Re: [Fxruby-users] hard time using images

[Jeroen v. d. Z. <je...@fo...>]

On Wednesday 07 July 2004 10:08 am, Andre' Wagner wrote:
> Hello folks,
>
> I think I'm failing to understand how do I manipulate a image widget
> in my application. I putted the FXImage in my app - and it appears ok
> - but if I try to setPixel in it then I get a segfault.
>
> I peeked into the examples, and I see they use a FXDCWindow and a
> FXCanvas, but I can't understand it very well. I looked into the
> tutorial and the docs but I haven't found anything that cleared my
> mind.
>
> Is there a image tutorial for FXRuby or something like that on the
> net? Or might someone give me a few pointers here?
>
> Thank you in advance,
>
> Andr=E9

The think to keep in mind is that there's two sides to FXImage: the
array of pixels which is kept in your program and the device-specific
bitmap which is kept in the display server.

Now, to keep memory down, by default FXImage ditches the pixel array
in the program, since USING the image in drawing operations normally
requires only the bitmap in the display server.  Of course, sometimes
you need the local pixel array, and there's a way to hang on to that,
by passing the IMAGE_KEEP option.  Also, there is a way to regenerate
the server-side bitmap from the local pixel array, which you can do
by calling render().  Finally, since you can use drawing commands
to draw things into the bitmap that is kept in the server, you can
read back the bitmap into the local image pixel array by calling
restore().

The API setPixel() works on the local image pixel array, and you
must make sure that the pixel array is kept around for that to
work properly.

Note also that the local pixel array is only deleted after the
server-side bitmap has been populated, which means basically
that prior to create() you still have full access to the local
pixel array.


Hope this helps,

	- Jeroen