GbtPNGFileFormat does actually write the image to a file

[Richard Sargent]

The following example had me puzzled for a while. I kept ending up with zero length PNG files.

Given a pixmap, such as is produced in #stsSnapshotWindow, the following should have written it to a file. This code is based on StsPowerTools class>>#savePixmapToFile:, but I notice that PNG is not an available snapshot target ... for  probably this  reason.

formatClass := CgPNGFileFormat.
CfsFileDescriptor remove: filename. "Ignore any error; file not found is expected"
pixmap depth: (pixmap depth min: formatClass stsMaxDepth).
image := pixmap getDeviceIndependentImage: pixmap rectangle.
fileDescriptor := CfsFileDescriptor
open: filename
oflag: OCREAT | OTRUNC | OWRONLY.
fileDescriptor isCfsError
ifTrue:
[pixmap freePixmap.
^self gbsMessenger
warn: 'Error occurred saving screen capture: %1'
with: fileDescriptor message].
success := formatClass new
unload: image
intoFileHandle: fileDescriptor
atOffset: 0.
fileDescriptor close.

The solution and explanation is provided by adding a subclass and implementing this method in it. In my case I created  a GbtPNGFileFormat class and successfully used it..

[Richard Sargent]

Dang! There should have been a NOT in the subject.

[Mariano Martinez Peck]

Hi Richard, 

Thanks for the report. I think you are correct. Could you please verify that the attached fileout does work for you.

Thanks in advance,

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Mariano Martinez Peck VAST Lead Consultant Senior Software Engineer  mp...@instantiations.com  @MartinezPeck  /mariano-martinez-peck  instantiations.com

[Richard Sargent]

My test case can be recreated using the following.
StsPowerTools snapshotTarget: CgPNGFileFormat formatName.
EtWindow basicNew stsSnapshotScreen.

This works for every other format, I believe. PNG is excluded, probably because it didn't work.

(See the Options/Snapshot menu item on EtWindows.)

The patch you provided looks good in the sense of capturing more information/detail.

But, the problem is that CgPNGFileFormat doesn't write anything to the file stream.

[Seth Berman]

Hi Richard,

I'm not sure how you applied the patch (perhaps manually?), but it seems to work for me.
Notice there are 2 methods in there.  #encode and #encode:

Then to hook it into StsPowerTools, you just create the method below
StsPowerTools class>stsSnapshotTargetPNG

self snapshotTarget: CgPNGFileFormat formatName

---------
then add this section to this existing method.
StsPowerTools class>>stsSnapshotTargetSubMenu
...
add: #stsSnapshotTargetPNG
label: '~PNG File'
enable: [self snapshotTarget ~= CgPNGFileFormat formatName]
toggle: [self snapshotTarget = CgPNGFileFormat formatName]
for: self;
...

- Seth

[Richard Sargent]

On Wed, Sep 10, 2025 at 10:50 AM 'Seth Berman' via VAST Community Forum <va-sma...@googlegroups.com> wrote:

Hi Richard,

I'm not sure how you applied the patch (perhaps manually?), but it seems to work for me.
Notice there are 2 methods in there.  #encode and #encode:

Yes, I did file it in manually. I don't know how I screwed it up.

I retried it and see the two methods. And, when I try it again, the snapshot works correctly.

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[Mariano Martinez Peck]

Hi Richard, 

FYI, this fix was tracked in case "74331: CgPNGEncoder >> encode: outputStream should actually write into outputStream" and will be shipped with VAST 15.

Thanks! 

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