FBG – Lightweight C Linux framebuffer graphics with parallelism

FBGraphics : Lightweight C graphics library for the Linux framebuffer with parralelism support

FBGraphics (FBG) is a simple C 24 bpp graphics library for the Linux framebuffer with parralelism support.

Features :

• Optional : Full parralelism, execute graphics code on multiple CPU cores with a single function
• Displaying and loading PNG images (provided by LodePNG )
• Bitmap fonts for drawing texts
• Bare-metal graphics primitive (pixels, rectangles)
• Double buffering
• 24 bpp only (may change in the future!)
• Easy to do fading and screen-clearing related effects (motion blur etc.)
• Framerate tracking & display for all cores
• Lightweight enough to be hackable; adapt to all kinds of needs (and still support parralelism easily)

The library is relatively generic, it only manipulate buffers and render them to the framebuffer device so it should be easy to extract some parts to adapt it to other means.

Table of Contents

• FBGraphics
  • About
    • Quickstart
    • Parralelism
    • Technical implementation
  • Benchmark
  • Documentation
  • Building
  • Screenshots
  • License

About

FBGraphics was made to produce fullscreen pixels effects easily with non-accelerated framebuffer by leveraging multi-core processors, it is a bit like a software GPU (much less complex and featured!), the initial target platform is a Raspberry PI 3B and extend to the NanoPI (and many others embedded devices), the library should just work with many others devices with a Linux framebuffer altough there is at the moment some restrictions on the supported framebuffer format (24 bits).

FBGraphics is lightweight and does not intend to be a fully featured graphics library, it provide a limited set of graphics primitive and a small set of useful functions to start doing framebuffer graphics right away with or without multi-core support.

If you want to use the parralelism features with more advanced graphics primitives, take a look at great libraries such as libgd or Adafruit GFX library which should be easy to integrate.

FBGraphics is fast but should be used with caution, no bounds checking happen on most primitives.

Multi-core support is totally optional and is only enabled when FBG_PARALLEL C definition is present.

Note : This library does not let you setup the framebuffer, it expect the framebuffer to be configured prior launch with a command such as :

fbset -fb /dev/fb0 -g 512 240 512 240 24 -vsync high
setterm -cursor off > /dev/tty0

Quickstart

The simplest example (without texts and images) :

#include <sys/stat.h>
#include <signal.h>

#include "fbgraphics.h"

int keep_running = 1;

void int_handler(int dummy) {
    keep_running = 0;
}

int main(int argc, char* argv[]) {
    signal(SIGINT, int_handler);

    struct _fbg *fbg = fbg_setup("/dev/fb0"); // you can also directly use fbg_init(); for "/dev/fb0"

    do {
        fbg_clear(fbg, 0); // can also be replaced by fbg_fill(fbg, 0, 0, 0);

        fbg_draw(fbg);

        fbg_rect(fbg, fbg->width / 2 - 32, fbg->height / 2 - 32, 16, 16, 0, 255, 0);

        fbg_pixel(fbg, fbg->width / 2, fbg->height / 2, 255, 0, 0);

        fbg_flip(fbg);

    } while (keep_running);

    fbg_close(fbg);

    return 0;
}

A simple quickstart example with most features (but no parralelism, see below) :

#include <sys/stat.h>
#include <signal.h>

#include "fbgraphics.h"

int keep_running = 1;

void int_handler(int dummy) {
    keep_running = 0;
}

int main(int argc, char* argv[]) {
    signal(SIGINT, int_handler);

    struct _fbg *fbg = fbg_init();

    struct _fbg_img *texture = fbg_loadPNG(fbg, "texture.png");
    struct _fbg_img *bb_font_img = fbg_loadPNG(fbg, "bbmode1_8x8.png");

    struct _fbg_font *bbfont = fbg_createFont(fbg, bb_font_img, 8, 8, 33);

    do {
        fbg_clear(fbg, 0);

        fbg_draw(fbg);

        fbg_image(fbg, texture, 0, 0, fbg->width, fbg->height);

        fbg_write(fbg, "Quickstart example\nFPS:", 4, 2);
        fbg_write(fbg, fbg->fps_char, 32 + 8, 2 + 8);

        fbg_rect(fbg, fbg->width / 2 - 32, fbg->height / 2 - 32, 16, 16, 0, 255, 0);

        fbg_pixel(fbg, fbg->width / 2, fbg->height / 2, 255, 0, 0);

        fbg_flip(fbg);

    } while (keep_running);

    fbg_freeImage(texture);
    fbg_freeImage(bb_font_img);
    fbg_freeFont(bbfont);

    fbg_close(fbg);

    return 0;
}

Note : Functions like fbg_clear or fbg_fpixel are fast functions, there is slower equivalent (but more parametrable) such as fbg_background

Parralelism

Exploiting multiple cores with FBGraphics is really easy, first you have to prepare 3 functions (of which two are optional if you don't have any allocations to do) of the following definition :

