refactor html mouse action

This reduces the source complexity of the html_mouse_action()
 previously this was a single function of several thousand
 lines with over 30 local variables allocated on the stack.

Variables are now mostly held in a single static structure which
 drasticaly reduces the size of stack frame required and improves
 lookup locality.

The generated code does cause two additional function calls as the
 compiler avoids inlining the sub functions. The optimiser seems to
 produce somewhat better code within the sub functions.

In the final analysis there appears to be no significant performance
 loss or gain with this change, just more readable source.

1 files changed, 738 insertions, 482 deletions

diff --git a/content/handlers/html/interaction.c b/content/handlers/html/interaction.c
index 651199ce2..fc688d1d1 100644
--- a/content/handlers/html/interaction.c
+++ b/content/handlers/html/interaction.c
@@ -560,189 +560,202 @@ mouse_action_drag_content(html_content *html,
 }
 
 
-/* exported interface documented in html/interaction.h */
-nserror html_mouse_track(struct content *c,
-			 struct browser_window *bw,
-			 browser_mouse_state mouse,
-			 int x, int y)
-{
-	return html_mouse_action(c, bw, mouse, x, y);
-}
+/**
+ * local structure containing all the mouse action state information
+ */
+struct mouse_action_state {
+	struct {
+		const char *status; /**< status text */
+		browser_pointer_shape pointer; /**< pointer shape */
+		enum {
+		      ACTION_NONE,
+		      ACTION_NOSEND, /**< do not send status and pointer message */
+		      ACTION_SUBMIT,
+		      ACTION_GO,
+		} action;
+	} result;
+
+	/** dom node */
+	struct dom_node *node;
+
+	/** html object */
+	struct {
+		struct box *box;
+		int pos_x;
+		int pos_y;
+	} html_object;
+
+	/** non html object */
+	hlcache_handle *object;
+
+	/** iframe */
+	struct browser_window *iframe;
+
+	/** link either from href or imagemap */
+	struct {
+		struct box *box;
+		nsurl *url;
+		const char *target;
+		bool is_imagemap;
+	} link;
+
+	/** gadget */
+	struct {
+		struct form_control *control;
+		struct box *box;
+		int box_x;
+		int box_y;
+		const char *target;
+	} gadget;
+
+	/** title */
+	const char *title;
+
+	/** candidate box for drag operation */
+	struct box *drag_candidate;
+
+	/** scrollbar */
+	struct {
+		struct scrollbar *bar;
+		int mouse_x;
+		int mouse_y;
+	} scroll;
+
+	/** text in box */
+	struct {
+		struct box *box;
+		int box_x;
+	} text;
+};
 
 
-/* exported interface documented in html/interaction.h */
-nserror
-html_mouse_action(struct content *c,
-		  struct browser_window *bw,
-		  browser_mouse_state mouse,
-		  int x, int y)
+/**
+ * iterate the box tree for deepest node at coordinates
+ *
+ * extracts mouse action node information by descending through
+ *  visible boxes setting more specific values for:
+ *
+ * box - deepest box at point
+ * html_object_box - html object
+ * html_object_pos_x - html object
+ * html_object_pos_y - html object
+ * object - non html object
+ * iframe - iframe
+ * url - href or imagemap
+ * target - href or imagemap or gadget
+ * url_box - href or imagemap
+ * imagemap - imagemap
+ * gadget - gadget
+ * gadget_box - gadget
+ * gadget_box_x - gadget
+ * gadget_box_y - gadget
+ * title - title
+ * pointer
+ *
+ * drag_candidate - first box with scroll
+ * padding_left - box with scroll
+ * padding_right
+ * padding_top
+ * padding_bottom
+ * scrollbar - inside padding box stops decent
+ * scroll_mouse_x - inside padding box stops decent
+ * scroll_mouse_y - inside padding box stops decent
+ *
+ * text_box - text box
+ * text_box_x - text_box
+ */
+static nserror
+get_mouse_action_node(html_content *html,
+		      int x, int y,
+		      struct mouse_action_state *man)
 {
-	html_content *html = (html_content *) c;
-	enum { ACTION_NONE, ACTION_SUBMIT, ACTION_GO } action = ACTION_NONE;
-	const char *title = 0;
-	nsurl *url = 0;
-	char *url_s = NULL;
-	size_t url_l = 0;
-	const char *target = 0;
-	char status_buffer[200];
-	const char *status = 0;
-	browser_pointer_shape pointer = BROWSER_POINTER_DEFAULT;
-	bool imagemap = false;
-	int box_x = 0, box_y = 0;
-	int gadget_box_x = 0, gadget_box_y = 0;
-	int html_object_pos_x = 0, html_object_pos_y = 0;
-	int text_box_x = 0;
-	struct box *url_box = 0;
-	struct box *gadget_box = 0;
-	struct box *text_box = 0;
 	struct box *box;
-	struct form_control *gadget = 0;
-	hlcache_handle *object = NULL;
-	struct box *html_object_box = NULL;
-	struct browser_window *iframe = NULL;
-	struct box *drag_candidate = NULL;
-	struct scrollbar *scrollbar = NULL;
-	plot_font_style_t fstyle;
-	int scroll_mouse_x = 0, scroll_mouse_y = 0;
-	int padding_left, padding_right, padding_top, padding_bottom;
-	union content_msg_data msg_data;
-	struct dom_node *node = html->layout->node; /* Default to the <HTML> */
-	union html_selection_owner sel_owner;
-	bool click = mouse & (BROWSER_MOUSE_PRESS_1 | BROWSER_MOUSE_PRESS_2 |
-			BROWSER_MOUSE_CLICK_1 | BROWSER_MOUSE_CLICK_2 |
-			BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2);
-
-	nserror res = NSERROR_OK;
-
-	/* handle open select menu */
-	if (html->visible_select_menu != NULL) {
-		return mouse_action_select_menu(html, bw, mouse, x, y);
-	}
-
-	/* handle content drag */
-	switch (html->drag_type) {
-	case HTML_DRAG_SELECTION:
-		return mouse_action_drag_selection(html, bw, mouse, x, y);
-
-	case HTML_DRAG_SCROLLBAR:
-		return mouse_action_drag_scrollbar(html, bw, mouse, x, y);
-
-	case HTML_DRAG_TEXTAREA_SELECTION:
-	case HTML_DRAG_TEXTAREA_SCROLLBAR:
-		return mouse_action_drag_textarea(html, bw, mouse, x, y);
-
-	case HTML_DRAG_CONTENT_SELECTION:
-	case HTML_DRAG_CONTENT_SCROLL:
-		return mouse_action_drag_content(html, bw, mouse, x, y);
-
-	case HTML_DRAG_NONE:
-		break;
+	int box_x = 0;
+	int box_y = 0;
 
