Am 24.06.2022 um 11:30 schrieb Mattias Gaertner via lazarus:
On Fri, 24 Jun 2022 11:09:17 +0200
Werner Pamler via lazarus<[email protected]> wrote:
[...] It is
my impression there is no way to register a new format in any way
without modifying the sources of TPicture.
TPicture:
class function SupportsClipboardFormat(FormatID: TClipboardFormat):
Boolean;
class procedure RegisterFileFormat(const AnExtension, ADescription: string;
AGraphicClass: TGraphicClass);
class procedure RegisterClipboardFormat(FormatID: TClipboardFormat;
AGraphicClass: TGraphicClass);
class procedure UnregisterGraphicClass(AClass: TGraphicClass);
class function FindGraphicClassWithFileExt(const Ext: string;
ExceptionOnNotFound: boolean = true): TGraphicClass;
Ah, of course. (I thought I had searched for "Register" in unit
graphics...). Now I saw that Vampyre also uses these TPicture class
methods to finally register their formats for TPicture. Thus, everything
should be fine.
But still the situation is not very satisfying.
First observation after installing VampyreImagingPackageExt (the other
package, VampyreImagingPackage, has no registration unit): I add TImage
to a form and load the Lazarus "paw" to it. Works fine at designtime,
but at runtime the image is empty. As the OP already noted Vampyre's
TImagingPNG class is not found. This is because the Vampyre formats are
registered only at designtime, but not at runtime of a project. But this
can be fixed easily: After adding unit *ImagingComponents *to the uses
clause, the "paw" is displayed at runtime, too.
Next complication comes into play if the user decides to uninstall
Vampyre. The problem is that every graphic type writes its class name to
the lfm file in front of the image data (Picture.Data). So, when a
picture was loaded into TImage while Vampyre was installed all the
images are brand-marked by the Vampyre classes, e.g. TImagingPNG rather
than TPortableNetworkGraphic:
This is the part of the lfm written when Vampyre is installed (I am
adding spaces to the hex data to see the digits:
object Image1: TImage
Left = 8
Height = 344
Top = 8
Width = 456
Picture.Data = {
0B 54 49 6D 61 67 69 6E 67 50 4E 47 89 50 4E 47 0D 0A 1A 0A 00 00
00 0D 49 48 44 52 00 00 01 C6
11 T I m a g i n g P N G // 11 is the
length byte
An image written by the LCL without Vampyre contains this:
object Image1: TImage
Left = 24
Height = 284
Top = 20
Width = 376
Picture.Data = {
17 54 50 6F 72 74 61 62 6C 65 4E 65 74 77 6F 72 6B 47 72 61 70 68
69 63 9A 3D 00 00 89 50 4E 47
23 T P o r t a b l e N e t w o r k G r a p h
i c
When such a project is loaded into a Lazarus without Vampyre at first
the VampyreImagingPackage and/or VampyreImagingPackageExt requirements
must be removed from the project. But, of course, the Vampyre image
class signatures are still in the lfm file, and the IDE refuses to load
the form with this error:
Unable to find the component class "TForm1".
It is not registered via RegisterClass and no lfm was found.
It is needed by unit:
D:\Prog_Lazarus\tests\_images\vampyre\format_registration\vampyre_stripped\unit1.lfm
I think this is the most confusing part of that issue. If it would say
"Unable to find class "TImagingPNG"" it would be much clearer.
However, I don't think that much can be done against that. There is
always a risk when using third-party components that irreversible
changes could occur. Hmm, well, somebody could write a tool the fix the
image classname header in the lfm's Picture.Data.
Werner
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