3 files changed, 65 insertions, 1 deletions
diff --git a/src/Makefile.am b/src/Makefile.am
index 5fe0d86..20fd98c 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -21,7 +21,7 @@
 # USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 bin_PROGRAMS = rotating_cubes
-rotating_cubes_SOURCES = main.cpp shader.cpp
+rotating_cubes_SOURCES = main.cpp shader.cpp check_rotation.cpp
 
 AM_CXXFLAGS= $(GLU3_CFLAGS)
 rotating_cubes_LDADD = $(FRAMEWORK_LIBS) $(GLU3_LIBS) -lEGL
diff --git a/src/check_rotation.cpp b/src/check_rotation.cpp
new file mode 100644
index 0000000..858bae3
--- /dev/null
+++ b/src/check_rotation.cpp
@@ -0,0 +1,45 @@
+#include <glu3.h>
+
+#include <cassert>
+#include <cmath>
+#include <cfloat>
+
+extern GLUmat4 rotate_x_axis(float theta);
+extern GLUmat4 rotate_y_axis(float theta);
+
+#define EPSILONS 2
+
+static inline bool equal(const float & a, const float & b)
+{
+	return (fabs(a - b) < EPSILONS * FLT_EPSILON);
+}
+
+static inline bool equal(const GLUvec4 & a, const GLUvec4 & b)
+{
+	return equal(a.values[0], b.values[0]) &&
+	       equal(a.values[1], b.values[1]) &&
+	       equal(a.values[2], b.values[2]) &&
+	       equal(a.values[3], b.values[3]);
+}
+
+static inline bool equal(const GLUmat4 & a, const GLUmat4 & b)
+{
+	return equal(a.col[0], b.col[0]) &&
+	       equal(a.col[1], b.col[1]) &&
+	       equal(a.col[2], b.col[2]) &&
+	       equal(a.col[3], b.col[3]);
+}
+
+void check_rotation(void)
+{
+	// Rotation by 0 and 2PI are equal (within 2 epsilons)
+	assert(equal(rotate_x_axis(0.0f), rotate_x_axis(2.0f * M_PI)));
+	assert(equal(rotate_y_axis(0.0f), rotate_y_axis(2.0f * M_PI)));
+	assert(equal(rotate_x_axis(M_PI) * rotate_x_axis(M_PI),
+	             rotate_x_axis(0.0f)));
+	assert(equal(rotate_y_axis(M_PI) * rotate_y_axis(M_PI),
+	             rotate_y_axis(0.0f)));
+
+	assert(equal(rotate_x_axis(M_PI) * rotate_y_axis(M_PI),
+		     rotate_y_axis(M_PI) * rotate_x_axis(M_PI)));
+}
diff --git a/src/main.cpp b/src/main.cpp
index 0cc151b..a9d4c74 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -42,6 +42,22 @@ static float orbit_angle = 0.0f;
 static float eye_distance = 15.0f;
 static float fov = 45.0f;
 
+GLUmat4 rotate_x_axis(float theta)
+{
+	return GLUmat4 (GLUvec4 (1.0f,         0.0f,        0.0f, 0.0f),
+			GLUvec4 (0.0f,  cosf(theta), sinf(theta), 0.0f),
+			GLUvec4 (0.0f, -sinf(theta), cosf(theta), 0.0f),
+			GLUvec4 (0.0f,         0.0f,        0.0f, 1.0f));
+}
+
+GLUmat4 rotate_y_axis(float theta)
+{
+	return GLUmat4 (GLUvec4 (cosf(theta), 0.0f, -sinf(theta), 0.0f),
+			GLUvec4 (0.0f,        1.0f,         0.0f, 0.0f),
+			GLUvec4 (sinf(theta), 0.0f,  cosf(theta), 0.0f),
+			GLUvec4 (0.0f,        0.0f,         0.0f, 1.0f));
+}
+
 static Uint32 t0;
 
 static GLuint bo;
@@ -473,6 +489,7 @@ timer_callback(Uint32 interval, void *not_used)
 	return interval;
 }
 
+extern void check_rotation(void);
 
 int
 main(int argc, char **argv)
@@ -480,6 +497,8 @@ main(int argc, char **argv)
 	(void) argc;
 	(void) argv;
 
+	check_rotation();
+
 	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER) < 0) {
 		exit(1);
 	}