-	default:
-		/* Unknown content related drag type */
-		assert(0 && "Unknown content related drag type");
-	}
+	/* initialise the mouse action state data */
+	memset(man, 0, sizeof(struct mouse_action_state));
+	man->node = html->layout->node; /* Default dom node to the <HTML> */
+	man->result.pointer = BROWSER_POINTER_DEFAULT;
 
 	/* search the box tree for a link, imagemap, form control, or
 	 * box with scrollbars
 	 */
-
 	box = html->layout;
 
 	/* Consider the margins of the html page now */
 	box_x = box->margin[LEFT];
 	box_y = box->margin[TOP];
 
-	/* descend through visible boxes setting more specific values for:
-	 * box - deepest box at point
-	 * html_object_box - html object
-	 * html_object_pos_x - html object
-	 * html_object_pos_y - html object
-	 * object - non html object
-	 * iframe - iframe
-	 * url - href or imagemap
-	 * target - href or imagemap or gadget
-	 * url_box - href or imagemap
-	 * imagemap - imagemap
-	 * gadget - gadget
-	 * gadget_box - gadget
-	 * gadget_box_x - gadget
-	 * gadget_box_y - gadget
-	 * title - title
-	 * pointer
-	 *
-	 * drag_candidate - first box with scroll
-	 * padding_left - box with scroll
-	 * padding_right
-	 * padding_top
-	 * padding_bottom
-	 * scrollbar - inside padding box stops decent
-	 * scroll_mouse_x - inside padding box stops decent
-	 * scroll_mouse_y - inside padding box stops decent
-	 *
-	 * text_box - text box
-	 * text_box_x - text_box
-	 */
 	do {
+		/* skip hidden boxes */
 		if ((box->style != NULL) &&
 		    (css_computed_visibility(box->style) ==
 		     CSS_VISIBILITY_HIDDEN)) {
-			continue;
+			goto next_box;
 		}
 
 		if (box->node != NULL) {
-			node = box->node;
+			man->node = box->node;
 		}
 
 		if (box->object) {
 			if (content_get_type(box->object) == CONTENT_HTML) {
-				html_object_box = box;
-				html_object_pos_x = box_x;
-				html_object_pos_y = box_y;
+				man->html_object.box = box;
+				man->html_object.pos_x = box_x;
+				man->html_object.pos_y = box_y;
 			} else {
-				object = box->object;
+				man->object = box->object;
 			}
 		}
 
 		if (box->iframe) {
-			iframe = box->iframe;
+			man->iframe = box->iframe;
 		}
 
 		if (box->href) {
-			url = box->href;
-			target = box->target;
-			url_box = box;
+			man->link.url = box->href;
+			man->link.target = box->target;
+			man->link.box = box;
+			man->link.is_imagemap = false;
 		}
 
 		if (box->usemap) {
-			url = imagemap_get(html, box->usemap,
-					box_x, box_y, x, y, &target);
-			if (url) {
-				imagemap = true;
-				url_box = box;
-			}
+			man->link.url = imagemap_get(html,
+						     box->usemap,
+						     box_x,
+						     box_y,
+						     x, y,
+						     &man->link.target);
+			man->link.box = box;
+			man->link.is_imagemap = true;
 		}
 
 		if (box->gadget) {
-			gadget = box->gadget;
-			gadget_box = box;
-			gadget_box_x = box_x;
-			gadget_box_y = box_y;
-			if (gadget->form)
-				target = gadget->form->target;
+			man->gadget.control = box->gadget;
+			man->gadget.box = box;
+			man->gadget.box_x = box_x;
+			man->gadget.box_y = box_y;
+			if (box->gadget->form) {
+				man->gadget.target = box->gadget->form->target;
+			}
 		}
 
 		if (box->title) {
-			title = box->title;
+			man->title = box->title;
 		}
 
-		pointer = get_pointer_shape(box, false);
+		man->result.pointer = get_pointer_shape(box, false);
 
 		if ((box->scroll_x != NULL) ||
 		    (box->scroll_y != NULL)) {
+			int padding_left;
+			int padding_right;
+			int padding_top;
+			int padding_bottom;
 
-			if (drag_candidate == NULL) {
-				drag_candidate = box;
+			if (man->drag_candidate == NULL) {
+				man->drag_candidate = box;
 			}
 
 			padding_left = box_x +
@@ -761,435 +774,620 @@ html_mouse_action(struct content *c,
 				/* mouse inside padding box */
 
 				if ((box->scroll_y != NULL) &&
-						(x > (padding_right -
-							SCROLLBAR_WIDTH))) {
+				    (x > (padding_right - SCROLLBAR_WIDTH))) {
 					/* mouse above vertical box scroll */
 
-					scrollbar = box->scroll_y;
-					scroll_mouse_x = x - (padding_right -
-							     SCROLLBAR_WIDTH);
-					scroll_mouse_y = y - padding_top;
+					man->scroll.bar = box->scroll_y;
+					man->scroll.mouse_x = x - (padding_right - SCROLLBAR_WIDTH);
+					man->scroll.mouse_y = y - padding_top;
 					break;
 
 				} else if ((box->scroll_x != NULL) &&
-						(y > (padding_bottom -
+					   (y > (padding_bottom -
 							SCROLLBAR_WIDTH))) {
 					/* mouse above horizontal box scroll */
 
