[英]Canvas with a semi-transparent background
我想創建一個具有半透明背景的畫布。 所以我嘗試過這樣的事情:
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class Main {
public static int WIDTH=500;
public static int HEIGHT=70;
public static void main (String [] args) {
Display display = new Display ();
Shell shell = new Shell(display);
shell.setSize(WIDTH,HEIGHT);
shell.setLayout(new GridLayout());
shell.setBackground(display.getSystemColor(SWT.COLOR_RED));
create(shell);
shell.pack();
shell.open ();
while (!shell.isDisposed ()) {
if (!display.readAndDispatch ()) display.sleep ();
}
display.dispose ();
}
private static void create(Shell shell){
Canvas c= new Canvas(shell, SWT.DOUBLE_BUFFERED);
GridData gd= new GridData();
gd.heightHint=HEIGHT-30;
gd.widthHint=WIDTH-30;
c.setLayoutData(gd);
c.setBackgroundMode(SWT.INHERIT_FORCE);
c.setBackground(new Color(shell.getDisplay(), 255, 255, 255, 100));
}
}
但是SWT似乎沒有考慮我用於“畫布”背景的顏色的Alpha部分(100),除非我輸入0,否則如果使用0,則畫布是完全透明的,在所有其他情況下,不透明。 我在這里犯了一些錯誤,還是SWT問題?
我在Windows 8上使用SWT。
正如greg-449指出的,這是Windows環境下SWT中的錯誤。 我在SWT中打開了一個缺陷: https : //bugs.eclipse.org/bugs/show_bug.cgi? id =528249
作為一種解決方法,我們總是可以自行設置GC繪畫畫布上的aplha,這種方法適用於所有環境:
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class Main {
public static int WIDTH=500;
public static int HEIGHT=70;
public static void main (String [] args) {
Display display = new Display ();
Shell shell = new Shell(display);
shell.setSize(WIDTH,HEIGHT);
shell.setLayout(new GridLayout());
shell.setBackground(display.getSystemColor(SWT.COLOR_RED));
create(shell);
shell.pack();
shell.open ();
while (!shell.isDisposed ()) {
if (!display.readAndDispatch ()) display.sleep ();
}
display.dispose ();
}
private static void create(Shell shell){
Canvas c= new Canvas(shell, SWT.DOUBLE_BUFFERED);
GridData gd= new GridData();
gd.heightHint=HEIGHT-30;
gd.widthHint=WIDTH-30;
c.setLayoutData(gd);
c.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_TRANSPARENT));
c.setBackgroundMode(SWT.INHERIT_FORCE);
c.addPaintListener(new PaintListener() {
public void paintControl(PaintEvent e) {
Rectangle clientArea = c.getClientArea();
e.gc.setAlpha(100);
e.gc.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_WHITE));
e.gc.fillRectangle(clientArea.x,clientArea.y,clientArea.width-1,clientArea.height-1);
}
});
}
}
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