Mega Code Archive
Delphi forms and the AnimateWindow API
<![CDATA[
Title: Delphi forms and the AnimateWindow API
Question: I like the roll and fade effects of the Window GUI. How do they apply on my forms?
Answer:
The Windows GUI is fulfilled of graphical effects: roll, fade and popups makes the interface attractive.
If you want apply the same effects to your forms you need only one API functio: AnimateWindow!
This API is of simple use and you only supply the handle of your form, how long the animation should take in milliseconds and a bunch of flags to specify effects and directions.
Try to place this code in the OnShow handler of your form:
...
AnimateWindow(Self.Handle, 250, AW_BLEND or AW_ACTIVATE);
...
Run the project and see the result. Cool, it isn't?
By default the function uses a roll effect, but you can change this using AW_SLIDE to obtain a slide effect, AW_CENTER to make the window collapse or expand or AW_BLEND to obtain a smooth fade effect.
In addition you can add the AW_ACTIVATE flag to specify that the form is appearing or AW_HIDE if you're hiding your form; this flag reverses the direction of the animation
When you use the roll or slide you can specify the direction of the effects along the horizontal and verticale axis adding the AW_HOR_POSITIVE or AW_HOR_NEGATIVE for x-axis and AW_VER_POSITIVE or AW_VER_NEGATIVE for y-axis.
All these flags are ignored when you use the AW_CENTER flag.
Experiment various combinations of flags and see the results!
After you've played for a while you will notice a quirk: some controls appears correctly, others are drawn erroneously and some other are not drawn at all!!
My first thought was: "Damn! It doesn't work". My second thought was: "Why?"
Well the reason is quite simple but the solution is aboring.
The MSDN documentation states that the windows procedures for the controls on a form may need to handle the WM_PRINT or WM_PRINTCLIENT to be used in conjuction with the AnimateWindow API. Those messages are used when Windows need to draw the contents of a control on a display context different from the screen (i.e. the printer or, as in our case, an offscreen bitmap). The documentation remarks that the window procedures for controls, common controls and dialog boxes already handle the messages.
This explain why some controls are drawn correctly: TButton, TCheckBox and TRadioButton, in example, owns and manage an underlying button control, therefore they handle messages correctly.
The garbled controls are a middle species since they own a button control but some parts are draw using the Delphi TCanvas and not the Windows GDI: TEdit, TRichEdit and others behave that way.
The invisible controls are the ones who does not own a window ar all and are all the TGraphic descendants like TShape and TBevel: these controls will never be drawn because they will never get the necessary messages.
Anyway, for every Delphi object descending from the TWinControl you can intercept and handle the WM_PRINTCLIENT message in this way:
unit TestGroupBox;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;
type
TTestGroupBox = class(TGroupBox)
private
{ Private declarations }
protected
{ Protected declarations }
procedure WMPrintClient(var Msg: TMessage); message WM_PRINTCLIENT;
public
{ Public declarations }
published
{ Published declarations }
end;
procedure Register;
implementation
procedure Register;
begin
RegisterComponents('Test', [TTestGroupBox]);
end;
{ TTestGroupBox }
procedure TTestGroupBox.WMPrintClient(var Msg: TMessage);
begin
PaintTo(HDC(Msg.WParam), 0, 0);
end;
end.
This is a sample component derived from the TGroupBox. Although the TGroupBox owns a window that is not a control neither a common control window, therefore the WM_PRINTCLIENT message is not handled.
Adding the message handler and using the PaintTo method to draw the control on a different display context is straightforward.
And now the boring part: this must be done for every control you want to use on you forms; moreover you must change all youR objects to new ones before you can safely use the AnimateWindow API.
Enjoy!
]]>