delphi - Flickering when TPageControl has many tabs -

my problem have tpagecontrol contains dynamically created number of tabs each containing single (alclient) tmemo. when number of tabs exceeds width of control , scroll arrows appear on tab header, (well large number) of controls start flicker lot. flicker occurs when pagecontrol visible once scroll out of view of tpagecontrol stops. when pagecontrol resized scroll arrows no longer required see of tabs flickering stops.

i'm confident problem caused scroll arrows causing painting occur because when set tpagecontrol.multiline true there no flickering. ideally wouldn't want use multiline tabs , hope can provide solution.

information form layout

i have (personal details) form contains number of tspeedbuttons, tlabels, tedits, timage , on. many of these elements inside of tscrollbox , grouped sections using tpanels. panels set altop in scrollbox , have autosize set true height never changes.

i have tried setting controls have doublebuffered set true possible , parentbackground/color = false sadly nothing works.

i had flickering issues before adding pagecontrols , using david's quick hack answer here tlabel , tgroupbox captions flicker on resize able improve flickering when resizing form. extending tlabel , removing background clearing paint procedure, recommended somewhere else, able 99% remove labels flickering when scrolling scrollbox have new flickering problem.

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here link stripped down version of form flickering occurring flickering example

personnel.detailsform.pas

unit personnel.detailsform;  interface  uses     winapi.windows, winapi.messages, system.sysutils, system.variants, system.classes, vcl.graphics,     vcl.controls, vcl.forms, vcl.dialogs, vcl.extctrls, system.actions,     vcl.actnlist, vcl.buttons, vcl.stdctrls, vcl.comctrls, vcl.winxctrls, vcl.imaging.jpeg;  type     tpersonneldetailsform = class(tform)         scrollbox_content: tscrollbox;         panel_addressdetails: tpanel;         gpanel_address: tgridpanel;         edit_homemobilephone: tedit;         edit_hometown: tedit;         edit_homestreet: tedit;         edit_homephone: tedit;         lbl_homestreet: tlabel;         lbl_homephone: tlabel;         lbl_mobilephone: tlabel;         lbl_hometown: tlabel;         edit_homestate: tedit;         edit_homeemail: tedit;         edit_homecountry: tedit;         edit_homefax: tedit;         lbl_homestate: tlabel;         lbl_fax: tlabel;         lbl_email: tlabel;         lbl_homecountry: tlabel;         edit_homepostcode: tedit;         lbl_homepostcode: tlabel;         panel_homeaddresstitle: tpanel;         panel_generalnotesdetails: tpanel;         gpanel_generalnotesdetails_: tgridpanel;         pagecontrol_generalnotes: tpagecontrol;         procedure formclose(sender: tobject; var action: tcloseaction);         procedure formshow(sender: tobject);         procedure formmousewheel(sender: tobject; shift: tshiftstate; wheeldelta: integer; mousepos: tpoint; var handled: boolean);     private         { private declarations }     public         { public declarations }     end;  var     personneldetailsform: tpersonneldetailsform;  implementation  {$r *.dfm}  uses     system.math,     system.dateutils,     system.threading,     system.regularexpressions,     system.strutils,     system.contnrs,     system.uitypes,     system.types,      winapi.shellapi,      vcl.extdlgs;  procedure enablecomposited(wincontrol: twincontrol); var     i: integer;     newexstyle: dword; begin     newexstyle := getwindowlong(wincontrol.handle, gwl_exstyle) or ws_ex_composited;     setwindowlong(wincontrol.handle, gwl_exstyle, newexstyle);      := 0 wincontrol.controlcount - 1         if wincontrol.controls[i] twincontrol             enablecomposited(twincontrol(wincontrol.controls[i])); end;  procedure tpersonneldetailsform.formclose(sender: tobject; var action: tcloseaction); begin     // close form , make sure frees     action := cafree; // should allow free on close     self.release; // sends release message backup end;  procedure tpersonneldetailsform.formmousewheel(sender: tobject; shift: tshiftstate; wheeldelta: integer; mousepos: tpoint;     var handled: boolean); var     ltopleft, ltopright, lbottomleft, lbottomright: integer;     lpoint: tpoint; begin     handled := true;      // first have position of control on screen     // mousepos coordinates based on screen positions.     lpoint := self.scrollbox_content.clienttoscreen(point(0, 0));     ltopleft := lpoint.x;     ltopright := ltopleft + self.scrollbox_content.width;     lbottomleft := lpoint.y;     lbottomright := lbottomleft + self.scrollbox_content.width;      if (mousepos.x >= ltopleft) , (mousepos.x <= ltopright) , (mousepos.y >= lbottomleft) , (mousepos.y <= lbottomright)     begin         // if mouse inside scrollbox coordinates,         // scroll setting .vertscrollbar.position.         self.scrollbox_content.vertscrollbar.position := self.scrollbox_content.vertscrollbar.position - wheeldelta;         handled := true;     end;      if findvclwindow(mousepos) tcombobox         handled := true; end;  procedure tpersonneldetailsform.formshow(sender: tobject); var     memo: tmemo;     tabsheet: ttabsheet;     ii: integer; begin     ii := 0 7     begin         memo := tmemo.create(self);         memo.align := talign.alclient;         memo.readonly := true;         memo.scrollbars := tscrollstyle.ssvertical;         memo.parentcolor := false;          tabsheet := ttabsheet.create(self);         tabsheet.insertcontrol(memo);         tabsheet.pagecontrol := self.pagecontrol_generalnotes;         tabsheet.caption := 'a new tabsheet ' + inttostr(ii);         tabsheet.tag := ii;          memo.text := 'a new memo ' + inttostr(ii);     end;      enablecomposited(self);      self.scrollbox_content.scrollinview(self.panel_addressdetails);     self.invalidate; end;  end.    

