Re: [Openexr-devel] Writing a tiled Rgba image file with tiles given

[Florian Kainz]

Hi Werner,

Thank you for your mail.

Class TiledRgbaOutputFile can already be used with a single-tile
buffer.  The base pointer in setFrameBuffer always points to the
memory location where pixel (0,0) would be if it existed.  If your
buffer contains only a single tile, and that tile does not include
pixel (0,0), then the base pointer just points outside the buffer.
This may seem weird, but it works.  For a more detailed explanation
please see section 2.2, Writing a Cropped Image, of this document:

    http://www.openexr.com/ReadingAndWritingImageFiles.pdf

Still, your library patch would make it possible to reduce the
number of setFrameBuffer calls when a file is read or written using
a single-tile frame buffer.

In its current form the patch is incomplete: the new flag has no
effect on YA (gray-scale + alpha) files.  Also, in order to be more
useful in conjunction with writeTiles (as opposed to writeTile),
setFrameBuffer should have separate "tile-relative coordinates"
flags for x and y.

Florian



Werner Benger wrote:
> Greetings,
>
>  I found a limitation in the class TiledRgbaOutputFile as provided in 
> the  IlmImf
> library, in that it seems to not allow writing a tile from a buffer 
> that  only
> contains this tile. By default it assumes that the provided pointer is  
> relative
> to an absolute buffer that contains the entire image. However, the  
> underlying
> class "Slice" already supports such relative data, and it's straightforward
> to just pass this parameter to the creation of such slices.
>
> Here are the modifications I made to the library, as I did not find another
> way to achieve the same. These changes seem to be simple and don't 
> break  any
> existing code while it just works for me then.
>
> Best regards,
>
>     Werner
>
>
> ==========================
> In file ImgTiledRgbaFile.h : 170
>
>     void        setFrameBuffer (const Rgba *base,
>                     size_t xStride,
>                     size_t yStride,
>                     bool   relativeBase = false);
>
>
>
> ========================
> In file ImgTiledRgbaFile.cpp : 374
>
> void
> TiledRgbaOutputFile::setFrameBuffer (const Rgba *base,
>                      size_t xStride,
>                      size_t yStride,
>                      bool   relativeBase)
> {
>   ...
>
>     fb.insert ("R", Slice (HALF, (char *) &base[0].r, xs, ys, 1,1, 0.0,  
> relativeBase, relativeBase) );
>     fb.insert ("G", Slice (HALF, (char *) &base[0].g, xs, ys, 1,1, 0.0,  
> relativeBase, relativeBase) );
>     fb.insert ("B", Slice (HALF, (char *) &base[0].b, xs, ys, 1,1, 0.0,  
> relativeBase, relativeBase) );
>     fb.insert ("A", Slice (HALF, (char *) &base[0].a, xs, ys, 1,1, 0.0,  
> relativeBase, relativeBase) );
> ...
> }
>
> ========================