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authorBehdad Esfahbod <behdad@gnome.org>2007-12-03 07:44:27 +0000
committerBehdad Esfahbod <behdad@src.gnome.org>2007-12-03 07:44:27 +0000
commit2db48b69d7679640419062f85b1e0a6fc9fe1e63 (patch)
treea7ea6b9e966eabb70fea9aef52a9a4b98cebfebe /examples/cairotwisted.c
parente5fc94517a02a87bd4b153ce188bc3215afe71af (diff)
downloadpango-2db48b69d7679640419062f85b1e0a6fc9fe1e63.tar.gz
Add some more comments to document the math involved.
2007-12-03 Behdad Esfahbod <behdad@gnome.org> * examples/cairotwisted.c: Add some more comments to document the math involved. svn path=/trunk/; revision=2510
Diffstat (limited to 'examples/cairotwisted.c')
-rw-r--r--examples/cairotwisted.c25
1 files changed, 21 insertions, 4 deletions
diff --git a/examples/cairotwisted.c b/examples/cairotwisted.c
index 5697e57a..dfdf521a 100644
--- a/examples/cairotwisted.c
+++ b/examples/cairotwisted.c
@@ -291,10 +291,27 @@ typedef struct {
} parametrized_path_t;
-/* Project a point x,y onto a parameterized path. The final point is
- * where you get if you walk on the path forward from the beginning for x
- * units, then stop there and walk another y units perpendicular to the
- * path at that point. */
+/* Project a point X,Y onto a parameterized path. The final point is
+ * where you get if you walk on the path forward from the beginning for X
+ * units, then stop there and walk another Y units perpendicular to the
+ * path at that point. In more detail:
+ *
+ * There's three pieces of math involved:
+ *
+ * - The parametric form of the Line equation
+ * http://en.wikipedia.org/wiki/Line
+ *
+ * - The parametric form of the Cubic Bézier curve equation
+ * http://en.wikipedia.org/wiki/B%C3%A9zier_curve
+ *
+ * - The Gradient (aka multi-dimensional derivative) of the above
+ * http://en.wikipedia.org/wiki/Gradient
+ *
+ * The parametric forms are used to answer the question of "where will I be
+ * if I walk a distance of X on this path". The Gradient is used to answer
+ * the question of "where will I be if then I stop, rotate left for 90
+ * degrees and walk straight for a distance of Y".
+ */
static void
point_on_path (parametrized_path_t *param,
double *x, double *y)