140 lines
5.1 KiB
Plaintext
140 lines
5.1 KiB
Plaintext
Tinct
|
|
=====
|
|
The ability to plot alpha-blended sprites is only provided by certain
|
|
versions of RISC OS provided by RISC OS Ltd (ie RISC OS Select), and
|
|
currently not by the latest versions provided by Castle (ie RISC OS 5)
|
|
There is currently no separate module available from RISC OS Ltd, nor a
|
|
version of Select that will function on an Iyonix. As such, users of machines
|
|
that will not run RISC OS 4 (and thus Select) cannot display images with
|
|
variable transparency (eg PNGs).
|
|
This module provides the necessary functionality to display alpha-blended
|
|
sprites both scaled and otherwise. It also provides functions for dithering
|
|
and performing bi-linear filtering to improve their appearance.
|
|
|
|
|
|
Technical information
|
|
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
|
|
To ensure future compatibilty, this module does not patch the OS in any way
|
|
and works in a totally legal way. It also does not write to itself in any
|
|
way, so is suitable for running from ROM.
|
|
Redirection to sprites is supported, although due to the overheads involved
|
|
with caching the colour translation tables it is not recommended that this is
|
|
done. There are some exceptions to this, however, as output to a 32bpp mode
|
|
does not cause the tables to be re-calculated, and redirecting to a sprite
|
|
that has the same characteristics as the current mode and palette has a
|
|
minimal overhead.
|
|
Tinct comes in two different variants - one that is slightly faster and
|
|
only suitable for memory architectures that support LDRH and STRH (denoted by
|
|
a '_h' filename suffix), and one that is suitable for all machines (denoted
|
|
by a '_b' filename suffix).
|
|
|
|
|
|
Format of a sprite with 8-bit alpha channel
|
|
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
|
|
The sprite format used by Tinct differs from those used by RISC OS Select,
|
|
and no facilities to manipulate or create the required format is provided.
|
|
All sprites used by Tinct must be 32bpp, and cannot have a mask.
|
|
The basic format of the sprite is shown below, with the restrictions to the
|
|
standard sprite format marked with an asterisk (*):
|
|
|
|
[+0] Offset to next sprite
|
|
[+4] Sprite name, up to 12 characters with trailing zeroes
|
|
[+16] Width in words - 1
|
|
[+20] Height in scan lines - 1
|
|
[+24] * First bit used (must be 0)
|
|
[+28] * Last bit used (must be 31)
|
|
[+32] Offset to sprite image
|
|
[+36] * Offset to sprite image (no mask allowed)
|
|
[+40] * Sprite type (must be &301680B5)
|
|
|
|
Whereas for normal sprites the sprite image would be a series of colour words
|
|
of the format RrGgBb00, alpha-blended sprites use the empty byte to specify
|
|
the alpha value, ie RrGgBbAa.
|
|
The alpha values represent the blending level on a linear scale where 0x00
|
|
represents that the source pixel is totally transparent and 0xff that it is
|
|
totally opaque. It should be noted that as a standard 32bpp sprite (eg as
|
|
created with !Paint) will have the alpha channel set to 0x00 by default no
|
|
output will be visible when plotting as an alpha-blended sprite.
|
|
|
|
|
|
SWIs provided
|
|
¯¯¯¯¯¯¯¯¯¯¯¯¯
|
|
Tinct provides four SWIs to plot sprites and one to convert sprites to their
|
|
32bpp equivalent. All values supplied to Tinct must be in OS units, and the
|
|
current OS clipping rectangle is used.
|
|
The sprite pointers provided are equivalent to calling OS_SpriteOp with
|
|
bit 9 of the reason code set. To plot a sprite by name, the sprite should
|
|
first be found by using OS_SpriteOp with reason code 0x18 and using the
|
|
returned sprite address.
|
|
|
|
|
|
Tinct_PlotAlpha (0x57240)
|
|
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨
|
|
Plots an alpha-blended sprite at the specified coordinates.
|
|
|
|
-> R2 Sprite pointer
|
|
R3 X coordinate
|
|
R4 Y coordinate
|
|
R7 Flag word
|
|
|
|
|
|
Tinct_PlotScaledAlpha (0x57241)
|
|
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨
|
|
Plots a scaled alpha-blended sprite at the specified coordinates.
|
|
|
|
-> R2 Sprite pointer
|
|
R3 X coordinate
|
|
R4 Y coordinate
|
|
R5 Scaled sprite width
|
|
R6 Scaled sprite height
|
|
R7 Flag word
|
|
|
|
|
|
Tinct_Plot (0x57242)
|
|
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨
|
|
Plots a sprite at the specified coordinates with a constant 0xff value for
|
|
the alpha channel, ie without a mask.
|
|
|
|
-> R2 Sprite pointer
|
|
R3 X coordinate
|
|
R4 Y coordinate
|
|
R7 Flag word
|
|
|
|
|
|
Tinct_PlotScaled (0x57243)
|
|
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨
|
|
Plots a scaled sprite at the specified coordinates with a constant 0xff value
|
|
for the alpha channel, ie without a mask.
|
|
|
|
-> R2 Sprite pointer
|
|
R3 X coordinate
|
|
R4 Y coordinate
|
|
R5 Scaled sprite width
|
|
R6 Scaled sprite height
|
|
R7 Flag word
|
|
|
|
|
|
Tinct_ConvertSprite (0x57244)
|
|
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨
|
|
Converts a paletted sprite into its 32bpp equivalent. Sufficient memory must
|
|
have previously been allocated for the sprite (44 + width * height * 4).
|
|
|
|
-> R2 Source sprite pointer
|
|
R3 Destination sprite pointer
|
|
|
|
|
|
Flag word
|
|
¯¯¯¯¯¯¯¯¯
|
|
All the SWIs provided by Tinct for plotting use a common flag word to
|
|
describe the manner in which the plot is performed. Each bit controls a
|
|
particular characteristic of the plotting:
|
|
|
|
0 Forcably read the screen base (only use if hardware scrolling)
|
|
1 Use bi-linear filtering when scaling sprites
|
|
2 Dither colours in 16bpp and below
|
|
3 Invert dither pattern
|
|
4+ Reserved (must be 0)
|
|
|
|
Although bi-linear filtering is only relevant during scaled plotting, this
|
|
situation occurs when the EigFactors of the mode are not equal. As such, an
|
|
application should always set their preferred flags to ensure consistency. |