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Annotation of 43BSDTahoe/new/X/doc/Xlib/ch03a.t, revision 1.1

1.1     ! root        1: .EQ
        !             2: delim $$
        !             3: .EN
        !             4: .NH
        !             5: Data Representation
        !             6: .XS
        !             7: Data Representation
        !             8: .XE
        !             9: .PP
        !            10: .IN "Definitions" "Bitmap"
        !            11: .IN "Definitions" "Pixmap"
        !            12: A Bitmap is a single plane (bit) rectangle.
        !            13: A Pixmap is a rectangle of pixels, and is therefore as ``deep'' as the
        !            14: display.
        !            15: For example, if your color display has four bits/pixel,
        !            16: a Pixmap is a rectangle of four bit pixels.
        !            17: In this implementation of the underlying protocol,
        !            18: the depth of the display is limited to 16 bit planes.
        !            19: .IN "Limitations" "Bits per Pixel"
        !            20: The subroutine interface, however, is designed to support display hardware of
        !            21: up to 32 bits per pixel.
        !            22: The ``pixel value'' can range from 0 to $2 sup n$,
        !            23: where \fIn\fP is the number of
        !            24: bits per pixel.
        !            25: .IN "Definitions" "Pixel values"
        !            26: .IN "Definitions" "Cursors"
        !            27: Cursors are used as mouse pointers and typically track the mouse; a
        !            28: cursor is an arbitrary two-color shape with an arbitrary ``hot spot''.
        !            29: .PP
        !            30: .IN "Definitions" "Locator"
        !            31: A Locator is
        !            32: an absolute point on the screen, represented as <x,y> with the X-coordinate
        !            33: in the most significant 16 bits and the Y-coordinate in the least significant
        !            34: 16 bits.
        !            35: .EQ
        !            36: delim off
        !            37: .EN
        !            38: .PP
        !            39: .IN "Definitions" "Bitmap"
        !            40: A Bitmap is represented by ((width + 15) / 16) * height * 2 bytes of data.
        !            41: Each row is stored starting on a word (16 bit) boundary, and is padded to
        !            42: the right to a 16 bit boundary.
        !            43: It is stored top line to bottom line in memory.
        !            44: It has a size of (width x height) pixels.
        !            45: .IN "Macro" "BitmapSize()"
        !            46: The macro \fIBitmapSize(width,height)\fP can be used to compute the size in
        !            47: bytes of the Bitmap.
        !            48: .IN "Definitions" "Bit Order"
        !            49: The
        !            50: bits are in scanline order, with each scanline padded if necessary to a
        !            51: multiple of 16 bits.
        !            52: Within a scanline, the bits are represented left to
        !            53: right, stored in 16-bit words.
        !            54: The least significant bit of a word is the leftmost visible pixel on the 
        !            55: display.
        !            56: Analysis showed that the bit reversal cpu time incurred on some
        !            57: machine architectures was small relative to the
        !            58: data transmission time,
        !            59: so a fixed client bitmap representation was selected for portability's sake.
        !            60: .PP
        !            61: .IN "Definitions" "Pixmap"
        !            62: .IN "Definitions" "XY-format"
        !            63: .IN "Definitions" "Z-format"
        !            64: A Pixmap can be represented in either `XY format' or `Z format'.
        !            65: In XY format,
        !            66: each plane is represented as a Bitmap, and the planes appear from most to least
        !            67: significant bit order.
        !            68: The total number of bytes is thus
        !            69: ((width + 15) / 16) * height * 2 * depth.
        !            70: .IN "Macro" "XYPixmapSize()"
        !            71: The macro \fIXYPixmapSize(width, height, planes)\fP can be used to
        !            72: compute the size in bytes of a Pixmap in XY format.
        !            73: In Z format, the pixels are in
        !            74: scanline order, left to right within a scanline.
        !            75: For hardware with 2 to 8
        !            76: planes, each pixel value is represented by a single byte;
        !            77: the total number of bytes
        !            78: is thus width * height.
        !            79: For hardware with 9 to 16 planes, each pixel value is
        !            80: represented by a 16-bit word; the total number of bytes is thus
        !            81: 2 * width * height.
        !            82: .IN "Macro" "BZPixmapSize()"
        !            83: .IN "Macro" "WZPixmapSize()"
        !            84: The macros \fIBZPixmapSize(width, height)\fP and 
        !            85: \fIWZPixmapSize(width, height)\fP
        !            86: can be used to compute the size in bytes of a pixmap in Z format for
        !            87: 2 to 8 bit planes and 9 to 16 bitplanes respectively.
        !            88: .IN "Restrictions" "Z-format"
        !            89: Z-format cannot be used on monochrome display hardware.
        !            90: .PP
        !            91: Background tiling uses Pixmaps to specify the
        !            92: pattern.
        !            93: Since you may want such patterns either relative to
        !            94: .IN "Definitions" "Tile Mode"
        !            95: the window or absolute, there is a concept of `tile mode' associated
        !            96: with a window, allowing the pattern to be absolutely positioned to the window,
        !            97: or relative to the parent window (often the root window).
        !            98: This allows alignment of patterns either to the window you are working
        !            99: in, or to the parent window.
        !           100: Both are useful; icon windows often want relative alignment, while
        !           101: normal windows usually want absolute alignment.
        !           102: .PP
        !           103: .IN "Macro" "BlackPixel"
        !           104: .IN "Macro" "WhitePixel"
        !           105: The pixel values \fIBlackPixel\fP and \fIWhitePixel\fP (0 and 1) are
        !           106: .IN "File" "<X/X.h>
        !           107: always defined on every display server, as defined in \fI<X/X.h>\fP.
        !           108: These constants are intended for use in monochrome applications.
        !           109: On color hardware, the colors of black and white may
        !           110: be redefined by the user.

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