SWT實現窗口始終最前以及透明窗口

從win2000開始,windows提供了一個新的api SetLayeredWindowAttributes,可以輕鬆實現透明窗口,在網上有許多vb,vc,delphi的示例程序,下面我來介紹一下如何使用swt來實現這一效果:

BOOL SetLayeredWindowAttributes(
HWND hwnd, // handle to the layered window
COLORREF crKey, // specifies the color key
BYTE bAlpha, // value for the blend function
DWORD dwFlags // action
);

Windows NT/2000/XP: Included in Windows 2000 and later.
Windows 95/98/Me: Unsupported.
Header: Declared in Winuser.h; include Windows.h.
Library: Use User32.lib.

一些常量:
WS_EX_LAYERED = 0x80000;
LWA_ALPHA = 0x2;
LWA_COLORKEY=0x1
其中dwFlags有LWA_ALPHA和LWA_COLORKEY
LWA_ALPHA被設置的話,通過bAlpha決定透明度.
LWA_COLORKEY被設置的話,則指定被透明掉的顏色爲crKey,其他顏色則正常顯示.
注:要使使窗體擁有透明效果,首先要有WS_EX_LAYERED擴展屬性(舊sdk也沒有的). 

 在SWT實現代碼：

import org.eclipse.swt.SWT;
import org.eclipse.swt.internal.win32.OS;
import org.eclipse.swt.internal.win32.TCHAR;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class TransparentForm extends Shell ...{
    public static void main(String args[]) ...{
        try ...{
            Display display = Display.getDefault();
            TransparentForm shell = new TransparentForm(display, SWT.SHELL_TRIM);
            shell.open();
            shell.layout();
            while (!shell.isDisposed()) ...{
                if (!display.readAndDispatch())
                    display.sleep();
            }
        } catch (Exception e) ...{
            e.printStackTrace();
        }
    }

    public TransparentForm(Display display, int style) ...{
        super(display, style);
        createContents();
    }

    protected void createContents() ...{
        setText("SWT Application");
        setSize(500, 375);
        setLayout(new GridLayout());
        OS.SetWindowLong(this.handle, OS.GWL_EXSTYLE, OS.GetWindowLong(
                this.handle, OS.GWL_EXSTYLE) ^ 0x80000);

        TCHAR lpLibFileName = new TCHAR(0, "User32.dll", true);
        int hInst = OS.LoadLibrary(lpLibFileName);
        if (hInst != 0) ...{
            String name = "SetLayeredWindowAttributes