-					scrollbar = box->scroll_x;
-					scroll_mouse_x = x - padding_left;
-					scroll_mouse_y = y - (padding_bottom -
-							SCROLLBAR_WIDTH);
+					man->scroll.bar = box->scroll_x;
+					man->scroll.mouse_x = x - padding_left;
+					man->scroll.mouse_y = y - (padding_bottom - SCROLLBAR_WIDTH);
 					break;
 				}
 			}
 		}
 
 		if (box->text && !box->object) {
-			text_box = box;
-			text_box_x = box_x;
+			man->text.box = box;
+			man->text.box_x = box_x;
 		}
-	} while ((box = box_at_point(&html->len_ctx, box, x, y,
-			&box_x, &box_y)) != NULL);
+
+	next_box:
+		/* iterate to next box */
+		box = box_at_point(&html->len_ctx, box, x, y, &box_x, &box_y);
+	} while (box != NULL);
 
 	/* use of box_x, box_y, or content below this point is probably a
 	 * mistake; they will refer to the last box returned by box_at_point */
-	assert(node != NULL);
 
-	if (scrollbar) {
-		status = scrollbar_mouse_status_to_message(
-				scrollbar_mouse_action(scrollbar, mouse,
-						scroll_mouse_x,
-						scroll_mouse_y));
-		pointer = BROWSER_POINTER_DEFAULT;
-	} else if (gadget) {
-		textarea_mouse_status ta_status;
-
-		switch (gadget->type) {
-		case GADGET_SELECT:
-			status = messages_get("FormSelect");
-			pointer = BROWSER_POINTER_MENU;
-			if (mouse & BROWSER_MOUSE_CLICK_1 &&
-			    nsoption_bool(core_select_menu)) {
-				html->visible_select_menu = gadget;
-				res = form_open_select_menu(c, gadget,
-						form_select_menu_callback,
-						c);
-				if (res != NSERROR_OK) {
-					NSLOG(netsurf, ERROR,
-					      "%s",
-					      messages_get_errorcode(res));
-					html->visible_select_menu = NULL;
-				}
-				pointer = BROWSER_POINTER_DEFAULT;
-			} else if (mouse & BROWSER_MOUSE_CLICK_1) {
-				msg_data.select_menu.gadget = gadget;
-				content_broadcast(c, CONTENT_MSG_SELECTMENU,
-						&msg_data);
-			}
-			break;
-		case GADGET_CHECKBOX:
-			status = messages_get("FormCheckbox");
-			if (mouse & BROWSER_MOUSE_CLICK_1) {
-				gadget->selected = !gadget->selected;
-				dom_html_input_element_set_checked(
-					(dom_html_input_element *)(gadget->node),
-					gadget->selected);
-				html__redraw_a_box(html, gadget_box);
-			}
-			break;
-		case GADGET_RADIO:
-			status = messages_get("FormRadio");
-			if (mouse & BROWSER_MOUSE_CLICK_1)
-				form_radio_set(gadget);
-			break;
-		case GADGET_IMAGE:
-			/* This falls through to SUBMIT */
-			if (mouse & BROWSER_MOUSE_CLICK_1) {
-				struct image_input_coords *coords, *oldcoords;
-				/** \todo Find a way to not ignore errors */
-				coords = calloc(1, sizeof(*coords));
-				if (coords == NULL) {
-					return NSERROR_OK;
-				}
-				coords->x = x - gadget_box_x;
-				coords->y = y - gadget_box_y;
-				if (dom_node_set_user_data(
-					    gadget->node,
-					    corestring_dom___ns_key_image_coords_node_data,
-					    coords, html__image_coords_dom_user_data_handler,
-					    &oldcoords) != DOM_NO_ERR)
-					return NSERROR_OK;
-				free(oldcoords);
-			}
-			/* Fall through */
-		case GADGET_SUBMIT:
-			if (gadget->form) {
-				snprintf(status_buffer, sizeof status_buffer,
-						messages_get("FormSubmit"),
-						gadget->form->action);
-				status = status_buffer;
-				pointer = get_pointer_shape(gadget_box, false);
-				if (mouse & (BROWSER_MOUSE_CLICK_1 |
-						BROWSER_MOUSE_CLICK_2))
-					action = ACTION_SUBMIT;
-			} else {
-				status = messages_get("FormBadSubmit");
-			}
-			break;
-		case GADGET_TEXTBOX:
-		case GADGET_PASSWORD:
-		case GADGET_TEXTAREA:
-			if (gadget->type == GADGET_TEXTAREA)
-				status = messages_get("FormTextarea");
-			else
-				status = messages_get("FormTextbox");
-
-			if (click && (html->selection_type !=
-					HTML_SELECTION_TEXTAREA ||
-					html->selection_owner.textarea !=
-					gadget_box)) {
-				sel_owner.none = true;
-				html_set_selection(html, HTML_SELECTION_NONE,
-						sel_owner, true);
-			}
+	assert(man->node != NULL);
+
+	return NSERROR_OK;
+}
 
-			ta_status = textarea_mouse_action(gadget->data.text.ta,
-					mouse, x - gadget_box_x,
-					y - gadget_box_y);
 
