Indicate vertical velocity through color

So far Linus has hated all of my attempts to visualize vertical velocity
through color. This time I'm trying something dramatically new: there is
no PURPLE involved. Maybe that will convince him of the value.

We simply calculate the vertical velocity for the current plot segment
(last sample point to this sample point - in this version even without
divisions by zero) and assign a label based on the rate of change. These
labels are translated through a predefined table into colors:

Dark green is +/- 5ft/min (stable)
Light green is descents up to 30ft/min and ascents up to 15ft/min
Yellow is descents up to 60ft/min and ascents up to 30ft/min
Orange is descents up to 100ft/min and ascents up to 60ft/min
Red is outside of those ranges - you are most likely in danger

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

1 files changed, 79 insertions, 12 deletions

diff --git a/profile.c b/profile.c
index b2679c5d5..1fa989dd1 100644
--- a/profile.c
+++ b/profile.c
@@ -10,7 +10,8 @@
 
 int selected_dive = 0;
 
-/* Plot info with smoothing and one-, two- and three-minute minimums and maximums */
+/* Plot info with smoothing, velocity indication
+ * and one-, two- and three-minute minimums and maximums */
 struct plot_info {
 	int nr;
 	int maxtime;
@@ -23,11 +24,23 @@ struct plot_info {
 		/* Depth info */
 		int val;
 		int smoothed;
+		enum { STABLE, SLOW, MODERATE, FAST, CRAZY } velocity;
 		struct plot_data *min[3];
 		struct plot_data *max[3];
 		int avg[3];
 	} entry[];
 };
+
+/* convert velocity to colors */
+typedef struct { double r, g, b; } rgb_t;
+static const rgb_t rgb[] = {
+	[STABLE]   = {0.0, 0.4, 0.0},
+	[SLOW]     = {0.4, 0.8, 0.0},
+	[MODERATE] = {0.8, 0.8, 0.0},
+	[FAST]     = {0.8, 0.5, 0.0},
+	[CRAZY]    = {1.0, 0.0, 0.0},
+};
+
 #define plot_info_size(nr) (sizeof(struct plot_info) + (nr)*sizeof(struct plot_data))
 
 /* Scale to 0,0 -> maxx,maxy */
@@ -70,6 +83,8 @@ static void set_source_rgb(struct graphics_context *gc, double r, double g, doub
  * current dive. However, we don't scale past less than
  * 30 minutes or 90 ft, just so that small dives show
  * up as such.
+ * we also need to add 180 seconds at the end so the min/max
+ * plots correctly
  */
 static int get_maxtime(struct plot_info *pi)
 {
@@ -234,7 +249,9 @@ static void plot_depth_profile(struct graphics_context *gc, struct plot_info *pi
 {
 	int i;
 	cairo_t *cr = gc->cr;
-	int begins, sec, depth;
+	int ends, sec, depth;
+	int *secs;
+	int *depths;
 	struct plot_data *entry;
 	int maxtime, maxdepth, marker;
 
@@ -278,24 +295,47 @@ static void plot_depth_profile(struct graphics_context *gc, struct plot_info *pi
 
 	entry = pi->entry;
 	set_source_rgba(gc, 1, 0.2, 0.2, 0.80);
-	begins = entry->sec;
-	move_to(gc, entry->sec, entry->val);
+	secs = (int *) malloc(sizeof(int) * pi->nr);
+	depths = (int *) malloc(sizeof(int) * pi->nr);
+	secs[0] = entry->sec;
+	depths[0] = entry->val;
 	for (i = 1; i < pi->nr; i++) {
 		entry++;
 		sec = entry->sec;
-		if (sec <= maxtime) {
+		if (sec <= maxtime || entry->val > 0) {
+			/* we want to draw the segments in different colors
+			 * representing the vertical velocity, so we need to
+			 * chop this into short segments */
+			rgb_t color = rgb[entry->velocity];
 			depth = entry->val;
+			set_source_rgb(gc, color.r, color.g, color.b);
+			move_to(gc, secs[i-1], depths[i-1]);
 			line_to(gc, sec, depth);
+			cairo_stroke(cr);
+			ends = i;
 		}
+		secs[i] = sec;
+		depths[i] = depth;
 	}
+	move_to(gc, secs[ends], depths[ends]);
 	gc->topy = 0; gc->bottomy = 1.0;
-	line_to(gc, MIN(sec,maxtime), 0);
-	line_to(gc, begins, 0);
+	line_to(gc, secs[ends], 0);
+	line_to(gc, secs[0], 0);
 	cairo_close_path(cr);
-	set_source_rgba(gc, 1, 0.2, 0.2, 0.20);
-	cairo_fill_preserve(cr);
 	set_source_rgba(gc, 1, 0.2, 0.2, 0.80);
 	cairo_stroke(cr);
+	/* now do it again for the neat fill */
+	gc->topy = 0; gc->bottomy = maxdepth;
+	set_source_rgba(gc, 1, 0.2, 0.2, 0.20);
+	move_to(gc, secs[0], depths[0]);
+	for (i = 1; i <= ends; i++) {
+		line_to(gc, secs[i],depths[i]);
+	}
+	gc->topy = 0; gc->bottomy = 1.0;
+	line_to(gc, secs[ends], 0);
+	line_to(gc, secs[0], 0);
+	cairo_close_path(gc->cr);
+	cairo_fill(gc->cr);
 }
 
 static int setup_temperature_limits(struct graphics_context *gc, struct plot_info *pi)
@@ -611,12 +651,39 @@ static struct plot_info *analyze_plot_info(struct plot_info *pi)
 	}
 
 	/* Smoothing function: 5-point triangular smooth */
-	for (i = 2; i < nr-2; i++) {
+	for (i = 2; i < nr-1; i++) {
 		struct plot_data *entry = pi->entry+i;
 		int val;
 
-		val = entry[-2].val + 2*entry[-1].val + 3*entry[0].val + 2*entry[1].val + entry[2].val;
-		entry->smoothed = (val+4) / 9;
+		if (i < nr-2) {
+			val = entry[-2].val + 2*entry[-1].val + 3*entry[0].val + 2*entry[1].val + entry[2].val;
+			entry->smoothed = (val+4) / 9;
+		}
+		/* vertical velocity in mm/sec */
+		if (entry[0].sec - entry[-1].sec) {
+			val = (entry[0].val - entry[-1].val) / (entry[0].sec - entry[-1].sec);
+			if (val < -304) /* ascent faster than -60ft/min */
+				entry->velocity = CRAZY;
+			else if (val < -152) /* above -30ft/min */
+				entry->velocity = FAST;
+			else if (val < -76) /* -15ft/min */
+				entry->velocity = MODERATE;
+			else if (val < -25) /* -5ft/min */
+				entry->velocity = SLOW;
+			else if (val < 25) /* very hard to find data, but it appears that the recommendations
+					      for descent are usually about 2x ascent rate; still, we want 
+					      stable to mean stable */
+				entry->velocity = STABLE;
+			else if (val < 152) /* between 5 and 30ft/min is considered slow */
+				entry->velocity = SLOW;
+			else if (val < 304) /* up to 60ft/min is moderate */
+				entry->velocity = MODERATE;
+			else if (val < 507) /* up to 100ft/min is fast */
+				entry->velocity = FAST;
+			else /* more than that is just crazy - you'll blow your ears out */
+				entry->velocity = CRAZY;
+		} else
+			entry->velocity = STABLE;
 	}
 
 	/* One-, two- and three-minute minmax data */