fix(render): fix arrow glitch with 0 ftx

The use of `acos(θ)` works better than `atan(θ)`. Just need to be careful with the `sign` of `fty`.
jtheoof · May 24, 2020 · ec6e6ab · ec6e6ab
1 parent 2adcf94
commit ec6e6ab
Showing 1 changed file with 2 additions and 5 deletions.
diff --git a/src/render.c b/src/render.c
@@ -1,5 +1,6 @@
 #include <gdk/gdk.h>
 #include <gtk/gtk.h>
+#include <math.h>
 #include <pango/pangocairo.h>
 
 #include "swappy.h"
@@ -105,11 +106,7 @@ static void render_shape_arrow(cairo_t *cr, struct swappy_paint_shape shape) {
     return;
   }
 
-  double theta = atan(fty / ftx);
-
-  if (ftx < DBL_EPSILON) {
-    theta = M_PI + theta;
-  }
+  double theta = copysign(1.0, fty) * acos(ftx / ftn);
 
   // Draw line
   cairo_save(cr);