Embedded Linux System Design and Development

326 Embedded Linux System Design and Development

addresses for memory mapping the frame buffer. The variable screen infor-

mation is read/write retrieved using the

FBIOGET_VSCREENINFO ioctl and set

using the

FBIOSET_VSCREENINFO ioctl. The fb_var_screeninfo structure

describes the geometry and timings of the current video mode. The next step

is to

mmap the hardware buffer into our application’s process space using the

mmap() system call.

Now we are ready for plotting our pixel. We take care of the various bit

depths and pixel-packing schemes. The

fb_var_screeninfo structure pro-

vides the bit length and offsets of individual color channels. Finally, using the

property (pixel (x,y) = (line_width * y) + x) of the linear frame buffer, we

plot the single ...