compositor: simplify the matrix inversion API

The compositor will likely do an order of magnitude less matrix
inversions than point transformations with an inverse, hence we do not
really need the optimised path for single-shot invert-and-transform.

Expose only the computing of the explicit inverse matrix in the API.

However, the matrix inversion tests need access to the internal
functions. Designate a unit test build by #defining UNIT_TEST, and
export the internal functions in that case.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

6 files changed, 81 insertions, 67 deletions

diff --git a/src/compositor.c b/src/compositor.c
index cb19f34..69ad60e 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -545,7 +545,7 @@ static void
 weston_surface_update_transform(struct weston_surface *surface)
 {
 	struct weston_matrix *matrix = &surface->transform.matrix;
-	struct weston_inverse_matrix *inverse = &surface->transform.inverse;
+	struct weston_matrix *inverse = &surface->transform.inverse;
 	struct weston_transform *tform;
 
 	if (!surface->transform.dirty)
diff --git a/src/compositor.h b/src/compositor.h
index 2064d67..5312665 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -230,7 +230,7 @@ struct weston_surface {
 
 		/* derived state, set up by weston_surface_update_transform */
 		struct weston_matrix matrix;
-		struct weston_inverse_matrix inverse;
+		struct weston_matrix inverse;
 		int enabled;
 	} transform;
 
diff --git a/src/matrix.c b/src/matrix.c
index 46ce56a..98ccf4c 100644
--- a/src/matrix.c
+++ b/src/matrix.c
@@ -29,6 +29,7 @@
 
 #include "matrix.h"
 
+
 /*
  * Matrices are stored in column-major order, that is the array indices are:
  *  0  4  8 12
@@ -116,6 +117,16 @@ swap_rows(double *a, double *b)
 	}
 }
 
+static inline void
+swap_unsigned(unsigned *a, unsigned *b)
+{
+	unsigned tmp;
+
+	tmp = *a;
+	*a = *b;
+	*b = tmp;
+}
+
 static inline unsigned
 find_pivot(double *column, unsigned k)
 {
@@ -133,16 +144,15 @@ find_pivot(double *column, unsigned k)
  * LU decomposition, forward and back substitution: Chapter 3.
  */
 
-WL_EXPORT int
-weston_matrix_invert(struct weston_inverse_matrix *inverse,
-		     const struct weston_matrix *matrix)
+MATRIX_TEST_EXPORT inline int
+matrix_invert(double *A, unsigned *p, const struct weston_matrix *matrix)
 {
-	double A[16];
-	unsigned p[4] = { 0, 1, 2, 3 };
 	unsigned i, j, k;
 	unsigned pivot;
 	double pv;
 
+	for (i = 0; i < 4; ++i)
+		p[i] = i;
 	for (i = 16; i--; )
 		A[i] = matrix->d[i];
 
@@ -150,9 +160,7 @@ weston_matrix_invert(struct weston_inverse_matrix *inverse,
 	for (k = 0; k < 4; ++k) {
 		pivot = find_pivot(&A[k * 4], k);
 		if (pivot != k) {
-			unsigned tmp = p[k];
-			p[k] = p[pivot];
-			p[pivot] = tmp;
+			swap_unsigned(&p[k], &p[pivot]);
 			swap_rows(&A[k], &A[pivot]);
 		}
 
@@ -168,30 +176,25 @@ weston_matrix_invert(struct weston_inverse_matrix *inverse,
 		}
 	}
 
-	memcpy(inverse->LU, A, sizeof(A));
-	memcpy(inverse->p, p, sizeof(p));
 	return 0;
 }
 
-WL_EXPORT void
-weston_matrix_inverse_transform(struct weston_inverse_matrix *inverse,
-				struct weston_vector *v)
+MATRIX_TEST_EXPORT inline void
+inverse_transform(const double *LU, const unsigned *p, GLfloat *v)
 {
 	/* Solve A * x = v, when we have P * A = L * U.
 	 * P * A * x = P * v  =>  L * U * x = P * v
 	 * Let U * x = b, then L * b = P * v.
 	 */
-	unsigned *p = inverse->p;
-	double *LU = inverse->LU;
 	double b[4];
 	unsigned j;
 
