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Re: Reading the dimensions of a sprite or JPEG on disk

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In article <ReWdnVLwIJhwvw__nZ2dnUU7-f2dnZ2d@brightview.co.uk>,
   Gerald Holdsworth <nospam@hollypops.co.uk> wrote:

> Sprite files contain multiple sprites, so you would need to specify 
> which sprite you wanted dimensions of.

I think I better describe what I'm after, because I run into more problems
than reading sprite dimensions alone.

I would like to be able to drag either a single sprite or a JPEG to my
window, after which the BASIC program saves a sprite thumbnail of it,
preferably to an existing sprite file. The thumbnail should be 40x40 pixels
at maximum. I haven't been able to find a detailed description (or any
description at all) of how to do this.

At this moment I use the ChangeFSI library for the conversion, as described
in a document called "CmdBasUse", found within the ChangeFSI application
directory. After having typed "LIBRARY "<ChangeFSI$Dir>.ChangeFSI" at the
top of my program, I have access to the following function:

error% =
FNChangeFSI(A$,spritearea%,workspace%,worklimit%,oksave%,okinfo%,RETURN
ram%,fast%)

A$ contains the paths and conversions details, as described in the same
document. Until now I only succeeded to convert small JPEGs, that are
converted to the desired sprite thumbnails indeed, but that are stored to
disc, rather than to an existing sprite file. Larger JPEGs fail to convert
at all, producing an error that I can't understand: "Unknown or missing
variable in "ChangeFSI" in "ChangeFSI" [sic] at line 1672" - a line that
has nothing to do with the routine in question. As I have very little to no
understanding of the parameters of the function, I assume that I don't use
them properly, although it does work for small JPEGs (smaller than 15KB,
approximately).

I let ChangeFSI create the spritearea%, as well as the workspace% and the
worklimit%, by entering -1,-1,0 respectively, as described in the document.
However, I've no idea what to do with the "RETURN ram%" parameter. I've
entered a random variable (r%), which seems to be accepted by the function.
But blindly experimenting with random spriteareas and workspaces has only
resulted in fatal errors so far. As usual, I've actually no idea what I'm
doing.

Would someone be willing to explain how to use this function properly, or
how to achieve my goal otherwise?

Kind regards,
Paul

-- 
https://riscos.sprie.nl

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Thread

Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-28 12:08 +0200
  Re: Reading the dimensions of a sprite or JPEG on disk News <chrisjohnson@spamcop.net> - 2022-05-28 11:37 +0100
    Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-28 12:48 +0200
      Re: Reading the dimensions of a sprite or JPEG on disk Gerald Holdsworth <nospam@hollypops.co.uk> - 2022-05-28 14:26 +0100
        Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-30 13:58 +0200
          Re: Reading the dimensions of a sprite or JPEG on disk Gerald Holdsworth <nospam@hollypops.co.uk> - 2022-05-30 15:16 +0100
            Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-30 16:51 +0200
              Re: Reading the dimensions of a sprite or JPEG on disk Gerald Holdsworth <nospam@hollypops.co.uk> - 2022-05-30 18:07 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-31 09:27 +0200
                Re: Reading the dimensions of a sprite or JPEG on disk Gerald Holdsworth <nospam@hollypops.co.uk> - 2022-05-31 12:12 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-31 15:30 +0200
                Re: Reading the dimensions of a sprite or JPEG on disk Gerald Holdsworth <nospam@hollypops.co.uk> - 2022-05-31 21:51 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk Steve Fryatt <news@stevefryatt.org.uk> - 2022-05-31 23:29 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk Martin Wuerthner <spamtrap@mw-software.com> - 2022-06-07 16:33 +0200
                Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-06-11 08:56 +0200
                Re: Reading the dimensions of a sprite or JPEG on disk Sprow <news@sprow.co.uk> - 2022-06-12 08:15 -0700
                Re: Reading the dimensions of a sprite or JPEG on disk Martin <News03@avisoft.f9.co.uk> - 2022-05-31 13:10 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-31 15:59 +0200
                Re: Reading the dimensions of a sprite or JPEG on disk News <chrisjohnson@spamcop.net> - 2022-05-31 16:28 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk News <chrisjohnson@spamcop.net> - 2022-05-31 16:51 +0100
                Re: Reading the dimensions of a sprite or JPEG on disk Paul Sprangers <Paul@sprie.nl> - 2022-05-31 18:33 +0200

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