[PATCH] Add support for libdivecomputer using DC_SAMPLE_GASMIX

[Linus Torvalds]

From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Tue, 3 Jan 2017 15:18:03 -0800
Subject: [PATCH] Add support for libdivecomputer using DC_SAMPLE_GASMIX

New libdivecomputer versions use DC_SAMPLE_GASMIX to indicate a gas
change (which contains the cylinder index we're changing to) rather than
SAMPLE_EVENT_GASCHANGE*.

Unlike the old GASCHANGE model, and despite the name, DC_SAMPLE_GASMIX
does not actually say what the mix is, it only specifies a cylinder
index.  We had already extended SAMPLE_EVENT_GASCHANGE2 to have the
cylinder index in the otherwise unused "flags" field, so this is not all
that different from what we used to do.

And subsurface internally already had the logic that "if we know what
the cylinder index is, take the gas mix from the cylinder data", so
we've already been able to transparently use _either_ the actual gas mix
or the cylinder index to show the event.

But we do want to make it an event rather than some sample data, because
we want to show it as such in the profile.  But because we are happy
with just the cylinder index, we'll just translate the DC_SAMPLE_GASMIX
thing to the SAMPLE_EVENT_GASCHANGE2 event, and nothing really changes
for subsurface.

libdivecomputer has made other changes, like indicating the initial
cylinder index with an early DC_SAMPLE_GASMIX report, but we've seen
that before too (in the form of early SAMPLE_EVENT_GASCHANGE events), so
that doesn't really end up changing anything for us either.

HOWEVER, one thing that is worth noticing: do *not* apply this patch and
then use an old libdivecomputer library that sends both the
DC_SAMPLE_GASMIX samples _and_ the deprecated SAMPLE_EVENT_GASCHANGE
events.  It will all *work*, but since subsurface will take either,
you'll then get duplicate gas mix events.

It's not like that is in any way fatal, but it might be a bit confusing.

Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
---

NOTE NOTE NOTE!

Note hat last HOWEVER in the commit message above. This patch is meant to 
go together with the libdivecomputer update that removes the deprecated 
gas change events (commit d0dbd1f6fd95: "Remove the deprecated gas 
change events") from upstream libdivecomputer. 

I have a merged libdivecomputer tree at

    git://github.com/torvalds/libdivecomputer.git Subsurface-branch

that goes along with this patch. If you use the previous subsurface 
branch and have ENABLE_DEPRECATED on (which it is by default), you'll end 
up with duplicate gas change events.

 core/libdivecomputer.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/core/libdivecomputer.c b/core/libdivecomputer.c
index 502cc042..d65e6513 100644
--- a/core/libdivecomputer.c
+++ b/core/libdivecomputer.c
@@ -271,6 +271,14 @@ static void handle_event(struct divecomputer *dc, struct sample *sample, dc_samp
 		current_gas_index = ev->gas.index;
 }
 
+static void handle_gasmix(struct divecomputer *dc, struct sample *sample, int idx)
+{
+	if (idx < 0 || idx >= MAX_CYLINDERS)
+		return;
+	add_event(dc, sample->time.seconds, SAMPLE_EVENT_GASCHANGE2, idx+1, 0, "gaschange");
+	current_gas_index = idx;
+}
+
 void
 sample_cb(dc_sample_type_t type, dc_sample_value_t value, void *userdata)
 {
@@ -322,6 +330,9 @@ sample_cb(dc_sample_type_t type, dc_sample_value_t value, void *userdata)
 			break;
 		sample->pressure[value.pressure.tank].mbar = rint(value.pressure.value * 1000);
 		break;
+	case DC_SAMPLE_GASMIX:
+		handle_gasmix(dc, sample, value.gasmix);
+		break;
 	case DC_SAMPLE_TEMPERATURE:
 		sample->temperature.mkelvin = C_to_mkelvin(value.temperature);
 		break;