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249 lines
7.2 KiB
Plaintext
249 lines
7.2 KiB
Plaintext
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The "bmp" library is a library for
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the express purpose of reading and
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writing Windows BMP files and other
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Windows DIB headers.
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It is written with portability,
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memory-efficiency, and reusability
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as it's primary goals.
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With this in mind, it can be used as
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the backend for an ICO/CUR handling
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library, works with packed-DIB data,
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only requires the first 0x36 bytes
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of a .BMP to be present, and can be
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used on KittenOS NEO, OpenOS, and
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just about any place with a desktop
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Lua interpreter available for use.
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(That said, it's not 5.1-tested.)
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That said, it does not handle all the
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possible bitmap formats, restricting
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itself to support of BI_RGB where
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possible, and BI_BITFIELDS to a
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limited extent.
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Given this covers most bitmaps that
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you are likely to generate, do not
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underestimate the use of this.
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The library has 2 fields:
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headerMinSzBMP,
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headerMinSzDIB: The minimum data you
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must have available when calling
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connect for a given format.
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The library has 3 functions:
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connect(get, set, cMode, packed):
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"Connects" to a bitmap. A very real
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implication of this is that the
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data get/set accesses is where the
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actual bitmap is, and this merely
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provides a way to access it in a
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useful form (as pixels).
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Technically, all but 'get' are
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optional, but I feel it necessary
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to document them as if they are
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implicitly left nil by those users
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who omit them because of their
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functionality.
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Due to this section being a rather
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long length, the paragraph
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separation is per-argument here.
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get is best described by:
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function (a) return dt:byte(a) end
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set, which is optional unless you
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call any of the set* functions in
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the resulting bitmap, has a longer
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description:
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function (a, v)
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dt = dt:sub(1, a - 1) ..
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string.char(v) ..
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dt:sub(a + 1)
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end
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Notably, while these are the
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canonical implementations of these
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functions, they are by no means
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the only implementations, and it
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is the purpose of these callbacks
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to allow choice in how you write
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them.
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cMode exists for cursor and icon
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handling. These images are split
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via a very horrifying mechanism
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into an AND mask, and a XOR mask.
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The XOR mask typically contains
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what could be called the actual
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image - the AND mask then acts
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as a sort of alpha mask, blacking
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out the areas where the XOR mask
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is then projected onto.
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It can be one of three values.
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It can be nil, in which case this
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is an ordinary DIB, with no evil
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nonsense applied to it -
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It can be "colour", in which case
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the XOR mask (the actual image in
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most cases) is shown -
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And it can be "mask", in which case
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the AND mask is accessed instead.
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(Notably, bpp, paletteSize, and
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ignoresPalette changes to the
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1bpp mask format in use here.)
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packed exists for the use of those
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bitmaps that don't have a BMP file
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header, the usual "BM". In this
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case, you can remove support for
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gap1 but allow yourself to avoid
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the BM header as a result.
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If not nil, it is how much to
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offset the indexes from 0-based
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offsets into a .BMP file to the
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final positions.
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The following table is useful for
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understanding this:
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1: Standard 1-indexed BMP handling,
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but with no gap1 support (!)
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-13: Standard 1-indexed handling of
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a packed DIB (no BMP header),
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such as a BITMAP or ICON
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resource (set cMode if ICON)
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-9: Standard 1-indexed handling of
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a CURSOR resource, which has
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a 2-short hotspot header
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prepareDIB(w, h, p, bpp, paletteSize
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, topDown, cMode) -> hd, sz, dp:
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(See prepareBMP if you want a .BMP
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file, but this describes how to
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use the arguments and returns.)
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This prepares a packed DIB, and
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returns three values:
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1. The header. (The palette, in
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the 4-byte-per-colour form,
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will follow immediately.)
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2. The buffer size, including the
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header in 1. The bytes that
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are not specified can be
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initialized in any fashion,
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as they are part of the colour
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and later image data itself.
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3. The pointer to the pixels for
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BM creation.
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w, h, p, and bpp are the usual -
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width, height, planes, pixel depth
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- but the paletteSize needs note.
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If the BPP is <= 8, then the size
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of the palette must not be 0.
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This is to avoid unintentionally
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triggering legacy features in the
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BMP format.
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topDown and cMode are essentially
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booleans that can safely be nil,
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where nil is interpreted as false.
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topDown indicates that the image is
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to be top-down rather than the
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standard upsidedown form of a BMP.
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This may look odd if streaming a
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BMP, so the option, while rather
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an odd one, has been included.
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cMode indicates that this image is
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intended for use in an ICON or
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CURSOR resource of some form, and
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should thus contain an AND mask.
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prepareBMP(...):
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This prepares a .BMP file. It has
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the same arguments and returns as
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prepareDIB, and indeed wraps it.
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Bitmap objects, while not read-only,
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do not particularly change if you
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write to them.
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Going out of bounds with a bitmap
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object will have hilarious results.
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...Don't do it.
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Anyway, they have these fields:
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width, height, planes: The usuals.
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(NOTE: Due to lack of examples,
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it is assumed that planes are a
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dimension more major than height.
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If this isn't the case, someone
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do tell me, preferably with an
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example and a way to open it that
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does not involve this library, so
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I can test and correct all of the
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code involving them.)
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bpp: Bits per pixel. This specifies
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a limit on numbers passed to
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and from the bitmap object,
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of 1 << bpp (2 ^ bpp).
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A number may not be equal to
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or exceed this limit.
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ignoresPalette: Used to indicate
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the palette is worthless and does
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not affect image contents in any
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way at all. If one exists.
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paletteCol: The amount of colours in
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the palette. Multiply by 4 for a
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byte count.
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paletteAddress: Useful for caching,
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the palette starts at this get/set
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address.
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dataAddress: Useful for caching,
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the data starts at this get/set
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address.
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dataFull: The size of the data of
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the image, according to the image.
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dsSpan: This is a hint for the cache
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and cannot be relied upon to be
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correct, only >= 1:
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Scanline length in bytes.
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dsPlane: This is a hint for the
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cache and cannot be relied upon to
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be correct, only >= 1:
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Plane length in bytes.
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getPalette(i): Gets the XRGB value
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of colour i as an integer.
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Do not go out of range of I.
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setPalette(i, v): Sets the XRGB
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value of colour i as an integer.
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Do not go out of range of I or V.
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getPixel(x, y, p): Returns the pixel
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value at X, Y, P. Do not go out of
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the range of X, Y or P.
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setPixel(x, y, p, v): Sets the pixel
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value at X, Y, P to V. Do not go
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out of the range of X, Y, P, or V.
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...in other words, about as much
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usability as a BufferedImage with
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getGraphics and createGraphics taken
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out of it for some crazy reason.
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The primary use of this library is
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because people like to use formats
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they happen to have actually heard
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of before, and everything but BMP is
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too complicated for low-memory OSes
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to stream from disk.
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-- This is released into
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the public domain.
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-- No warranty is provided,
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implied or otherwise.
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