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Old 04-27-2005, 11:09 AM   #1
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Registered: Jul 2004
Location: Germany
Posts: 24

Rep: Reputation: 15
GTK/GDK 1.2 GdkPixmap: Set a pixel with a color

based on
I copied part of the code (I gave up to fully understand the code after a few hours) in a program written by me. I get so far to write a procedure which sets on wished x,y coordinates a black point. Responsible for placing a black point is a modified version of the draw_brush() procedure from the example. But I want to set a pixel in any color, not just a black one. I did not found out how to do this. I think it has something to do with widget->style->black_gc. Unfortunately I did not found out how to modify black_gc.
In Delphi I would simply write canvas.pixels[x,y] := $7f0000; to set the pixel on the position x,y to a medium red. I did not figured out how to do similar things with gtk.
Could anyone please help me?
Old 04-27-2005, 05:25 PM   #2
LQ Newbie
Registered: Jul 2004
Location: Germany
Posts: 24

Original Poster
Rep: Reputation: 15
I have a solution

After one day of searching, I have now a solution for my problem :

static void draw_point( GtkWidget *widget, gdouble x, gdouble y, long color) {
GdkColor colors[1];
GdkGC *color_gc = gdk_gc_new (widget->window);
if (pixmap1 != NULL) {
GdkRectangle update_rect;
update_rect.x = x;
update_rect.y = y;
update_rect.width = 1;
update_rect.height = 1;
colors[0].red = (color>>16&0xff)*256;
colors[0].green = (color>>8&0xff)*256;
colors[0].blue = (color>>0&0xff)*256;
gdk_colormap_alloc_color (gdk_colormap_get_system(), &colors[0], FALSE, TRUE);
gdk_gc_set_foreground (color_gc, colors);
gdk_draw_point(pixmap1, color_gc, x, y);
gtk_widget_draw (widget, &update_rect);
} else {
printf("draw_point: Error, pixmap1 not defined\n");
I do not understand everything, especialy why GdkColor colors[1]; needs to be an array (It has only one element), but it is working now. One day to figure out how to set a pixel on the drawing interface black and an other to find out how to set a pixel to wished color. How efficient
I hope that I will understand the code better tomorrow.
Old 01-14-2013, 01:48 AM   #3
Registered: Aug 2004
Distribution: Lubuntu Live OS
Posts: 432

Rep: Reputation: 30
If I would like to change pixel / canvas of imageS

This Linux program can help?

PhotoShop CS2 now FREE!

Last edited by fhleung; 01-19-2013 at 10:11 PM.


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