-			if (ta_status & TEXTAREA_MOUSE_EDITOR) {
-				pointer = get_pointer_shape(gadget_box, false);
-			} else {
-				pointer = BROWSER_POINTER_DEFAULT;
-				status = scrollbar_mouse_status_to_message(
-						ta_status >> 3);
-			}
-			break;
-		case GADGET_HIDDEN:
-			/* not possible: no box generated */
-			break;
-		case GADGET_RESET:
-			status = messages_get("FormReset");
-			break;
-		case GADGET_FILE:
-			status = messages_get("FormFile");
-			if (mouse & BROWSER_MOUSE_CLICK_1) {
-				msg_data.gadget_click.gadget = gadget;
-				content_broadcast(c, CONTENT_MSG_GADGETCLICK,
-						&msg_data);
+/**
+ * process mouse activity on a form gadget
+ */
+static nserror
+gadget_mouse_action(html_content *html,
+		    browser_mouse_state mouse,
+		    int x, int y,
+		    struct mouse_action_state *mas)
+{
+	struct content *c = (struct content *)html;
+	textarea_mouse_status ta_status;
+	union content_msg_data msg_data;
+	nserror res;
+	bool click;
+	click = mouse & (BROWSER_MOUSE_PRESS_1 | BROWSER_MOUSE_PRESS_2 |
+			 BROWSER_MOUSE_CLICK_1 | BROWSER_MOUSE_CLICK_2 |
+			 BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2);
+
+	switch (mas->gadget.control->type) {
+	case GADGET_SELECT:
+		mas->result.status = messages_get("FormSelect");
+		mas->result.pointer = BROWSER_POINTER_MENU;
+		if (mouse & BROWSER_MOUSE_CLICK_1 &&
+		    nsoption_bool(core_select_menu)) {
+			html->visible_select_menu = mas->gadget.control;
+			res = form_open_select_menu(c,
+						    mas->gadget.control,
+						    form_select_menu_callback,
+						    c);
+			if (res != NSERROR_OK) {
+				NSLOG(netsurf, ERROR, "%s",
+				      messages_get_errorcode(res));
+				html->visible_select_menu = NULL;
 			}
-			break;
-		case GADGET_BUTTON:
-			/* This gadget cannot be activated */
-			status = messages_get("FormButton");
-			break;
+			mas->result.pointer = BROWSER_POINTER_DEFAULT;
+		} else if (mouse & BROWSER_MOUSE_CLICK_1) {
+			msg_data.select_menu.gadget = mas->gadget.control;
+			content_broadcast(c,
+					  CONTENT_MSG_SELECTMENU,
+					  &msg_data);
 		}
+		break;
 
-	} else if (object && (mouse & BROWSER_MOUSE_MOD_2)) {
-
-		if (mouse & BROWSER_MOUSE_DRAG_2) {
-			msg_data.dragsave.type = CONTENT_SAVE_NATIVE;
-			msg_data.dragsave.content = object;
-			content_broadcast(c, CONTENT_MSG_DRAGSAVE, &msg_data);
-
-		} else if (mouse & BROWSER_MOUSE_DRAG_1) {
-			msg_data.dragsave.type = CONTENT_SAVE_ORIG;
-			msg_data.dragsave.content = object;
-			content_broadcast(c, CONTENT_MSG_DRAGSAVE, &msg_data);
+	case GADGET_CHECKBOX:
+		mas->result.status = messages_get("FormCheckbox");
+		if (mouse & BROWSER_MOUSE_CLICK_1) {
+			mas->gadget.control->selected = !mas->gadget.control->selected;
+			dom_html_input_element_set_checked(
+				(dom_html_input_element *)(mas->gadget.control->node),
+				mas->gadget.control->selected);
+			html__redraw_a_box(html, mas->gadget.box);
 		}
+		break;
 
-		/* \todo should have a drag-saving object msg */
+	case GADGET_RADIO:
+		mas->result.status = messages_get("FormRadio");
+		if (mouse & BROWSER_MOUSE_CLICK_1) {
+			form_radio_set(mas->gadget.control);
+		}
+		break;
 
-	} else if (iframe) {
-		int pos_x, pos_y;
-		float scale = browser_window_get_scale(bw);
+	case GADGET_IMAGE:
+		/* This falls through to SUBMIT */
+		if (mouse & BROWSER_MOUSE_CLICK_1) {
+			struct image_input_coords *coords, *oldcoords;
+			/** \todo Find a way to not ignore errors */
+			coords = calloc(1, sizeof(*coords));
+			if (coords == NULL) {
+				return NSERROR_OK;
+			}
+			coords->x = x - mas->gadget.box_x;
+			coords->y = y - mas->gadget.box_y;
+			if (dom_node_set_user_data(
+				mas->gadget.control->node,
+				corestring_dom___ns_key_image_coords_node_data,
+				coords,
+				html__image_coords_dom_user_data_handler,
+				&oldcoords) != DOM_NO_ERR) {
+				return NSERROR_OK;
+			}
+			free(oldcoords);
+		}
+		/* Fall through */
 
-		browser_window_get_position(iframe, false, &pos_x, &pos_y);
+	case GADGET_SUBMIT:
+		if (mas->gadget.control->form) {
+			static char status_buffer[200];
+
+			snprintf(status_buffer,
+				 sizeof status_buffer,
+				 messages_get("FormSubmit"),
+				 mas->gadget.control->form->action);
+			mas->result.status = status_buffer;
+			mas->result.pointer = get_pointer_shape(mas->gadget.box,
+								false);
+			if (mouse & (BROWSER_MOUSE_CLICK_1 |
+				     BROWSER_MOUSE_CLICK_2)) {
+				mas->result.action = ACTION_SUBMIT;
+			}
+		} else {
+			mas->result.status = messages_get("FormBadSubmit");
+		}
+		break;
 
-		if (mouse & BROWSER_MOUSE_CLICK_1 ||
-		    mouse & BROWSER_MOUSE_CLICK_2) {
-			browser_window_mouse_click(iframe, mouse,
-						   (x * scale) - pos_x,
-						   (y * scale) - pos_y);
+	case GADGET_TEXTBOX:
+	case GADGET_PASSWORD:
+	case GADGET_TEXTAREA:
+		if (mas->gadget.control->type == GADGET_TEXTAREA) {
+			mas->result.status = messages_get("FormTextarea");
 		} else {
-			browser_window_mouse_track(iframe, mouse,
-						   (x * scale) - pos_x,
-						   (y * scale) - pos_y);
+			mas->result.status = messages_get("FormTextbox");
 		}
-	} else if (html_object_box) {
 
