Re: How Do I Draw A Bitmap?
- From: Eric Mader <mader jtcsv com>
- To: Havoc Pennington <hp redhat com>
- Cc: gtk-app-devel-list gnome org
- Subject: Re: How Do I Draw A Bitmap?
- Date: Thu, 12 Jul 2001 10:56:38 -0700
Thanks for the reply.
At 07:43 PM 7/11/2001, Havoc Pennington wrote:
Eric Mader <mader jtcsv com> writes:
> I'm trying to write a little GNOME application to test a 3rd party
> font scaler; I've got as far as getting the bitmaps for the
> characters from the scaler, but I can't find a way to draw them.
Somehow I doubt the bitmaps are GdkBitmaps. What is the exact type and
format of these bitmaps?
The scaler returns an array of bits, one per pixel. I can control whether
or not it pads a row to a multiple of one, two or four bytes. I've got it
set to not pad. I was using gdk_bitmap_create_from_data() to make the
From the sample code I have, it looks like this takes an array of bits as
I get them from the scaler. Have I missed something?
> The first thing I tried was gdk_draw_bitmap(). When I link my
> application, that symbol doesn't get resolved.
That's because it doesn't exist. ;-)
So I gathered, but it *is* in gdk.h, so you can't blame me for expecting it
to be there...
> (On a whim I tried to use gdk_draw_pixmap() instead; that prints out
> some strange messages about incompatible parameters and exits - I
> assume because the bitmap is the wrong depth?)
Bitmaps are simply 1-bit pixmaps. Most drawables will be 8-bit or
The depth refers to the size of a pixel. So in bitmaps, each pixel is
on or off, one bit. Color displays use a lot more bits per pixel.
gdk_draw_pixmap() simply copies blocks of memory around; if you don't
have matching depths then nothing logical happens. Each 8 or 24 pixels
in the bitmap would make up one color pixel with a random ugly color.
So this is not allowed.
Assuming you actually had a GdkBitmap, which seems unlikely from a 3rd
party font scaler, the way you would typically draw it would be to set
it as a clip mask (gdk_gc_set_clip_mask()), then draw a rectangle.
Well, if I don't have a GdkBitmap, and can't easily make one from the bits
I get from the scaler, what do I do?
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