From aabe4314d5116950b45b3d7e48afe482b6d4e4a7 Mon Sep 17 00:00:00 2001
From: wp_xyz <wp_xxyyzzz@gmx.net>
Date: Tue, 11 Jan 2022 12:07:20 +0100
Subject: [PATCH] TAChart: Fix missing minor ticks when an axis is inverted by
 means of a linear axis transform. Issue #39546.

(cherry picked from commit b8f2e92f039f04ed5f614c7b95ec971803498089)
---
 components/tachart/tachartaxis.pas | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/components/tachart/tachartaxis.pas b/components/tachart/tachartaxis.pas
index 92ba8b682c..30211e613a 100644
--- a/components/tachart/tachartaxis.pas
+++ b/components/tachart/tachartaxis.pas
@@ -574,6 +574,8 @@ procedure TChartAxis.Draw;
     j: Integer;
     minorMarks: TChartValueTextArray;
     m: TChartValueText;
+    isFlipped: Boolean;
+    trMin, trMax: Double;
   begin
     if IsNan(AMin) or (AMin = AMax) then exit;
     for j := 0 to Minors.Count - 1 do begin
@@ -582,10 +584,15 @@ procedure TChartAxis.Draw;
       with FHelper.Clone do
         try
           FAxis := Minors[j];
+          trMin := FAxisTransf(AMin);
+          trMax := FAxisTransf(AMax);
           // Only draw minor marks strictly inside the major mark interval.
-          FValueMin := Max(FAxisTransf(AMin), FValueMin);
-          FValueMax := Min(FAxisTransf(AMax), FValueMax);
-          if FValueMax <= FValueMin then
+          isFlipped := (AMin < AMax) and (trMin > trMax);
+          FValueMin := Max(trMin, FValueMin);
+          FValueMax := Min(trMax, FValueMax);
+          if (not isFlipped and (FValueMax <= FValueMin)) or 
+             (isFlipped and (FValueMax >= FValueMin))
+          then
             continue;
           ExpandRange(FValueMin, FValueMax, -EPS);
           FClipRangeDelta := 1;