The V40 picture.datatype
distributed with OS 3.1 had several
weak points and missing features which made it inadequate when
the first RTG systems with true-color support became available.
For this reason, nowadays the original V40/V42 version has been obsoleted
by third party replacements featuring true-color support and other
useful extensions.
OS 3.5 integrates a rewritten picture.datatype
whose API tries
to be as compatible as possible to these unofficial versions.
The V44 picture.datatype
works transparently with both
CyberGraphX and Picasso 96. It also integrates color
reduction algorithms to convert high/true-color pictures to
palette-mapped bitmaps. The API allows the programmer to choose among
several quantization and dithering techniques to get better quality or
faster conversion.
palette-mapped
direct-mapped
native bitmap
RTG bitmap
graphics.library
or by the RTG system.
For backwards compatibility, the unofficial V43 picture.datatype
implementations which were distributed with CyberGraphX and
Picasso 96 behaved just like the V42 and eariler implementations
by default. The picture returned to the application was stored
in a native planar bitmap, up to 8 bitplanes deep.
In order to let the datatype allocate custom bitmaps (chunky 8bpp or hi/truecolor), the application should set the PDTA_DestMode attribute to PMODE_V43.
This has changed as of V44. PMODE_V43 is now active by default. Applications should never expect to get a native bitmap from the picture.datatype unless they explicitly ask for PMODE_V42.
The following summary shows the different behaviour kept by all
the known implementations of the picture.datatype
:
picture.datatype V40/V42 (OS 3.1)
picture.datatype V43 (CyberGraphX)
picture.datatype V43 (Picasso 96)
PMODE_V42
. However, the returned
bitmap is NOT native.
picture.datatype V44 (OS 3.5)
PMODE_V43
. It can be explicitly
forced to PMODE_V42
.
The V42 mode is retained in picture.datatype
V44 for backwards
compatibility only. Use of the V42 mode in new applications is
STRONGLY DISCOURAGED. The V43 mode provides better performance
for both the internal operations carried out by the datatype and
for most bitmap to screen blitting operations.
picture.datatype
PDTM_WRITEPIXELARRAY
PDTM_READPIXELARRAY
picture.datatype
PDTA_SourceMode
PDTA_DestMode
PDTA_UseFriendBitMap
PDTA_MaskPlane
PDTA_WhichPicture
PDTA_GetNumPictures
PDTA_MaxDitherPens
PDTA_DitherQuality
PDTA_AllocatedPens
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