 	/* Forward substitution, column version, solves L * b = P * v */
 	/* The diagonal of L is all ones, and not explicitly stored. */
-	b[0] = v->f[p[0]];
-	b[1] = (double)v->f[p[1]] - b[0] * LU[1 + 0 * 4];
-	b[2] = (double)v->f[p[2]] - b[0] * LU[2 + 0 * 4];
-	b[3] = (double)v->f[p[3]] - b[0] * LU[3 + 0 * 4];
+	b[0] = v[p[0]];
+	b[1] = (double)v[p[1]] - b[0] * LU[1 + 0 * 4];
+	b[2] = (double)v[p[2]] - b[0] * LU[2 + 0 * 4];
+	b[3] = (double)v[p[3]] - b[0] * LU[3 + 0 * 4];
 	b[2] -= b[1] * LU[2 + 1 * 4];
 	b[3] -= b[1] * LU[3 + 1 * 4];
 	b[3] -= b[2] * LU[3 + 2 * 4];
@@ -225,5 +228,23 @@ weston_matrix_inverse_transform(struct weston_inverse_matrix *inverse,
 
 	/* the result */
 	for (j = 0; j < 4; ++j)
-		v->f[j] = b[j];
+		v[j] = b[j];
+}
+
+WL_EXPORT int
+weston_matrix_invert(struct weston_matrix *inverse,
+		     const struct weston_matrix *matrix)
+{
+	double LU[16];		/* column-major */
+	unsigned perm[4];	/* permutation */
+	unsigned c;
+
+	if (matrix_invert(LU, perm, matrix) < 0)
+		return -1;
+
+	weston_matrix_init(inverse);
+	for (c = 0; c < 4; ++c)
+		inverse_transform(LU, perm, &inverse->d[c * 4]);
+
+	return 0;
 }
diff --git a/src/matrix.h b/src/matrix.h
index 21c1e78..04b179f 100644
--- a/src/matrix.h
+++ b/src/matrix.h
@@ -28,11 +28,6 @@ struct weston_matrix {
 	GLfloat d[16];
 };
 
-struct weston_inverse_matrix {
-	double LU[16];	/* column-major */
-	unsigned p[4];	/* permutation */
-};
-
 struct weston_vector {
 	GLfloat f[4];
 };
@@ -50,10 +45,20 @@ void
 weston_matrix_transform(struct weston_matrix *matrix, struct weston_vector *v);
 
 int
-weston_matrix_invert(struct weston_inverse_matrix *inverse,
+weston_matrix_invert(struct weston_matrix *inverse,
 		     const struct weston_matrix *matrix);
+
+#ifdef UNIT_TEST
+#  define MATRIX_TEST_EXPORT WL_EXPORT
+
+int
+matrix_invert(double *A, unsigned *p, const struct weston_matrix *matrix);
+
 void
-weston_matrix_inverse_transform(struct weston_inverse_matrix *inverse,
-				struct weston_vector *v);
+inverse_transform(const double *LU, const unsigned *p, GLfloat *v);
+
+#else
+#  define MATRIX_TEST_EXPORT static
+#endif
 
 #endif /* WESTON_MATRIX_H */
diff --git a/tests/Makefile.am b/tests/Makefile.am
index e9d96ac..a1f361e 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -6,7 +6,7 @@ endif
 
 
 AM_CFLAGS = $(GCC_CFLAGS)
-AM_CPPFLAGS = -I../src
+AM_CPPFLAGS = -I../src -DUNIT_TEST
 
 matrix_test_SOURCES =				\
 	matrix-test.c				\
diff --git a/tests/matrix-test.c b/tests/matrix-test.c
index 76d93ad..6fdab83 100644
--- a/tests/matrix-test.c
+++ b/tests/matrix-test.c
@@ -30,6 +30,11 @@
 
 #include "matrix.h"
 
+struct inverse_matrix {
+	double LU[16];		/* column-major */
+	unsigned perm[4];	/* permutation */
+};
+
 static struct timespec begin_time;
 
 static void
@@ -81,9 +86,9 @@ determinant(const struct weston_matrix *m)
 }
 
 static void
-print_permutation_matrix(const struct weston_inverse_matrix *m)
+print_permutation_matrix(const struct inverse_matrix *m)
 {
-	const unsigned *p = m->p;
+	const unsigned *p = m->perm;
 	const char *row[4] = {
 		"1 0 0 0\n",
 		"0 1 0 0\n",
@@ -95,7 +100,7 @@ print_permutation_matrix(const struct weston_inverse_matrix *m)
 }
 
 static void
-print_LU_decomposition(const struct weston_inverse_matrix *m)
+print_LU_decomposition(const struct inverse_matrix *m)
 {
 	unsigned r, c;
 
@@ -128,7 +133,7 @@ print_LU_decomposition(const struct weston_inverse_matrix *m)
 }
 
 static void
-print_inverse_data_matrix(const struct weston_inverse_matrix *m)
+print_inverse_data_matrix(const struct inverse_matrix *m)
 {
 	unsigned r, c;
 
@@ -140,7 +145,7 @@ print_inverse_data_matrix(const struct weston_inverse_matrix *m)
 
 	printf("permutation: ");
 	for (r = 0; r < 4; ++r)
-		printf(" %u", m->p[r]);
+		printf(" %u", m->perm[r]);
 	printf("\n");
 }
 
