Add Layer->GetExtent method about geo-gdal-ffi HOT 7 CLOSED

It's in Geo::GDAL::FFI::new since those are semi-automatic, to wrap it into Layer class is manual work. There's no Extent class and I'm not sure one is needed. This can be used as it is now by creating the extent as $e = [0,0,0,0] before the call and giving $t as a parameter.

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What about to get the extent for an existing layer?

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OK, I figured it out.

    my $int = 1;
    my $extent = [0,0,0,0];
    my $e = Geo::GDAL::FFI::OGR_L_GetExtent ($$layer, $extent, \$int);
    print 'Gives: ' . join ' ', @$extent;
    #  Gives: 0 100000 0 100000

Is this in the docs somewhere? Or a pointer to the calling convention?

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I usually add it to the docs when I wrap it. Calling it from the root class is left as an exercise to the user, it's a combination of looking at the GDAL docs and similar cases here. Note that the raw API may be incorrect since it is there by the header file parser.

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There might be some possibility to generate the methods using a factory approach if there are similarities in how they are handled. For example the Identity, Union etc methods for layers all look like they differ only in the Geo::GDAL::FFI::OGR_L_* call. Same for CreateField and CreateGeomField.

A quick check of argument sets is below.

grep 'attach' FFI.pm | gawk -vFS='/' '{print $2}' | sort | uniq -c | sort -n | sed 's/^[ ]*//' | gawk -vFS=' ' '$1 > 4'

5 opaque double double double double double double
5 opaque int opaque
5 opaque string double
6 int
7 opaque int int*
7 opaque opaque opaque opaque GDALProgressFunc opaque
8 opaque GDALProgressFunc opaque
8 opaque string string
9 opaque double
10 opaque double double double
10 opaque int int
11 opaque double double double double double
11 opaque int*
13 opaque string_pointer
13 string
18 opaque double double double double
44 opaque string
57 opaque int
71 opaque opaque
103
219 opaque

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PR for factory creation of overlay methods is in #10. Let me know if there are other obvious candidates

I'll submit PRs for other methods as I wrap them for my own code.

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Issue fixed by PR #11

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