bisect functionality to navigate documents

This uses the jumplist to implement a bisect functionality between the
last two jump points. ^j and ^k are bound to bisect forward and backward
respectively.
Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>

config.c

@@ -298,7 +298,8 @@ config_load_default(zathura_t* zathura)
   girara_shortcut_add(gsession, GDK_SHIFT_MASK,   GDK_KEY_space,      NULL, sc_scroll,                   NORMAL,     FULL_UP,         NULL);
   girara_shortcut_add(gsession, GDK_CONTROL_MASK, GDK_KEY_o,          NULL, sc_jumplist,                 NORMAL,     BACKWARD,        NULL);
   girara_shortcut_add(gsession, GDK_CONTROL_MASK, GDK_KEY_i,          NULL, sc_jumplist,                 NORMAL,     FORWARD,         NULL);
-
+  girara_shortcut_add(gsession, GDK_CONTROL_MASK, GDK_KEY_j,          NULL, sc_bisect,                   NORMAL,     FORWARD,         NULL);
+  girara_shortcut_add(gsession, GDK_CONTROL_MASK, GDK_KEY_k,          NULL, sc_bisect,                   NORMAL,     BACKWARD,        NULL);
   girara_shortcut_add(gsession, 0,                GDK_KEY_n,          NULL, sc_search,                   NORMAL,     FORWARD,         NULL);
   girara_shortcut_add(gsession, 0,                GDK_KEY_N,          NULL, sc_search,                   NORMAL,     BACKWARD,        NULL);
 
@@ -401,6 +402,7 @@ config_load_default(zathura_t* zathura)
   girara_shortcut_mapping_add(gsession, "follow",            sc_follow);
   girara_shortcut_mapping_add(gsession, "goto",              sc_goto);
   girara_shortcut_mapping_add(gsession, "jumplist",          sc_jumplist);
+  girara_shortcut_mapping_add(gsession, "bisect",            sc_bisect);
   girara_shortcut_mapping_add(gsession, "navigate",          sc_navigate);
   girara_shortcut_mapping_add(gsession, "navigate_index",    sc_navigate_index);
   girara_shortcut_mapping_add(gsession, "print",             sc_print);

shortcuts.c

@@ -716,7 +716,8 @@ sc_scroll(girara_session_t* session, girara_argument_t* argument,
 
 
 bool
-sc_jumplist(girara_session_t* session, girara_argument_t* argument, girara_event_t* UNUSED(event), unsigned int UNUSED(t))
+sc_jumplist(girara_session_t* session, girara_argument_t* argument,
+            girara_event_t* UNUSED(event), unsigned int UNUSED(t))
 {
   g_return_val_if_fail(session != NULL, false);
   g_return_val_if_fail(session->global.data != NULL, false);
@@ -748,6 +749,135 @@ sc_jumplist(girara_session_t* session, girara_argument_t* argument, girara_event
   return false;
 }
 
