linux_framebuffer_simpletest.c

#include <stdlib.h> 
#include <unistd.h> 
#include <stdio.h> 
#include <fcntl.h> 
#include <linux/fb.h> 
#include <sys/mman.h> 
#include <sys/ioctl.h> 

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/fb0", O_RDWR); 
    if (fbfd == -1) { 
        perror("Error: cannot open framebuffer device"); 
        exit(1); 
    } 
    printf("The framebuffer device was opened successfully.\n"); 

    // Get fixed screen information 
    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) { 
        perror("Error reading fixed information"); 
        exit(2); 
    } 

    // Get variable screen information 
    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) { 
        perror("Error reading variable information"); 
        exit(3); 
    } 

    printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel); 

    // 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) { 
        perror("Error: failed to map framebuffer device to memory"); 
        exit(4); 
    } 
    printf("The framebuffer device was mapped to memory successfully.\n"); 

    x = 100; y = 100; // Where we are going to put the pixel 

    // Figure out where in memory to put the pixel 
    for (y = 100; y < 300; y++) 
        for (x = 100; x < 300; x++) { 

            location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) + 
                       (y+vinfo.yoffset) * finfo.line_length; 

            if (vinfo.bits_per_pixel == 32) { 
                *(fbp + location) = 100; // Some blue 
                *(fbp + location + 1) = 15+(x-100)/2; // A little green 
                *(fbp + location + 2) = 200-(y-100)/5; // A lot of red 
                *(fbp + location + 3) = 0; // No transparency 
        //location += 4; 
            } else { //assume 16bpp 
                int b = 10; 
                int g = (x-100)/6; // A little green 
                int r = 31-(y-100)/16; // A lot of red 
                unsigned short int t = r<<11 | g << 5 | b; 
                *((unsigned short int*)(fbp + location)) = t; 
            } 

        } 
    munmap(fbp, screensize); 
    close(fbfd); 
    return 0; 
}