On 15 Nov 2017, at 09:36, Ben Coman <btc@openInWorld.com> wrote:

On 15 November 2017 at 17:27, Esteban Lorenzano <estebanlm@gmail.com> wrote:

> On 15 Nov 2017, at 02:05, Ben Coman <btc@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�� ?)

Esteban

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.
  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.

side note: I do not recommend using the UFFI type in declarations. In the long way is worst for comprehension and maintainability. This thingy:

^self ffiCall: #(int FPDF_GetPageSizeByIndex(
  FPDF_DOCUMENT *document,
  int page_index,
  FFIFloat64 * width,
  FFIFloat64 * height))

would be better as in original version:

^self ffiCall: #(int FPDF_GetPageSizeByIndex(
  FPDF_DOCUMENT *document,
  int page_index,
  double * width,
  double * height))

Thanks for the heads up.

cheers -ben