['metadata']['offset']) * 1000 * -1
+                tjaConverted['measures'][idx_m]['fumenOffset'] = tjaOffset - measureDurationFullMeasure
             else:
-                # Compute the 1st measure's offset by subtracting the 2nd measure's duration from the tjaOffset
-                if idx_m == 1:
-                    tjaOffset = float(tja['metadata']['offset']) * 1000 * -1
-                    tjaConverted['measures'][idx_m-1]['fumenOffset'] = tjaOffset - measureDurationPrev
                 # Use the previous measure's offset plus the previous duration to compute the current measure's offset
                 measureOffsetPrev = tjaConverted['measures'][idx_m-1]['fumenOffset']
                 measureFumen['fumenOffset'] = measureOffsetPrev + measureDurationPrev + measureTJA['delay']

testing/data/butou5.tja

@@ -1,5 +1,5 @@
 BPM:148
-OFFSET:-2.245
+OFFSET:-1.84
 
 COURSE:Oni
 LEVEL:8

testing/data/linda.tja

@@ -1,6 +1,6 @@
 //リンダリンダ
 BPM:62
-OFFSET:-3.980
+OFFSET:-4.005
 
 COURSE:Oni
 LEVEL:5