@@ -175,22 +180,6 @@ randomize_matrix(struct weston_matrix *m)
 #endif
 }
 
-static void
-invert_matrix(struct weston_matrix *m)
-{
-	struct weston_inverse_matrix q;
-	unsigned i;
-
-	if (weston_matrix_invert(&q, m) != 0) {
-		m->d[0] = NAN;
-		return;
-	}
-
-	for (i = 0; i < 4; ++i)
-		weston_matrix_inverse_transform(&q,
-			(struct weston_vector *)&m->d[i * 4]);
-}
-
 /* Take a matrix, compute inverse, multiply together
  * and subtract the identity matrix to get the error matrix.
  * Return the largest absolute value from the error matrix.
@@ -199,15 +188,14 @@ static double
 test_inverse(struct weston_matrix *m)
 {
 	unsigned i;
-	struct weston_inverse_matrix q;
+	struct inverse_matrix q;
 	double errsup = 0.0;
 
-	if (weston_matrix_invert(&q, m) != 0)
+	if (matrix_invert(q.LU, q.perm, m) != 0)
 		return INFINITY;
 
 	for (i = 0; i < 4; ++i)
-		weston_matrix_inverse_transform(&q,
-			(struct weston_vector *)&m->d[i * 4]);
+		inverse_transform(q.LU, q.perm, &m->d[i * 4]);
 
 	m->d[0] -= 1.0f;
 	m->d[5] -= 1.0f;
@@ -309,21 +297,21 @@ static void __attribute__((noinline))
 test_loop_speed_inversetransform(void)
 {
 	struct weston_matrix m;
-	struct weston_inverse_matrix inv;
+	struct inverse_matrix inv;
 	struct weston_vector v = { { 0.5, 0.5, 0.5, 1.0 } };
 	unsigned long count = 0;
 	double t;
 
-	printf("\nRunning 3 s test on weston_matrix_inverse_transform()...\n");
+	printf("\nRunning 3 s test on inverse_transform()...\n");
 
 	weston_matrix_init(&m);
-	weston_matrix_invert(&inv, &m);
+	matrix_invert(inv.LU, inv.perm, &m);
 
 	running = 1;
 	alarm(3);
 	reset_timer();
 	while (running) {
-		weston_matrix_inverse_transform(&inv, &v);
+		inverse_transform(inv.LU, inv.perm, v.f);
 		count++;
 	}
 	t = read_timer();
@@ -336,11 +324,11 @@ static void __attribute__((noinline))
 test_loop_speed_invert(void)
 {
 	struct weston_matrix m;
-	struct weston_inverse_matrix inv;
+	struct inverse_matrix inv;
 	unsigned long count = 0;
 	double t;
 
-	printf("\nRunning 3 s test on weston_matrix_invert()...\n");
+	printf("\nRunning 3 s test on matrix_invert()...\n");
 
 	weston_matrix_init(&m);
 
@@ -348,7 +336,7 @@ test_loop_speed_invert(void)
 	alarm(3);
 	reset_timer();
 	while (running) {
-		weston_matrix_invert(&inv, &m);
+		matrix_invert(inv.LU, inv.perm, &m);
 		count++;
 	}
 	t = read_timer();
@@ -364,7 +352,7 @@ test_loop_speed_invert_explicit(void)
 	unsigned long count = 0;
 	double t;
 
-	printf("\nRunning 3 s test on computing the explicit inverse matrix...\n");
+	printf("\nRunning 3 s test on weston_matrix_invert()...\n");
 
 	weston_matrix_init(&m);
 
@@ -372,7 +360,7 @@ test_loop_speed_invert_explicit(void)
 	alarm(3);
 	reset_timer();
 	while (running) {
-		invert_matrix(&m);
+		weston_matrix_invert(&m, &m);
 		count++;
 	}
 	t = read_timer();
@@ -385,7 +373,7 @@ int main(void)
 {
 	struct sigaction ding;
 	struct weston_matrix M;
-	struct weston_inverse_matrix Q;
+	struct inverse_matrix Q;
 	int ret;
 	double errsup;
 	double det;
@@ -402,7 +390,7 @@ int main(void)
 	M.d[2] = 6.0;	M.d[6] = 18.0;	M.d[10] = -12;	M.d[14] = 0.0;
 	M.d[3] = 0.0;	M.d[7] = 0.0;	M.d[11] = 0.0;	M.d[15] = 1.0;
 
-	ret = weston_matrix_invert(&Q, &M);
+	ret = matrix_invert(Q.LU, Q.perm, &M);
 	printf("ret = %d\n", ret);
 	printf("det = %g\n\n", determinant(&M));