Drawing lines

[Douglas Hay]

I want to draw a line chart with PHP. If I make my Draw() function the only
function call, it works fine. But if I display other data, and then call my
Draw() function, I get a bunch of graphics characters, and some text. The
text says I have already defined the header info. Here is the ledgible part
of the text

Warning: Cannot modify header information - headers already sent by (output
started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
/home/virtual/site8/fst/var/www/html/laps/lib.php on line 498

Here is my Draw() function. I just cut and pasted some code off a website.
I can't even draw a single line yet!

<?php
function Draw()
{
Header("Content-type: image/jpeg");
$image = ImageCreate(200 ,150);
$gray = ImageColorAlloc ate($image,204, 204,204);
$blue = ImageColorAlloc ate($image,0,0, 255);
ImageLine($imag e,10,10,150,30, $blue);
ImageJPEG($imag e);
ImageDestroy($i mage);
}?>

Any ideas why I cannot call the Header function here, or why my web page
just shows a bunch of text and graphic characters ?

Thanks,
Doug

[Stephen Oakes]

Re: Drawing lines


"Douglas Hay" <xxx@xxx.com> wrote...[color=blue]
> Any ideas why I cannot call the Header function here[/color]

Make sure your <?php statement is the very start of the file. Any white
space will count as HTML output. Any HTML output sends the headers.

--
Stephen Oakes

[Erwin Moller]

Re: Drawing lines

Douglas Hay wrote:
[color=blue]
> I want to draw a line chart with PHP. If I make my Draw() function the
> only
> function call, it works fine. But if I display other data, and then call
> my
> Draw() function, I get a bunch of graphics characters, and some text. The
> text says I have already defined the header info. Here is the ledgible
> part of the text[/color]

Hi,

2 things I can think of:
1) Did you echo anything?
Like echo "myvar = $myvar";
This can also be caused by whitespaces before the script starts.

2) Maybe you made some error, and PHP spits it out.
So you are generating text (errormessages) .

Tip:
View the result of the image in a texteditor, and look for errorlines.

Good luck.

Regards,
Erwin Moller

[Jerry Stuckle]

Re: Drawing lines

Douglas Hay wrote:[color=blue]
> I want to draw a line chart with PHP. If I make my Draw() function the only
> function call, it works fine. But if I display other data, and then call my
> Draw() function, I get a bunch of graphics characters, and some text. The
> text says I have already defined the header info. Here is the ledgible part
> of the text
>
> Warning: Cannot modify header information - headers already sent by (output
> started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
> /home/virtual/site8/fst/var/www/html/laps/lib.php on line 498
>
> Here is my Draw() function. I just cut and pasted some code off a website.
> I can't even draw a single line yet!
>
> <?php
> function Draw()
> {
> Header("Content-type: image/jpeg");
> $image = ImageCreate(200 ,150);
> $gray = ImageColorAlloc ate($image,204, 204,204);
> $blue = ImageColorAlloc ate($image,0,0, 255);
> ImageLine($imag e,10,10,150,30, $blue);
> ImageJPEG($imag e);
> ImageDestroy($i mage);
> }?>
>
> Any ideas why I cannot call the Header function here, or why my web page
> just shows a bunch of text and graphic characters ?
>
> Thanks,
> Doug
>
>[/color]
Doug,

That's correct. Headers must be sent BEFORE anything else is sent.

You're example will create a page with a single jpeg. You can't have
any other content on the page.


--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[Craig Storey]

Re: Drawing lines

Douglas Hay wrote:[color=blue]
> I want to draw a line chart with PHP. If I make my Draw() function the only
> function call, it works fine. But if I display other data, and then call my
> Draw() function, I get a bunch of graphics characters, and some text. The
> text says I have already defined the header info. Here is the ledgible part
> of the text
>
> Warning: Cannot modify header information - headers already sent by (output
> started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
> /home/virtual/site8/fst/var/www/html/laps/lib.php on line 498
>
> Here is my Draw() function. I just cut and pasted some code off a website.
> I can't even draw a single line yet!
>
> <?php
> function Draw()
> {
> Header("Content-type: image/jpeg");
> $image = ImageCreate(200 ,150);
> $gray = ImageColorAlloc ate($image,204, 204,204);
> $blue = ImageColorAlloc ate($image,0,0, 255);
> ImageLine($imag e,10,10,150,30, $blue);
> ImageJPEG($imag e);
> ImageDestroy($i mage);
> }?>
>
> Any ideas why I cannot call the Header function here, or why my web page
> just shows a bunch of text and graphic characters ?
>
> Thanks,
> Doug
>
>[/color]
If you have used echoe/print etc.. then headers are already sent. To
get around this problem use two pages/php scripts. The first is the
display file containing your formatting page stuff. Somewhere in that
file you call the second script that creates the jpg, using <img
src="jpg-generating-php.php"> which is the script you alreay posted that
draws lines. This second script does set the headers, but they are
expected in the image tag.

Good luck.

[Douglas Hay]

Re: Drawing lines

Thanks for all the help, Craig's suggestion worked great and I got it
working now.

Thanks to all of you!

Doug

"Craig Storey" <crig.storey@nr c.ca> wrote in message
news:d3h5rt$evr $1@nrc-news.nrc.ca...[color=blue]
> Douglas Hay wrote:[color=green]
> > I want to draw a line chart with PHP. If I make my Draw() function the[/color][/color]
only[color=blue][color=green]
> > function call, it works fine. But if I display other data, and then[/color][/color]
call my[color=blue][color=green]
> > Draw() function, I get a bunch of graphics characters, and some text.[/color][/color]
The[color=blue][color=green]
> > text says I have already defined the header info. Here is the ledgible[/color][/color]
part[color=blue][color=green]
> > of the text
> >
> > Warning: Cannot modify header information - headers already sent by[/color][/color]
(output[color=blue][color=green]
> > started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
> > /home/virtual/site8/fst/var/www/html/laps/lib.php on line 498
> >
> > Here is my Draw() function. I just cut and pasted some code off a[/color][/color]
website.[color=blue][color=green]
> > I can't even draw a single line yet!
> >
> > <?php
> > function Draw()
> > {
> > Header("Content-type: image/jpeg");
> > $image = ImageCreate(200 ,150);
> > $gray = ImageColorAlloc ate($image,204, 204,204);
> > $blue = ImageColorAlloc ate($image,0,0, 255);
> > ImageLine($imag e,10,10,150,30, $blue);
> > ImageJPEG($imag e);
> > ImageDestroy($i mage);
> > }?>
> >
> > Any ideas why I cannot call the Header function here, or why my web page
> > just shows a bunch of text and graphic characters ?
> >
> > Thanks,
> > Doug
> >
> >[/color]
> If you have used echoe/print etc.. then headers are already sent. To
> get around this problem use two pages/php scripts. The first is the
> display file containing your formatting page stuff. Somewhere in that
> file you call the second script that creates the jpg, using <img
> src="jpg-generating-php.php"> which is the script you alreay posted that
> draws lines. This second script does set the headers, but they are
> expected in the image tag.
>
> Good luck.[/color]