[FFmpeg-devel] [PATCH] adjust y in pad filter

[Benoit Fouet]

On Tue, 11 May 2010 14:55:44 -0700 Baptiste Coudurier wrote:
> On 05/11/2010 02:38 PM, Michael Niedermayer wrote:
> > On Tue, May 11, 2010 at 10:55:22PM +0200, Reimar D?ffinger wrote:
> >> On Tue, May 11, 2010 at 12:38:29PM -0700, Baptiste Coudurier wrote:
> >>> On 05/11/2010 12:32 PM, Reimar D?ffinger wrote:
> >>>> On Tue, May 11, 2010 at 11:04:48AM -0700, Baptiste Coudurier wrote:
> >>>>> On 05/11/2010 10:55 AM, Baptiste Coudurier wrote:
> >>>>>> On 05/11/2010 10:50 AM, Reimar D?ffinger wrote:
> >>>>>>> On Tue, May 11, 2010 at 10:33:51AM -0700, Baptiste Coudurier wrote:
> >>>>>>>> I believe that it is simpler and obvious for everybody that
> >>>>>>>> 0,0 coordinates are bottom left corner and not top left corner.
> >>>>>>>
> >>>>>>> Not to me, I've never understood why it should be, does anyone
> >>>>>>> number line numbers on a page from bottom to top?
> >>>>>>> Why the should pixels suddenly be counted that way?
> >>>>>>
> >>>>>> What about maths ?
> >>>>>>
> >>>>>
> >>>>> To elaborate, it is about geometry.
> >>>>> In geometry, 0,0 is bottom left.
> >>>>
> >>>> No, 0,0 is just the distinguished point, there's no "left", "bottom" or
> >>>> whatever in geometry, even if it is usually drawn like that.
> >>>
> >>> Just stop here. That's what I'm talking about, "usually drawn", you
> >>> just agreed with me, and I bet 90% of the _users_ of the filter.
> >>
> >> Hard for me to imagine that 90% of users would expect the pad filter to
> >> take geometric coordinates the way they were illustrated in their maths
> >> books but using pixels as units and only accepting integer values instead
> >> of assuming it would use pixel indexes just like their photo editing
> >> applications...
> >
> > putting the origin at the top left makes sense for left-to-right writing
> > people. i dont think it makes sense to people who primarely
> > used right to left scripts in their lifes. And i wonder what the han/kanji
> > using people would think of this.
> >
> > i really think we could expend this bikeshed by involving them
> 
> Well, I really think you guys are so much involved in graphic 
> development and array adressing that your view is altered.
> 
> When I refer to x and y as coordinates, it really seems obvious to me, 
> that they refer to the geometric meaning of placing a figure, and I 
> think this is exactly what the pad filter is about according to its 
> parameters: width:height:x:y
> 
>   h _______________
>    |               |
>    |   _________   |
>    |  |         |  |
>   y|  |_________|  |
>    |               |
>   0|_______________|
>    0  x            w
> 
> 
> This is pretty agnostic from the way people are writing text IMHO.
> 

the way e.g. the video4linux API did it is that it defines the
rectangle structure names as follow:
left     Horizontal offset of the top, left corner of the rectangle, in pixels.
top      Vertical offset of the top, left corner of the rectangle, in pixels.
width    Width of the rectangle, in pixels.
height   Height of the rectangle, in pixels.

I agree with Baptiste that (x,y) coordinates tend to refer to the picture above.

just my 2 cents though.

Ben