<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 14 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hello,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have come across what seems to be a bug, or at least a bit of a “gotcha”. My C code is essentially<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>char* imageData = malloc(size);<o:p></o:p></p><p class=MsoNormal>…<o:p></o:p></p><p class=MsoNormal>imageSurface = cairo_image_surface_create_for_data(imageData,<o:p></o:p></p><p class=MsoNormal> CAIRO_FORMAT_RGB24,<o:p></o:p></p><p class=MsoNormal> width,height,<o:p></o:p></p><p class=MsoNormal> stride);<o:p></o:p></p><p class=MsoNormal> cairo_set_source_surface(cairoCtxt, imageSurface,(double)x, (double)y);<o:p></o:p></p><p class=MsoNormal>cairo_paint(cairoCtxt);<o:p></o:p></p><p class=MsoNormal>/* Fix/Workaround goes here */<o:p></o:p></p><p class=MsoNormal>cairo_surface_destroy(imageSurface);<o:p></o:p></p><p class=MsoNormal>free(imageData);<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This code works fine when given a cairoCtxt opened on an xlib_surface or a win32_surface, but NOT a pdf or internal surface. In these latter cases the image data appears garbled.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The reason for this, is that (irrespective of the surface) the imageSurface reference count is 1 at the free() - because it is still registered as the source in cairoCtxt, and so I guess strictly speaking I am not at liberty to call the free() statement. It would appear that for PDF surfaces, at least, this is significant.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The solution/workaround is to insert the line<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>cairo_set_source_rgb(cairoCtxt, 1.,1.,1.);<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>at the /* Fix/Workaround goes here */ comment (perhaps a cairo_surface_flush(cairo_get_target(cairoCtxt)) would work too ?? ). Presumably by explicitly changing the source, this forces the PDF surface to execute whatever it hasn’t done already with the existing source, and – of course – the reference count drops to 0. It seems a bit obscure to have to do this ? <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>There doesn’t appear to a way of registering a callback to be executed when the surface reference count drops to zero, so I wonder how else application programmers are supposed to handle this situation ? <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='mso-fareast-language:EN-GB'>Cheers<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-GB'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-GB'>Phil Cope (Senior Software Engineer, Software Solutions Group, GE)<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>