Use lookup tables for pixel upconversion
You have to loop many times when converting e.g. 2 bits to 8,
so have a couple of lookup tables to speed things up. We still
use bit replication to get from 8 bits to 16 bits though.
diff --git a/common/rfb/PixelFormat.cxx b/common/rfb/PixelFormat.cxx
index 9e762d9..366c0a3 100644
--- a/common/rfb/PixelFormat.cxx
+++ b/common/rfb/PixelFormat.cxx
@@ -32,6 +32,42 @@
using namespace rfb;
+rdr::U8 PixelFormat::upconvTable[256*8];
+
+class PixelFormat::Init {
+public:
+ Init();
+};
+
+PixelFormat::Init PixelFormat::_init;
+
+
+PixelFormat::Init::Init()
+{
+ int bits;
+
+ // Bit replication is almost perfect, but not quite. And
+ // a lookup table is still quicker when there is a large
+ // difference between the source and destination depth.
+
+ for (bits = 1;bits <= 8;bits++) {
+ int i, maxVal;
+ rdr::U8 *subTable;
+
+ maxVal = (1 << bits) - 1;
+ subTable = &upconvTable[(bits-1)*256];
+
+ for (i = 0;i <= maxVal;i++)
+ subTable[i] = i * 255 / maxVal;
+
+ // Duplicate the table so that we don't have to care about
+ // the upper bits when doing a lookup
+ for (;i < 256;i += maxVal+1)
+ memcpy(&subTable[i], &subTable[0], maxVal+1);
+ }
+}
+
+
PixelFormat::PixelFormat(int b, int d, bool e, bool t,
int rm, int gm, int bm, int rs, int gs, int bs)
: bpp(b), depth(d), trueColour(t), bigEndian(e),
diff --git a/common/rfb/PixelFormat.h b/common/rfb/PixelFormat.h
index c3db878..db12988 100644
--- a/common/rfb/PixelFormat.h
+++ b/common/rfb/PixelFormat.h
@@ -105,6 +105,12 @@
int redBits, greenBits, blueBits;
int maxBits, minBits;
bool endianMismatch;
+
+ static rdr::U8 upconvTable[256*8];
+
+ class Init;
+ friend class Init;
+ static Init _init;
};
}
diff --git a/common/rfb/PixelFormat.inl b/common/rfb/PixelFormat.inl
index 4bc4a70..f9fb125 100644
--- a/common/rfb/PixelFormat.inl
+++ b/common/rfb/PixelFormat.inl
@@ -102,55 +102,33 @@
inline void PixelFormat::rgbFromPixel(Pixel p, rdr::U16 *r, rdr::U16 *g, rdr::U16 *b) const
{
- int mb, rb, gb, bb;
+ rdr::U8 _r, _g, _b;
- /* Bit replication is much cheaper than multiplication and division */
+ _r = p >> redShift;
+ _g = p >> greenShift;
+ _b = p >> blueShift;
- mb = minBits;
- rb = redBits;
- gb = greenBits;
- bb = blueBits;
+ _r = upconvTable[(redBits-1)*256 + _r];
+ _g = upconvTable[(greenBits-1)*256 + _g];
+ _b = upconvTable[(blueBits-1)*256 + _b];
- *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;
- }
+ *r = _r << 8 | _r;
+ *g = _g << 8 | _g;
+ *b = _b << 8 | _b;
}
inline void PixelFormat::rgbFromPixel(Pixel p, rdr::U8 *r, rdr::U8 *g, rdr::U8 *b) const
{
- int mb, rb, gb, bb;
+ rdr::U8 _r, _g, _b;
- /* Bit replication is much cheaper than multiplication and division */
+ _r = p >> redShift;
+ _g = p >> greenShift;
+ _b = p >> blueShift;
- 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;
- }
+ *r = upconvTable[(redBits-1)*256 + _r];
+ *g = upconvTable[(greenBits-1)*256 + _g];
+ *b = upconvTable[(blueBits-1)*256 + _b];
}