Differences

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--- formats:frm16 [2010-09-26 21:26] – edheldil
+++ formats:frm16 [2011-11-21 22:36] (current) – [Scanline Lookup Table, LUT] edheldil
@@ Line 1: / Line 1: @@
 ==== FRM16 ====
-*.frm16 files are images, used for many things like UI elements, icons, minimaps, textures, portraits ... Also they are embedded in .SEQ16 and .MDL16 files. They use 16bits (2 bytes) per color and between 2 and 3 bits for transparency.
+*.frm16 files are simple bitmap images, used for many things like UI elements, icons, minimaps, textures, portraits ... In Lionheart, even more of them is actually embedded as frames in .SEQ16 and .MDL16 files. They use 16 bits per color and 8 bits for transparency (the older format probably used between 2 and 3 bits for transparency).
-Allegedly they are cached form of .FRM files which in turn are created from .TGA files. To speed up loading, they do not use any JPEG-type compression like FRM files and use only RLE and 16bit colors. They reside in Cache/ subdir, which supports the theory. In some related games (Ricochet) it's possible to delete .FRM16 files and they get recreated automatically from FRM ones. Unfortunately there are not any .FRM files in Lionheart.
+Supposedly they are cached form of .FRM files which in turn are created from .TGA files. To speed up loading, they do not use any JPEG-type compression like FRM files and use only RLE and 16bit colors. They reside in Cache/ subdir, which supports the theory. In some related games (Ricochet) it's allegedly possible to delete .FRM16 files and get them recreated automatically from FRM files. Unfortunately there are not any .FRM files in Lionheart.
-FRM16 file consists of a header and up to five layers. Layers are a way to encode alpha (transparency) in FRM16 files - the first layer is opaque (possibly with fully transparent pixels), the second layer is 80% opacity (FIXME: or 20% ?) and so on.
+FRM16 file consists of a header and up to five layers. Each layer consists of pixel data followed by a lookup table to first pixels of each image row.
-  * header
-  * Opaque layer
-    * Scanline LUT for the opaque layer
-  * 80% opacity layer
-    * Scanline LUT for the 80% layer
-  * 60% opacity layer
-    * Scanline LUT for the 60% layer
-  * 40% opacity layer
-    * Scanline LUT for the 40% layer
-  * 20% opacity layer
-    * Scanline LUT for the 20% layer
-Any (FIXME: even the fully opaque) layer might be missing
+Depending on a file type, pixels are either uncompressed (type 64), or RLE-compressed (file type 68). Only the type 68 allows transparency.
-[FIXME: quotes on FRM/FRM16 and JPEG-like compression]
+In the older incarnations of the format, layers were probably a way to encode alpha (transparency) in FRM16 files - the first layer would be opaque (possibly with fully transparent pixels in type 68), the second layer would be 80% opacity and so on with the fifth one being 20% opacity.
-[FIXME: links to convertors by Balder, Miloch, ...]
+However in Lionheart the layers are used differently. If the image is type 68, the first layer is the same as above, but the second and third layers are never used. The fifth layer contains pixels which are semitransparent - but only their RGB colors. The alpha information for the fifth layer is in the fourth layer, but WITHOUT the RLE information. In other words, the alpha layer is unusable without the RGB one. It's stupid and makes incremental loading of type 68 images complicated.
-There are at least two types of FRM16 files - type 64 and type 68. Type 64 uses uncompressed pixels, while type 68 uses RLE.
+Perhaps the 2nd and 3rd layers, unused in Lionheart, could be reused for height and normal maps for fake 3D effect (2.5D).
