UI: Hide & shrink scroll-bars based on cursor position

Scroll-bars are now hidden unless the cursor approaches them, in which case they
smoothly grow and become more & more visible. Note that since 0d309144020168e55,
scroll-bars are drawn on top of editor contents. There's no more jumping of
buttons when scroll-bars appear.

Technical notes:
* AZones are used to adjust scrollbars based on mouse movements

  We may want to support screen level AZones if we want scrollbars to also
  smoothly appear when approaching them from a different area.
  I also plan to make further changes to AZones to clean up stuff a bit.
* Had to move AZone handling to a post ARegion init stage, since we need the
  updated View2D data from there.
* View2D masks and scroller rectangles are now updated on every redraw. It's
  cheap to do that though.

1 files changed, 98 insertions, 38 deletions

diff --git a/source/blender/editors/screen/area.c b/source/blender/editors/screen/area.c
index 58dbebd2b75..e86655ab2cf 100644
--- a/source/blender/editors/screen/area.c
+++ b/source/blender/editors/screen/area.c
@@ -203,6 +203,24 @@ void ED_area_azones_update(ScrArea *sa, const int mouse_xy[2])
 				break;
 			}
 		}
+		else if (az->type == AZONE_REGION_SCROLL) {
+			/* only if mouse is not hovering the azone */
+			if (BLI_rcti_isect_pt_v(&az->rect, mouse_xy) == false) {
+				View2D *v2d = &az->ar->v2d;
+
+				if (az->direction == AZ_SCROLL_VERT) {
+					az->alpha = v2d->alpha_vert = 0;
+					changed = true;
+				}
+				else if (az->direction == AZ_SCROLL_HOR) {
+					az->alpha = v2d->alpha_hor = 0;
+					changed = true;
+				}
+				else {
+					BLI_assert(0);
+				}
+			}
+		}
 	}
 
 	if (changed) {
@@ -464,6 +482,12 @@ static void region_draw_azones(ScrArea *sa, ARegion *ar)
 					area_azone_tag_update(sa);
 				}
 			}
+			else if (az->type == AZONE_REGION_SCROLL) {
+				if (az->alpha != 0.0f) {
+					area_azone_tag_update(sa);
+				}
+				/* Don't draw this azone. */
+			}
 		}
 	}
 
@@ -1043,7 +1067,7 @@ static void region_azone_tria(ScrArea *sa, AZone *az, ARegion *ar)
 }	
 
 
-static void region_azone_initialize(ScrArea *sa, ARegion *ar, AZEdge edge, const bool is_fullscreen)
+static void region_azone_edge_initialize(ScrArea *sa, ARegion *ar, AZEdge edge, const bool is_fullscreen)
 {
 	AZone *az = NULL;
 	const bool is_hidden = (ar->flag & (RGN_FLAG_HIDDEN | RGN_FLAG_TOO_SMALL)) == 0;
@@ -1074,21 +1098,76 @@ static void region_azone_initialize(ScrArea *sa, ARegion *ar, AZEdge edge, const
 	
