Re: [fpc-pascal]How to use Linux libraries?
Hi, Micha, and thanks for your detailled answer. In fact, you are right. I do not force JPEG. Though, it is one of the most common file formats. I also thought about using an external program to convert any type of image into one easy to read format and then reading this one in. This 'quick and dirty method' may be ok as a workaround, but is not very optimal for permanent usage, because I have to load&execute i.e. Imagemagick's 'convert' for every particular picture. This is slow and causing a relatively high activity on the harddisk, therefore I discontinued this thought very soon. The better solution will definitely be to convert data inside my application, because it loads once and then can convert continuously picture by picture (I plan to use a WEB-CAM for something like a simple motion detection, i.e., so I will have to convert permanently, not only once at program start). What I am not understanding is: --- Most programs I can see in SuSE Linux use shared object libraries. These libraries are ready to use modules, can be used within multiple programs, and save me from re-inventing all this basic stuff again and again. There already was somebody who wrote these libraries and solved all problems with time, so why should I decide to do the same bloody way? (I also use the MySQL library without starting to analyze and re-code the whole communication protocol!) What (in addition) is making me think is: I have a friend who writes (with FPC) his own graphical applications for Windoze - with complete GUI support. He wrote once a library to simplify the API of Windoze, and now he can use Windoze in a procedural way. Looks relatively easy. He simply uses existing Windoze *.dll files to do all this basic stuff and also does not have to worry about how to read in a JPG in detail. The *.dll's do this job, and he simply has to call them the right way. I may be totally wrong, but as far as I understand, Linux' *.so files are the same as Windoze' *.dll files in their meaning. So shouldn't it be possible to use them in the same manner, by loading them and talking to them? | Oh, one more thing - Pasjpeg unit uses TStream classes and you said you | dont like Classes. But, really, they are so simple - I guarantee that | you will be glad when you learn how to use them and when you see what | TStream and it's descendants can do for you. Classes are possibly fine, otherwise they would not be such common. But as far as I understand, you cannot mix Class Style programming and OOP programming in one program (would also make life not easier, even when this would work). This means that I would have to re-write a lot of code only to be able to use it longer. --> Makes no real sense to me. mfg Ing. Rainer Hantsch ___ fpc-pascal maillist - [EMAIL PROTECTED] http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal]How to use Linux libraries?
- Original Message - From: "Rainer Hantsch" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, July 26, 2003 9:06 AM Subject: Re: [fpc-pascal]How to use Linux libraries? > The better solution will definitely be to convert data inside my application, > because it loads once and then can convert continuously picture by picture (I > plan to use a WEB-CAM for something like a simple motion detection, i.e., so I > will have to convert permanently, not only once at program start). if you want to capture the data from a web-cam the best would be to directly collect the data from it, it might be in a yuv color space which would be a pain in the ass to convert. You could use v4l perhaps? I don't know how to do it though. Haven't touch a linux system in years :( > I may be totally wrong, but as far as I understand, Linux' *.so files are the > same as Windoze' *.dll files in their meaning. So shouldn't it be possible to > use them in the same manner, by loading them and talking to them? Yes Rainer, .dll and .so are the same. Generally speaking they are files that contains code fragments (functions) much like an executable but that can be loaded dynamically at runtime. To use an .so library you need to load it in your program. Check the FPC docs (http://www.freepascal.org/docs-html/prog/progch11.html#x197-19900011) Under windows you can use LoadLibrary, GetProcAddress (to load functions) and FreeLibrary, these functions are defined in the windows unit. Under Linux you have to use dlopen, dlsym, dlclose which are in the shared library 'dl'. As far as I know there is no interface to this library but they are really easy to setup in your program: //taken from the FPC OpenGL package by Sebastian Guenther (?) const RTLD_LAZY = $001; RTLD_NOW = $002; RTLD_BINDING_MASK = $003; function dlopen(Name: PChar; Flags: LongInt) : Pointer; extdecl; external 