{"id":74,"date":"2007-05-12T13:36:43","date_gmt":"2007-05-12T11:36:43","guid":{"rendered":" http:\/\/www.nsonic.de\/blog\/2007\/05\/transparent-wincontrols\/"},"modified":"2007-05-12T13:39:56","modified_gmt":"2007-05-12T11:39:56","slug":"transparent-wincontrols","status":"publish","type":"post","link":"https:\/\/www.nsonic.de\/blog\/2007\/05\/transparent-wincontrols\/","title":{"rendered":"Transparent WinControls"},"content":{"rendered":"

In article <7kv799$\nefd8@forums.borland.com \n \n>, Robert wrote:
\n> WMEraseBkgnd message fills the TWincontrol with the brush color of the
\n> control, that makes the control opaque. Is it posible to make a
\n> TWincontrol transparent?<\/em><\/p>\n

Well, you have half the answer: since it is WM_ERASEBKGND that causes
\nthe background fill, trap the message and block it.<\/p>\n

Here is my standard reply on this transparent issue:<\/p>\n

> Please give me help on how to make a descendent class of TGroupBox
\n> transparent. Thanks in advance.<\/p>\n

Scott,<\/p>\n

a quick & dirty method is<\/p>\n

[code lang=”delphi”]
\n groupbox1.Brush.style := bsclear;
\n groupbox1.handleneeded;
\n setwindowlong( groupbox1.handle, GWL_EXSTYLE, WS_EX_TRANSPARENT );[\/code]<\/p>\n

in the forms OnCreate event handler.<\/p>\n

To do that kind of stuff right, create a new control derived from
\nTGroupbox, override its CreateParam method like this:<\/p>\n

[code lang=”delphi”]
\n private \/\/ in control declaration
\n Procedure CreateParams( Var params: TCreateParams ); override;<\/p>\n

Procedure TTransparentGroupbox.CreateParams( Var params: TCreateParams
\n);
\nbegin
\n inherited CreateParams( params );
\n params.ExStyle := params.ExStyle or WS_EX_TRANSPARENT;
\nend;<\/p>\n

Add a handler for the WM_ERASEBKGND message:<\/p>\n

Procedure WMEraseBkGnd( Var msg: TWMEraseBkGnd );
\n message WM_ERASEBKGND;<\/p>\n

Procedure TTransparentGroupbox.WMEraseBkGnd( Var msg: TWMEraseBkGnd );
\nbegin
\n SetBkMode( msg.DC, TRANSPARENT );
\n msg.result := 1;
\nend;
\n[\/code]<\/p>\n

That is the basic frame for a TWinControl descendent. For a
\nTGraphicsControl you would drop the CreateParams (since only WinControls
\nhave that method) and override the create constructor. After calling the
\ninherited constructor you modify the ControlStyle of the control:
\n[code lang=”delphi”]
\n ControlStyle := ControlStyle – [csOpaque];
\n [\/code]
\nTransparency actually works better for TGraphicControls than for
\nTWinControls. The latter have problems if the control is moved or the
\nbackground needs to change. Delphi container controls (like form or
\npanel) are always created with the WS_CLIPCHILDREN style, which
\nautomatically excludes the area under child controls from updates, so
\nthe background will not be updated if required. Removing the
\nWS_CLIPCHILDREN style from a controls parent is possible with
\n[code lang=”delphi”]
\n SetWindowLong( parent.handle, GWL_STYLE,
\n GetWIndowLong( parent.handle, GWL_STYLE )
\n and not WS_CLIPCHILDREN );
\n[\/code]
\nBut that may lead to accessive flicker on screen updates. <\/p>\n

Peter Below (TeamB)
\n100113.1101@compuserve.com <\/p>\n

)
\nNo e-mail responses, please, unless explicitly requested!<\/p>\n

[tags]Delphi, Components[\/tags]<\/p>\n","protected":false},"excerpt":{"rendered":"

In article , Robert wrote: > WMEraseBkgnd message fills the TWincontrol with the brush color of the > control, that makes the control…<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":""},"categories":[11],"tags":[90,75],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p71Tml-1c","_links":{"self":[{"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/posts\/74"}],"collection":[{"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/comments?post=74"}],"version-history":[{"count":0,"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/posts\/74\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/media?parent=74"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/categories?post=74"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.nsonic.de\/blog\/wp-json\/wp\/v2\/tags?post=74"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}