 }
 
+static void region_azone_scrollbar_initialize(ScrArea *sa, ARegion *ar, AZScrollDirection direction)
+{
+	rcti scroller_vert = (direction == AZ_SCROLL_VERT) ? ar->v2d.vert : ar->v2d.hor;
+	AZone *az = MEM_callocN(sizeof(*az), __func__);
+
+	BLI_addtail(&sa->actionzones, az);
+	az->type = AZONE_REGION_SCROLL;
+	az->ar = ar;
+	az->direction = direction;
+
+	if (direction == AZ_SCROLL_VERT) {
+		az->ar->v2d.alpha_vert = 0;
+	}
+	else if (direction == AZ_SCROLL_HOR) {
+		az->ar->v2d.alpha_hor = 0;
+	}
+
+	BLI_rcti_translate(&scroller_vert, ar->winrct.xmin, ar->winrct.ymin);
+	az->x1 = scroller_vert.xmin - AZONEFADEIN;
+	az->y1 = scroller_vert.ymin - AZONEFADEIN;
+	az->x2 = scroller_vert.xmax + AZONEFADEIN;
+	az->y2 = scroller_vert.ymax + AZONEFADEIN;
+
+	BLI_rcti_init(&az->rect, az->x1, az->x2, az->y1, az->y2);
+}
+
+static void region_azones_scrollbars_initialize(ScrArea *sa, ARegion *ar)
+{
+	const View2D *v2d = &ar->v2d;
+
+	if ((v2d->scroll & V2D_SCROLL_VERTICAL)   && ((v2d->scroll & V2D_SCROLL_SCALE_VERTICAL)   == 0)) {
+		region_azone_scrollbar_initialize(sa, ar, AZ_SCROLL_VERT);
+	}
+	if ((v2d->scroll & V2D_SCROLL_HORIZONTAL) && ((v2d->scroll & V2D_SCROLL_SCALE_HORIZONTAL) == 0)) {
+		region_azone_scrollbar_initialize(sa, ar, AZ_SCROLL_HOR);
+	}
+}
+
 
 /* *************************************************************** */
 
-static void region_azone_add(ScrArea *sa, ARegion *ar, const int alignment, const bool is_fullscreen)
+static void region_azones_add(const bScreen *screen, ScrArea *sa, ARegion *ar, const int alignment)
 {
+	const bool is_fullscreen = screen->state == SCREENFULL;
+
 	/* edge code (t b l r) is along which area edge azone will be drawn */
-	
-	if (alignment == RGN_ALIGN_TOP)
-		region_azone_initialize(sa, ar, AE_BOTTOM_TO_TOPLEFT, is_fullscreen);
+
+	if (ar->regiontype == RGN_TYPE_HEADER && ar->winy + 6 > sa->winy) {
+		/* The logic for this is: when the header takes up the full area,
+		 * disallow hiding it to view the main window.
+		 *
+		 * Without this, you can drag down the file selectors header and hide it
+		 * by accident very easily (highly annoying!), the value 6 is arbitrary
+		 * but accounts for small common rounding problems when scaling the UI,
+		 * must be minimum '4' */
+	}
+	else if (alignment == RGN_ALIGN_TOP)
+		region_azone_edge_initialize(sa, ar, AE_BOTTOM_TO_TOPLEFT, is_fullscreen);
 	else if (alignment == RGN_ALIGN_BOTTOM)
-		region_azone_initialize(sa, ar, AE_TOP_TO_BOTTOMRIGHT, is_fullscreen);
+		region_azone_edge_initialize(sa, ar, AE_TOP_TO_BOTTOMRIGHT, is_fullscreen);
 	else if (alignment == RGN_ALIGN_RIGHT)
-		region_azone_initialize(sa, ar, AE_LEFT_TO_TOPRIGHT, is_fullscreen);
+		region_azone_edge_initialize(sa, ar, AE_LEFT_TO_TOPRIGHT, is_fullscreen);
 	else if (alignment == RGN_ALIGN_LEFT)
-		region_azone_initialize(sa, ar, AE_RIGHT_TO_TOPLEFT, is_fullscreen);
+		region_azone_edge_initialize(sa, ar, AE_RIGHT_TO_TOPLEFT, is_fullscreen);
+
+	if (is_fullscreen) {
+		fullscreen_azone_initialize(sa, ar);
+	}
+
+	region_azones_scrollbars_initialize(sa, ar);
 }
 
 /* dir is direction to check, not the splitting edge direction! */
@@ -1193,7 +1272,7 @@ static bool region_is_overlap(ScrArea *sa, ARegion *ar)
 	return 0;
 }
 