-		if (click && (html->selection_type != HTML_SELECTION_CONTENT ||
-				html->selection_owner.content !=
-						html_object_box)) {
+		if (click &&
+		    (html->selection_type != HTML_SELECTION_TEXTAREA ||
+		     html->selection_owner.textarea != mas->gadget.box)) {
+			union html_selection_owner sel_owner;
 			sel_owner.none = true;
-			html_set_selection(html, HTML_SELECTION_NONE,
-					sel_owner, true);
+			html_set_selection(html,
+					   HTML_SELECTION_NONE,
+					   sel_owner,
+					   true);
 		}
-		if (mouse & BROWSER_MOUSE_CLICK_1 ||
-				mouse & BROWSER_MOUSE_CLICK_2) {
-			content_mouse_action(html_object_box->object,
-					bw, mouse,
-					x - html_object_pos_x,
-					y - html_object_pos_y);
+
+		ta_status = textarea_mouse_action(mas->gadget.control->data.text.ta,
+						  mouse,
+						  x - mas->gadget.box_x,
+						  y - mas->gadget.box_y);
+
+		if (ta_status & TEXTAREA_MOUSE_EDITOR) {
+			mas->result.pointer = get_pointer_shape(mas->gadget.box, false);
 		} else {
-			content_mouse_track(html_object_box->object,
-					bw, mouse,
-					x - html_object_pos_x,
-					y - html_object_pos_y);
-		}
-	} else if (url) {
-		if (nsoption_bool(display_decoded_idn) == true) {
-			res = nsurl_get_utf8(url, &url_s, &url_l);
-			if (res != NSERROR_OK) {
-				/* Unable to obtain a decoded IDN. This is not
-				 *  a fatal error.  Ensure the string pointer
-				 *  is NULL so we use the encoded version.
-				 */
-				url_s = NULL;
-			}
+			mas->result.pointer = BROWSER_POINTER_DEFAULT;
+			mas->result.status = scrollbar_mouse_status_to_message(ta_status >> 3);
 		}
+		break;
 
-		if (title) {
-			snprintf(status_buffer, sizeof status_buffer, "%s: %s",
-					url_s ? url_s : nsurl_access(url), title);
-		} else {
-			snprintf(status_buffer, sizeof status_buffer, "%s",
-					url_s ? url_s : nsurl_access(url));
+	case GADGET_HIDDEN:
+		/* not possible: no box generated */
+		break;
+
+	case GADGET_RESET:
+		mas->result.status = messages_get("FormReset");
+		break;
+
+	case GADGET_FILE:
+		mas->result.status = messages_get("FormFile");
+		if (mouse & BROWSER_MOUSE_CLICK_1) {
+			msg_data.gadget_click.gadget = mas->gadget.control;
+			content_broadcast(c,
+					  CONTENT_MSG_GADGETCLICK,
+					  &msg_data);
 		}
+		break;
 
-		status = status_buffer;
+	case GADGET_BUTTON:
+		/* This gadget cannot be activated */
+		mas->result.status = messages_get("FormButton");
+		break;
+	}
 
-		if (url_s != NULL)
-			free(url_s);
+	return NSERROR_OK;
+}
 
-		pointer = get_pointer_shape(url_box, imagemap);
 
-		if (mouse & BROWSER_MOUSE_CLICK_1 &&
-				mouse & BROWSER_MOUSE_MOD_1) {
-			/* force download of link */
-			browser_window_navigate(bw,
-				url,
-				content_get_url(c),
-				BW_NAVIGATE_DOWNLOAD,
-				NULL,
-				NULL,
-				NULL);
+/**
+ * process mouse activity on an iframe
+ */
+static nserror
+iframe_mouse_action(struct browser_window *bw,
+		    browser_mouse_state mouse,
+		    int x, int y,
+		    struct mouse_action_state *mas)
+{
+	int pos_x, pos_y;
+	float scale;
+
+	scale = browser_window_get_scale(bw);
 
-		} else if (mouse & BROWSER_MOUSE_CLICK_2 &&
-				mouse & BROWSER_MOUSE_MOD_1) {
-			msg_data.savelink.url = url;
-			msg_data.savelink.title = title;
-			content_broadcast(c, CONTENT_MSG_SAVELINK, &msg_data);
+	browser_window_get_position(mas->iframe, false, &pos_x, &pos_y);
 
-		} else if (mouse & (BROWSER_MOUSE_CLICK_1 |
-				BROWSER_MOUSE_CLICK_2))
-			action = ACTION_GO;
+	if (mouse & BROWSER_MOUSE_CLICK_1 ||
+	    mouse & BROWSER_MOUSE_CLICK_2) {
+		browser_window_mouse_click(mas->iframe,
+					   mouse,
+					   (x * scale) - pos_x,
+					   (y * scale) - pos_y);
 	} else {
-		bool done = false;
-
-		/* frame resizing */
-		if (browser_window_frame_resize_start(bw, mouse, x, y,
-				&pointer)) {
-			if (mouse & (BROWSER_MOUSE_DRAG_1 |
-					BROWSER_MOUSE_DRAG_2)) {
-				status = messages_get("FrameDrag");
-			}
-			done = true;
+		browser_window_mouse_track(mas->iframe,
+					   mouse,
+					   (x * scale) - pos_x,
+					   (y * scale) - pos_y);
+	}
+	mas->result.action = ACTION_NOSEND;
+
+	return NSERROR_OK;
+}
+
+
+/**
+ * process mouse activity on an html object
+ */
+static nserror
+html_object_mouse_action(html_content *html,
+			 struct browser_window *bw,
+			 browser_mouse_state mouse,
+			 int x, int y,
+			 struct mouse_action_state *mas)
+{
+	bool click;
+	click = mouse & (BROWSER_MOUSE_PRESS_1 | BROWSER_MOUSE_PRESS_2 |
+			 BROWSER_MOUSE_CLICK_1 | BROWSER_MOUSE_CLICK_2 |
+			 BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2);
+
+	if (click &&
+	    (html->selection_type != HTML_SELECTION_CONTENT ||
+	     html->selection_owner.content != mas->html_object.box)) {
+		union html_selection_owner sel_owner;
+		sel_owner.none = true;
+		html_set_selection(html, HTML_SELECTION_NONE, sel_owner, true);
+	}
+
+	if (mouse & BROWSER_MOUSE_CLICK_1 ||
+	    mouse & BROWSER_MOUSE_CLICK_2) {
+		content_mouse_action(mas->html_object.box->object,
+				     bw,
+				     mouse,
+				     x - mas->html_object.pos_x,
+				     y - mas->html_object.pos_y);
+	} else {
+		content_mouse_track(mas->html_object.box->object,
+				    bw,
+				    mouse,
+				    x - mas->html_object.pos_x,
+				    y - mas->html_object.pos_y);
+	}
+
+	mas->result.action = ACTION_NOSEND;
+	return NSERROR_OK;
+}
+
+
+/**
+ * process mouse activity on a link
+ */
+static nserror
+link_mouse_action(html_content *html,
+		  struct browser_window *bw,
+		  browser_mouse_state mouse,
+		  int x, int y,
+		  struct mouse_action_state *mas)
+{
+	nserror res;
+	char *url_s = NULL;
+	size_t url_l = 0;
+	static char status_buffer[200];
+	union content_msg_data msg_data;
+
+	if (nsoption_bool(display_decoded_idn) == true) {
+		res = nsurl_get_utf8(mas->link.url, &url_s, &url_l);
+		if (res != NSERROR_OK) {
+			/* Unable to obtain a decoded IDN. This is not
+			 *  a fatal error.  Ensure the string pointer
+			 *  is NULL so we use the encoded version.
+			 */
+			url_s = NULL;
 		}
+	}
 
