Googled and found a macro...
#define RGB(R,G,B) {(R<<16)|(G<<8)|B,(R*65535)/255,(G*65535)/255,(B*65535)/255}
I have tried it with a handful of rgb values and it works (used
gtk_widget_modify_bg to change the surface colour of some dialogs), like
GdkColor col = RGB(0,0,255);
gtk_widget_modify_bg ( dlg , GTK_STATE_NORMAL , &col );
A few changes were needed to my api. For example, on Windows I returned
colorrefs as int function values. That is not possible for GdkColor structs, so
I changed the api to return a COLORREF parameter instead with
typedef GdkColor COLORREF; // for Gtk
typedef int COLORREF; // for Windows
It works, but I still don't understand colours...
Q1. the pixel component of the GdkColor struct is (R<<16)|(G<<8)|B, but is the
other way around in the Windows RGB macro R|(G<<16)|(B<<16). I am puzzled by
this. I am also puzzled by the pixel value being 32 bits (r,g,b,alpha) while
the combined size of the r,g,b intensities is 48. Why is this?
Q2. while googling I came across this for GdkColor: 'the programmer provides
the r,g and b intensities and GDK fills in the pixel component.' When does GDK
do this? By what functions?
Q3. I have tried reading about Colormaps and Colors in the GDK reference
manual, but I am getting stuck on the basics. For example in the Description
what does this mean: 'A colormap is an object that contains the mapping between
the color values stored in memory and the RGB values that are used to display
color values. In general, colormaps only contain significant information for
pseudo-color visuals, but even for other visual types, a colormap object is
required in some circumstances.' Does it mean 'a colormap is a list of
GdkColors like a palette'? Is the RGB value mentioned in the description the
pixel component in the GdkColor?
Q4. For GdkColor the manual says 'the GdkColor structure is used to describe an
allocated or unallocated color'. What does allocated and unallocated color mean?
Q5. The Colormaps and Colors Reference contains several functions, but I did
not use any of them. It still worked with the colours coming out the way I
expected. When are these functions used/needed? Or are they becoming obsolete?
--- On Fri, 13/8/10, Ken Resander <kresan...@yahoo.com> wrote:
From: Ken Resander <kresan...@yahoo.com>
Subject: Any RGB macro in Gtk?
To: gtk-list@gnome.org
Date: Friday, 13 August, 2010, 6:48 PM
I would like to port some Windows programs to Ubuntu+Gtk. These contain several
large colour lookup tables using the Windows RGB macro. For example:
static COLALTINFO safealts [ NUMCOLITEMS ]
=
{
{ RGB(0xF0,0xF8,0xFF),RGB(0xFF,0xFF,0xFF) ,RGB(0x00,0x00,0x00) },
{ RGB(0xFA,0xEB,0xD7),RGB(0xFF,0xFF,0xCC) ,RGB(0x00,0x00,0x00) },
....
I have not done any drawing yet with Gtk and don't know how colours work, but
there are thousands of RGB macro calls and it would very tedious and error
prone if I have to change them manually. I really don't want to touch the RGB
colour values in the lookup tables, but I probably would have change the
COLALTINFO definition to match the way Gtk represents colour.
Is there a RGB macro in Gtk/Gdk, or can such macro be
written?
P.S.
The Windows RGB macro builds a 24-bit int constant (COLORREF).
and is defined as follows:
#define RGB(r, g ,b) ((DWORD) (((BYTE) (r) | \
((WORD) (g) << 8)) | \
(((DWORD) (BYTE) (b)) << 16)))
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