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Docs: LCL/graphics. Updates TPicture.ReadData topic for changes in 05f867ee. Issue #40685.

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* The method is private and will not appear in generated documentation. It had content, so I updated it.
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dsiders 2024-01-18 00:39:15 +00:00
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docs/xml/lcl/graphics.xml
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@ -6410,22 +6410,69 @@ Use <var>Height</var> to the height of the image in the Graphic property.
<short>Width of the image stored in the Graphic property.</short>
</element>
<!-- this is private and not visible in documentation -->
<element name="TPicture.ReadData">
<short>Reads data for the persistent object during LCL streaming.</short>
<short>
Reads data for the persistent object during LCL streaming.
</short>
<descr>
<p>
ReadData implements the procedure used to read a persistent object during LCL
streaming. Stream is the TStream instance with the data for the persistent
<var>ReadData</var> is used to read a persistent object during LCL streaming.
<var>Stream</var> is the TStream instance with the data for the persistent
object.
</p>
<p>
ReadData is used by the TFiler instance for the class type.
ReadData checks the content in Stream for header information which identifies
the image format. It creates a new instance of the image class which is used
to read the raw image content.
</p>
<p>
Content in Stream includes the name for the graphic class needed to read or
write the image data. For an image created using Delphi, and then used in a
Lazarus project, this presents a problem. For example: Lazarus uses the
TPortableNetworkGraphic class to handle .PNG images. Delphi uses the TPngImage
class. This difference in image headers is handled in the ReadData method by
substituting the graphic class needed in Lazarus based on the registered
graphic class names or extensions. Other differences in Stream, like the size
for image data (omitted by a Delphi-generated image), are also handled in the
method.
</p>
<p>
The ReadData method in the TGraphic class instance is called to load the
content for registered graphic classes. LoadFromStream in TGraphic is called
for images which do not use one of the registered classes known to Lazarus.
</p>
<p>
The TGraphic instance created and loaded in the method is assigned to the
Graphic property prior to exit. The OnChange and OnProgress event handlers in
Graphic are set to the Changed and Progress methods in TPicture.
</p>
<p>
The Graphic property is set to <b>Nil</b> if an unsupported image format is
detected in Stream.
</p>
<p>
The Changed method is called prior to exit to signal an assigned OnChange event
handler in the class instance.
</p>
</descr>
<seealso/>
<version>
Modified in LCL 4.0 to handle image data using unregistered class names and
with omitted image size information.
</version>
<seealso>
<link id="TPicture.Graphic"/>
<link id="TPicture.Changed"/>
<link id="TPicture.WriteData"/>
<link id="TGraphic"/>
<link id="TGraphic.OnChange"/>
<link id="TGraphic.OnProgress"/>
</seealso>
</element>
<element name="TPicture.ReadData.Stream">
<short>TStream instance with the data for the persistent object.</short>
<short>
TStream instance with the data for the persistent object.
</short>
</element>
<element name="TPicture.SetBitmap">