[SOLVED] Does TLazIntfImage.AlphaBlend not work on Linux?
lazarus / 39-Graphics

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Aistis · 2024-01-08 07:48

Hello,
I'm making an image editor for pixel art graphics as a hobby and I am
moving from working purely with TBitmap to working with TLazIntfImage.

On Windows, this code runs without problems and works as expected by
blending a transparent ImageDataDrawPreview onto ImageData:
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 combined :=
TLazIntfImage.Create(0, 0);combined.DataDescription :=
GetDescriptionFromDevice(0);combined.SetSize(ImageData.Width, ImageDat
a.Height);combined.CopyPixels(ImageData);combined.AlphaBlend(ImageData
DrawPreview, nil, 0, 0);DrawCanvas.Picture.Bitmap.LoadFromIntfImage(co
mbined);FreeAndNil(combined);
On Linux Mint 21.2 and Debian 12 however, it doesn't blend and
AlphaBlend instead makes the whole image black.

Does anybody have any ideas, fixes, or workarounds for this?

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wp · 2024-01-08 11:39

Can you post a small project?

Found the attached project on my disk which demonstrates blending of
two TLazIntfImages, and I just checked that it works in Mint 21.1 as
well as in Windows. However, it does not directly call
TLazIntfImage.AlphaBlend and does the blending manually, but this is
essentially the same code as in AlphaBlend.

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Aistis · 2024-01-08 12:10

Quote from: wp on January 08, 2024, 12:39:25 pmCan you post a small
project?

Here's a small project and a demonstration of applying a transparent
image over a white image which makes it black on Linux Mint 21.2.

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wp · 2024-01-08 15:08

It seems that the Description is not created with Alpha channel by
calling GetDescriptionFromDevice(0). I added AddAlphaToDescription,
and then it works in both Windows and Mint:

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 procedure
TForm1.AlphaBlendTest;var  combined: TLazIntfImage;  d:
TRawImageDescription;begin  ImageData := TLazIntfImage.Create(0, 0); 
ImageData.DataDescription := GetDescriptionFromDevice(0);  d :=
ImageData.DataDescription;  AddAlphaToDescription(d, 8); 
ImageData.DataDescription := d;   ImageData.SetSize(128, 128); 
ImageData.FillPixels(colRed); //White);   ImageDataDrawPreview :=
TLazIntfImage.CreateCompatible(ImageData, ImageData.Width,
ImageData.Height);  ImageDataDrawPreview.FillPixels(FPColor($FFFF,
$FFFF, $FFFF, $7F7F));   combined :=
TLazIntfImage.CreateCompatible(ImageData, ImageData.Width,
ImageData.Height);  combined.CopyPixels(ImageData);  if TestAlphaBlend
then    combined.AlphaBlend(ImageDataDrawPreview, nil, 0, 0);  
Image1.Picture.Bitmap.LoadFromIntfImage(combined);  
FreeAndNil(combined);  FreeAndNil(ImageData); 
FreeAndNil(ImageDataDrawPreview);end;

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Aistis · 2024-01-08 15:41

Quote from: wp on January 08, 2024, 04:08:41 pmIt seems that the
Description is not created with Alpha channel by calling
GetDescriptionFromDevice(0). I added AddAlphaToDescription, and then
it works in both Windows and Mint:

Thank you, it seems to be working now. Marking as solved.