'dl'; function dlsym(Lib: Pointer; Name: PChar) : Pointer; extdecl; external 'dl'; function dlclose(Lib: Pointer): LongInt; extdecl; external 'dl'; function LoadLibrary(Name: PChar): THandle; begin Result := THandle(dlopen(Name, RTLD_LAZY)); end; function GetProcAddress(Lib: THandle; ProcName: PChar): Pointer; begin Result := dlsym(Pointer(Lib), ProcName); end; function FreeLibrary(Lib: THandle): Boolean; begin if Lib = 0 then Result := False else Result := dlClose(Pointer(Lib)) = 0; end; //THandle should be defined in SysUtils but a 32bit integer should do the job if you don't want to include the unit. With those functions you can actually load dynamic (shared) libraries into your program but you'll still need an interface to use that libraries functions. In that interface you declare the data types and functions without implementing them, sort of the 'interface' section of a pascal unit or a C's .h file. It's worth noticing that there are two main calling mechanism for functions STDCALL and CDECL, under linux I guess you'll find mainly the CDECL type. Check the zLib and OpenGL packages (among others) for FPC, they are available on the FPC site. There you'll see how it works. btw if you need a pascal interface to the libjpeg.so then you should translate the libjpeg.h or whatever it's called to pascal. You can use the h2pas util as a start. as a final note, check thoroughly (sp?) the FPC docs, they are awesome and they cover almost everything in a lot of detail. Check also the packages sources and the contributed units, a lot of good tips can be learn from there and they are usually very easy (short) to read sources. I hope this long email has been of some help :) ciao, Ivan ___ fpc-pascal maillist - [EMAIL PROTECTED] http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal]How to use Linux libraries?
> to > > use them in the same manner, by loading them and talking to them? > > Yes Rainer, .dll and .so are the same. Generally speaking they are files > that contains code fragments (functions) much like an executable but that > can be loaded dynamically at runtime. > To use an .so library you need to load it in your program. Check the FPC > docs (http://www.freepascal.org/docs-html/prog/progch11.html#x197-19900011) > Under windows you can use LoadLibrary, GetProcAddress (to load functions) > and FreeLibrary, these functions are defined in the windows unit. > Under Linux you have to use dlopen, dlsym, dlclose which are in the shared > library 'dl'. As far as I know there is no interface to this library but > they are really easy to setup in your program: Don't! Use unit dynlibs. (there are some examples in docs/dynlibex) Dynlibs is basically a very small wrapper that encapsulates this. However it will avoid quite a few platform dependant ifdef's. > //taken from the FPC OpenGL package by Sebastian Guenther (?) > const > RTLD_LAZY = $001; > RTLD_NOW = $002; > RTLD_BINDING_MASK = $003; > > function dlopen(Name: PChar; Flags: LongInt) : Pointer; extdecl; external > 'dl'; > function dlsym(Lib: Pointer; Name: PChar) : Pointer; extdecl; external > 'dl'; > function dlclose(Lib: Pointer): LongInt; extdecl; external 'dl'; Since e.g. these are exactly the same on BSD, just in lib 'c'. etc etc. ___ fpc-pascal maillist - [EMAIL PROTECTED] http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal]How to use Linux libraries?
On Sat, 26 Jul 2003, Rainer Hantsch wrote: > I may be totally wrong, but as far as I understand, Linux' *.so files are the > same as Windoze' *.dll files in their meaning. So shouldn't it be possible to > use them in the same manner, by loading them and talking to them? You can. Using them statically (i.e. the system loads the needed library) is transparant on all systems. See the manual, chapter I advised you. It describes exactly what you need. To load libraries dynamically, you can use the dynlibs unit. It contains cross-platform handling of shared libraries. > | Oh, one more thing - Pasjpeg unit uses TStream classes and you said you > | dont like Classes. But, really, they are so simple - I guarantee that > | you will be glad when you learn how to use them and when you see what > | TStream and it's descendants can do for you. > > Classes are possibly fine, otherwise they would not be such common. But as far > as I understand, you cannot mix Class Style programming and OOP programming > in one program (would also make life not easier, even when this would work). It _IS_ possible to do so. Only you cannot do the following: TA = Object ... end; and then TB = Class(TA) ... end; i.e. you cannot mix class/object descendents. But you can use them together in 1 program, without problem. Michael. ___ fpc-pascal maillist - [EMAIL PROTECTED] http://lists.freepascal.org/mailman/listinfo/fpc-pascal