+==== Header ====
 Header (36 bytes)
 ^ Offset ^ Size ^ Description  ^
 | 0x00 | 2 | Signature (0x1032) |
-| 0x02 | 2 | Anchor X ? |
+| 0x02 | 2 | Anchor X |
-| 0x04 | 2 | Anchor Y ? |
+| 0x04 | 2 | Anchor Y |
 | 0x06 | 2 | Width in pixels (portraits = 90, areas = 779) |
 | 0x08 | 2 | Height in pixels (portraits = 111, areas = 330) |
@@ Line 38: / Line 27: @@
 | 0x0c | 2 | Type (64 or 68) |
 | 0x0e | 2 | Unknown, possibly padding, always 0 in standalone files |
-| 0x10 | 4 | Data size for opaque layer |
+| 0x10 | 4 | Bitmap size for the 1st, opaque layer |
-| 0x14 | 4 | Data size for % layer |
+| 0x14 | 4 | Bitmap size for the 2nd layer, unused |
-| 0x18 | 4 | Data size for % layer |
+| 0x18 | 4 | Bitmap size for the 3rd layer, unused |
-| 0x1c | 4 | Data size for % layer |
+| 0x1c | 4 | Bitmap size for the 4th layer, alpha |
-| 0x20 | 4 | Data size for % layer |
+| 0x20 | 4 | Bitmap size for the 5th layer, RGB |
 ==== Layers ====
-Layer
+Each layer consists of a bitmap and a scanline lookup table (LUT).
-^ Offset ^ Size ^ Description  ^
-==== Pixel Encoding, RLE ====
-Pixel color is encoded as a 16bit word, probably with a common 5-6-5 RGB? encoding. FIXME: How are fully transparent pixels encoded?
+==== Bitmap ====
-Type 64 files do not use any compression. Each layer contains all Width x Height pixels.
+Pixel color is encoded as a 16bit word, with a 5-6-5 RGB encoding. FIXME: How are fully transparent pixels encoded?
-Type 68 FRM16 files use Run Length Encoding, RLE. Each image scanline consists of a series of pixel runs. The scheme uses two highest bits in the first byte of each run. If bit 7 is set, bits 0-6 contain number of pixels to skip. If bit 7 is clear and bit 6 is set, bits 0-5 contain number of 16bit pixels which follow. If both bits 7 and 6 are cleared, bits 0-5 contain a number of repetitions of the following 16 bit pixel.
+Type 64 files do not use any compression. Each bitmap consists of width x height pixels of 2 bytes each.
+Type 68 FRM16 files use Run Length Encoding, RLE. Each bitmap line consists of variable number of pixel runs. The RLE scheme uses two highest bits in the first byte of each run. If bit 7 is set, bits 0-6 contain number of pixels to skip in the resulting image. If bit 7 is clear and bit 6 is set, bits 0-5 contain number of 16bit pixels which follow. If both bits 7 and 6 are cleared, bits 0-5 contain a number of repetitions of the following 16 bit pixel.
-==== Color Encoding ====
+For example:
+  42 ff fe ff fc  05 00 00
+would result in
+  __ __  ff fe  ff fc  00 00  00 00  00 00  00 00  00 00
+(First one pixel (0x81 & 0x7f) is skipped, then two (0x42 & 0x3f) whitish pixels are copied, then a black pixel is copied 5 times)
-Pixels' color is encoded as a 16bit word, probably with a common 5-6-5 RGB? encoding. Transparent pixels ...
+In type 68 files, the first 4 bytes in a bitmap is a DWORD containing bitmap's size in bytes. Since LUT's size is known (2 * height), it allows to read or skip the bitmap or whole layer without decoding it. However, the same number is already in the header, so its usefullness is unclear.
+==== Scanline Lookup Table, LUT ====
+Array of 32bit indices into bitmap pointing to beginnings of each bitmap scanline. The first index is 0 in type 64 files, 4 in type 68 files.
+^ Offset ^ Size ^ Description ^
+| 0x00 | 4 | Offset of the 1st scanline (0 in type 64 files, 4 in type 68 files) |
+| 0x04 | 4 | Offset of the 2nd scanline |
+| ...|||
+| height * 4 - 4 | 4 | Offset of the last scanline |
+==== References ====
+[FIXME: quotes on FRM/FRM16 and JPEG-like compression]
+[FIXME: links to convertors by Balder, Miloch, ...]