[PATCH] Avoid plotting when ProfileWidget2::plotDive is called speciously.

[K. "pestophagous" Heller]

One indirect call site of plotDive, MainTab::acceptChanges, can
trigger a replot several times during one pass through
acceptChanges.  Avoiding some of the replots is both an
optimization and a small bug-fix.  A replot could happen when
displayed_dive is presently zeroed-out, which made no sense.

Signed-off-by: K. Heller <pestophagous at gmail.com>
---
 dive.h                           |  5 +++++
 qt-ui/profile/profilewidget2.cpp | 17 +++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/dive.h b/dive.h
index cef1106..cdb05ee 100644
--- a/dive.h
+++ b/dive.h
@@ -562,6 +562,11 @@ static inline struct divecomputer *get_dive_dc(struct dive *dive, int nr)
 	return dc;
 }
 
+static inline bool dive_has_meaningful_state(struct dive *dive)
+{
+	return dive && (dive->id > 0);
+}
+
 extern timestamp_t dive_endtime(const struct dive *dive);
 
 extern void make_first_dc(void);
diff --git a/qt-ui/profile/profilewidget2.cpp b/qt-ui/profile/profilewidget2.cpp
index 3ccd1bb..2fa8f88 100644
--- a/qt-ui/profile/profilewidget2.cpp
+++ b/qt-ui/profile/profilewidget2.cpp
@@ -489,17 +489,22 @@ void ProfileWidget2::resetZoom()
 // Currently just one dive, but the plan is to enable All of the selected dives.
 void ProfileWidget2::plotDive(struct dive *d, bool force)
 {
+	if (!d) {
+		if (selected_dive == -1)
+			return;
+		d = current_dive; // display the current dive
+	}
+
+	// check for 'meaningful' dive. saves spurious repaint(s) while carrying out
+	// updates due to clicking 'Apply changes' (or similar actions)
+	if (!dive_has_meaningful_state(d))
+		return;
+
 	static bool firstCall = true;
 	QTime measureDuration; // let's measure how long this takes us (maybe we'll turn of TTL calculation later
 	measureDuration.start();
 
 	if (currentState != ADD && currentState != PLAN) {
-		if (!d) {
-			if (selected_dive == -1)
-				return;
-			d = current_dive; // display the current dive
-		}
-
 		// No need to do this again if we are already showing the same dive
 		// computer of the same dive, so we check the unique id of the dive
 		// and the selected dive computer number against the ones we are
-- 
2.5.0