use exponential increments for zooming

1 files changed, 3 insertions, 2 deletions

diff --git a/src/viewport.c b/src/viewport.c
index dd289d3..e42c729 100644
--- a/src/viewport.c
+++ b/src/viewport.c
@@ -2,6 +2,7 @@
 
 #include <stdbool.h>
 #include <stdlib.h>
+#include <math.h>
 
 struct imv_viewport {
   double scale;
@@ -159,8 +160,8 @@ void imv_viewport_zoom(struct imv_viewport *view, const struct imv_image *image,
   const int wc_x = view->buffer.width/2;
   const int wc_y = view->buffer.height/2;
 
-  double delta_scale = 0.04 * view->buffer.width * amount / image_width;
-  view->scale += delta_scale;
+  const double scale_factor = exp(0.04 * view->buffer.width * amount / image_width);
+  view->scale *= scale_factor;
 
   const double min_scale = 0.1;
   const double max_scale = 100;