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A C module for manipulating bitmap graphics
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fonts Fixed the fonts/ instructions Jan 16, 2018
ftypefont There is now `bm_free_font()` function that uses the `dtor` member of… May 30, 2017
misc Added support for Sean Barrett's stb_image library. Jan 23, 2018
Makefile Added support for SFont/GrafX2-style fonts. May 12, 2018 I something in my last update to the readme Aug 19, 2018
bmp.h Added some sampling functions for `bm_blit_callback()` and documentat… Jan 3, 2019

Bitmap API

A C library for manipulating bitmap 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");
    return 0;

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


  • 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.
  • 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.

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, and add -DUSESTB 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][dawk] script. Type make docs to create the documentation.

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.
  • 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.
    • pbm.c and xpm.c: Samples on how to use the module with PBM and XPM file formats. to_xbm.c contains a function that can output a bitmap as a XBM.
    • The kmeans/ subdirectory 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.


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