Re: [Linux-fbdev-users] Endianness issues using the framebuffer

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----- Original Message ----- 
From: "Roger Leigh" <rl...@wh...>
To: <lin...@li...>
Sent: Monday, June 27, 2005 4:46 PM
Subject: [Linux-fbdev-users] Endianness issues using the framebuffer

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> Hi folks,
>
> I'm looking into writing a program which will use the framebuffer to
> display rendered fonts and some graphics.  However, I've not yet found
> much in the way of programming documentation.  Is there anything you
> would recommend?
>
> (I've looked at SDL, directfb and GGI sources, but they are very
> complex.)
>
> Using the comments in <linux/fb.h> and some simple examples I found,
> I've written the sample code below.  However, none of the examples I
> saw made any use of the fb_bitfield information.  I ran into problems
> when I tried my (i386 tested) code on a PPC.  After fixing the code,
> it still doesn't work.  I have the bizarre situation that if I run it
> under X11 (using XF86_FBDev), I see the glyphs rendered fine, but if I
> run it on the console the colours are mucked up, and I can't see any
> change in the bitfield data.
>
> Are there any examples of painting simple RGB pixel data onto any
> arbitrary framebuffer device which also works on big and little endian
> systems.  I'm sure this is fairly simple once you know how!
>
> Additionally, is there any documentation about how colourmaps and the
> other framebuffer features work?
>
>
> Many thanks,
> Roger
>
>
> This program simply renders each ASCII character in turn and paints
> it.  You might need to change the fb device and font path.  It's
> currently hard-coded for RBG LCDs, but is simple to change for a CRT.
>
> Compile with
> c99 -o ft-lcd ft-lcd.c `freetype-config --cflags --libs`
>
> #include <unistd.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <fcntl.h>
> #include <linux/fb.h>
> #include <sys/ioctl.h>
> #include <sys/mman.h>
>
> #include <ft2build.h>
> #include FT_FREETYPE_H
>
> void fail (const char *reason)
> {
>   fprintf (stderr, "%s\n", reason);
>   exit (EXIT_FAILURE);
> }
>
> int
> main()
> {
>   int fbfd = 0;
>   struct fb_var_screeninfo vinfo;
>   struct fb_fix_screeninfo finfo;
>   long int screensize = 0;
>   char *fbp = 0;
>   int x = 0, y = 0;
>   long int location = 0;
>
>   // Open the file for reading and writing
>   fbfd = open("/dev/fb/0", O_RDWR);
>   if (fbfd < 0)
>     fail("Error: cannot open framebuffer device.");
>
>   // Get fixed screen information
>   if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo))
>     fail("Error reading fixed information.");
>
>   // Get variable screen information
>   if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo))
>     fail("Error reading variable information.");
>
>   printf("%ux%u (%ux%u), %ubpp\n", vinfo.xres, vinfo.yres,
> vinfo.xres_virtual, vinfo.yres_virtual, vinfo.bits_per_pixel );
>   printf("offsets: x=%u, y=%u\n", vinfo.xoffset, vinfo.yoffset);
>   printf("red: o=%u, l=%u, mr=%u\n", vinfo.red.offset, vinfo.red.length,
vinfo.red.msb_right);
>   printf("green: o=%u, l=%u, mr=%u\n", vinfo.green.offset,
vinfo.green.length, vinfo.green.msb_right);
>   printf("blue: o=%u, l=%u, mr=%u\n", vinfo.blue.offset,
vinfo.blue.length, vinfo.blue.msb_right);
>   printf("transp: o=%u, l=%u, mr=%u\n", vinfo.transp.offset,
vinfo.transp.length, vinfo.transp.msb_right);
>
>   unsigned int red_max = 1 << vinfo.red.length;
>   unsigned int green_max = 1 << vinfo.green.length;
>   unsigned int blue_max = 1 << vinfo.blue.length;
>   unsigned int transp_max = 1 << vinfo.transp.length;
>
>   unsigned int red_mask = 0;
>   for (unsigned int i=0; i<vinfo.red.length; ++i)
>     red_mask |= 1 << (vinfo.red.offset + i);
>   unsigned int green_mask = 0;
