Re: [Freetype] Windows code displaying garbage - any help?

[Peter Montgomery]

Jason,

I was looking through your code when I suddenly realized that part of it
was mine!  I recognized my macro, the comment about padding, and my
coding and variable naming style.  I hunted through my sent email and
found the message I posted to this list regarding making a Windows BMP
from a FreeType bitmap.  Because of this, I realized I better jump in a
see what I can do.

1 - Have you tried saving the bitmap that FreeType generates and loading
it into a Paint Program as a raw image?  I find this sometimes help to
make sure that the data you have is formatted the way you think it is.
Many paint programs let you load a raw image where there is no header,
and you manually tell it the dimensions and the number of channels.

2 - You mention that it's "much bigger than you expected."  How big did
you expect it to be?  I can't even find the code where you set the size
of the FreeType bitmap.  Is this all the code or just a part of it?

3 - Where do you actually render the font?  I'm not a FreeType stud (I
basically got it working in my app and haven't touched it since) but in
looking over my code, there is a call to "FT_Load_Glyph( )" which does
the actual rendering of the font letter.  I find no such call in your
code.

4 - You say you want to render at 300, 300.   The way to do this is to
render the font into the FreeType bitmap at offset 0,0 and then BLT the
bitmap into the window at 300,300.  It appears that you are rendering at
300, 300 (e.g. the calls to "pen_x = 300;" and "pen_y = 300;") and then
BLTing at 300, 300 as well.

4 - Are you rendering aliased or non-aliased fonts?  You are creating a
Windows BMP that with a single channel of 8 bits per pixel, but you are
creating a color palette that has only two entries.  A two entry palette
implies aliased font rendering.  I assume that this:

for( int h = 0; h < 2; h++ )
    {
        i.bmiColors[h].rgbBlue   = h;
        i.bmiColors[h].rgbGreen  = h;
        i.bmiColors[h].rgbRed    = h;
    }

is the code where you create the palette.  Making things worse, you are
creating a palette with the values of 0 and 1, which would make for a
very dark image.  If you re-read my original post, you'll see that I
say, "Having said all of that, remember that even though you view it is
a B&W image, Windows views it as a 256 color image.  This means you'll
need to create a palette with RGB entries that go from 0 to 255."

5 - Assuming you are rendering anti-aliased fonts, then FreeType returns
a B&W image that has a single channel with 8 bits per pixel.  Because of
this, the "easiest" way to view it is to create a palletted BMP (as
described above) rather than copying the data into a true RGB image.
However, your BMP header is a bit of a mess as it is describing some
sort of half palette/half RGB image.  You set "biClrUsed" to zero, but
this implies an image with no palette.  Here's some info on the BMP
spec:

----------------------
biClrUsed Specifies the number of color indexes in the color table
actually used by the bitmap. If this value is 0, the bitmap uses the
maximum number of colors corresponding to the value of the biBitCount
field.
----------------------

You need to create a palette with 256 entries and specify 256 for the
"biClrUsed" member of the structure.

6 - You do a "CreateDIBSection" call and pass the parameter
"DIB_RGB_COLORS".  This means you are creating a BMP with no palette,
but you NEED a palette to get an image that displays properly.  You need
to pass "DIB_PAL_COLORS" instead.

In general, things are a bit of a mess.  So, here's my recommended plan
of action:

1 - Before you do anything else, do what I say at the top of this
message.  Either tweak your code or write a new (simple) app that
renders a FreeType bitmap into a file (as a stream of rendered bytes)
and then use a paint program to load it as a raw image.

2 - Re-read the BMP spec since it seems that you are not fully
comprehending all the details of the file format.  It's a pain, but you
need to dot your "i"s and cross you "t"s to get a properly formatted BMP
that will work.

3 - Someone suggested that you manually create a BMP and BLT that first.
Do it.  His suggestion to create a square is a good one in that you can
write some simple code to draw two horizontal lines and then a loop to
create the verticals.  Make sure that the square is smaller than your
entire BMP so that you can check to see if it is centered properly.

4 - Make the manually created image SMALL!  A BMP that's 10 X 10 pixels
with an 8 X 8 square in it should do the trick.  This way you can look
at the values in the debugger and see that they are correct if it
doesn't BLT as you expect.  With regards to the guy who gave you grief,
regardless of how he said it, his basic point is correct - get into the
debugger and check to make sure the image is what you think it is.

5 - Once you KNOW that's working, then start working on converting a
FreeType image into a BMP image and BLT'ing it to screen.

Tackle the job in small steps where you can verify that each step is
working before proceeding on to the next.  It seems to me that you are
not intimately familiar with Windows BMP images and the MANY
idiosyncrasies they have.  You need to get familiar with them before you
can be confident that your code will ever work properly.

    Thanks,
    PeterM