Bitmap API

A C library for manipulating bitmap/raster graphics in memory and on disk.

#include <stdio.h>
#include "bmp.h"

int main(int argc, char *argv[]) {
    Bitmap *b = bm_create(128,128);

    bm_set_color(b, bm_atoi("white"));
    bm_puts(b, 30, 60, "Hello World");

    bm_save(b, "out.gif");
    bm_free(b);
    return 0;
}

The code is licensed under the terms of the MIT-0 License. See the file LICENSE for details.

Attribution is appreciated, but not required.

Features:

• Supported formats:
  • Windows BMP: loads 4-, 8- and 24-bit uncompressed BMP files, saves as 24-bit.
  • GIF, PCX and TGA files can be loaded and saved without third-party dependencies.
  • PNG through libpng
    • support for palettized images is incomplete.
  • JPEG through libjpeg
  • Alternatively, PNG and JPEG files can be loaded through the Sean Barrett's stb_image image loader library. stb_image supports a couple of additional formats, such as PSD, PIC and PNM binary formats. See bm_load_stb() for more information. A copy of stb_image.h has been placed in /3rd-party/stb_image.h.
  • Likewise, PNG and JPEG images can be saved through Sean Barrett's stb_image_write image writer library. A copy of stb_image_write.h has been placed in /3rd-party/stb_image_write.h.
  • NetPBM formats (PBM, PGM and PPM), in ASCII or binary variants.
• Supports manipulation of OpenGL textures, SDL surfaces, GDI contexts. See the bm_bind() function. It can also serve as a back end for Cairo graphics
• Support for SDL2's SDL_RWops file manipulation routines for loading images in the supported formats.
• Primitives: Lines, circles, elipses, bezier curves, polygons, etc.
  • Clipping rectangles are obeyed.
• Floodfill and filled primitives.
• Image resizing: nearest neighbour, bilinear and bicubic.
• Blitting, blitting with color masks, scaled and rotated blitting.
• Text rendering: FreeType support and built-in 8-bit style raster fonts, and support for SFont and GrafX2-style fonts.
• Filtering with kernels and smoothing.
• CSS-style colors.
• Loading images from XBM and X PixMap data.
• Cross platform. It's been known to compile under Windows (MinGW), Linux, Android and Web via Emscripten.
• Support for Damien Guard's ZX Origins 8×8 pixel fonts.

The fonts/ directory contains some 8-bit style bitmap fonts in XBM format.

Getting Started

Copy bmp.c and bmp.h to your project directory, and add bmp.c to your list of files to compile.

To enable PNG support you need zlib and libpng (the development versions) installed. If you are using GCC, do the following:

• Use these flags -DUSEPNG `libpng-config --cflags` when compiling.
• Add `libpng-config --ldflags` -lz when linking.

Other compilers might have diffent flags. See the libpng documentation for your platform.

Likewise, to enable JPEG support, you need libjpeg installed and specify the -DUSEJPG command line option when compiling and add -ljpeg to your linker options.

To use stb_image, put the stb_image.h file in the same directory as bmp.c (or use your compiler's -I option to point it to stb_image.h's path), and add -DUSESTB to your compiler flags.

Similarly, to use stb_image_write, put the stb_image_write.h file in the same directory as bmp.c, and add -DUSESTBW to your compiler flags.

Use bm_create() to create Bitmap objects and bm_free() to destroy them.

bm_bind() can be used to wrap a Bitmap object around an existing buffer of bytes, such as OpenGL textures and SDL surfaces.

The Makefile generates HTML documentation from bmp.h through the d.awk script. Type make docs to create the documentation.

A basic CMakeLists.txt file is also provided for CMake, but you might need to adapt it to your specific needs. To build with CMake, use the following commands:

