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Old 3 Weeks Ago
attilio attilio is offline
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Default graphics with c piping to postscript

Hello.
I'm interested to have graphic output using c code, but without a graphic library for c (es cairo).
The idea is to use only printf to obtain, in stdout, commands in postscript language.
Examples of postscript commands are
Code:
0 0 moveto
100 100 rlineto
stroke
Then I would like to pipe these commands to ghostscript.
I'm not able to set the right pipe sintax in the shell command.

This is the code of the c program.

Code:
#include<stdio.h>
int main(){
        char c;
        int i;
        for (i=0; i<10; i++){
                printf("%d %d %s\n",0,5*i,"moveto");
                printf("%d %d %s\n",100,0,"rlineto");
                printf("%s\n","stroke");
                scanf("%c",&c);
        }
}
The output, in postscript code, traces 10 parallel lines.
The scanf line is useful to obtain pauses between one line and the next.

Supposing the code is compiled in a.out,
the following two commands work:
Code:
$ ./a.out >output-file
$ gs output-file
and you can see ten lines. Then gs waits for other commands in its prompt. If you type "quit" gs exits.

But I'm not able to pipe and to see a line after each "enter".
The "enter"s are needed (due to scanf) and wanted to obtain a graphic that proceeds step by step.
I tried
./a.out | gs -
but didn't work.
I tried also with a fifo, but it didn't work.

I'm not sure to have been able to explain the problem.
Is there anybody iterested that can suggest me the correct piping command in order to see a line drawed after each "enter"?
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Old 3 Weeks Ago
bsdun's Avatar
bsdun bsdun is offline
Real Name: Steve
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Posts: 6
Default

When you pipe a.out into gs, a.out sends all it's output to gs and stops running. I don't think you can pipe one line at a time.

When I use C, I use it in a combination with Lua language, because Lua is written as a C library and work perfectly together with C. Lua is designed to work with large amount of text and data and can be embedded in C and C++ programs. With Lua you would have os.execute() to call gs after each line. Free Lua book from Lua's author:
https://www.lua.org/pil/contents.html
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Old 3 Weeks Ago
attilio attilio is offline
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Thank you bsdun.
You are right, a.out writes all his output and, then, all the output is piped.
I tested it with something like this
Code:
$ ./a.out |cat > /dev/pts/2
where the output of cat in sent to a terminal window different from that from which I run a.out.
Also with a fifo the behaviour is the same:

On terminal window A
Code:
$ mkfifo  xxx
$ ./a.out > xxx
and on a different terminal window B
Code:
$ cat xxx
produces output in B all together at the end, when a.out stops.

Does this depend on a bufferization of the output?
If yes, is it possible to eliminate bufferization?

Thank you also for the interesting reference to LUA. I don't know it at all.
I will read something about.
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Old 3 Weeks Ago
IdOp's Avatar
IdOp IdOp is offline
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Another thought is that gs might wait until its standard input closes before processing anything received from it. If that's so, and I don't know if it is or not, then un-buffering probably wouldn't help.
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Old 3 Weeks Ago
attilio attilio is offline
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Maybe idOp.

Anyway, when one uses gs in interactive mode
Code:
$ gs
gs offers a prompt and the graphic output is in real time.
So gs would seem to have different behaviours according to wher the input comes from.

Effectively, I have tried
Code:
gs -
and, until I type ctrl-D to comunicate the end of file, nothing appears on the window dedicated to the graphics.

Does this mean that gs waits for the command list to finish before executing them,
or can stdin be bufferized too? Boh (italian expression to say "I don't know").

Thank you idOp
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Old 3 Weeks Ago
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Quote:
Originally Posted by attilio View Post
Effectively, I have tried
Code:
gs -
and, until I type ctrl-D to comunicate the end of file, nothing appears on the window dedicated to the graphics.
That's an interesting idea. I tried it, and a blank graphics window comes up. Also, gs offers no prompt on the terminal since it's not in interactive mode. I assume it is reading from the terminal like it would from a file. I can type in some commands, such as from your program, nothing shows in the graphics widow. When I hit Ctrl-D the graphics window disappears, so it's not possible to see if it "drew the commands". But it does suggest it may be waiting for the whole file (in this case std input) before doing anything.

Quote:
Does this mean that gs waits for the command list to finish before executing them,
or can stdin be bufferized too?
To me it suggests the first part. As to the second part, I am not an expert in that, I'd guess that if it were buffered it might still get a line at a time when one's ready, but am really not sure.
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