RE: [Fxruby-users] hard time using images

[Oliver S. <ol...@mo...>]

Hi, I'll give this a shot...

I think what you want is the canvas/dc paradigm.  An FXImageView is usually
for displaying static image files such as .bmp or .jpg.  Since you want to
create an image from scratch, the right way to do it is to replace your
FXImageView with an FXCanvas and forget about the FXImage for now.  It's
kind of complicated to explain briefly, but think of an FXDCWindow (which
contains an FXDC) as an artist.  You give the artist a brush and some paint
and a canvas and tell him to draw lines and pixels.  So something like this
untested code:

@canvas = FXCanvas.new(...)

@canvas.connect(SEL_PAINT) {
	FXDCWindow.new(@canvas) { |dc|
		dc.foreground = "white"
		dc.fillRectangle(0, 0, @canvas.width, @canvas.height)
		dc.foreground = "black"
		dc.drawPoint(20, 20) # draw a pixel
	}
}

But it gets more complicated.  Note that you should paint on the canvas
during the SEL_PAINT handler.  This ensures that FOX knows to display the
changes on the screen.  You can tell FOX to send a new SEL_PAINT message by
calling @canvas.update when you need it.

Now, while that method works, the problem with drawing on an FXCanvas is
that the user can see you draw.  So during slow operations the user will see
flicker as you update the painting.  That's where the FXImage comes in.  The
FXImage is an off-screen buffer that you can paint on just like an FXCanvas.
Look at the bounce.rbw example - it uses the FXCanvas to display the scene
to the user, but all actual drawing is done on the FXImage "behind the
scenes".  When the FXImage has been changed, the program calls
@canvas.update.  Then, when SEL_PAINT arrives, it uses dc.drawImage to throw
the entire FXImage onto the canvas at once.  Thus, less chance of flicker.
This technique is called 'double buffering'.

Actually, bounce.rbw is a great place to start.  You can see how it creates
the FXImage - first by calling the constructor, but then in SEL_CONFIGURE
(sent when the window is created or resized) the buffer is actually created
(i.e. memory for it is allocated) and given a size.  Drawing to the buffer
before it's created may be the source of your crash, although I'm not sure.

So, to summarize, you can draw to an FXImage anytime after it's created and
sized, but when you're done call @canvas.update and wait for the SEL_PAINT
to flip the image onto the FXCanvas the user will see.  Or, just draw to the
FXCanvas directly from SEL_PAINT if you don't care about flicker or only
need to draw once.  Read the help for FXDC for a list of drawing methods and
operations.  Drawing an entire screen of individual pixels is going to be
pretty slow, by the way... :|  Hope some of this is helpful,

Oliver

> -----Original Message-----
> From: fxr...@li...
> [mailto:fxr...@li...]On Behalf Of Andre'
> Wagner
> Sent: Wednesday, July 07, 2004 10:10 AM
> To: fxr...@li...
> Subject: Re: [Fxruby-users] hard time using images
>
>
> Thank you so much for the very complete info! However, I still can't
> draw :-( So let us speak ruby. I wrote this small class:
>
> require 'fox'
> include Fox
>
> class Test
>
>         def initialize
>                 app = FXApp.new
>                 main_window = FXMainWindow.new(app, "test", nil,
> nil, DECOR_ALL, 500, 330,
> 540, 370)
>
>                 # Image
>                 image = FXImage.new(app, nil, 0, 30, 30)
>                 imageview = FXImageView.new(main_window, image)
>
>                 # Set a pixel
>                 image.setPixel(10, 10, FXRGB(255, 255, 255))
>
>                 app.create
>                 main_window.show
>                 app.run
>         end
>
> end
> t = Test.new
>
> When the code gets into the setPixel, I get a segfault. What am I
> missing?
>
> Thank you in advance,
>
> André
>
> --
> © Andre' Wagner - 2004 - All rights reserved
>
>
>
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