GUAC-803: Actually scroll when the scrollbar handle is dragged.

src/terminal/scrollbar.c

@@ -213,14 +213,8 @@ void guac_terminal_scrollbar_flush(guac_terminal_scrollbar* scrollbar) {
     calculate_state(scrollbar, &new_state, &new_value);
 
     /* Notify of scroll if value is changing */
-    if (new_value != old_value) {
-
-        /* TODO: Call scroll value handler */
-        guac_client_log(scrollbar->client, GUAC_LOG_DEBUG,
-                "SCROLL: min=%i max=%i value=%i",
-                scrollbar->min, scrollbar->max, new_value);
-
-    }
+    if (new_value != old_value && scrollbar->scroll_handler)
+        scrollbar->scroll_handler(scrollbar, new_value);
 
     /* Reposition container if moved */
     if (old_state->container_x != new_state.container_x

src/terminal/scrollbar.h

@@ -96,12 +96,21 @@ typedef struct guac_terminal_scrollbar_render_state {
 
 } guac_terminal_scrollbar_render_state;
 
+typedef struct guac_terminal_scrollbar guac_terminal_scrollbar;
+
+/**
+ * Handler which is called whenever the scrollbar value changes outside a call
+ * to guac_terminal_scrollbar_set_value().
+ */
+typedef void guac_terminal_scrollbar_scroll_handler(
+        guac_terminal_scrollbar* scrollbar, int value);
+
 /**
  * A scrollbar, made up of a containing layer and inner draggable handle. The
  * position of the handle within the layer represents the value of the
  * scrollbar.
  */
-typedef struct guac_terminal_scrollbar {
+struct guac_terminal_scrollbar {
 
     /**
      * The client associated with this scrollbar.
@@ -177,7 +186,18 @@ typedef struct guac_terminal_scrollbar {
      */
     int drag_current_y;
 
-} guac_terminal_scrollbar;
+    /**
+     * The function to call when the scrollbar handle is being dragged, and
+     * the new scrollbar value needs to be handled and assigned.
+     */
+    guac_terminal_scrollbar_scroll_handler* scroll_handler;
+
+    /**
+     * Arbitrary reference to data related to this scrollbar.
+     */
+    void* data;
+
+};
 
 /**
  * Allocates a new scrollbar, associating that scrollbar with the given client

src/terminal/terminal.c

@@ -264,6 +264,10 @@ guac_terminal* guac_terminal_create(guac_client* client,
     term->scrollbar = guac_terminal_scrollbar_alloc(term->client,
             GUAC_DEFAULT_LAYER, width, height, term->term_height);
 
+    /* Associate scrollbar with this terminal */
+    term->scrollbar->data = term;
+    term->scrollbar->scroll_handler = guac_terminal_scroll_handler;
+
     /* Init terminal */
     guac_terminal_reset(term);
 
@@ -1472,6 +1476,24 @@ int guac_terminal_send_mouse(guac_terminal* term, int x, int y, int mask) {
 
 }
 
+void guac_terminal_scroll_handler(guac_terminal_scrollbar* scrollbar, int value) {
+
+    guac_terminal* terminal = (guac_terminal*) scrollbar->data;
+
+    /* Calculate change in scroll offset */
+    int delta = -value - terminal->scroll_offset;
+
+    /* Update terminal based on change in scroll offset */
+    if (delta < 0)
+        guac_terminal_scroll_display_down(terminal, -delta);
+    else if (delta > 0)
+        guac_terminal_scroll_display_up(terminal, delta);
+
+    /* Update scrollbar value */
+    guac_terminal_scrollbar_set_value(scrollbar, value);
+
+}
+
 void guac_terminal_clipboard_reset(guac_terminal* term, const char* mimetype) {
     guac_common_clipboard_reset(term->clipboard, mimetype);
 }

src/terminal/terminal.h

@@ -388,6 +388,19 @@ int guac_terminal_send_key(guac_terminal* term, int keysym, int pressed);
  */
 int guac_terminal_send_mouse(guac_terminal* term, int x, int y, int mask);
 
+/**
+ * Handles a scroll event received from the scrollbar associated with a
+ * terminal.
+ *
+ * @param scrollbar
+ *     The scrollbar that has been scrolled.
+ *
+ * @param value
+ *     The new value that should be stored within the scrollbar, and
+ *     represented within the terminal display.
+ */
+void guac_terminal_scroll_handler(guac_terminal_scrollbar* scrollbar, int value);
+
 /**
  * Clears the current clipboard contents and sets the mimetype for future
  * contents.