+
+bool
+sc_bisect(girara_session_t* session, girara_argument_t* argument,
+          girara_event_t* UNUSED(event), unsigned int t)
+{
+  g_return_val_if_fail(session != NULL, false);
+  g_return_val_if_fail(session->global.data != NULL, false);
+  zathura_t* zathura = session->global.data;
+  g_return_val_if_fail(argument != NULL, false);
+  g_return_val_if_fail(zathura->document != NULL, false);
+
+  unsigned int number_of_pages, cur_page, prev_page, prev2_page;
+  bool have_prev, have_prev2;
+
+  zathura_jump_t* prev_jump = NULL;
+  zathura_jump_t* prev2_jump = NULL;
+
+  number_of_pages= zathura_document_get_number_of_pages(zathura->document);
+  cur_page = zathura_document_get_current_page_number(zathura->document);
+
+  prev_page = prev2_page = 0;
+  have_prev = have_prev2 = false;
+
+  /* save position at current jump point */
+  zathura_jumplist_save(zathura);
+
+  /* process arguments */
+  int direction;
+  if (t > 0 && t <= number_of_pages) {
+    /* jump to page t, and bisect between cur_page and t */
+    page_set(zathura, t-1);
+    zathura_jumplist_add(zathura);
+    if (t-1 > cur_page) {
+      direction = BACKWARD;
+    } else {
+      direction = FORWARD;
+    }
+
+  } else if (argument != NULL)  {
+    direction = argument->n;
+
+  } else {
+    return false;
+  }
+
+  cur_page = zathura_document_get_current_page_number(zathura->document);
+
+  if (zathura_jumplist_has_previous(zathura)) {
+    /* If there is a previous jump, get its page */
+    zathura_jumplist_backward(zathura);
+    prev_jump = zathura_jumplist_current(zathura);
+    if (prev_jump) {
+      prev_page = prev_jump->page;
+      have_prev = true;
+    }
+
+    if (zathura_jumplist_has_previous(zathura)) {
+      /* If there is a second previous jump, get its page. */
+      zathura_jumplist_backward(zathura);
+      prev2_jump = zathura_jumplist_current(zathura);
+      if (prev2_jump) {
+        prev2_page = prev2_jump->page;
+        have_prev2 = true;
+      }
+      zathura_jumplist_forward(zathura);
+    }
+    zathura_jumplist_forward(zathura);
+  }
+
+  /* now, we are back at the initial jump. prev_page and prev2_page contain
+   the pages for previous and second previous jump if they exist. */
+
+  /* bisect */
+  switch(direction) {
+    case FORWARD:
+      if (have_prev && cur_page <= prev_page) {
+        /* add a new jump point */
+        if (cur_page < prev_page) {
+          page_set(zathura, (cur_page + prev_page)/2);
+          zathura_jumplist_add(zathura);
+        }
+
+      } else if (have_prev2 && cur_page <= prev2_page) {
+        /* save current position at previous jump point */
+        if (cur_page < prev2_page) {
+          zathura_jumplist_backward(zathura);
+          zathura_jumplist_save(zathura);
+          zathura_jumplist_forward(zathura);
+
+          page_set(zathura, (cur_page + prev2_page)/2);
+          zathura_jumplist_save(zathura);
+        }
+      } else {
+        /* none of prev_page or prev2_page comes after cur_page */
+        page_set(zathura, (cur_page + number_of_pages - 1)/2);
+        zathura_jumplist_add(zathura);
+      }
+      break;
+
+    case BACKWARD:
+      if (have_prev && prev_page <= cur_page) {
+        /* add a new jump point */
+        if (prev_page < cur_page) {
+          page_set(zathura, (cur_page + prev_page)/2);
+          zathura_jumplist_add(zathura);
+        }
+
+      } else if (have_prev2 && prev2_page <= cur_page) {
+        /* save current position at previous jump point */
+        if (prev2_page < cur_page) {
+          zathura_jumplist_backward(zathura);
+          zathura_jumplist_save(zathura);
+          zathura_jumplist_forward(zathura);
+
+          page_set(zathura, (cur_page + prev2_page)/2);
+          zathura_jumplist_save(zathura);
+        }
+
+      } else {
+        /* none of prev_page or prev2_page comes before cur_page */
+        page_set(zathura, cur_page/2);
+        zathura_jumplist_add(zathura);
+      }
+      break;
+  }
+  return false;
+}
+
+
 bool
 sc_search(girara_session_t* session, girara_argument_t* argument,
           girara_event_t* UNUSED(event), unsigned int UNUSED(t))

shortcuts.h

@@ -172,7 +172,7 @@ bool sc_rotate(girara_session_t* session, girara_argument_t* argument, girara_ev
 bool sc_scroll(girara_session_t* session, girara_argument_t* argument, girara_event_t* event, unsigned int t);
 
 /**
- * Scroll through the pages
+ * Navigate through the jumplist
  *
  * @param session The used girara session
  * @param argument The used argument
@@ -182,6 +182,17 @@ bool sc_scroll(girara_session_t* session, girara_argument_t* argument, girara_ev
  */
 bool sc_jumplist(girara_session_t* session, girara_argument_t* argument, girara_event_t* event, unsigned int t);
 
+/**
+ * Bisect through the document
+ *
+ * @param session The used girara session
+ * @param argument The used argument
+ * @param event Girara event
+ * @param t Number of executions
+ * @return true if no error occured otherwise false
+ */
+bool sc_bisect(girara_session_t* session, girara_argument_t* argument, girara_event_t* event, unsigned int t);
+
 /**
  * Search through the document for the latest search item
  *