Re: [PATCH 2/5] commands: splash: honour line_length

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Sep 26, 2024 at 07:31:49AM +0200, Ahmad Fatoum wrote:
> On 25.09.24 16:34, Sascha Hauer wrote:
> > the splash command has an option for setting a background colour. This
> > doesn't always fill the whole screen as expected.
> > 
> > struct fb_info has a line_length field that specifies the length in
> > bytes of a single line. That length may be bigger than the actually
> > visible area as specified by xres. In this case filling the area as
> > calculated by xres*yres fills the invisible pixels between xres and
> > line_length, but it doesn't fill the whole visible area. Fix this by
> > iterating over the lines, filling the visible area of each line.
> 
> I have trouble understanding this. What is line_length if not
> bytes per pixel multiplied by xres?

Some hardware might have alignment restrictions on the address where the
new line starts. In that case line_length is longer than xres*bpp. Also
the picture in the framebuffer might be wider than the visible area.

In my case I allocate a framebuffer for the biggest resolution the
monitor supports. When changing the resolution to a smaller one I can
keep the framebuffer and still show something useful by keeping
line_length and just adjusting xres.

Sascha

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