From d9239872c71d117f78ce6c109cd9ab42e2d80c6b Mon Sep 17 00:00:00 2001
From: David Robillard <d@drobilla.net>
Date: Sun, 3 Nov 2019 19:02:38 +0100
Subject: X11: Only merge expose events if they intersect

Towards actual fine-grained exposure.  This uses the previous behaviour if
expose events intersect to reduce redundant drawing, but dispatches expose
events immediately (after flushing and pending configure events) if they don't
to support partial redraws.
---
 pugl/detail/x11.c | 58 ++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/pugl/detail/x11.c b/pugl/detail/x11.c
index e576b49..871c16b 100644
--- a/pugl/detail/x11.c
+++ b/pugl/detail/x11.c
@@ -586,8 +586,17 @@ puglWaitForEvent(PuglView* view)
 	return PUGL_SUCCESS;
 }
 
+static bool
+exposeEventsIntersect(const PuglEvent* a, const PuglEvent* b)
+{
+	return !(a->expose.x + a->expose.width < b->expose.x ||
+	         b->expose.x + b->expose.width < a->expose.x ||
+	         a->expose.y + a->expose.height < b->expose.y ||
+	         b->expose.y + b->expose.height < a->expose.y);
+}
+
 static void
-merge_expose_events(PuglEvent* dst, const PuglEvent* src)
+mergeExposeEvents(PuglEvent* dst, const PuglEvent* src)
 {
 	if (!dst->type) {
 		*dst = *src;
@@ -615,6 +624,26 @@ sendRedisplayEvent(PuglView* view)
 	XSendEvent(view->impl->display, view->impl->win, False, 0, (XEvent*)&ev);
 }
 
+static void
+flushPendingConfigure(PuglView* view)
+{
+	PuglEvent* const configure = &view->impl->pendingConfigure;
+
+	if (configure->type) {
+		view->frame.x      = configure->configure.x;
+		view->frame.y      = configure->configure.y;
+		view->frame.width  = configure->configure.width;
+		view->frame.height = configure->configure.height;
+
+		view->backend->resize(view,
+		                      (int)view->frame.width,
+		                      (int)view->frame.height);
+
+		view->eventFunc(view, configure);
+		configure->type = 0;
+	}
+}
+
 PUGL_API PuglStatus
 puglDispatchEvents(PuglWorld* world)
 {
@@ -712,7 +741,20 @@ puglDispatchEvents(PuglWorld* world)
 
 		if (event.type == PUGL_EXPOSE) {
 			// Expand expose event to be dispatched after loop
-			merge_expose_events(&view->impl->pendingExpose, &event);
+			if (view->impl->pendingConfigure.type ||
+			    (view->impl->pendingExpose.type &&
+			     exposeEventsIntersect(&view->impl->pendingExpose, &event))) {
+				mergeExposeEvents(&view->impl->pendingExpose, &event);
+			} else {
+				if (view->impl->pendingExpose.type) {
+					puglEnterContext(view, true);
+					flushPendingConfigure(view);
+					puglDispatchEvent(view, &view->impl->pendingExpose);
+					puglLeaveContext(view, true);
+				}
+
+				view->impl->pendingExpose = event;
+			}
 		} else if (event.type == PUGL_CONFIGURE) {
 			// Expand configure event to be dispatched after loop
 			view->impl->pendingConfigure = event;
@@ -732,17 +774,7 @@ puglDispatchEvents(PuglWorld* world)
 			const bool mustExpose = expose->type && expose->expose.count == 0;
 			puglEnterContext(view, mustExpose);
 
-			if (configure->type) {
-				view->frame.x      = configure->configure.x;
-				view->frame.y      = configure->configure.y;
-				view->frame.width  = configure->configure.width;
-				view->frame.height = configure->configure.height;
-
-				view->backend->resize(view,
-				                      (int)view->frame.width,
-				                      (int)view->frame.height);
-				view->eventFunc(view, &view->impl->pendingConfigure);
-			}
+			flushPendingConfigure(view);
 
 			if (mustExpose) {
 				view->eventFunc(view, &view->impl->pendingExpose);
-- 
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