From: Maurizio Colucci <seguso.forever at tin.it>
To: Olivier Andrieu <andrieu at ijm.jussieu.fr>, lablgtk at kaba.or.jp
Subject: Re: Loading a texture from file and applying it?
Date: Thu, 19 Aug 2004 19:34:19 +0200
References: <200408181845.37672.seguso.forever at tin.it> <20040819.120933.41629782.oandrieu at nerim.net>
In-Reply-To: <20040819.120933.41629782.oandrieu at nerim.net>
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On Thursday 19 August 2004 12:09, Olivier Andrieu wrote:
>  Maurizio Colucci [Wed, 18 Aug 2004]:
>  > Hello again,
>  >
>  > In lablgl + lablgtk, I need to load a texture from file and apply it to
>  > a triangle.
>  >
>  > More precisely: GlTex.image2d wants a byte array as a GlPix. I need
>  > to know how to create a GlPix from a png file (or similar).
>
> You can use GdkPixbuf: it will load the png file and convert it into a
> "pixel buffer" structure. You then need to convert this into a Raw
> array.
>
> The easiest way is to do this:
> ,----
>
> | let raw_of_pixbuf pb kind =
> |   Raw.of_string (Gpointer.string_of_region (GdkPixbuf.get_pixels pb))
> | ~kind
>
> `----
>

Thank you very much Olivier. I was looking at ocamlimages, so your hint was 
very useful. I still have some doubt though.

This is the code I have managed to write so far:

  let pb = GdkPixbuf.from_file "avatar1giu.bmp" in
  let wt = GdkPixbuf.get_width pb in
  let ht = GdkPixbuf.get_height pb in
  let wt2 = round wt in
  let ht2 = round ht in
  let pb_sc = GdkPixbuf.create ~width:wt2 ~height:ht2 
    ~bits:8 (* 8 bits per sample * 4 samples=32 bits *)
    ~has_alpha:true () in
  GdkPixbuf.scale ~dest:pb_sc ~width:wt2 ~height:ht2 pb;
  let raw_of_pixbuf pb kind =
    Raw.of_string (Gpointer.string_of_region
		     (GdkPixbuf.get_pixels pb)) ~kind in
  let raw = raw_of_pixbuf pb_sc  ??? in


1. As you can see, I don't know what to pass as kind. Could you please tell 
me?

2. Do you see other errors?

3. What do I do with this raw array? At the end, I need a GlPix.t to pass to 
GlTex.image_2d. Must I use GlPix.of_raw? 

4. Before calling GlTex.image_2d, I have to set the alpha value of my image 
manually, pixel per pixel (to set up color key). What can I use to read and 
write the red, green, blue and alpha values?

> But that will copy the pixel data twice: once from the pixbuf into a
> caml string then from the caml string into the raw array, so it's not
> as efficient as it could be.

That's not important because texture creation is done on initialization.
>
> It's possible to share the pixel data between the pixbuf and the raw
> array but it's a bit messy (breaks encapsulation). If you're
> interested, I can send you the code to do this.
>
>  > The GlPix should have rgba format, and the png file may not have
>  > alpha information.
>
> Use GdkPixbuf.get_has_alpha and GdkPixbuf.add_alpha .

Thanks for your patience :-)

-- 
Maurizio Colucci
http://logicaldesktop.sourceforge.net