On 15 November 2017 at 20:47, Esteban Lorenzano <esteba...@gmail.com> wrote:
>
>
> On 15 Nov 2017, at 09:36, Ben Coman <b...@openinworld.com> wrote:
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>
>
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> On 15 November 2017 at 17:27, Esteban Lorenzano <esteba...@gmail.com>
> wrote:
>
>>
>>
>> > On 15 Nov 2017, at 02:05, Ben Coman <b...@openinworld.com> wrote:
>> >
>> > What is the recommended way for a C basic type to be
>> passed-by-reference to function wanting to use it for output.
>> > For example 'width' & 'height' here in this library unction...
>> >
>> > int FPDF_GetPageSizeByIndex(FPDF_DOCUMENT document,
>> > int page_index,
>> > double* width,
>> > double* height);
>> >
>> > void mytestGetPageSizeByIndex(doc) {
>> > double width, height;
>> > FPDF_GetPageSizeByIndex(doc, 0, &width, &height);
>> > printf("width=%f, height=%f\n", width, height);
>> > }
>> >
>> > gives...
>> > width=200.000000, height=200.000000
>> >
>> >
>> >
>> > In Pharo I'm trying...
>> >
>> > FFIOpaqueObject subclass: #FPDF_DOCUMENT
>> >
>> > FPDF_GetPageSizeByIndex__document: document
>> > page_index: page_index
>> > width: width
>> > height: height
>> > ^self ffiCall: #(int FPDF_GetPageSizeByIndex(
>> > FPDF_DOCUMENT *document,
>> > int page_index,
>> > FFIFloat64 * width,
>> > FFIFloat64 * height))
>> >
>> >
>> > testGetPageSizeByIndex
>> > | document page_index width height result|
>> > PDFium FPDF_InitLibrary.
>> > document := PDFium FPDF_LoadDocument__file_path: helloPdf
>> password: ''.
>> > width := 0.0.
>> > height := 0.0.
>> > page_index := 0. "Its zero based"
>> > result := PDFium FPDF_GetPageSizeByIndex__document: document
>> > page_index: 0
>> > width: width
>> > height: height.
>> > PDFium FPDF_CloseDocument__document: document.
>> > PDFium FPDF_DestroyLibrary.
>> > self assert: document isNull not. "Document opened okay, and btw
>> this works for a different pageCount test"
>> > self assert: result > 0. "Non-zero for success. 0 for error
>> (document or page not found)"
>> > self halt.
>> >
>> >
>> > and at the halt the Inspector shows...
>> > result = 1
>> > width = 0.0
>> > height = 0.0
>>
>> no, that will not work :)
>> what you need to do here is to pass a “buffer” to contain the width and
>> height:
>>
>> testGetPageSizeByIndex
>> | document page_index widthBuffer heightBuffer width height
>> result|
>> PDFium FPDF_InitLibrary.
>> document := PDFium FPDF_LoadDocument__file_path: helloPdf
>> password: ''.
>> widthBuffer := ByteArray new: (FFIFloat64 typeSize).
>> heightBuffer := ByteArray new: (FFIFloat64 typeSize).
>>
>
> Thanks Esteban. That worked. However I needed a minor tweak...
> widthBuffer := ByteArray new: (FFIFloat64 new typeSize).
> or...
> widthBuffer := ByteArray new: (FFIFloat64 externalTypeSize).
>
>
> Now it would be nice to do...
> widthBuffer := FFIFloat64 newBuffer.
>
>
> you know, I thought the same :)
> but since I’m officially on holiday I didn’t do it (yet).
>
> If you want to add an issue and send a PR, it would be perfect :)
>
>
> which could be implemented...
> FFIExternalType class >> newBuffer.
> ^ByteArray new: (self externalTypeSize)
>
> testGetPageSizeByIndex
> | document page_index widthBuffer heightBuffer width height result|
> PDFium FPDF_InitLibrary.
> document := PDFium FPDF_LoadDocument__file_path: helloPdf
> password: ''.
> widthBuffer := FFIFloat64 buffer.
> heightBuffer := FFIFloat64 buffer.
> page_index := 0. "Its zero based"
> result := PDFium FPDF_GetPageSizeByIndex__document: document
> page_index: 0
> width: widthBuffer
> height: heightBuffer.
> width := widthBuffer doubleAt: 1.
> height := heightBuffer doubleAt: 1.
>
>
>
> btw, a broader curiousity even though this is likely set in stone and not
> even your personal choice - why "FFIFloat64" and not "FFIDouble" ?
> widthBuffer := FFIDouble newBuffer.
> would be a nice match to the callout declaration.
>
>
> because the ABI defines float64 as the right name, heh.
> and yes, it was not my personal choice ;)
>
>
> Would it be overkill to have in Pharo an empty FFIDouble subclassed from
> FFIFloat64 ?
> the superclass being explicit about the format, while the subclass
> provides a nice identifier for users?
>
>
> maybe it is overkilling. Because also… where do you put the limit?
> (doubles, floats, longs, etc… ?)
>
>
Well, there are not so many... ??
cheers -ben
