Tinct ===== This module provides the necessary functionality to display alpha-blended sprites both scaled and otherwise. It also provides functions for dithering, error diffusion and performing bi-linear filtering to improve their appearance. Technical information ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ To ensure future compatibility, 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 frequently. There are some exceptions to this, however, as redirecting to a 16bpp or 32bpp mode sprite does not require any translation tables, and redirecting to a sprite that has the same mode and palette as the previous destination that Tinct was used for causes a minimum overhead as the translation tables are checked and cached values are used if possible. Format of a sprite with 8-bit alpha channel ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ The sprite format used by Tinct differs from those used by RISC OS Select, and whilst facilities are supplied to convert sprites into the required format, no facilities are provided to manipulate them. All sprites used by Tinct must be 32bpp, and cannot have a standard RISC OS mask specified. 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 [+28] Last bit used [+32] Offset to sprite image [+36] * Offset to sprite image (no mask allowed) [+40] * Sprite type (must be 0x301680B5) 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. Error handling ¨¨¨¨¨¨¨¨¨¨¨¨¨¨ If an incorrect sprite is attempted to be used, Tinct currently always returns error number 0x700 (SBadSpriteFile) rather than the specific cause of the problem (eg. BadDPI, BadMSFlags or BadPixelDepth) as OS_SpriteOp would do. There are several technical reasons for this behaviour, and future versions of Tinct may return more descriptive errors depending on the cause. SWIs provided ŻŻŻŻŻŻŻŻŻŻŻŻŻ 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). As sprites with 16bpp or 32bpp do not have palettes, conversion cannot be performed on these variants. All sprites must be supplied with a full palette, eg 8bpp must have 256 palette entries. -> R2 Source sprite pointer R3 Destination sprite pointer Tinct_AvailableFeatures (0x57245) ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ Returns the features available to the caller by specifying bits in the flag word. The features available are unique for each mode, although the current version of Tinct supports the same subset of features for all modes. -> R0 Feature to test for, or 0 for all features <- R0 Features available Tinct_Compress (0x57246) ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ Compresses an image using a fast algorithm. Sufficient memory must have been previously allocated for the maximum possible compressed size. This value is equal to 28 + (width * height * 4) * 33 / 32. -> R0 Source sprite pointer R2 Output data buffer R3 Output bytes available R7 Flag word <- R0 Size of compressed data Tinct_Decompress (0x57247) ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ Decompresses an image previously compressed. Sufficient memory must have been previously allocated for the decompressed data (44 + width * height * 4) where width and height are available at +0 and +4 of the compressed data respectively. -> R0 Input data buffer R2 Output data buffer R7 Flag word (currently 0) <- R0 Size of decompressed data Flag word (plotting) ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ 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 Forcibly 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 Perform error diffusion if bit 2 clear, invert dither pattern if set 4 Horizontally fill the current graphics window with the sprite 5 Vertically fill the current graphics window with the sprite 6 Forcibly read the palette (only use if changing palette outside of the WIMP) 7 Use OS_SpriteOp to perform final plotting (see note) 8+ Reserved (must be 0) if bit 7 is clear, background colour to blend the alpha channel to otherwise If a bit is set in the flag word that cannot be honoured by the current version of Tinct then it is ignored. Tinct_AvailableFeatures can be used to test in advance what flags will be honoured. Bi-linear filtering ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ 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. The case of XEig * 2 = YEig (rectangular pixel modes) for even height sprites is a special case and has optimised code implemented. There is an upper limit to the size of sprite that can be bi-linear filtered. The checks that are currently made are: scaled_width / sprite_width < 256 scaled_height / sprite_height < 256 scaled_width * max(sprite_height, scaled_height) < 32,768 It should be noted that as bi-linear filtering is performed as a pre-filter, it carries a sizable overhead. However, as all scaling calculations are performed during this filter, tiled plotting (bits 4 and 5) are affected by a smaller margin (in certain cases a speed gain can be achieved). As bi-linear filtering is performed using a pre-filter, it can be used in association with OS_SpriteOp rendering. Error diffusion and dithering ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ If both error diffusion and dithering are enabled then the image is plotted using only dithering, but with the dither pattern inverted. This enables an application to provide the user with what appears to be a higher quality image by redrawing every frame with the flag toggled. There is a significant speed difference between dithering and error diffusion, and Tinct does not support error diffusion in all colour depths. If error diffusion is requested, but cannot be performed by Tinct then dithering with an inverted pattern is used (as if bits 2 and 3 were set). There is an upper limit to the size of sprite that Tinct can perform error diffusion on. This is currently set to a display width of 2047 pixels wide with an unlimited height. Any attempt to use a higher resolution will result in dithered rendering with an inverted pattern (ie bits 2 and 3 set). As error diffusion and dithering are implemented during the plot cycle, it is not possible to use them in association with OS_SpriteOp rendering. However, the bits should be set as future versions of Tinct may respect them for users of RISC OS 3.1 where true colour sprites are not supported. Sprite filling ¨¨¨¨¨¨¨¨¨¨¨¨¨¨ If filling is specified, then the supplied co-ordinate is the offset of the pattern relative to (0, 0) used for the fill. For example, a 64x64 sprite that is plotted with bits 4 and 5 set and a position of (32, 16) would fill the current graphics window with multiple copies of the image stating with the first image plotted at (-32, -48). The caller should not concern itself with the size of the image being tiled as small images are internally optimised where possible to maximise the plotting speed. Rendering using OS_SpriteOp ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ It can be useful to use Tinct to perform the rendering to using OS_SpriteOp. There are two general situations where this may be useful: 1) To output to a printer driver 2) To allow hardware acceleraton (such as a ViewFinder card) By using Tinct rather than a direct OS_SpriteOp call, it allows the caller to retain certain features Tinct provides (such as sprite filling and a limited version of the standard alpha blending) and allows the caller to have a common plotting interface. When using this feature for alpha-blended sprites, the background colour specified in the top 24-bits of the flag word is used for blending with any pixels that are not transparent. This requires that Tinct requires a second copy of the sprite in memory to modify which may present a significant overhead in some situations. Plotting opaquely does not have any such overheads. Using OS_SpriteOp rendering does not currently work on RISC OS 3.1 or earlier due to the lack of support for true colour sprites. Future versions of Tinct may remove this restriction. Flag word (compression) ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ The flag word used by Tinct_Compress can be used to improve the compression ratio by performing pre-filtering on the data. The flags below relate only to compression and should not be passed to Tinct_Decompress. 0 Image is opaque, remove the alpha channel prior to compression All unspecified bits are reserved for future expansion and as such should be set to 0. Compressed data format ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ Certain aspects of the compressed data format are guaranteed to remain constant, so may be used by applications. +0 Sprite width +4 Sprite height +8 Sprite name (12 chars) +20 Compression flags +24 Number of bytes of data following The method of compression is not guaranteed to remain constant over future revisions of Tinct, but subsequent versions will decompress data compressed with previous versions. Contact details ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ If you would like to report a problem relating to Tinct, provide feedback, or request a licence for a commercial product, please use the details below: Address: 5 Queens Close, East Markham, Newark, Nottinghamshire, NG22 0QY. UK E-mail: info@tinct.net Website: www.tinct.net Copyright and licence details ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ Tinct is İ copyright Richard Wilson, 2004. Distribution and usage ¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨ Unrestricted use of Tinct is hereby granted for any non-commercial product. Any use as part of a commercial product requires written consent from the author. No charge may be made relating to the distribution of this software, and this copyright information should be included in all copies of the software. Modified versions of this program may not be distributed without the authors consent, nor may modified versions of the source code or relating files.