mkdir build; cd build
cmake -G "Unix Makefiles" ..
make

Additional Utilities

• The fonts/ directory contains some 8×8 bitmap fonts in XBM format that can be loaded via the bm_make_xbm_font() function.
  • Most of the fonts are based on 80's home computers, drawn from the examples at http://damieng.com/blog/2011/02/20/typography-in-8-bits-system-fonts
  • The INSTRUCTIONS file contains information for using them.
  • The tomthumb.c file contains a 4×6 font based on the "Tom Thumb" monospace font at http://robey.lag.net/2010/01/23/tiny-monospace-font.html
• The ftypefont/ directory contains a wrapper for FreeType to allow rendering of freetype-supported fonts on Bitmap structures.
• The misc/ directory contains
  • gif.c and gif.h - code for programmatically manipulating animated GIFs. It originates from the file I used to develop the GIF encoder/decoder originally.
  • cairoback.c - A demo of how the bitmap objects can be used as a back-end for the Cairo graphics library
  • The palette/ subdirectory contains a utility for generating palettes and converting images to those palettes.
  • xpm.c: Samples on how to use the module with the XPM file format. to_xbm.c contains a function that can output a bitmap as a XBM.
  • The kmeans.c contains a program that uses K-means clustering to identify the dominant colors in an image.
  • imgdup.c is a program that scans directories for duplicate images using the dHash algorithm.
  • nanosvg.c is an example of how to use the library with Mikko Mononen's NanoSVG library to load SVG files.
  • bm_microui.c contains functions to render rxi's microui graphical user interfaces to a Bitmap structure.
  • cp437.c and cp437.h contains a Code page 437 BmFont and some utility functions to draw a grid-based TUI screen.
  • bdffont.c contains code to load and draw BDF fonts as BmFont objects.
  • bgichr.h is a set of functions that can handle old Borland BGI fonts (usually files with a .CHR extension) as BmFont objects.

References

• BMP file format on Wikipedia
• Bresenham's line algorithm on Wikipedia
• http://members.chello.at/~easyfilter/bresenham.html
• Flood fill on Wikipedia
• Midpoint circle algorithm on Wikipedia
• http://web.archive.org/web/20110706093850/http://free.pages.at/easyfilter/bresenham.html
• Typography in 8 bits: System fonts
• GIF89a specification
• Nelson, M.R. : "LZW Data Compression", Dr. Dobb's Journal, October 1989.
• http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art011
• What's In A GIF by Matthew Flickinger
• http://web.archive.org/web/20100206055706/http://www.qzx.com/pc-gpe/pcx.txt
• http://www.shikadi.net/moddingwiki/PCX_Format
• Truevision TGA on Wikipedia
• http://paulbourke.net/dataformats/tga/
• http://www.ludorg.net/amnesia/TGA_File_Format_Spec.html
• X PixMap on Wikipedia
• A simple libpng example program
• http://www.fileformat.info/format/xpm/egff.htm
• "Fast Bitmap Rotation and Scaling" By Steven Mortimer, Dr Dobbs' Journal, July 01, 2001
  http://www.drdobbs.com/architecture-and-design/fast-bitmap-rotation-and-scaling/184416337
• http://www.efg2.com/Lab/ImageProcessing/RotateScanline.htm
• Image Filtering in Lode's Computer Graphics Tutorial
• Grayscale on Wikipedia
• Xiaolin Wu's line algorithm on Wikipedia.
• Michael Abrash's article in the June 1992 issue of Dr Dobbs' Journal.
• The README file in the SFont distribution discusses the details.
• This forum post contains a discussion of the GrafX2 format
• Here are some SFont/GrafX2 font resources:
  • https://opengameart.org/content/a-package-of-8-bit-fonts-for-grafx2-and-linux
  • https://opengameart.org/content/new-original-grafx2-font-collection
  • https://opengameart.org/content/the-collection-of-8-bit-fonts-for-grafx2-r2; SaikyoBlack.png comes from here

TODO

• Support for PCF fonts (now that I support BDF fonts).
  • See also https://en.wikipedia.org/wiki/Portable_Compiled_Format
  • https://web.archive.org/web/20010215151331if_/http://myhome.hananet.net/~bumchul/xfont/pcf.txt
  • You'll find some font examples at https://github.com/Tecate/bitmap-fonts
• If I'm going to have bm_rotate_cw() and bm_rotate_ccw() functions, then I ought to have flip horizontal and vertical functions as well for completeness.
• Since bm_rotate_cw() and bm_rotate_ccw() functions take the clipping rect into account, I should consider doing the same for some of the other API functions for consistency, like bm_resample() and co. Also the flip functions suggested above.
• Support for QOI files. I was going to just pull in the reference implementation, but the qoi_decode() function didn't look like it'd fit in nicely with the BmReader interface.
• Rotating ritmaps with three sheers: https://cohost.org/tomforsyth/post/891823-rotation-with-three