On Sat, 2009-12-26 at 13:51 +0100, Louise Hoffman wrote:

Dear developers,

I am trying to make a GIMP plugin that can open a new drawable on the screen. Just like when you make one from File->New.

It should be 800x600 24bit greyscale.

File->New creates a new image, not a new drawable.

Your code writes to the GimpDrawable struct, but this struct is read-only and must not be written to by the plug-in. I suggest that you take a look at other plug-ins that create new images.

Sven

Louise Hoffman wrote:

Dear developers,

I am trying to make a GIMP plugin that can open a new drawable on the screen. Just like when you make one from File->New.

Hi!

You can't show a drawable by itself, it needs to be in an image. Also, an image can't show itself, you must create a display for that. You are also using the API in weird ways, for example, objects such as layers and images are represented by integers in the plug-in context.

You are also saying that the plug-in takes the active image and drawable as parameter, but since you are creating a new image, you are not interested in those values (I assume) so there is no point in specifying these as arguments to the hello-world procedure.

I have attached a rewritten version of main.c (called hello-world.c since that is a name that doesn't conflict as much) that should do what you want. You might also want to consider using a scripting language like Scheme or Python for this.

/ Martin

Quoting Louise Hoffman :

When I select the plugin in GIMP I get these errors:

Calling error for procedure 'gimp-drawable-width': Procedure 'gimp-drawable-width' has been called with an invalid ID for argument 'drawable'. Most likely a plug-in is trying to work on a layer that doesn't exist any longer.
...

Your invocation of 'gimp_install_procedure' specifies NULL for the image_type. This is probably what you want -- you don't need an image opened in order to create a new image -- but this means that you shouldn't be using GIMP_PDB_IMAGE and GIMP_PDB_DRAWABLE in your GimpParamDef (if there is no image open when you execute the plug-in, those parameters can't be provided).

As a side note, I don't understand why you define your own 'MyDrawable' struct when it is identical to the GimpDrawable struct already available.

Louise Hoffman wrote:

hello-world.c:73: warning: passing argument 1 of ‘gimp_drawable_set_pixel’ makes integer from pointer without a cast /usr/include/gimp-2.0/libgimp/gimpdrawable_pdb.h:89: note: expected ‘gint32’ but argument is of type ‘struct GimpDrawable *’

As I said, in the plug-in context layers (and drawables) are identified by integers, not pointers. Looks like you try to use a struct pointer again.

Plug-ins run in their own process and thus pointer-passing doesn't work.

/ Martin

Louise Hoffman wrote:

Now I don't get any errors, but I don't see the pixel either...

/* Trying to set a pixel at x=5,y=5 with value 150 in 24 bit color */ const guint8 *pixel;
pixel = (guint8 *) "150";
gboolean s;
s = gimp_drawable_set_pixel (layer, 5, 5, 24, pixel); printf ("Was the pixel set?: %i", s);

Hi again!

No you got an error. 0, or FALSE, means "error" which you can read in the documentation for the function:

http://developer.gimp.org/api/2.0/libgimp/libgimp-gimpdrawable.html#gimp-drawable-set-pixel

There you can also read that the num_channels parameter shall be the "The number of channels for the pixel.". You try to pass the number of bits, 24. Even that is wrong since you create the layer with an alpha channel, so the correct wrong thing to pass would be 32.

/ Martin

On Sat, 2009-12-26 at 19:03 +0100, Louise Hoffman wrote:

You can't show a drawable by itself, it needs to be in an image. Also, an image can't show itself, you must create a display for that. You are also using the API in weird ways, for example, objects such as layers and images are represented by integers in the plug-in context.

You are also saying that the plug-in takes the active image and drawable as parameter, but since you are creating a new image, you are not interested in those values (I assume) so there is no point in specifying these as arguments to the hello-world procedure.

This is my first attempt to write a GIMP plugin, as you probably have guessed by now =)

I strongly suggest that you read the tutorial on developer.gimp.org then:

http://developer.gimp.org/writing-a-plug-in/1/index.html

and perhaps study the code of a plug-in that does something similar to what you want to achieve. Writing a plug-in without any idea of how the GIMP API works is not going to be a fun experience.

Sven

On Sun, 2009-12-27 at 11:18 +0100, Louise Hoffman wrote:

I strongly suggest that you read the tutorial on developer.gimp.org then:

http://developer.gimp.org/writing-a-plug-in/1/index.html

I read that one, and it was from that, I copied a lot of the code. I was why I had all this pointer and structs at first =)

The code you showed us was definitely not copied from there. And it is correct to use the GimpDrawable struct from plug-ins. Martins advice that plug-ins would only refer to drawables by their integer ID is incorrect.

Sven

Sven Neumann wrote:

On Sun, 2009-12-27 at 11:18 +0100, Louise Hoffman wrote:

I strongly suggest that you read the tutorial on developer.gimp.org then:

http://developer.gimp.org/writing-a-plug-in/1/index.html

I read that one, and it was from that, I copied a lot of the code. I was why I had all this pointer and structs at first =)

The code you showed us was definitely not copied from there. And it is correct to use the GimpDrawable struct from plug-ins. Martins advice that plug-ins would only refer to drawables by their integer ID is incorrect.

I would like to point out that the GimpDrawable struct in libgimp has a member

gint32 drawable_id; /* drawable ID */

so plug-ins still refers to drawables in the core through an ID, even though it might be indirectly through a pointer to the libgimp GimpDrawable structure.

I agree however that my advice was misleading and stand corrected.

/ Martin