Nfw.Linux.FrameBuffer

An easy to use library for interacting with the Linux framebuffer interface (/dev/fbX).

NuGet

dotnet add package Nfw.Linux.FrameBuffer

Samples: Get Info From Display

This small snippet will open the provided device and use ioctls to discover its identifier and display parameters:

using(RawFrameBuffer fb = new RawFrameBuffer("/dev/fb0")) {
    Console.WriteLine($"Display Device => {fb.Device} Name => {fb.Id} Width => {fb.PixelWidth} Height => {fb.PixelHeight} Bpp => {fb.PixelDepth}");
}

Samples: Write Pixels

This snippet shows how you can write raw pixel data (on a 16bpp screen this shows as Black and Red hatch):

using(RawFrameBuffer fb = new RawFrameBuffer("/dev/fb0")) {                
    // For each pixel, flop between 0x00 and 0x80
    byte[] data = new byte[fb.PixelWidth * fb.PixelHeight * (fb.PixelDepth / 8)];
    byte flopMe = 0x00;
    for (int x = 0; x < data.Length; x += (fb.PixelDepth / 8)) {
        for (int pixelByte = 0; pixelByte < (fb.PixelDepth / 8); pixelByte++) {
            data[x + pixelByte] = flopMe;                    
        }
        flopMe = (flopMe == 0x00) ? (byte) 0x80 : (byte) 0x00;
    }
    fb.WriteRaw(data);    
}

Samples: Displaying an Image

This snippet uses the fantastic ImageSharp library to load an image, which must be in the same bitdepth as the framebuffer, then write it to the framebuffer:

using(RawFrameBuffer fb = new RawFrameBuffer("/dev/fb0")) {                
    byte[] pixelBytes = new byte[fb.PixelWidth * fb.PixelHeight * (fb.PixelDepth / 8)];

    // Load from source
    using(Image loadedImage = Image.Load(filename)) {
        // Resize to fit screen
        loadedImage.Mutate(x => {            
            x.Resize(fb.PixelWidth, fb.PixelHeight);            
        });

        // Write the raw pixel data into a buffer
        loadedImage.CopyPixelDataTo(pixelBytes);
        fb.WriteRaw(pixelBytes);
    }
}

More useful is converting from whatever the image format is on disk, to the framebuffer's format, see the DisplayImage Sample - which uses ImageSharp AND convert the image to the same pixel format as the display before writing the pixel data itself to the framebuffer.

Notes

• The RawFrameBuffer constructor can optionally be told NOT to probe via ioctl on construction, instead post-construction you must call RefreshDeviceInfo() before you can render anything.
• The RawFrameBuffer constructor can also be optionally provided an ILogger, perhaps via IoC, for logging/diagnostics.
• In the case where your FB device can be mirrored, I suggest writing to the fastest (i.e. /dev/fb0 is often HW accelerated) then mirroring via something like the raspi2fb tool to effectively 'double buffer'.

References

• https://en.wikipedia.org/wiki/Linux_framebuffer
• https://www.kernel.org/doc/Documentation/fb/api.txt

Attribution

• https://github.com/nickdu088/FrameBuffer

IMAGE LICENSE

The Sample Image used is an original watercolor by the author's wife: Katie Yocom. License for this file is CC BY-NC-ND 4.0.

Changelog

• 1.0.3:
  • Blank() now defaults to FB_BLANK_NORMAL
  • PowerDown() was added for previous behavior
  • Also exposes a Blank(byte) which takes arbitrary ioctl value.