Lazarus Custom Drawn Controls

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The Lazarus Custom Drawn Controls are a set of controls equivalent to the standard Lazarus controls, but which draw themselves. They can have many uses, including the ability to fully customize the drawing, the ability to have exactly the same look in different platforms and also a higher consistency of behavior.

This set of controls is divided into two parts:

  • the custom drawn controls which are necessary for implementing Lazarus widgetsets and will in future be located in the unit lazarus/lcl/customdrawncontrols.pas. These are described here.
  • all other custom drawn controls, which are used often, but aren't indispensable to implement a LCL custom drawn widgetset. Those are located in the package lazarus/components/customdrawn. These are described in the page Lazarus Custom Drawn Package

At the moment all custom drawn controls are in the customdrawn package.

How do these components work?

The basic programming technique utilized by this set of controls is explained in the page Developing with Graphics#Create a custom control which draws itself.

The code of the controls itself is implemented in the unit customdrawncontrols.pas, but this unit has no drawing code at all. Customdrawncontrols.pas has all the code to process all keyboard and mouse events of the control and implements all of it's behavior. Each instance of a control has a Drawer connected to it. A Drawer in our nomenclature (an instance of the TCDDrawer class) is the same thing as a theme rendering engine or similar. The unit customdrawndrawers.pas manages the list of all known drawers and it also declares all basic data types for the State and StateEx, which contain all the information which the control passes to the drawer about the current state of the control so that it can have all required information to draw it.

Only 1 instance of each drawer exists in the program and all controls just refer to it, through the drawers manager in customdrawndrawers.pas. Each control has a property called DrawStyle which allows us to choose from an enumerated type which draw style to use and then customdrawndrawers.pas converts this information into a Drawer instance. One can spacify the dsDefault DrawStyle which will then use the style specified in the global variable DefaultStyle. This was done to allow changing the style of all controls at one by changing this global variable and then calling Invalidate on the controls. Bellow one can see a code snipet from customdrawndrawers.pas which shows the exposed methods to managed the list of drawers and also the Default style:

<delphi> unit customdrawndrawers; //...

 TCDDrawStyle = (
   // The default is given by the DefaultStyle global variable
   // Don't implement anything for this drawer
   dsDefault = 0,
   // This is a common drawer, with a minimal implementation on which other
   // drawers base on
   // Operating system styles
   dsWinCE, dsWin2000, dsWinXP,
   dsKDE, dsGNOME, dsMacOSX,
   // Other special styles for the user
   dsExtra1, dsExtra2, dsExtra3, dsExtra4, dsExtra5,
   dsExtra6, dsExtra7, dsExtra8, dsExtra9, dsExtra10

//... procedure RegisterDrawer(ADrawer: TCDDrawer; AStyle: TCDDrawStyle); function GetDefaultDrawer: TCDDrawer; function GetDrawer(AStyle: TCDDrawStyle): TCDDrawer;


 DefaultStyle: TCDDrawStyle = dsCommon; // For now default to the most complete one, later per platform


Each Drawer class has methods to draw all controls and also all available primitives. All new drawers created by users should inherited from the class TCDCommonDrawer which is the basic common drawer declared in the unit customdrawn_common.pas. If you don't inherit from it, the application might crash if it hits an abstract method. This is the most complete drawer which implements all abstract methods from it's base class, so inheriting form it one guarantees that there will never be crashes due to yet unimplemented methods. Other drawers can override the desired methods to change the drawing style.

The dsCommon drawer uses only TCanvas for all it's rendering, but other themes might also use TLazIntfImage and TFPImageCanvas instead, in order to have a faster pixel access. This programming technique is described in Developing with Graphics#Working with TLazIntfImage.

Color Palette

Drawers have also access to a color Palette, which has the usual system colors from the LCL. In their native platform by default drawers will load their colors from the operating system via the LCL, but outside their native platform drawers will use a standard color palette.


 TCDColorPalette = class
   ScrollBar, Background, ActiveCaption, InactiveCaption,
   Menu, Window, WindowFrame, MenuText, WindowText, CaptionText,
   ActiveBorder, InactiveBorder, AppWorkspace, Highlight, HighlightText,
   BtnFace, BtnShadow, GrayText, BtnText, InactiveCaptionText,
   BtnHighlight, color3DDkShadow, color3DLight, InfoText, InfoBk,
   HotLight, GradientActiveCaption, GradientInactiveCaption,
   MenuHighlight, MenuBar, Form: TColor;
 { There are 5 possible sources of input for color palettes:
  palDefault  - Uses palNative when the operating system matches the drawer style,
                palFallback otherwise
  palNative   - Obtain from the operating system
  palFallback - Use the fallback colors of the drawer
  palUserConfig-Load it from the user configuration files, ToDo
  palCustom   - The user application has set its own palette
 TCDPaletteKind = (palDefault, palNative, palFallback, palUserConfig, palCustom);
 { TCDDrawer }
 TCDDrawer = class
   Palette: TCDColorPalette;
   constructor Create; virtual;
   destructor Destroy; override;
   procedure SetPaletteKind(APaletteKind: TCDPaletteKind);
   procedure LoadNativePaletteColors;
   procedure LoadFallbackPaletteColors; virtual;


As the code above shows, one can choose where the colors should come from: From the operating system current theme, from the default of the drawer or defined by the user application. This allows one to change all colors of an application at run time by just changing the palette.

Custom drawn controls which duplicate LCL controls


This is a fully custom drawn button.

Usage example:

<delphi> uses customdrawnextras;

procedure TForm1.FormCreate(Sender: TObject); var

 MyButton: TCDButton;


 MyButton := TCDButton.Create(Self);
 MyButton.Parent := Self;
 MyButton.DrawStyle := dsWin2000;
 MyButton.Left := 100;
 MyButton.Top := 100;
 MyButton.Width := 200;
 MyButton.Height := 50;
 MyButton.Caption := 'My Button';
 MyButton.Color := clRed;
 MyButton.OnClick := @HandleButtonClick;

end; </delphi>

Custom drawn buttons.png


This is a fully custom drawn check box.



This is a fully custom drawn group box.


Substitutes TTrackBar



Substitutes TTabControl


Substitutes TPageControl


Custom Drawn Packages

Moved here: Lazarus Custom Drawn Package

Other good custom drawn components for Lazarus


See Also