-static void region_rect_recursive(wmWindow *win, ScrArea *sa, ARegion *ar, rcti *remainder, rcti *overlap_remainder, int quad, bool add_azones)
+static void region_rect_recursive(wmWindow *win, ScrArea *sa, ARegion *ar, rcti *remainder, rcti *overlap_remainder, int quad)
 {
 	rcti *remainder_prev = remainder;
 	int prefsizex, prefsizey;
@@ -1421,30 +1500,8 @@ static void region_rect_recursive(wmWindow *win, ScrArea *sa, ARegion *ar, rcti
 	if (!ar->overlap) {
 		*overlap_remainder = *remainder;
 	}
-	
-	/* in end, add azones, where appropriate */
-	if (ar->regiontype == RGN_TYPE_HEADER && ar->winy + 6 > sa->winy) {
-		/* The logic for this is: when the header takes up the full area,
-		 * disallow hiding it to view the main window.
-		 *
-		 * Without this, you can drag down the file selectors header and hide it
-		 * by accident very easily (highly annoying!), the value 6 is arbitrary
-		 * but accounts for small common rounding problems when scaling the UI,
-		 * must be minimum '4' */
-	}
-	else if (add_azones) {
-		const bScreen *screen = WM_window_get_active_screen(win);
 
-		if (ELEM(screen->state, SCREENNORMAL, SCREENMAXIMIZED)) {
-			region_azone_add(sa, ar, alignment, false);
-		}
-		else {
-			region_azone_add(sa, ar, alignment, true);
-			fullscreen_azone_initialize(sa, ar);
-		}
-	}
-
-	region_rect_recursive(win, sa, ar->next, remainder, overlap_remainder, quad, add_azones);
+	region_rect_recursive(win, sa, ar->next, remainder, overlap_remainder, quad);
 }
 
 static void area_calc_totrct(ScrArea *sa, int window_size_x, int window_size_y)
@@ -1574,7 +1631,7 @@ void ED_area_update_region_sizes(wmWindowManager *wm, wmWindow *win, ScrArea *ar
 	/* region rect sizes */
 	rect = area->totrct;
 	overlap_rect = rect;
-	region_rect_recursive(win, area, area->regionbase.first, &rect, &overlap_rect, 0, false);
+	region_rect_recursive(win, area, area->regionbase.first, &rect, &overlap_rect, 0);
 
 	for (ARegion *ar = area->regionbase.first; ar; ar = ar->next) {
 		region_subwindow(ar);
@@ -1615,13 +1672,10 @@ void ED_area_initialize(wmWindowManager *wm, wmWindow *win, ScrArea *sa)
 	/* area sizes */
 	area_calc_totrct(sa, window_size_x, window_size_y);
 
-	/* clear all azones, add the area triange widgets */
-	area_azone_initialize(win, screen, sa);
-
 	/* region rect sizes */
 	rect = sa->totrct;
 	overlap_rect = rect;
-	region_rect_recursive(win, sa, sa->regionbase.first, &rect, &overlap_rect, 0, true);
+	region_rect_recursive(win, sa, sa->regionbase.first, &rect, &overlap_rect, 0);
 	sa->flag &= ~AREA_FLAG_REGION_SIZE_UPDATE;
 	
 	/* default area handlers */
@@ -1629,7 +1683,10 @@ void ED_area_initialize(wmWindowManager *wm, wmWindow *win, ScrArea *sa)
 	/* checks spacedata, adds own handlers */
 	if (sa->type->init)
 		sa->type->init(wm, sa);
-	
+
+	/* clear all azones, add the area triange widgets */
+	area_azone_initialize(win, screen, sa);
+
 	/* region windows, default and own handlers */
 	for (ar = sa->regionbase.first; ar; ar = ar->next) {
 		region_subwindow(ar);
@@ -1646,6 +1703,9 @@ void ED_area_initialize(wmWindowManager *wm, wmWindow *win, ScrArea *sa)
 			/* prevent uiblocks to run */
 			UI_blocklist_free(NULL, &ar->uiblocks);
 		}
+
+		/* Some AZones use View2D data which is only updated in region init, so call that first! */
+		region_azones_add(screen, sa, ar, ar->alignment & ~RGN_SPLIT_PREV);
 	}
 }