Double buffer support in Framebuffer?

[Dave Hylands]

Hi Philip,

Replying to all this time.

On Wed, Apr 27, 2011 at 4:24 PM, siqiao chen <siqiaochen at gmail.com> wrote:
> Hello, Could I ask how do I enable double buffer support in FrameBuffer
> device?
> I think I could manually increase xres_virtual/yres_virtual to 2 times of
> the display size in video driver and swap xoffset/yoffset after VSync.  But
> could I know if this is the right way to do double buffering or this
> function is already built-in?

You're on the right track. You only need to double xres_virtual or
yres_virtual, not both.

Let's suppose that your display is 800x480. Then your display driver
needs to size the framebuffer to be 800x960, and you'd use
FBIOPAN_DISPLAY to toggle between 0,0 and 0,480.

The driver has to support the double sized framebuffer and the pan
command (or maybe you can modify yoffset directly? I haven't tried
this approach myself).

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com