From 4eef1f1bff3c1494eb9a9ddd96beea135ea140d1 Mon Sep 17 00:00:00 2001
From: Philippe Teuwen <phil@teuwen.org>
Date: Mon, 5 Oct 2020 10:07:16 +0200
Subject: [PATCH] Trim: GraphPixelsPerPoint mush remain a power of zoom_offset

---
 client/src/proxguiqt.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/client/src/proxguiqt.cpp b/client/src/proxguiqt.cpp
index 0e791d77a..15b96a16a 100644
--- a/client/src/proxguiqt.cpp
+++ b/client/src/proxguiqt.cpp
@@ -689,13 +689,19 @@ void Plot::Move(int offset) {
 
 void Plot::Trim(void) {
     uint32_t lref, rref;
+    const double zoom_offset = 1.148698354997035; // 2**(1/5)
     if ((CursorAPos == 0) || (CursorBPos == 0)) { // if we don't have both cursors set
         lref = GraphStart;
         rref = GraphStop;
     } else {
         lref = CursorAPos < CursorBPos ? CursorAPos : CursorBPos;
         rref = CursorAPos < CursorBPos ? CursorBPos : CursorAPos;
-        GraphPixelsPerPoint = GraphPixelsPerPoint * (GraphStop - GraphStart) / (rref - lref);
+        // GraphPixelsPerPoint mush remain a power of zoom_offset
+        double GPPPtarget = GraphPixelsPerPoint * (GraphStop - GraphStart) / (rref - lref);
+        while (GraphPixelsPerPoint < GPPPtarget) {
+            GraphPixelsPerPoint *= zoom_offset;
+        }
+        GraphPixelsPerPoint /= zoom_offset;
         CursorAPos -= lref;
         CursorBPos -= lref;
     }