fb_example.c

/* EXAMPLE BY amarullz.com */

/* Includes Needed Headers for Framebuffer */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>

/* Android Framebuffer Device */
#define ANDROID_FRAMEBUFFER "/dev/graphics/fb0"

/* Defining Data-Types for shorting usage */
typedef unsigned char   byte;
typedef unsigned int    dword;    /* RGBX using 4bytes per pixel */
typedef byte *          bytep;
typedef dword *         dwordp;

/* Variable */
static int fb = 0;                      // FrameBuffer Handler
static struct fb_fix_screeninfo fbfix;  // Fixed Info
static struct fb_var_screeninfo fbvar;  // Vars Info
static dwordp buffer;                   // Framebuffer Data

int init_framebuffer(){
  fb = open(ANDROID_FRAMEBUFFER, O_RDWR, 0);

  if (fb>0) {
    // Retrive Framebuffer Fix&Var Informations
    ioctl(fb, FBIOGET_FSCREENINFO, &fbfix);
    ioctl(fb, FBIOGET_VSCREENINFO, &fbvar);

    // Retrive Framebuffer Memory Location
    buffer = (dwordp) mmap(0, fbfix.smem_len, PROT_READ|PROT_WRITE, MAP_SHARED, fb, 0);

    return 1;
  }

  return 0;
}

//-- RELEASE AMARULLZ GRAPHIC
void close_framebuffer() {
  if (fb > 0) {
    munmap(buffer, fbfix.smem_len);
    close(fb);
  }
}

void syncfb(){
  fsync(fb);
  fbvar.yoffset   = 0;
  fbvar.activate |= FB_ACTIVATE_NOW | FB_ACTIVATE_FORCE;
  ioctl(fb, FBIOPUT_VSCREENINFO, &fbvar);
}

int posxy(int x, int y){
  /*
    fbfix.line_length = length by bytes not by pixels.
    Because 1 pixel was 4 bytes, we need to div it with 4

      return (y * (fbfix.line_length/4)) + x;

    But for faster calculation, bitwise is better.
  */
  return (y * (fbfix.line_length >> 2)) + x;
}
void setpixel(int x, int y, dword color) {
  buffer[posxy(x,y)]=color;
}
dword getpixel(int x, int y) {
  return buffer[posxy(x,y)];
}

/* Build 32bit Color From RGBA Channels */
dword RGBA(byte r, byte g, byte b, byte a) {
  return (dword)
         (
           ((r & 0xff) << 16) |
           ((g & 0xff) << 8) |
           (b & 0xff) |
           ((a & 0xff) << 24)
         );
}
dword RGB(byte r, byte g, byte b) {
  return RGBA(r, g, b, 0xff);
}
byte GetR(dword color) {
  return (byte) ((color >> 16) & 0xff);
}
byte GetG(dword color) {
  return (byte) ((color >> 8) & 0xff);
}
byte GetB(dword color) {
  return (byte) (color & 0xff);
}
byte GetA(dword color) {
  return (byte) ((color >> 24) & 0xff);
}

int main(int argc, char *argv[])
{
  if (init_framebuffer()==0){
    /* Error */
    return -1;
  }

  // Pause Parent Proccess First, so framebuffer
  // will not interrupted by recovery
  int parent_pid = getppid();
  kill(parent_pid, 19);

  // Draw Rectangle
  int x, y;
  for (y=0; y<fbvar.yres; y++){
    for (x=0; x<fbvar.xres; x++){
      // Blue = 44, 100, 200
      setpixel(x, y, RGB(44, 100, 200));
    }
  }

  // Show It On Display
  syncfb();

  sleep(3);

  // Draw Other Rectangle
  for (y=0; y<fbvar.yres; y++){
    for (x=0; x<fbvar.xres; x++){
      // Red
      setpixel(x, y, RGB(180, 50, 50));
    }
  }

  // Show It On Display
  syncfb();

  sleep(3);

  // Resume Parent Pid
  kill(parent_pid, 18);

  close_framebuffer();
  return 0;
}