Hi,

I'm trying to read the ARGB data of an image by invoking the PDTM_READPIXELARRAY method on a datatype object (with bpa.pbpa_PixelFormat = PBPAFMT_RGBA).

The intention is to cache the raw data. The image will later be rendered via WritePixelArray( ..., RECTFMT_RGBA).

It appears that neither reading nor rendering works correctly: the alpha channel is ignored. I'm aware that this approach doesn't work under OS3 but shouldn't this work under MorphOS?!

PDTM_READPIXELARRAY works correctly (at least with PBPAFMT_ARGB) but WritePixelArray() ignores alpha channel completely. You need undocumented WritePixelArrayAlpha() instead.

Quote:

In that case I'll use a custom function. Does anybody have a working solution that is faster than the read-mix-write approach (read to an off-screen buffer with ReadPixelArray(), use CPU to mix with image, write back with WritePixelArray())?

Just use WritePixelArrayAlpha() and you benefit from possible future enhancements:

#ifndef WritePixelArrayAlpha
#define WritePixelArrayAlpha(__p0, __p1, __p2, __p3, __p4, __p5, __p6, __p7, __p8, __p9) \
LP10(216, ULONG , WritePixelArrayAlpha, \
APTR , __p0, a0, \
UWORD , __p1, d0, \
UWORD , __p2, d1, \
UWORD , __p3, d2, \
struct RastPort *, __p4, a1, \
UWORD , __p5, d3, \
UWORD , __p6, d4, \
UWORD , __p7, d5, \
UWORD , __p8, d6, \
ULONG , __p9, d7, \
, CYBERGRAPHICS_BASE_NAME, 0, 0, 0, 0, 0, 0)
#endif

It is same as WritePixelArray() except that last argument is not pixel format but global alpha (0x0 - 0xffffffff) and it supports ARGB pixel format only.

It is really private but it has spread to OS4 and AROS and available in AfA OS also.


[ Edited by itix on 2007/3/15 0:18 ]

Quote:
Thanks for the help. I have noticed that under MorphOS, my test code only works correctly with ARGB (as you said) but under AfaOS, it only works with RGBA?! ARGB gives a blank rectangle. Any idea?

I suppose AfA OS is broken.

On second look, the culprit seems to be the png datatype. WritePixelArrayAlpha() works fine but all alpha values are zero. I was under the impression that warpPNG and/or akPNG would fully support alpha (they both have an option in their GUI).

Oops, it was the picture datatype. Everything works fine now.

Honestly datatypes suck.

Alpha works with PDTM_WRITEPIXELARRAY as well (at least under MorphOS/CGfx and WinUAE/Picasso96) but some combinations of pic-dt and cgfx may cause problems.

akPNG supports alpha - it has been tested under the configs mentioned before.