Remove RGBX structure.

The pixels are still packed as RGBX in memory but
no structure is created, it’s just a contiguous buffer.

Interpolation is now done with SIMD on integer values.

- Add SIMD define.

Makefile

@@ -1,10 +1,11 @@
 CXX     = clang++
-CXXFLAGS = -std=c++11 -W -Wall -O3 -ffast-math -Werror -g
+CXXFLAGS = -std=c++11 -W -Wall -O3 -ffast-math -g -Werror
+DEFINES = -DSIMD
 BUILD_DIR=/tmp
 IMG=img/lena.ppm
 
 all: rotation.cpp
-	$(CXX) $(CXXFLAGS) $< -o $(BUILD_DIR)/rotation
+	$(CXX) $(CXXFLAGS) $(DEFINES) $< -o $(BUILD_DIR)/rotation
 
 clean:
 	@rm -f *~ *.o .*.swp *.ppm cachegrind.out.*