Hi,

I'm a relative newbie trying to have a GIMP plugin draw a line (among other things).

I found gdk_draw_line which seems to be what I want. But I don't know what to do about drawable. I of course have the GimpDrawable, and I have a guint8 array which holds the data from the GimpDrawable:

gint32 drawable_ID; int x1, y1, x2, y2;
guint8 *source_data;
GimpDrawable *drawable;
GimpPixelRgn source_region;

if (!(drawable = (GimpDrawable *) gimp_drawable_get (drawable_ID))) return FALSE;
has_selection = gimp_drawable_mask_bounds (drawable_ID, &x1, &y1, &x2, &y2);

if (!(source_data = g_new (guchar, drawable->bpp * (x2-x1) * (y2-y1)))) return FALSE;
gimp_pixel_rgn_init (&source_region, drawable, x1, y1, x2-x1, y2-y1, FALSE, FALSE);
gimp_pixel_rgn_get_rect (&source_region, source_data, x1, y1, x2-x1, y2-y1);

But I don't see how to get or make a GdkDrawable which I can pass to gdk_draw_line. Do I need to create a GdkPixmap from source_data, and draw into that?

Thanks,
-Adam

On Sat, 2009-05-30 at 00:00 +0200, Sven Neumann wrote:

Hi,

On Fri, 2009-05-29 at 17:51 -0400, Adam C Powell IV wrote:

I'm a relative newbie trying to have a GIMP plugin draw a line (among other things).

I found gdk_draw_line which seems to be what I want.

It is not what you want. GDK is a drawing toolkit used by GTK+ for drawing user interfaces. It is not meant and not suited for drawing to GIMP drawables.

You probably want to use the procedures gimp-paint or gimp-pencil that allow you to draw strokes using the paintbrush or pencil tools.

I see. I was hoping to avoid the complexity of choosing brushes and whatnot, and just draw a simple line with squared-off end...

But okay. A search for "gimp plugin draw line" doesn't turn up anything looking helpful. Can you point me to an object or method to get started?

Thanks,
-Adam

I'm sorry, I'm developing a C plugin (tried Scheme first and it was DOG slow). Is there a C equivalent? All I'm seeing is gimp-paintbrush-register.

Funny, a search for "gimp c api line" turns up this thread. :-) Going further, searching for "gimp plugin api draw line" and restricting to developer.gimp.org turns up GDK drawing primitives.

So it sounds like the best way to proceed is to wrap the pixel data into a GdkPixbuf and use GDK to draw into it. Figured there might be a more straightforward way to go from a GimpDrawable to a GdkDrawable (since it is after all the "GIMP Drawing Kit"). Hmm, and there's a GimpCanvas object, but that doesn't seem to be a plugin thing.

Thanks, Adam

On Sat, 2009-05-30 at 19:20 -0400, Rob Antonishen wrote:

Here is the code to draw a single pixel line, black on white, on the drawable "layer" and x1 y1 are one end and x2 y2 are the other.

(gimp-context-set-brush "Circle (01)") (gimp-context-set-foreground "Black") (gimp-context-set-background "White") (gimp-context-set-opacity 100)
(gimp-context-set-paint-mode NORMAL-MODE) (gimp-pencil layer 4 (vector x1 y1 x2 x2)) (gimp-displays-flush)

0,0 is upper left hand side. This is with the pencil tool. Replace with any other tool as desired, for example: (gimp-paintbrush-default layer 4 (vector x1 y1 x2 y2))

Hope that helps,

-Rob A>

Indeed. So where is the C API documentation for drawing lines? When I search, all that comes up is one C paintbrush function, the Scheme interface, and this email thread.

I've spent a bunch of time at http://developer.gimp.org/api/2.0/libgimp/ to no avail... (That's a lot of how I produced the code snippet in the message which started this thread.)

Ah, a grep search through /usr/include/gimp-2.0/libgimp turned up gimpvectors, with a bezier line method. Why didn't I see it earlier? Ah, on developer.gimp.org there's no text next to the object name, no Description, no Details, no indication that this is how one draws lines.

So I guess I create a gimpvectors object somehow, then use gimp_vectors_bezier_stroke_new_moveto() and gimp_vectors_bezier_stroke_lineto()? Or should I gimp_vectors_stroke_new_from_points()? How do I "stroke" the resulting path?

Sven, just got your replies, thanks. Still scratching my head. I'll bang on it for a bit longer, and go back to Gdk if I can't make it work.

Thanks, Adam

On Sat, 2009-05-30 at 21:56 -0400, Rob Antonishen wrote:

Sure, but the call process should be the same. Just use the equivalent C API calls, no?

-Rob A>

On 5/30/09, Adam C Powell IV wrote:

I'm sorry, I'm developing a C plugin (tried Scheme first and it was DOG slow). Is there a C equivalent? All I'm seeing is gimp-paintbrush-register.

Funny, a search for "gimp c api line" turns up this thread. :-) Going further, searching for "gimp plugin api draw line" and restricting to developer.gimp.org turns up GDK drawing primitives.