-		/* if clicking in the main page, remove the selection from any
-		 * text areas */
-		if (!done) {
+	if (mas->title) {
+		snprintf(status_buffer,
+			 sizeof status_buffer,
+			 "%s: %s",
+			 url_s ? url_s : nsurl_access(mas->link.url),
+			 mas->title);
+	} else {
+		snprintf(status_buffer,
+			 sizeof status_buffer,
+			 "%s",
+			 url_s ? url_s : nsurl_access(mas->link.url));
+	}
 
-			if (click && html->focus_type != HTML_FOCUS_SELF) {
-				union html_focus_owner fo;
-				fo.self = true;
-				html_set_focus(html, HTML_FOCUS_SELF, fo,
-						true, 0, 0, 0, NULL);
-			}
-			if (click && html->selection_type !=
-					HTML_SELECTION_SELF) {
-				sel_owner.none = true;
-				html_set_selection(html, HTML_SELECTION_NONE,
-						sel_owner, true);
-			}
+	if (url_s != NULL) {
+		free(url_s);
+	}
+
+	mas->result.status = status_buffer;
+
+	mas->result.pointer = get_pointer_shape(mas->link.box,
+						mas->link.is_imagemap);
+
+	if (mouse & BROWSER_MOUSE_CLICK_1 &&
+	    mouse & BROWSER_MOUSE_MOD_1) {
+		/* force download of link */
+		browser_window_navigate(bw,
+					mas->link.url,
+					content_get_url((struct content *)html),
+					BW_NAVIGATE_DOWNLOAD,
+					NULL,
+					NULL,
+					NULL);
+
+	} else if (mouse & BROWSER_MOUSE_CLICK_2 &&
+		   mouse & BROWSER_MOUSE_MOD_1) {
+		msg_data.savelink.url = mas->link.url;
+		msg_data.savelink.title = mas->title;
+		content_broadcast((struct content *)html,
+				  CONTENT_MSG_SAVELINK,
+				  &msg_data);
+
+	} else if (mouse & (BROWSER_MOUSE_CLICK_1 | BROWSER_MOUSE_CLICK_2)) {
+		mas->result.action = ACTION_GO;
+	}
+
+	return NSERROR_OK;
+}
+
+
+/**
+ * process mouse activity if it is not anything else
+ */
+static nserror
+default_mouse_action(html_content *html,
+		  struct browser_window *bw,
+		  browser_mouse_state mouse,
+		  int x, int y,
+		  struct mouse_action_state *mas)
+{
+	struct content *c = (struct content *)html;
+	bool done = false;
+
+	/* frame resizing */
+	if (browser_window_frame_resize_start(bw, mouse, x, y, &mas->result.pointer)) {
+		if (mouse & (BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2)) {
+			mas->result.status = messages_get("FrameDrag");
+		}
+		done = true;
+	}
 
-			if (text_box) {
-				int pixel_offset;
-				size_t idx;
-
-				font_plot_style_from_css(&html->len_ctx,
-						text_box->style, &fstyle);
-
-				guit->layout->position(&fstyle,
-						       text_box->text,
-						       text_box->length,
-						       x - text_box_x,
-						       &idx,
-						       &pixel_offset);
-
-				if (selection_click(&html->sel, mouse,
-						text_box->byte_offset + idx)) {
-					/* key presses must be directed at the
-					 * main browser window, paste text
-					 * operations ignored */
-					html_drag_type drag_type;
-					union html_drag_owner drag_owner;
-
-					if (selection_dragging(&html->sel)) {
-						drag_type = HTML_DRAG_SELECTION;
-						drag_owner.no_owner = true;
-						html_set_drag_type(html,
-								drag_type,
-								drag_owner,
-								NULL);
-						status = messages_get(
-								"Selecting");
-					}
-
-					done = true;
+	/* if clicking in the main page, remove the selection from any
+	 * text areas */
+	if (!done) {
+		union html_selection_owner sel_owner;
+		bool click;
+		click = mouse & (BROWSER_MOUSE_PRESS_1 | BROWSER_MOUSE_PRESS_2 |
+				 BROWSER_MOUSE_CLICK_1 | BROWSER_MOUSE_CLICK_2 |
+				 BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2);
+
+		if (click && html->focus_type != HTML_FOCUS_SELF) {
+			union html_focus_owner fo;
+			fo.self = true;
+			html_set_focus(html, HTML_FOCUS_SELF, fo,
+				       true, 0, 0, 0, NULL);
+		}
+		if (click && html->selection_type != HTML_SELECTION_SELF) {
+			sel_owner.none = true;
+			html_set_selection(html, HTML_SELECTION_NONE,
+					   sel_owner, true);
+		}
+
+		if (mas->text.box) {
+			int pixel_offset;
+			size_t idx;
+			plot_font_style_t fstyle;
+
+			font_plot_style_from_css(&html->len_ctx,
+						 mas->text.box->style,
+						 &fstyle);
+
+			guit->layout->position(&fstyle,
+					       mas->text.box->text,
+					       mas->text.box->length,
+					       x - mas->text.box_x,
+					       &idx,
+					       &pixel_offset);
+
+			if (selection_click(&html->sel,
+					    mouse,
+					    mas->text.box->byte_offset + idx)) {
+				/* key presses must be directed at the
+				 * main browser window, paste text
+				 * operations ignored */
+				html_drag_type drag_type;
+				union html_drag_owner drag_owner;
+
+				if (selection_dragging(&html->sel)) {
+					drag_type = HTML_DRAG_SELECTION;
+					drag_owner.no_owner = true;
+					html_set_drag_type(html,
+							   drag_type,
+							   drag_owner,
+							   NULL);
+					mas->result.status = messages_get("Selecting");
 				}
 
