Fixed a problem with re-centering when magnifying.

Author: vaelen

unix/xmandelbrot.c

@@ -385,11 +385,15 @@ int main(argc,argv)
       {
         viewport.x_scale *= 0.75;
         viewport.y_scale *= 0.75;
+        viewport.x_shift *= 0.75;
+        viewport.y_shift *= 0.75;
       }
       else if (event.xbutton.button == 3)
       {
         viewport.x_scale *= 1.25;
         viewport.y_scale *= 1.25;
+        viewport.x_shift *= 1.25;
+        viewport.y_shift *= 1.25;
       }
       calculate(display, window, gc, palette, max_iterations, viewport);
       break;