From 0c5b0b101e4d40fa7420b9ed2fdaeeae8bd03e2a Mon Sep 17 00:00:00 2001
From: Basile Burg <basile.b@gmx.com>
Date: Sun, 14 Aug 2022 14:33:57 +0200
Subject: [PATCH] editor, add the ecScrollCenteredDown and ecScrollCenteredUp
 actions

---
 CHANGELOG.md      |  3 +++
 src/u_synmemo.pas | 27 +++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fd480e5d..a77f6db4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,9 @@
 ## Enhancements
 
 - Editor, added the _Redo All_ action.
+- Editor, added the _ecScrollCenteredDown_ and _ecScrollCenteredUp_ actions. Only available using shortcuts and
+  binded by default to <kbd>UP/DOWN</kbd>+<kbd>CTRL</kbd>+<kbd>ALT</kbd>, they allow to maintain the caret at the center
+  of the text view while scrolling.
 
 ## Bugs fixed
 
diff --git a/src/u_synmemo.pas b/src/u_synmemo.pas
index 97f18bfb..3f6a3be6 100644
--- a/src/u_synmemo.pas
+++ b/src/u_synmemo.pas
@@ -382,6 +382,7 @@ type
     procedure setDscannerOptions(dsEnabled: boolean; dsDelay: integer);
     procedure centerCursor();
     procedure redoAll();
+    procedure scrollCentered(down: boolean);
     //
     property IdentifierMatchOptions: TIdentifierMatchOptions read fMatchOpts write setMatchOpts;
     property Identifier: string read fIdentifier;
@@ -483,6 +484,8 @@ const
   ecSelLeftWordEdge     = ecUserFirst + 32;
   ecSelRightWordEdge    = ecUserFirst + 33;
   ecRedoAll             = ecUserFirst + 34;
+  ecScrollCenteredUp    = ecUserFirst + 35;
+  ecScrollCenteredDown  = ecUserFirst + 36;
 var
   D2Syn: TSynD2Syn;     // used as model to set the options when no editor exists.
   TxtSyn: TSynTxtSyn;   // used as model to set the options when no editor exists.
@@ -1484,6 +1487,8 @@ begin
     AddKey(ecSmartWordLeft, 0, [], 0, []);
     AddKey(ecSmartWordRight, 0, [], 0, []);
     AddKey(ecRedoAll, 0, [], 0, []);
+    AddKey(ecScrollCenteredDown, VK_DOWN, [ssCtrl, ssAlt], 0, []);
+    AddKey(ecScrollCenteredUp, VK_UP, [ssCtrl, ssAlt], 0, []);
   end;
 end;
 
@@ -1524,6 +1529,8 @@ begin
     'ecSelLeftWordEdge':    begin Int := ecSelLeftWordEdge; exit(true); end;
     'ecSelRightWordEdge':   begin Int := ecSelRightWordEdge; exit(true); end;
     'ecRedoAll':            begin Int := ecRedoAll; exit(true); end;
+    'ecScrollCenteredUp':   begin Int := ecScrollCenteredUp; exit(true); end;
+    'ecScrollCenteredDown': begin Int := ecScrollCenteredDown; exit(true); end;
     else exit(false);
   end;
 end;
@@ -1565,6 +1572,8 @@ begin
     ecSelLeftWordEdge:    begin Ident := 'ecSelLeftWordEdge'; exit(true); end;
     ecSelRightWordEdge:   begin Ident := 'ecSelRightWordEdge'; exit(true); end;
     ecRedoAll:            begin Ident := 'ecRedoAll'; exit(true); end;
+    ecScrollCenteredUp:   begin Ident := 'ecScrollCenteredUp'; exit(true); end;
+    ecScrollCenteredDown: begin Ident := 'ecScrollCenteredDown'; exit(true); end;
     else exit(false);
   end;
 end;
@@ -1699,6 +1708,10 @@ begin
       gotoWordEdge(true);
     ecRedoAll:
       redoAll();
+    ecScrollCenteredUp:
+      scrollCentered(false);
+    ecScrollCenteredDown:
+      scrollCentered(true);
   end;
   if fOverrideColMode and not SelAvail then
   begin
@@ -2135,6 +2148,20 @@ begin
   TopView := NewTopLine;
 end;
 
+procedure TDexedMemo.scrollCentered(down: boolean);
+begin
+  centerCursor();
+  if down then
+  begin
+    ExecuteCommand(ecScrollDown, #0, nil);
+    CaretY := CaretY - 1;
+  end else
+  begin
+    ExecuteCommand(ecScrollUp, #0, nil);
+    CaretY := CaretY + 1;
+  end;
+end;
+
 procedure TDexedMemo.ShowPhobosDoc;
 var
   str: string;