personnel.detailsform.dfm

object personneldetailsform: tpersonneldetailsform   left = 0   top = 0   caption = 'personnel details form'   clientheight = 371   clientwidth = 800   color = clbtnface   doublebuffered = true   font.charset = default_charset   font.color = clwindowtext   font.height = -13   font.name = 'segoe ui'   font.style = []   oldcreateorder = false   onclose = formclose   onmousewheel = formmousewheel   onshow = formshow   pixelsperinch = 96   textheight = 17   object scrollbox_content: tscrollbox     left = 0     top = 0     width = 800     height = 371     vertscrollbar.smooth = true     vertscrollbar.tracking = true     align = alclient     taborder = 0     object panel_addressdetails: tpanel       tag = 101       left = 0       top = 0       width = 796       height = 174       align = altop       padding.left = 5       padding.top = 5       padding.right = 5       padding.bottom = 5       parentbackground = false       taborder = 0       object gpanel_address: tgridpanel         left = 6         top = 30         width = 784         height = 138         align = alclient         bevelouter = bvnone         columncollection = <           item             sizestyle = ssabsolute             value = 105.000000000000000000           end           item             value = 50.000762951094850000           end           item             sizestyle = ssabsolute             value = 105.000000000000000000           end           item             value = 49.999237048905160000           end>         controlcollection = <           item             column = 3             control = edit_homemobilephone             row = 1           end           item             column = 1             control = edit_hometown             row = 1           end           item             column = 1             control = edit_homestreet             row = 0           end           item             column = 3             control = edit_homephone             row = 0           end           item             column = 0             control = lbl_homestreet             row = 0           end           item             column = 2             control = lbl_homephone             row = 0           end           item             column = 2             control = lbl_mobilephone             row = 1           end           item             column = 0             control = lbl_hometown             row = 1           end           item             column = 1             control = edit_homestate             row = 2           end           item             column = 3             control = edit_homeemail             row = 2           end           item             column = 1             control = edit_homecountry             row = 3           end           item             column = 3             control = edit_homefax             row = 3           end           item             column = 0             control = lbl_homestate             row = 2           end           item             column = 2             control = lbl_fax             row = 3           end           item             column = 2             control = lbl_email             row = 2           end           item             column = 0             control = lbl_homecountry             row = 3           end           item             column = 1             control = edit_homepostcode             row = 4           end           item             column = 0             control = lbl_homepostcode             row = 4           end>         padding.left = 1         padding.top = 1         padding.right = 1         padding.bottom = 1         rowcollection = <           item             sizestyle = ssabsolute             value = 27.000000000000000000           end           item             sizestyle = ssabsolute             value = 27.000000000000000000           end           item             sizestyle = ssabsolute             value = 27.000000000000000000           end           item             sizestyle = ssabsolute             value = 27.000000000000000000           end           item             sizestyle = ssabsolute             value = 27.000000000000000000           end>         taborder = 0         object edit_homemobilephone: tedit           left = 498           top = 29           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 6           text = 'mobile phone'         end         object edit_hometown: tedit           left = 107           top = 29           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 1           text = 'home town'         end         object edit_homestreet: tedit           left = 107           top = 2           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 0           text = 'home street'         end         object edit_homephone: tedit           left = 498           top = 2           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 5           text = 'home phone'         end         object lbl_homestreet: tlabel           left = 2           top = 2           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'street: '           color = clbtnface           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentcolor = false           parentfont = false           transparent = true           layout = tlcenter           explicitleft = 61           explicitwidth = 44           explicitheight = 17         end         object lbl_homephone: tlabel           left = 393           top = 2           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'home phone: '           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentfont = false           layout = tlcenter           explicitleft = 408           explicitwidth = 88           explicitheight = 17         end         object lbl_mobilephone: tlabel           left = 393           top = 29           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'mobile phone: '           