adfExplorer (version 0.1.8)

rawToBitmap: Convert raw data into a bitmap or vice versa

Description

Convert raw data into a bitmap or vice versa (i.e., binary data) conform Amiga specifications.

Usage

rawToBitmap(x, invert.bytes = F, invert.longs = T)
bitmapToRaw(x, invert.bytes = T, invert.longs = T)

Value

Returns a vector of raw data in case of bitmapToRaw, and a vector of binary raw values in case of rawToBitmap.

Arguments

x

A vector of raw data, in case rawToBitmap is used. A vector of raw, interger or logical values should be used in case of bitmapToRaw. In the latter case each value in the vector is interpreted as a bit and should be a multiple of 8 long.

invert.bytes

A logical value. When set to TRUE, the bit order of bytes are reversed.

invert.longs

A logical value. When set to TRUE, the bit order of long values (32 bits) are reversed. When x does not have a multiple length of 32 bits or 4 bytes, x will be padded with zeros to the right, but the result will be trimmed to correspond with the length of x. Note that data might get lost this way.

Author

Pepijn de Vries

Details

A bitmap is simply put a map of bits (binary data, which can be interpeted as 0 or 1; or FALSE and TRUE). Bitmaps can have several purposes, also on the Commodore Amiga. The Amiga file system uses a bitmap to indicates which blocks are occupied with data and which are free. Bitmaps can also be used in bitmap images where each bit indicates which color should be used for a specific pixel in an image. These function can be used to convert raw data into usable bitmaps or vice versa.

As the Commodore Amiga is a big-endian system (most significant bit first) using a 32 bit CPU, it may sometimes necessary to invert the bits of a byte or longs (4 bytes, 32 bits), which can be done with the arguments 'invert.bytes' and 'invert.longs' respectively.

See Also

Other raw.operations: amigaDateToRaw(), amigaIntToRaw(), displayRawData(), rawToAmigaDate(), rawToAmigaInt()

Examples

## The bitmap block of the example disk is located at block
## number 882 (note that this is not true for all disks,
## the actual location is stored in the root block)
data(adf.example)
bitmap.block <- amigaBlock(adf.example, 881)

## bitmap data are stored in bytes 5 up to 224 in this block:
bitmap.raw <- bitmap.block@data[5:224]

## let's get the bitmap from the raw data:
bitmap <- rawToBitmap(bitmap.raw)

## Whe can now get the occupied blocks (minus one is used for
## the discrepancy in indexing):
which(bitmap != as.raw(0x01)) - 1

## we can also do the reverse:
bitmap.raw.new <-  bitmapToRaw(bitmap)
## it should be the same as the original raw data:
all(bitmap.raw.new == bitmap.raw)

## WARNING: don't use these methods to directly
## modify an amigaDisk objects bitmap block. The
## file system on that object may get corrupted.
## All methods in this package should update the
## bitmap block automatically and cleanly...