// optional function
void *fragmentStart(struct _fbg *fbg) {
    // typically used to allocate your per-thread data
    // see full_example.c for more informations

    return NULL; // return your user data here
}

void fragment(struct _fbg *fbg, struct _fragment_user_data *user_data) {
    // this function will be executed by each threads
    // you are free to call any FBG graphics primitive here
    
    fbg_fclear(fbg, 0);
    
    // you are also free to fill each threads back buffer the way you want to
    // fbg->task_id : thread identifier (starting at 1, 0 is reserved for the main thread)
    // each threads will draw an horizontal line, the shade of the blue color will change based on the thread it is drawn from
    int x = 0, y = 0;
    for (y = fbg->task_id; y < fbg->height; y += 4) {
        for (x = 0; x < fbg->width; x += 1) {
            int i = (x + y * fbg->width) * 3;
            fbg->back_buffer[i] = fbg->task_id * 85; // note : BGR format
            fbg->back_buffer[i + 1] = 0;
            fbg->back_buffer[i + 2] = 0;
        }
    }
    
    // simple graphics primitive (4 blue rectangle which will be handled by different threads in parallel)
    fbg_rect(fbg, fbg->task_id * 32, 0, 32, 32, 0, 0, 255);
}

// optional function
void fragmentStop(struct _fbg *fbg, struct _fragment_user_data *data) {
    // typically used to free your per-thread data
    // see full_example.c for more informations
}

Then you have to create a 'Fragment' which is a FBG multi-core task :

fbg_createFragment(fbg, fragmentStart, fragment, fragmentStop, 3, 7);

Where :

• fbg is the main library data structure returned by fbg_init or fbg_setup
• fragmentStart is a C function which will be executed when the thread start (can be NULL)
• fragment is a C function which will be executed indefinitly for each threads and where all the draw code will happen
• fragmentStop is a C function which will be executed when the thread end (can be NULL)
• 3 is the number of parallel tasks (this will launch 3 threads)
• 7 is the buffer queue length for each threads (the amount of frame buffers stored in the internal ringbuffer queue)

And finally you just have to make a call to your fragment function in your drawing loop and call fbg_draw !

fragment(fbg, NULL);
fbg_draw(fbg, 1);

The second argument to fbg_draw tell FBG to synchronize with all the threads, it will wait until all the data are received from all the threads, if disabled, data from some threads may not arrive in time and make it into the second frame.

Note : This example will use 4 threads (including your app one) for drawing things on the screen but calling the fragment function in your drawing loop is totally optional, you could for example make use of threads for intensive drawing tasks and just use the main thread to draw the GUI or the inverse etc. it is up to you!

And that is all you have to do!

See simple_parallel_example.c example for the full code.

Note : You can only create one Fragment per fbg instance, another call to fbg_createFragment will stop all tasks for the passed fbg context and will create a new set of tasks.

Technical implementation

FBGraphics threads come with their own fbg context data which is essentialy a copy of the actual fbg context, they make use of C atomic types.

Each threads begin by fetching a pre-allocated buffer from a freelist, then the fragment function is called to fill that buffer, the thread wait (using a pthread barrier) for all others to finish their drawing task and then place the buffer into a ringbuffer data structure which will be fetched upon calling fbg_draw , the buffers are then mixed into the main back buffer and put back into the freelist.

FBGraphics parralelism make use of the liblfds library for the Ringbuffer and Freelist data structure.

Benchmark

Full example

Fullscreen per pixels perlin noise with texture mapping and scrolling (unoptimized)

Device: Raspberry PI 3B ( Quad Core 1.2GHz )

Settings: 320x240

Cores used to draw graphics FPS 1 42 FPS 2 81 FPS 3 118 FPS

Documentation

All usable functions and structures are documented in the fbgraphics.h file

Examples demonstrating all features are also available in the examples directory.

Building

C11 standard should be supported by the C compiler.

All examples make use of the framebuffer device /dev/fb0 and can be built by typing make into the examples directory then run them by typing ./run_quickstart for example (this handle the framebuffer setup prior launch), you will need to compile liblfds for the parralelism features. (see below)

All examples were tested on a Raspberry PI 3B with framebuffer settings : 512x240 24 bpp

For the default build (no parralelism), FBGraphics come with a header file fbgraphics.h and a C file fbgraphics.c to be included / compiled with your program, you will also need to compile the lodepng.c library, see the examples directory for examples of Makefile.

For parralelism support, FBG_PARALLEL need to be defined and you will need the liblfds library :

• Get latest liblfds 7.1.1 package on the official website
• uncompress, go into the directory liblfds711
• go into the directory build/gcc_gnumake
• type make in a terminal
• liblfds711.a can now be found in the bin directory, you need to link against it when compiling (see examples)

To compile parallel examples, just copy liblfds711.a / liblfds711.h file and liblfds711 directory into the examples directory then type make .

Screenshots

License

BSD, see LICENSE file