Converting to RGB might involve a precision increase
Need to do more than a simple shift to get the appropriate
new value. This isn't quite as exact as a proper multiplication
and division, but the error is so small it's not worth the
extra cycles.
diff --git a/common/rfb/PixelFormat.inl b/common/rfb/PixelFormat.inl
index 90d8e6d..5743e49 100644
--- a/common/rfb/PixelFormat.inl
+++ b/common/rfb/PixelFormat.inl
@@ -1,4 +1,4 @@
-/* Copyright 2009 Pierre Ossman for Cendio AB
+/* Copyright 2009-2014 Pierre Ossman for Cendio AB
*
* This is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -78,10 +78,28 @@
inline void PixelFormat::rgbFromPixel(Pixel p, ColourMap* cm, rdr::U16 *r, rdr::U16 *g, rdr::U16 *b) const
{
if (trueColour) {
- /* We don't need to mask since we shift out unwanted bits */
- *r = (p >> redShift) << redConvShift;
- *g = (p >> greenShift) << greenConvShift;
- *b = (p >> blueShift) << blueConvShift;
+ int mb, rb, gb, bb;
+
+ /* Bit replication is much cheaper than multiplication and division */
+
+ mb = minBits;
+ rb = redBits;
+ gb = greenBits;
+ bb = blueBits;
+
+ *r = (p >> redShift) << (16 - rb);
+ *g = (p >> greenShift) << (16 - gb);
+ *b = (p >> blueShift) << (16 - bb);
+
+ while (mb < 16) {
+ *r = *r | (*r >> rb);
+ *g = *g | (*g >> gb);
+ *b = *b | (*b >> bb);
+ mb <<= 1;
+ rb <<= 1;
+ gb <<= 1;
+ bb <<= 1;
+ }
} else if (cm) {
int ir, ig, ib;
cm->lookup(p, &ir, &ig, &ib);
@@ -100,9 +118,28 @@
inline void PixelFormat::rgbFromPixel(Pixel p, ColourMap* cm, rdr::U8 *r, rdr::U8 *g, rdr::U8 *b) const
{
if (trueColour) {
- *r = (p >> redShift) << (redConvShift - 8);
- *g = (p >> greenShift) << (greenConvShift - 8);
- *b = (p >> blueShift) << (blueConvShift - 8);
+ int mb, rb, gb, bb;
+
+ /* Bit replication is much cheaper than multiplication and division */
+
+ mb = minBits;
+ rb = redBits;
+ gb = greenBits;
+ bb = blueBits;
+
+ *r = (p >> redShift) << (8 - rb);
+ *g = (p >> greenShift) << (8 - gb);
+ *b = (p >> blueShift) << (8 - bb);
+
+ while (mb < 8) {
+ *r = *r | (*r >> rb);
+ *g = *g | (*g >> gb);
+ *b = *b | (*b >> bb);
+ mb <<= 1;
+ rb <<= 1;
+ gb <<= 1;
+ bb <<= 1;
+ }
} else {
rdr::U16 r2, g2, b2;