[SOLVED] Error in Scanline example (from years...)
lazarus / 39-Graphics

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jipété · 2024-06-20 18:21

Hello,

In the last /usr/share/lazarus/3.4.0/examples/scanline, one can read,
lines 22-23 of unit1.pas :
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i     This
example demonstrates how to    - create an image with an internal
format similar to Delphi''s pf24bitand then, line 79 :
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   // create
an image with a format similar to Delphi''s pf32bitSo, where is the
truth ? 24 or 32 ?

Then, lines 115 and 116 :
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i //
LineStart is pointer to the start of a scanline with the following
format:// 4 bytes per pixel. First byte is blue, second green, third
is red.So I ask : what is the format of the missing fourth byte ?

And finally, one can read :
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i line 121 :
// fill line with [b]gray[/b]line 123 : PByte(LineStart)[i]:=0; // set
red, green and blue to 0 (i.e. black)
I'm lost...
(of course, the image is black with a diagonal red line)

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Handoko · 2024-06-20 18:35

The fourth byte is for alpha value (transparency). If you want to
learn more about scanline and pixel format I recommend this demo:
https://forum.lazarus.freepascal.org/index.php/topic,37242.msg488758.h
tml#msg488758

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jipété · 2024-06-21 09:35

Hello,

Thanks for the link, very interesting.

But regarding the errors in the text at the beginning of
/usr/share/lazarus/3.4.0/examples/scanline/unit1.pas, what can I (we)
do ?

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Handoko · 2024-06-21 14:27

You can report it at the bugtrackter:
https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues

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bytebites · 2024-06-21 17:09

Line 79 says:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  // create
an image with a format similar to Delphi's pf32bit

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jipété · 2024-06-27 07:36

Hello,

sorry for the delay but the forum didn't notify me that there was a
reply...

Quote from: bytebites on June 21, 2024, 07:09:48 pmLine 79 says:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  // create
an image with a format similar to Delphi's pf32bit   Yes we know. So
what ?

In my first post there are two lines that talk about the same thing
but in a different way, and an unanswered question...
beginning_of_post.png



Quote from: Handoko on June 21, 2024, 04:27:36 pmYou can report it at
the bugtrackter:
https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues
Done :
https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues/41003
Thanks for the link.

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jipété · 2024-06-29 14:50

will be fixed in 3.6.