From c06c71b091b576a9f055abee87cf3cb297549717 Mon Sep 17 00:00:00 2001
From: Martin Preuss <martin@aquamaniac.de>
Date: Mon, 5 Jan 2026 00:43:47 +0100
Subject: [PATCH] added AQDG_Data_DifferenceY()

---
 src/lib/aqdiagram/data/diff.c | 30 ++++++++++++++++++++++++++++++
 src/lib/aqdiagram/data/diff.h |  3 +++
 2 files changed, 33 insertions(+)

diff --git a/src/lib/aqdiagram/data/diff.c b/src/lib/aqdiagram/data/diff.c
index 99f158a..123117a 100644
--- a/src/lib/aqdiagram/data/diff.c
+++ b/src/lib/aqdiagram/data/diff.c
@@ -84,3 +84,33 @@ double AQDG_Data_GetAbsMinDiffY(const AQDG_GRAPH_DATAPAIR_LIST *dpList)
 
 
 
+AQDG_GRAPH_DATAPAIR_LIST *AQDG_Data_DifferenceY(const AQDG_GRAPH_DATAPAIR_LIST *dpList)
+{
+  if (dpList && AQDG_Graph_DataPair_List_GetCount(dpList)) {
+    AQDG_GRAPH_DATAPAIR_LIST *newList;
+    const AQDG_GRAPH_DATAPAIR *dp;
+
+    newList=AQDG_Graph_DataPair_List_new();
+    dp=AQDG_Graph_DataPair_List_First(dpList);
+    if (dp) {
+      double lastValue;
+
+      lastValue=AQDG_Graph_DataPair_GetValueY(dp);
+      while(dp) {
+	AQDG_GRAPH_DATAPAIR *newDp;
+	double v;
+
+	v=AQDG_Graph_DataPair_GetValueY(dp);
+	newDp=AQDG_Graph_DataPair_dup(dp);
+	AQDG_Graph_DataPair_SetValueY(newDp, v-lastValue);
+	AQDG_Graph_DataPair_List_Add(newDp, newList);
+	lastValue=v;
+	dp=AQDG_Graph_DataPair_List_Next(dp);
+      }
+      return newList;
+    }
+  }
+  return NULL;
+}
+
+
diff --git a/src/lib/aqdiagram/data/diff.h b/src/lib/aqdiagram/data/diff.h
index 9e0bd76..bea49b2 100644
--- a/src/lib/aqdiagram/data/diff.h
+++ b/src/lib/aqdiagram/data/diff.h
@@ -20,6 +20,9 @@ extern "C" {
 
 
 AQDG_API double AQDG_Data_GetAbsMinDiffX(const AQDG_GRAPH_DATAPAIR_LIST *dpList);
+AQDG_API double AQDG_Data_GetAbsMinDiffY(const AQDG_GRAPH_DATAPAIR_LIST *dpList);
+
+AQDG_API AQDG_GRAPH_DATAPAIR_LIST *AQDG_Data_DifferenceY(const AQDG_GRAPH_DATAPAIR_LIST *dpList);