rking · May 4, 2013 05:50 · May 4, 2013
diff --git a/fb.c b/fb.c
@@ -0,0 +1,77 @@
+#include <unistd.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <linux/fb.h>
+#include <sys/mman.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) {
+        printf("Error: cannot open framebuffer device.\n");
+        exit(1);
+    }
+    printf("The framebuffer device was opened successfully.\n");
+
+    // Get fixed screen information
+    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
+        printf("Error reading fixed information.\n");
+        exit(2);
+    }
+
+    // Get variable screen information
+    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
+        printf("Error reading variable information.\n");
+        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) {
+        printf("Error: failed to map framebuffer device to memory.\n");
+        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
+            } 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;
+}