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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: Making a cross-hair visible
Date: Fri, 12 Aug 2016 00:20:15 +0200
Organization: Decebal Computing
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On Thursday 11 Aug 2016 23:36 CEST, silvio@internet.com wrote:

> On 08/11/2016 11:14 PM, Cecil Westerhof wrote:
>> I am dabbling with Swing to do some GUI stuff. This is relatively
>> new for me. At the moment I draw a rectangle for cropping an image.
>> The position is selected by clicking on the centre from where I
>> think the rectangle should be placed. This can be a little of, so I
>> have to fine-tune it. For this I draw a little cross in the centre.
>> Problem is that I paint it in black and when the centre is black, I
>> will not see it. And with every colour I choose I can have this
>> problem. Is there a smart way to make the cross always visible?
>>
>> I was thinking about a timer function which would alternate the
>> colour of the cross between black and white, but was wondering if
>> there is a better way.
>>
>> At the moment my code is:
>> protected void paintComponent(Graphics g) {
>> Graphics2D g2       = (Graphics2D) g;
>> int        centerX  = x + cropWidth  / 2;
>> int        centerY  = y + cropHeight / 2;
>>
>> super.paintComponent(g); g2.setStroke(stroke);
>> g.setColor(rectColor); g.drawImage(image, 0, 0, imageWidth,
>> imageHeight, null); g.drawRect(x, y, cropWidth, cropHeight);
>> g.drawLine(centerX - crossLength, centerY, centerX + crossLength,
>> centerY); g.drawLine(centerX, centerY - crossLength, centerX,
>> centerY + crossLength); }
>>
>
> Either do a black crosshair with a white border or draw in XOR-mode.

Why did I do not think about that. :'-(

I had already been experimenting and I got a good result with:
    new Color(0, 255, 0)
as the cross colour. But that this colour is not significantly used in
my pictures, does not mean it is the same in others.

I changed the last part to (it has to be cleaned up of-course):
        g2.setStroke(new BasicStroke(4.0f));
        g.setColor(new Color(255, 255, 255));
        g.drawLine(centerX - crossLength, centerY, centerX + crossLength, centerY);
        g.drawLine(centerX, centerY - crossLength, centerX, centerY + crossLength);
        g2.setStroke(new BasicStroke(2.0f));
        g.setColor(new Color(0, 0, 0));
        g.drawLine(centerX - crossLength, centerY, centerX + crossLength, centerY);
        g.drawLine(centerX, centerY - crossLength, centerX, centerY + crossLength);

And that works great on the blackbird where I did not see the cross earlier on.

Maybe I should do the same for the rectangle itself.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof