O, I get it! Thank you for your explanation!


On Wed, Apr 27, 2011 at 8:22 PM, Dave Hylands [off-list ref] wrote:

Hi Philip,

Replying to all this time.

On Wed, Apr 27, 2011 at 4:24 PM, siqiao chen [off-list ref] wrote:

quoted

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

quoted

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

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