Double buffer support in Framebuffer?

Double buffer support in Framebuffer?

[siqiao chen]

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?


 Thank you!

                                                    Philip Chen
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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@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

Double buffer support in Framebuffer?

[siqiao chen]

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


On Wed, Apr 27, 2011 at 8:22 PM, Dave Hylands <dhylands@gmail.com> wrote:

> Hi Philip,
>
> Replying to all this time.
>
> On Wed, Apr 27, 2011 at 4:24 PM, siqiao chen <siqiaochen@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
>
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