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentfont = false           layout = tlcenter           explicitleft = 402           explicitwidth = 94           explicitheight = 17         end         object lbl_hometown: tlabel           left = 2           top = 29           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'town: '           color = clbtnface           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentcolor = false           parentfont = false           transparent = true           layout = tlcenter           explicitleft = 64           explicitwidth = 41           explicitheight = 17         end         object edit_homestate: tedit           left = 107           top = 56           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 2           text = 'home state'         end         object edit_homeemail: tedit           left = 498           top = 56           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 7           text = 'home email'         end         object edit_homecountry: tedit           left = 107           top = 83           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 3           text = 'home country'         end         object edit_homefax: tedit           left = 498           top = 83           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 8           text = 'home fax'         end         object lbl_homestate: tlabel           left = 2           top = 56           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'state: '           color = clbtnface           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentcolor = false           parentfont = false           transparent = true           layout = tlcenter           explicitleft = 66           explicitwidth = 39           explicitheight = 17         end         object lbl_fax: tlabel           left = 393           top = 83           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'fax: '           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentfont = false           layout = tlcenter           explicitleft = 467           explicitwidth = 29           explicitheight = 17         end         object lbl_email: tlabel           left = 393           top = 56           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'email: '           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentfont = false           layout = tlcenter           explicitleft = 454           explicitwidth = 42           explicitheight = 17         end         object lbl_homecountry: tlabel           left = 2           top = 83           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'country: '           color = clbtnface           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentcolor = false           parentfont = false           transparent = true           layout = tlcenter           explicitleft = 47           explicitwidth = 58           explicitheight = 17         end         object edit_homepostcode: tedit           left = 107           top = 110           width = 284           height = 25           align = alclient           bevelinner = bvnone           bevelouter = bvnone           taborder = 4           text = 'home post code'         end         object lbl_homepostcode: tlabel           left = 2           top = 110           width = 103           height = 25           align = alclient           alignment = tarightjustify           caption = 'post code: '           color = clbtnface           font.charset = default_charset           font.color = clwindowtext           font.height = -13           font.name = 'segoe ui'           font.style = [fsbold]           parentcolor = false           parentfont = false           transparent = true           layout = tlcenter           explicitleft = 35           explicitwidth = 70           explicitheight = 17         end       end       object panel_homeaddresstitle: tpanel         left = 6         top = 6         width = 784         height = 24         align = altop         alignment = taleftjustify         bevelouter = bvnone         caption = ' home address '         color = clmedgray         font.charset = default_charset         font.color = clwindowtext         font.height = -13         font.name = 'segoe ui'         font.style = [fsbold, fsunderline]         parentbackground = false         parentfont = false         taborder = 1       end     end     object panel_generalnotesdetails: tpanel       tag = 303       left = 0       top = 174       width = 796       height = 172       align = altop       autosize = true       padding.left = 5       padding.top = 5       padding.right = 5       padding.bottom = 5       parentbackground = false       taborder = 1       object gpanel_generalnotesdetails_: tgridpanel         left = 6         top = 6         width = 784         height = 160         align = altop         bevelouter = bvnone         columncollection = <           item             value = 100.000000000000000000           end>         controlcollection = <           item             column = 0             control = pagecontrol_generalnotes             row = 0           end>         padding.left = 1         padding.top = 1         padding.right = 1         padding.bottom = 1         rowcollection = <           item             sizestyle = ssabsolute             value = 160.000000000000000000           end>         taborder = 0         object pagecontrol_generalnotes: tpagecontrol           left = 2           top = 2           width = 780           height = 158           align = alclient           taborder = 0         end       end     end   end end 

i figured out problem caused quick hack david answered tlabel , tgroupbox captions flicker on resize after removed mad flickering when tpagecontrol tab scroll buttons visible went away. i'll have @ more in-depth solution , see if can of flickering seeing before.