Documentation: C API comments in include/

include/c/sk_matrix.h

Index: include/c/sk_matrix.h
diff --git a/include/c/sk_matrix.h b/include/c/sk_matrix.h
index 12d946547fe84b924e138465800997641e3c8518..83f0122b00a89d4c5b2e7357e1502a12dbc59ccf 100644
--- a/include/c/sk_matrix.h
+++ b/include/c/sk_matrix.h
@@ -15,14 +15,33 @@
 
 SK_C_PLUS_PLUS_BEGIN_GUARD
 
+/** Set the matrix to identity */
 void sk_matrix_set_identity(sk_matrix_t*);
 
+/** Set the matrix to translate by (tx, ty). */
 void sk_matrix_set_translate(sk_matrix_t*, float tx, float ty);
+/**
+    Preconcats the matrix with the specified translation.
+        M' = M * T(dx, dy)
+*/
 void sk_matrix_pre_translate(sk_matrix_t*, float tx, float ty);
+/**
+    Postconcats the matrix with the specified translation.
+        M' = T(dx, dy) * M
+*/
 void sk_matrix_post_translate(sk_matrix_t*, float tx, float ty);
 
+/** Set the matrix to scale by sx and sy. */
 void sk_matrix_set_scale(sk_matrix_t*, float sx, float sy);
+/**
+    Preconcats the matrix with the specified scale.
+        M' = M * S(sx, sy)
+*/
 void sk_matrix_pre_scale(sk_matrix_t*, float sx, float sy);
+/**
+    Postconcats the matrix with the specified scale.
+        M' = S(sx, sy) * M
+*/
 void sk_matrix_post_scale(sk_matrix_t*, float sx, float sy);
 
 SK_C_PLUS_PLUS_END_GUARD