>   for (unsigned int i=0; i<vinfo.green.length; ++i)
>     green_mask |= 1 << (vinfo.green.offset + i);
>   unsigned int blue_mask = 0;
>   for (unsigned int i=0; i<vinfo.blue.length; ++i)
>     blue_mask |= 1 << (vinfo.blue.offset + i);
>   unsigned int transp_mask = 0;
>   for (unsigned int i=0; i<vinfo.transp.length; ++i)
>     transp_mask |= 1 << (vinfo.transp.offset + i);
>
>
>   // Figure out the size of the screen in bytes
>   screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
>
>   // Map the device to memory
>   fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
>      fbfd, 0);
>   if ((int)fbp == -1)
>     fail("Error: failed to map framebuffer device to memory.\n");
>
>   // Now setup FreeType
>   FT_Library library;
>   FT_Face face;
>
>   int error = FT_Init_FreeType( &library );
>   if ( error )
>     {
>       fail ("Failed to initialise FreeType");
>     }
>
>   error = FT_New_Face( library,
"/usr/share/fonts/truetype/ttf-bitstream-vera/VeraMono.ttf", 0, &face );
>   if ( error == FT_Err_Unknown_File_Format )
>     {
>       fail ("Unsupported font format");
>     }
>   else if ( error )
>     {
>       fail ("Error reading font file");
>     }
>
>   error = FT_Set_Char_Size ( face,
>      0,
>      12 * 64,
>      100,
>      100 );
>   if (error)
>     {
>       fail ("Error setting char size");
>     }
>
>   // Display each ASCII printable char
>   for (FT_ULong n = 33; n < 127; ++n)
>     {
>       FT_UInt glyph_index = FT_Get_Char_Index (face, n);
>
>       FT_Load_Glyph (face,
>      glyph_index,
>      FT_LOAD_DEFAULT|FT_LOAD_TARGET_LCD);
>
>       error = FT_Render_Glyph (face->glyph,
>        FT_RENDER_MODE_LCD);
>
>       if (error)
> {
>   fail ("Error rendering glyph");
> }
>
>       if (n == '_')
> continue;
>
>       FT_Bitmap *bitmap = &face->glyph->bitmap;
>
>       //      printf ("Glyph '%c': %d * %d\n", (char) n, bitmap->width,
bitmap->rows);
>
>       //printf ("Bitmap top: %d\nBitmap left: %d\n",
face->glyph->bitmap_top,
>       //      face->glyph->bitmap_left);
>
>       for (y=0; y<200; ++y)
> for (x=0; x<200; ++x)
>   {
>     location = ((x + 0)+vinfo.xoffset) *
>       (vinfo.bits_per_pixel/8) +
>       ((y + 0)+vinfo.yoffset) * finfo.line_length;
>
>     if ( vinfo.bits_per_pixel == 32 ) {
>       unsigned int *pixel = (int *) (fbp + location);
>       *pixel = 0;
>     }
>   }
>
>       for (y=0; y<bitmap->rows; ++y)
> for (x=0; x< (bitmap->width / 3); ++x)
>   {
>     location = ((x + face->glyph->bitmap_left)+vinfo.xoffset) *
>       (vinfo.bits_per_pixel/8) +
>       ((y + face->glyph->bitmap_top)+vinfo.yoffset) * finfo.line_length;
>
>     unsigned int r = *(bitmap->buffer + (y * bitmap->pitch) + (x*3 + 0));
>     //     r *= (red_max /8);
>     unsigned int g = *(bitmap->buffer + (y * bitmap->pitch) + (x*3 + 1));
>     //     g *= (red_max /8);
>     unsigned int b = *(bitmap->buffer + (y * bitmap->pitch) + (x*3 + 2));
>     //     b *= (red_max /8);
>
>     // printf("r=%u, g=%u, b=%u\n", r, g, b);
>
>     if ( vinfo.bits_per_pixel == 32 ) {
>       unsigned int *pixel = (int *) (fbp + location);
>       *pixel = 0;
>
>       // This works when I run under X11_FBDev (i.e. the
>       // colours are correct), but if I run on the console, I
>       // get a mess and mostly blue colours...
>
>       *pixel |= ((r << vinfo.red.offset)   & red_mask);
>       *pixel |= ((g << vinfo.green.offset) & green_mask);
>       *pixel |= ((r << vinfo.blue.offset)  & blue_mask);
>
>     }
>   }
>
>       sleep (1);
>
>     }
>
>   return 0;
> }
>
>
> - -- 
> Roger Leigh
>                 Printing on GNU/Linux?  http://gimp-print.sourceforge.net/
>                 Debian GNU/Linux        http://www.debian.org/
>                 GPG Public Key: 0x25BFB848.  Please sign and encrypt your
mail.
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