From 79281774a6f1e72aa6fba99dd9b3524b3cd5a2cd Mon Sep 17 00:00:00 2001
From: Jose Diez <jose.manuel.diez@gmail.com>
Date: Wed, 11 Nov 2015 15:02:07 +0000
Subject: Improved zoom behaviour

---
 src/main.c     |  6 +++---
 src/viewport.c | 36 +++++++++++++++++++++++++++++++++++-
 src/viewport.h |  7 ++++++-
 3 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/src/main.c b/src/main.c
index cbbe493..a7b115c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -184,10 +184,10 @@ int main(int argc, char** argv)
             case SDLK_RIGHT:  imv_navigator_next_path(&nav);           break;
             case SDLK_EQUALS:
             case SDLK_i:
-            case SDLK_UP:     imv_viewport_zoom(&view, 1);             break;
+            case SDLK_UP:     imv_viewport_zoom(&view, &img, KBD, 1);  break;
             case SDLK_MINUS:
             case SDLK_o:
-            case SDLK_DOWN:   imv_viewport_zoom(&view, -1);            break;
+            case SDLK_DOWN:   imv_viewport_zoom(&view, &img, KBD, -1); break;
             case SDLK_a:     imv_viewport_scale_to_actual(&view, &img);break;
             case SDLK_r:     imv_viewport_scale_to_window(&view, &img);break;
             case SDLK_c:      imv_viewport_center(&view, &img);        break;
@@ -203,7 +203,7 @@ int main(int argc, char** argv)
           }
           break;
         case SDL_MOUSEWHEEL:
-          imv_viewport_zoom(&view, e.wheel.y);
+          imv_viewport_zoom(&view, &img, MOUSE, e.wheel.y);
           break;
         case SDL_MOUSEMOTION:
           if(e.motion.state & SDL_BUTTON_LMASK) {
diff --git a/src/viewport.c b/src/viewport.c
index bb2e92e..38deabc 100644
--- a/src/viewport.c
+++ b/src/viewport.c
@@ -71,13 +71,47 @@ void imv_viewport_move(struct imv_viewport *view, int x, int y)
   view->locked = 1;
 }
 
-void imv_viewport_zoom(struct imv_viewport *view, int amount)
+void imv_viewport_zoom(struct imv_viewport *view, const struct imv_image *img, enum imv_zoom_source src, int amount)
 {
+  double prevScale = view->scale;
+  int x, y;
+
+  if(src == MOUSE) {
+    SDL_GetMouseState(&x, &y);
+    /* Translate mouse coordinates to projected coordinates */
+    x -= view->x;
+    y -= view->y;
+  } else x = y = 0;
+
+  int scaledWidth = img->width * view->scale;
+  int scaledHeight = img->height * view->scale;
+  if(x > scaledWidth) {
+    x = scaledWidth;
+  }
+
+  if(y > scaledHeight) {
+    y = scaledHeight;
+  }
+
   view->scale += amount * 0.1;
   if(view->scale > 100)
     view->scale = 10;
   else if (view->scale < 0.01)
     view->scale = 0.1;
+
+  double changeX = x - (x * (view->scale / prevScale));
+  double changeY = y - (y * (view->scale / prevScale));
+
+  if(amount < 0 &&
+    (view->x <= 0 && (view->x + changeX > 0 || !changeX))) {
+    view->x = 0;
+  } else view->x += changeX;
+
+  if(amount < 0 &&
+    (view->y <= 0 && (view->y + changeY > 0 || !changeY))) {
+    view->y = 0;
+  } else view->y += changeY;
+
   view->redraw = 1;
   view->locked = 1;
 }
diff --git a/src/viewport.h b/src/viewport.h
index 8538e33..6dd17fb 100644
--- a/src/viewport.h
+++ b/src/viewport.h
@@ -33,6 +33,11 @@ struct imv_viewport {
   int locked;
 };
 
+enum imv_zoom_source {
+  MOUSE,
+  KBD
+};
+
 void imv_init_viewport(struct imv_viewport *view, SDL_Window *window);
 void imv_destroy_viewport(struct imv_viewport *view);
 
@@ -40,7 +45,7 @@ void imv_viewport_toggle_fullscreen(struct imv_viewport*);
 void imv_viewport_toggle_playing(struct imv_viewport*, struct imv_image*);
 void imv_viewport_reset(struct imv_viewport*);
 void imv_viewport_move(struct imv_viewport*, int, int);
-void imv_viewport_zoom(struct imv_viewport*, int);
+void imv_viewport_zoom(struct imv_viewport*, const struct imv_image*, enum imv_zoom_source, int);
 void imv_viewport_center(struct imv_viewport*, const struct imv_image*);
 void imv_viewport_scale_to_actual(struct imv_viewport*, const struct imv_image*);
 void imv_viewport_scale_to_window(struct imv_viewport*, const struct imv_image*);
-- 
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