diff options
Diffstat (limited to 'quantize.c')
| -rw-r--r-- | quantize.c | 27 |
1 files changed, 24 insertions, 3 deletions
@@ -234,6 +234,17 @@ SubdivColorMap(NewColorMapType * NewColorSubdiv, j++, QuantizedColor = QuantizedColor->Pnext) SortArray[j] = QuantizedColor; + /* + * Because qsort isn't stable, this can produce differing + * results for the order of tuples depending on platform + * details of how qsort() is implemented. + * + * We mitigate this problem by sorting on all three axes rather + * than only the one specied by SortRGBAxis; that way the instability + * can only become an issue if there are multiple color indices + * referring to identical RGB tuples. Older versions of this + * sorted on only the one axis. + */ qsort(SortArray, NewColorSubdiv[Index].NumEntries, sizeof(QuantizedColorType *), SortCmpRtn); @@ -298,12 +309,22 @@ SubdivColorMap(NewColorMapType * NewColorSubdiv, /**************************************************************************** Routine called by qsort to compare two entries. *****************************************************************************/ + static int SortCmpRtn(const void *Entry1, const void *Entry2) { - - return (*((QuantizedColorType **) Entry1))->RGB[SortRGBAxis] - - (*((QuantizedColorType **) Entry2))->RGB[SortRGBAxis]; + QuantizedColorType *entry1 = (*((QuantizedColorType **) Entry1)); + QuantizedColorType *entry2 = (*((QuantizedColorType **) Entry2)); + + /* sort on all axes of the color space! */ + int hash1 = entry1->RGB[SortRGBAxis] * 256 * 256 + + entry1->RGB[(SortRGBAxis+1) % 3] * 256 + + entry1->RGB[(SortRGBAxis+2) % 3]; + int hash2 = entry2->RGB[SortRGBAxis] * 256 * 256 + + entry2->RGB[(SortRGBAxis+1) % 3] * 256 + + entry2->RGB[(SortRGBAxis+2) % 3]; + + return hash1 - hash2; } /* end */ |