From tkpapp at gmail.com  Wed Apr 18 08:17:32 2012
From: tkpapp at gmail.com (Tamas K Papp)
Date: Wed, 18 Apr 2012 10:17:32 +0200
Subject: [cl-pdf-devel] gradients
Message-ID: <87mx69bgir.fsf@gmail.com>

Hi,

I would like to write a plotting function that draws image plots
(plotting a matrix in 2d using colors).  It would be useful to use
gradients; in particular, paint a rectangle where the four corners each
have a color and the each point in the rectangle has a color which is a
convex combination of the corner colors.  I think this is called a
gradient in most libraries, but I could not figure out how to do it in
cl-pdf (I have to admit that I didn't find gradients in the library,
maybe I didn't look hard enough).  Suggestions/examples would be
welcome.

Best,

Tamas



From eric.marsden at free.fr  Thu Apr 19 07:17:34 2012
From: eric.marsden at free.fr (Eric Marsden)
Date: Thu, 19 Apr 2012 09:17:34 +0200
Subject: [cl-pdf-devel] gradients
In-Reply-To: <87mx69bgir.fsf@gmail.com>
References: <87mx69bgir.fsf@gmail.com>
Message-ID: <4F8FBC0E.2080008@free.fr>

On 18/04/2012 10:17, Tamas K Papp wrote:

> I would like to write a plotting function that draws image plots
> (plotting a matrix in 2d using colors).  It would be useful to use
> gradients; in particular, paint a rectangle where the four corners each
> have a color and the each point in the rectangle has a color which is a
> convex combination of the corner colors.  I think this is called a
> gradient in most libraries, but I could not figure out how to do it in
> cl-pdf (I have to admit that I didn't find gradients in the library,
> maybe I didn't look hard enough).

Hi,

Gradients of this sort are called shading patterns in PDF (available 
from PDF version 1.3). Several types of shading patterns are available: 
function-based, axial, radial, Gourad-shaded. cl-pdf doesn't have any 
support for this, but it shouldn't be very hard to add.

The PDF specification is available from

    http://www.adobe.com/devnet/pdf/pdf_reference_archive.html

You want section 4.6.3.

-- 
Eric