-			} else if (mouse & BROWSER_MOUSE_PRESS_1) {
-				sel_owner.none = true;
-				selection_clear(&html->sel, true);
+				done = true;
 			}
 
-			if (selection_defined(&html->sel)) {
-				sel_owner.none = false;
-				html_set_selection(html, HTML_SELECTION_SELF,
-						sel_owner, true);
-			} else if (click && html->selection_type !=
-					HTML_SELECTION_NONE) {
-				sel_owner.none = true;
-				html_set_selection(html, HTML_SELECTION_NONE,
-						sel_owner, true);
-			}
+		} else if (mouse & BROWSER_MOUSE_PRESS_1) {
+			sel_owner.none = true;
+			selection_clear(&html->sel, true);
+		}
+
+		if (selection_defined(&html->sel)) {
+			sel_owner.none = false;
+			html_set_selection(html,
+					   HTML_SELECTION_SELF,
+					   sel_owner,
+					   true);
+		} else if (click &&
+			   html->selection_type != HTML_SELECTION_NONE) {
+			sel_owner.none = true;
+			html_set_selection(html,
+					   HTML_SELECTION_NONE,
+					   sel_owner,
+					   true);
 		}
+	}
 
-		if (!done) {
-			if (title)
-				status = title;
-
-			if (mouse & BROWSER_MOUSE_DRAG_1) {
-				if (mouse & BROWSER_MOUSE_MOD_2) {
-					msg_data.dragsave.type =
-							CONTENT_SAVE_COMPLETE;
-					msg_data.dragsave.content = NULL;
-					content_broadcast(c,
-							CONTENT_MSG_DRAGSAVE,
-							&msg_data);
+	if (!done) {
+		union content_msg_data msg_data;
+		if (mas->title) {
+			mas->result.status = mas->title;
+		}
+
+		if (mouse & BROWSER_MOUSE_DRAG_1) {
+			if (mouse & BROWSER_MOUSE_MOD_2) {
+				msg_data.dragsave.type = CONTENT_SAVE_COMPLETE;
+				msg_data.dragsave.content = NULL;
+				content_broadcast(c,
+						  CONTENT_MSG_DRAGSAVE,
+						  &msg_data);
+			} else {
+				if (mas->drag_candidate == NULL) {
+					browser_window_page_drag_start(bw,
+								       x, y);
 				} else {
-					if (drag_candidate == NULL) {
-						browser_window_page_drag_start(
-								bw, x, y);
-					} else {
-						html_box_drag_start(
-								drag_candidate,
-								x, y);
-					}
-					pointer = BROWSER_POINTER_MOVE;
+					html_box_drag_start(mas->drag_candidate,
+							    x, y);
 				}
+				mas->result.pointer = BROWSER_POINTER_MOVE;
 			}
-			else if (mouse & BROWSER_MOUSE_DRAG_2) {
-				if (mouse & BROWSER_MOUSE_MOD_2) {
-					msg_data.dragsave.type =
-							CONTENT_SAVE_SOURCE;
-					msg_data.dragsave.content = NULL;
-					content_broadcast(c,
-							CONTENT_MSG_DRAGSAVE,
-							&msg_data);
+		} else if (mouse & BROWSER_MOUSE_DRAG_2) {
+			if (mouse & BROWSER_MOUSE_MOD_2) {
+				msg_data.dragsave.type = CONTENT_SAVE_SOURCE;
+				msg_data.dragsave.content = NULL;
+				content_broadcast(c,
+						  CONTENT_MSG_DRAGSAVE,
+						  &msg_data);
+			} else {
+				if (mas->drag_candidate == NULL) {
+					browser_window_page_drag_start(bw,
+								       x, y);
 				} else {
-					if (drag_candidate == NULL) {
-						browser_window_page_drag_start(
-								bw, x, y);
-					} else {
-						html_box_drag_start(
-								drag_candidate,
-								x, y);
-					}
-					pointer = BROWSER_POINTER_MOVE;
+					html_box_drag_start(mas->drag_candidate,
+							    x, y);
 				}
+				mas->result.pointer = BROWSER_POINTER_MOVE;
 			}
 		}
-		if (mouse && mouse < BROWSER_MOUSE_MOD_1) {
-			/* ensure key presses still act on the browser window */
-			union html_focus_owner fo;
-			fo.self = true;
-			html_set_focus(html, HTML_FOCUS_SELF, fo,
-					true, 0, 0, 0, NULL);
+	}
+
+	if (mouse && mouse < BROWSER_MOUSE_MOD_1) {
+		/* ensure key presses still act on the browser window */
+		union html_focus_owner fo;
+		fo.self = true;
+		html_set_focus(html, HTML_FOCUS_SELF, fo, true, 0, 0, 0, NULL);
+	}
+
+	return NSERROR_OK;
+}
+
+
+/**
+ * handle non dragging mouse actions
+ */
+static nserror
+mouse_action_drag_none(html_content *html,
+		       struct browser_window *bw,
+		       browser_mouse_state mouse,
+		       int x, int y)
+{
+	struct content *c = (struct content *)html;
+	union content_msg_data msg_data;
+
+	nserror res;
+	/**
+	 * computed state
+	 *
+	 * not on heap to avoid allocation or stack because it is large
+	 */
+	static struct mouse_action_state mas;
+
+	res = get_mouse_action_node(html, x, y, &mas);
+	if (res != NSERROR_OK) {
+		return res;
+	}
+
+	if (mas.scroll.bar) {
+		mas.result.status = scrollbar_mouse_status_to_message(
+				scrollbar_mouse_action(mas.scroll.bar,
+						       mouse,
+						       mas.scroll.mouse_x,
+						       mas.scroll.mouse_y));
+		mas.result.pointer = BROWSER_POINTER_DEFAULT;
+
+	} else if (mas.gadget.control) {
+		res = gadget_mouse_action(html, mouse, x, y, &mas);
+
+	} else if ((mas.object != NULL) && (mouse & BROWSER_MOUSE_MOD_2)) {
+
+		if (mouse & BROWSER_MOUSE_DRAG_2) {
+			msg_data.dragsave.type = CONTENT_SAVE_NATIVE;
+			msg_data.dragsave.content = mas.object;
+			content_broadcast(c, CONTENT_MSG_DRAGSAVE, &msg_data);
+
+		} else if (mouse & BROWSER_MOUSE_DRAG_1) {
+			msg_data.dragsave.type = CONTENT_SAVE_ORIG;
+			msg_data.dragsave.content = mas.object;
+			content_broadcast(c, CONTENT_MSG_DRAGSAVE, &msg_data);
 		}
+
+		/* \todo should have a drag-saving object msg */
+
+	} else if (mas.iframe != NULL) {
+		res = iframe_mouse_action(bw, mouse, x, y, &mas);
+
+	} else if (mas.html_object.box != NULL) {
+		res = html_object_mouse_action(html, bw, mouse, x, y, &mas);
+
+	} else if (mas.link.url != NULL) {
+		res = link_mouse_action(html, bw, mouse, x, y, &mas);
+
+	} else {
+		res = default_mouse_action(html, bw, mouse, x, y, &mas);
+
+	}
+	if (res != NSERROR_OK) {
+		return res;
 	}
 
