Re: Still not understanding pixmaps vs RGBs

[Taura Milana <learfox furry ao net>]

On 2001.12.14 13:50 Lewin A.R.W. Edwards wrote:
> Sorry, I'm probably missing something major, but I don't see what 
> pixmaps gain me and I'd be really appreciative of some more explanation. 
> Currently my application works like this:
>
> * Render content into an RGB buffer (Still image decoding and some 
> special postprocessing). This buffer is the size of the source image, 
> not the screen size.
> * Decimate or expand content, using my own hand-rolled code, into a 
> second RGB buffer that is screen-sized.
> * Draw the RGB buffer into a darea that covers the whole screen (this 
> step is slow).

I don't think you would need RGB buffers *AND* GdkPixmaps togeather.
You can do all the drawing on client side to yer RGB buffer then send
it to the X server to a GdkWindow and yer all done.

For double buffering just create an extra buffer on your client
side and draw to it each time then send it to the X server's GdkWindow.


> One of the reasons I wanted to move to pixmaps is that someone here 
> recently told me the pixmap functions support resizing. However, they 
> don't. gdk_draw_pixmap is a 1:1 copy (possibly with clipping). Are there 
> functions, maybe in XLib, that will do pixmap resizing (scaling) for me? 
> My decimation/expansion code is horribly inefficient, I think.

Unfortunatly no, I worked with Xlib for 5 years and there is no
such function. If you want to do resizing yer going to have to use
RDK RGB buffers soly and `blit' each pixel using your own zooming
code.


> One of the other reasons I wanted to move to pixmaps is that they are 

Move? You said resize?


> the same memory layout as the screen, which is 16bpp - so I'd have 30% 
> less data to move around compared to the same sized RGB buffer. So I 
> wanted access to the internal structure of the pixmap, on the assumption 
> that it was internally a header (dimensions, depth, phase of the moon 
> information) followed by a flat display-format buffer.

Moving is easier, resizing is hard.


> Is a pixmap something like a PICT on the Macintosh, i.e. more like a 
> metafile format than just a frame buffer? Or is it like a 
> device-dependent bitmap on Windows?

It's an abstract offscreen X server side graphical object that you
can draw on only by using Gdk or Xlib functions. It can never be
interacted with on the client side.

It's not a file format since its format may change depending on Visual,
Depth, X Server brand, etc...


--
Sincerely,                  ,"-_                         \|/
-Capt. Taura M.             ,   O=__                    --X--
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                  http://furry.ao.net/~learfox/