From: Nicolas FRANCOIS (AKA El Bofo) <nicolas.francois@free.fr> To: "Jun P.FURUSE" <Jun.Furuse@inria.fr> Cc: Caml List <caml-list@inria.fr> Subject: [Caml-list] Re: Problem with Graph module Date: Tue, 18 Jun 2002 19:01:39 +0200 Message-ID: <20020618190139.69122974.nicolas.francois@free.fr> (raw) In-Reply-To: <20020618.114831.1025221351.Jun.Furuse@inria.fr> Le Tue, 18 Jun 2002 11:48:31 +0200 (CEST) "Jun P.FURUSE" <Jun.Furuse@inria.fr> a écrit : > I verified that this code prints out "BUG" when X display has less > than 24bits color depth. In such environment, the colour mapping from > Graphics to X is not one-to-one. This means that point_color may not > always return the exact colour which you drew on the screen. > For example, in an X display of 15bpp, the Graphics colour 0xffffff > and 0xf8f8f8 are translated to the same X white colour. > This is also true for the default white background color of Graphics. > point_color returns 0xf8f8f8, not 0xffffff, this is why the above > code prints out "BUG". OK. Now I have this simple problem : I can use Direct Rendering from X with my Voodoo card in 15 bits, and correct color translation in 24 bits. is that right ? > In Camllight, the translation between Caml colour and X colour > performs communication between programs and the X server. Since it is > highly expensive operation, the colour translation of O'Caml Graphics > is rewritten, so that it would never ask the X server about > colours. It improves the speed of colour query impressively. > Unfortunately, the both colour translation code do not return always > the same result. The different behavior of the Nicolas' O'Caml and > Camllight programs can be explained by this difference of colour > translation. Who said computer science is not an exact one ? > I think this does not mean the new colour translation of O'Caml is > buggy. Even in Camllight, the same things can happen, unless the colour > translation is one-to-one. (It happens less, but not never.) > > The important things (which should be noted in graphics.mli) are that > > * you may get different colour index from one you draw, > > * the colour indices predefined in Graphics for the basic colours > such as white, blue, red, etc can be just canonical candidate > indices for them. > > You should not compare these colour indices against the colours > got from the screen. For example, in Nicolas' program, instead of > comparing Graphics.white, we should use the colour index obtained > from the screen at the begining of the program: > > let screen_white = point_color 0 0 > (* this can be different from Graphics.white *) Great. Thanks for the tip. Euh, and what if I have to test several colors ? Oh, yes, here it is : let screen_from_color c = set_color x; plot 0 0; point_color 0 0;; Right ? I'll try it now. \bye, and thanks again. -- Nicolas FRANCOIS http://nicolas.francois.free.fr A TRUE Klingon programmer does NOT comment his code ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
next prev parent reply index Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-06-17 1:04 [Caml-list] " Nicolas FRANCOIS (AKA El Bofo) 2002-06-17 13:23 ` Jun P.FURUSE 2002-06-17 17:38 ` [Caml-list] Nicolas FRANCOIS (AKA El Bofo) 2002-06-18 9:48 ` [Caml-list] Re: Problem with Graph module Jun P.FURUSE 2002-06-18 16:53 ` Nicolas FRANCOIS (AKA El Bofo) [this message] 2002-06-18 23:13 ` Nicolas FRANCOIS (AKA El Bofo)
Reply instructions: You may reply publically to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20020618190139.69122974.nicolas.francois@free.fr \ --to=nicolas.francois@free.fr \ --cc=Jun.Furuse@inria.fr \ --cc=caml-list@inria.fr \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
caml-list - the Caml user's mailing list Archives are clonable: git clone --mirror https://inbox.ocaml.org/caml-list AGPL code for this site: git clone https://public-inbox.org/ public-inbox