-	if (!iframe && !html_object_box) {
-		msg_data.explicit_status_text = status;
+	/* send status and pointer message */
+	if (mas.result.action != ACTION_NOSEND) {
+		msg_data.explicit_status_text = mas.result.status;
 		content_broadcast(c, CONTENT_MSG_STATUS, &msg_data);
 
-		msg_data.pointer = pointer;
+		msg_data.pointer = mas.result.pointer;
 		content_broadcast(c, CONTENT_MSG_POINTER, &msg_data);
 	}
 
 	/* fire dom click event */
 	if (mouse & BROWSER_MOUSE_CLICK_1) {
-		fire_generic_dom_event(corestring_dom_click, node, true, true);
+		fire_generic_dom_event(corestring_dom_click, mas.node, true, true);
 	}
 
 	/* deferred actions that can cause this browser_window to be destroyed
 	 * and must therefore be done after set_status/pointer
 	 */
-	switch (action) {
+	switch (mas.result.action) {
 	case ACTION_SUBMIT:
 		res = form_submit(content_get_url(c),
-				  browser_window_find_target(bw, target, mouse),
-				  gadget->form,
-				  gadget);
+				  browser_window_find_target(bw,
+							     mas.gadget.target,
+							     mouse),
+				  mas.gadget.control->form,
+				  mas.gadget.control);
 		break;
 
 	case ACTION_GO:
 		res = browser_window_navigate(
-				browser_window_find_target(bw, target, mouse),
-				url,
+				browser_window_find_target(bw,
+							   mas.link.target,
+							   mouse),
+				mas.link.url,
 				content_get_url(c),
 				BW_NAVIGATE_HISTORY,
 				NULL,
@@ -1197,15 +1395,74 @@ html_mouse_action(struct content *c,
 				NULL);
 		break;
 
+	case ACTION_NOSEND:
 	case ACTION_NONE:
 		res = NSERROR_OK;
 		break;
 	}
 
+	return res;
+}
+
+
+/* exported interface documented in html/interaction.h */
+nserror html_mouse_track(struct content *c,
+			 struct browser_window *bw,
+			 browser_mouse_state mouse,
+			 int x, int y)
+{
+	return html_mouse_action(c, bw, mouse, x, y);
+}
+
+
+/* exported interface documented in html/interaction.h */
+nserror
+html_mouse_action(struct content *c,
+		  struct browser_window *bw,
+		  browser_mouse_state mouse,
+		  int x, int y)
+{
+	html_content *html = (html_content *)c;
+	nserror res;
+
+	/* handle open select menu */
+	if (html->visible_select_menu != NULL) {
+		return mouse_action_select_menu(html, bw, mouse, x, y);
+	}
+
+	/* handle content drag */
+	switch (html->drag_type) {
+	case HTML_DRAG_SELECTION:
+		res = mouse_action_drag_selection(html, bw, mouse, x, y);
+		break;
+
+	case HTML_DRAG_SCROLLBAR:
+		res = mouse_action_drag_scrollbar(html, bw, mouse, x, y);
+		break;
+
+	case HTML_DRAG_TEXTAREA_SELECTION:
+	case HTML_DRAG_TEXTAREA_SCROLLBAR:
+		res = mouse_action_drag_textarea(html, bw, mouse, x, y);
+		break;
+
+	case HTML_DRAG_CONTENT_SELECTION:
+	case HTML_DRAG_CONTENT_SCROLL:
+		res = mouse_action_drag_content(html, bw, mouse, x, y);
+		break;
+
+	case HTML_DRAG_NONE:
+		res =  mouse_action_drag_none(html, bw, mouse, x, y);
+		break;
+
+	default:
+		/* Unknown content related drag type */
+		assert(0 && "Unknown content related drag type");
+	}
+
 	if (res != NSERROR_OK) {
 		NSLOG(netsurf, ERROR, "%s", messages_get_errorcode(res));
 	}
-
+	
 	return res;
 }
 
@@ -1217,7 +1474,6 @@ html_mouse_action(struct content *c,
  * \param  key	The UCS4 character codepoint
  * \return true if key handled, false otherwise
  */
-
 bool html_keypress(struct content *c, uint32_t key)
 {
 	html_content *html = (html_content *) c;