Re: How to render 8-bit raster graphics

[Michael J M Thomson <mjmt internode on net>]

Janet Mini wrote:
> Hello all,
>
> I'm new to gtkmm.
> I have some 8-bit grayscale images that I want to display in a gtkmm 
> application.
> I want to display them as a sequence of frames as an animation like a 
> movie playback.
> And I will also add some texts on top of the animation.
>
> Does anybody have any good idea how to do it properly with performance 
> (speed)?
>
> Shall I use the gnome canvas widget?
> I tested that I could use a look up table and duplicate my 8-bit data 
> for each of the RGB channel and create a RGB pixbuf.

> But is it possible that I use the grayscale visual and display just my 
> 8-bit grayscale images on the canvas instead of using RGB?
>
> Thank you in advance for any help and suggestion.
>
> Regards,
> Janet

Gdk::Pixbuf will load data from most file formats for you, converting as it 
goes from whatever depth to its RGB[A] colorspace using optimized C and lookup 
tables and such (looks the same as XFree's code actually). I'd go with letting 
pixbufs do this work for you, rather than bothering with grayscale or 8-bit 
visuals (which aren't always available or are done in software by X anyway).

It's then easy to render your pixbufs to say a Gtk::DrawingArea (a canvas for 
just one image at a time is overkill), with 
da.get_window()->draw_pixbuf(da.get_style()->get_bg_gc(0), pixbufs[i], ...)

Rendering into pixbuf isn't the API's strong suit though, maybe just draw your 
pixbuf to the window first, then e.g. a Pango::Layout separately after that for 
the text, with da.get_window()->draw_layout(...).

Draw each frame of the animation from a Glib::signal_timeout() callback (don't 
worry about handling drawingarea exposes, double buffering will take care of 
it), and there you are.

--
Michael J M Thomson

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