Merge pull request #34 from peres/interpolate16_5_3

Add a new function to interpolate a pair of 16 bits values with weights 5 and 3, respectively.

2 files changed, 11 insertions, 4 deletions

diff --git a/graphics/scaler/aspect.cpp b/graphics/scaler/aspect.cpp
index 85768fbced..85b79ab6cd 100644
--- a/graphics/scaler/aspect.cpp
+++ b/graphics/scaler/aspect.cpp
@@ -79,10 +79,7 @@ static inline void interpolate5Line(uint16 *dst, const uint16 *srcA, const uint1
 		}
 	} else {
 		while (width--) {
-			// TODO: We really would like to use interpolate16_5_3, but that
-			// does not exist (yet), so we use this trick instead.
-			uint16 tmp = *srcA++;
-			*dst++ = interpolate16_5_2_1<ColorMask>(*srcB++, tmp, tmp);
+			*dst++ = interpolate16_5_3<ColorMask>(*srcB++, *srcA++);
 		}
 	}
 }
diff --git a/graphics/scaler/intern.h b/graphics/scaler/intern.h
index 4addd6d3bd..7317745e62 100644
--- a/graphics/scaler/intern.h
+++ b/graphics/scaler/intern.h
@@ -77,6 +77,16 @@ static inline unsigned interpolate16_3_1(unsigned p1, unsigned p2) {
 }
 
 /**
+ * Interpolate two 16 bit pixels with weights 5 and 3 and 1, i.e., (5*p1+3*p2)/8.
+ */
+template<typename ColorMask>
+static inline unsigned interpolate16_5_3(unsigned p1, unsigned p2) {
+	const unsigned lowbits = (((p1 & ColorMask::kLowBits) << 2) + (p1 & ColorMask::kLow3Bits)
+		                   + ((p2 & ColorMask::kLow2Bits) << 1) + (p2 & ColorMask::kLow3Bits)) & ColorMask::kLow3Bits;
+	return ((p1*5 + p2*3) - lowbits) >> 3;
+}
+
+/**
  * Interpolate two 16 bit pixels with weights 7 and 1, i.e., (7*p1+p2)/8.
  */
 template<typename ColorMask>