From 8cd4a9079a3a4343c2e2fa34d41901569541ec98 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 1 Mar 2025 12:27:50 -0500
Subject: reformat displacement when unit changes

---
 main.c   |  6 +++++-
 ui.c     | 15 +++++++++++++++
 ui.h     |  1 +
 widget.c |  8 ++++++++
 widget.h |  2 ++
 5 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/main.c b/main.c
index 2710bfa..9783fd1 100644
--- a/main.c
+++ b/main.c
@@ -157,7 +157,11 @@ displacement_row(mu_Context *ctx, UI *ui) {
 		set_displacement(ui);
 		set_all_volume_flow_rate(ui);
 	}
-	w_select(ctx, &ui->displacement_unit);
+	if (w_select(ctx, &ui->displacement_unit) & MU_RES_CHANGE) {
+		printf("displacement unit changed\n");
+		fflush(stdout);
+		set_displacement_unit(ui);
+	}
 }
 
 static void
diff --git a/ui.c b/ui.c
index 3fca1ae..216a10b 100644
--- a/ui.c
+++ b/ui.c
@@ -16,6 +16,9 @@ static const char *const volume_units[] = {"cc", "l", "ci"};
 static const VolumeMaker volume_makers[nelem(volume_units)] = {
 	cubic_centimetre, litre, cubic_inch,
 };
+static const VolumeReader volume_readers[nelem(volume_units)] = {
+	as_cubic_centimetre, as_litre, as_cubic_inch,
+};
 
 static const char *const pressure_units[] = {"mbar", "kPa", "bar", "psi"};
 static const PressureMaker pressure_makers[nelem(pressure_units)] = {
@@ -65,6 +68,18 @@ set_displacement(UI *ui) {
 	}
 }
 
+void
+set_displacement_unit(UI *ui) {
+	VolumeMaker maker;
+	Volume disp;
+	VolumeReader reader;
+
+	maker = volume_makers[ui->displacement_unit.oldidx];
+	disp = maker(ui->displacement.value);
+	reader = volume_readers[ui->displacement_unit.idx];
+	w_set_field(&ui->displacement, reader(disp));
+}
+
 void
 set_map(UI *ui, int idx) {
 	int unit_idx;
diff --git a/ui.h b/ui.h
index f1c4137..1238325 100644
--- a/ui.h
+++ b/ui.h
@@ -21,6 +21,7 @@ typedef struct {
 
 void init_ui(UI *ui);
 void set_displacement(UI *ui);
+void set_displacement_unit(UI* ui);
 void set_map(UI *ui, int idx);
 void set_ve(UI *ui, int idx);
 void set_volume_flow_rate(UI *ui, int idx);
diff --git a/widget.c b/widget.c
index cc9d894..46c7b07 100644
--- a/widget.c
+++ b/widget.c
@@ -32,11 +32,18 @@ w_field(mu_Context *ctx, w_Field *f) {
 	return changed ? MU_RES_CHANGE : 0;
 }
 
+void
+w_set_field(w_Field *f, double val) {
+	f->value = val;
+	snprintf(f->buf, sizeof(f->buf), "%lf", val);
+}
+
 void
 w_init_select(w_Select *select, int nopts, const char *const opts[]) {
 	select->nopts = nopts;
 	select->opts = opts;
 	select->idx = 0;
+	select->oldidx = 0;
 	select ->active = 0;
 }
 
@@ -65,6 +72,7 @@ w_select(mu_Context *ctx, w_Select *select) {
 		res = MU_RES_ACTIVE;
 		for (i = 0; i < select->nopts; i++) {
 			if (mu_button(ctx, select->opts[i])) {
+				select->oldidx = select->idx;
 				select->idx = i;
 				res |= MU_RES_CHANGE;
 				select->active = 0;
diff --git a/widget.h b/widget.h
index 546ed1c..bc6a375 100644
--- a/widget.h
+++ b/widget.h
@@ -9,12 +9,14 @@ typedef struct {
 
 void w_init_field(w_Field *f);
 int w_field(mu_Context *ctx, w_Field *f);
+void w_set_field(w_Field *f, double v);
 
 
 typedef struct {
 	int nopts;
 	const char *const *opts;
 	int idx; /* index of selected option. */
+	int oldidx; /* index of previously selected option. */
 	int active;
 } w_Select;
 
-- 
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