So it sounds like the best way to proceed is to wrap the pixel data into a GdkPixbuf and use GDK to draw into it. Figured there might be a more straightforward way to go from a GimpDrawable to a GdkDrawable (since it is after all the "GIMP Drawing Kit"). Hmm, and there's a GimpCanvas object, but that doesn't seem to be a plugin thing.

Thanks, Adam

On Sat, 2009-05-30 at 19:20 -0400, Rob Antonishen wrote:

Here is the code to draw a single pixel line, black on white, on the drawable "layer" and x1 y1 are one end and x2 y2 are the other.

(gimp-context-set-brush "Circle (01)") (gimp-context-set-foreground "Black") (gimp-context-set-background "White") (gimp-context-set-opacity 100)
(gimp-context-set-paint-mode NORMAL-MODE) (gimp-pencil layer 4 (vector x1 y1 x2 x2)) (gimp-displays-flush)

0,0 is upper left hand side. This is with the pencil tool. Replace with any other tool as desired, for example: (gimp-paintbrush-default layer 4 (vector x1 y1 x2 y2))

Hope that helps,

-Rob A>

--
GPG fingerprint: D54D 1AEE B11C CE9B A02B C5DD 526F 01E8 564E E4B6

Engineering consulting with open source tools http://www.opennovation.com/

-Adam

On Sun, 2009-05-31 at 23:13 -0400, Liam R E Quin wrote:

On Sun, 2009-05-31 at 15:35 -0400, Adam C Powell IV wrote:

Indeed. So where is the C API documentation for drawing lines?

At the risk of stating the obvious, you do realise, I hope, that GIMP is a bitmap editor, and not a drawing program? If you are trying to create vector art, e.g. SVG or EPS, Inkscape or librsvg are better things to investigate.

Yes, thanks. In this regard, GIMP doesn't differ from Gdk -- which has a well-exposed API for drawing lines, and not just horizontal or vertical ones.

I'm making an image processing plugin which uses lines over image features to visualize some of the output. I should be able to release it soon.

There's also the Gfig plugin (filters->render->Gfig) that does some drawing and might be a source of ideas.

Ooh, very cool. Thanks!

-Adam

Okay, one more bit of help should finish this. :-)

On Sun, 2009-05-31 at 11:50 +1000, David Hodson wrote:

On Sat, 2009-05-30 at 20:47 -0400, Adam C Powell IV wrote:

I'm sorry, I'm developing a C plugin (tried Scheme first and it was DOG slow). Is there a C equivalent? All I'm seeing is gimp-paintbrush-register.

Open Gimp
Select Help > Procedure Browser
In the search box, type "brush"
Click on "gimp-context-set-brush"
Read the documentation
In your plugin, add the line:

gboolean result = gimp_context_set_brush("Circle (01)");

Rinse, lather, repeat.

(The hardest part is changing the dashes in the name to underscores.)

Thanks very much, this and Rob's sequence got me almost there. And apologies to Rob, Liam and Sven for missing this post on Scheme -> C procedure names until after my Sunday replies.

But using gimp_pencil (drawable_ID, etc.) in C only draws on the main window. I want it to draw on the preview or window as appropriate.

Here's my function in a nutshell:

if (!(drawable = (GimpDrawable *) gimp_drawable_get (drawable_ID))) return FALSE;
has_selection = gimp_drawable_mask_bounds (drawable_ID, &x1, &y1, &x2, &y2);

if (!(source_data = g_new (guchar, drawable->bpp * (x2-x1) * (y2-y1)))) return FALSE;
gimp_pixel_rgn_init (&source_region, drawable, x1, y1, x2-x1, y2-y1, FALSE, FALSE);
gimp_pixel_rgn_get_rect (&source_region, source_data, x1, y1, x2-x1, y2-y1);

// Do some stuff to source_data

gimp_pixel_rgn_init (&output_region, drawable, x1, y1, x2-x1, y2-y1, (preview == NULL), TRUE);

gimp_pixel_rgn_set_rect (&output_region, source_data + y1*rowskip, 0, y1, full_width, y2-y1);

// I want to draw the lines here

if (preview) gimp_drawable_preview_draw_region (GIMP_DRAWABLE_PREVIEW (preview), &output_region);
else
{
gimp_drawable_flush (drawable); gimp_drawable_merge_shadow (bs_param->drawable_ID, TRUE); gimp_drawable_update (bs_param->drawable_ID, x1, y1, win_width, win_height); }

This is called by both the "invalidated" callback of the preview in the dialog, and also the run() method of the plugin after "OK".

The first non-lines part works fine: the changes to source_data get merged into the preview when it's running, and into the original image when I click "OK".

However, it draws the lines on the original image when the preview is running in the dialog. So that messes up the image analysis (Do some stuff... above) when that runs at the end of run(). And gimp_pixel_rgn_set_rect overwrites the lines, so they're all gone.

How can I get this to behave like gimp_pixel_rgn_set_rect , i.e. draw on the preview in preview mode, and draw on the original window in run() ? Can I draw the lines into the output_region somehow?

-Adam