[Cyan]<Imaging>6.0>NewPixels>Pixels.mesa!5

Pixels.mesa

Copyright © 1985, 1986 by Xerox Corporation. All rights reserved.

Frank Crow, June 5, 1986 1:24:01 pm PDT

Basic operations on two-dimensional arrays of pixels. A pixel consists of an arbitrary number of values (samples) addressed at the same position. A pixel is supposed to represent the information behind a displayed spot, not all of which is necessarily visible to the viewer. One typical pixel format consists of 4 samples, one each for alpha, red, green, and blue.

DIRECTORY

Basics USING[BYTE],

Terminal USING[Virtual],

Atom USING[PropList],

Rope USING[ROPE],

Imager USING[Context, Rectangle],

SampleMapOps USING[SubMap, Buffer];

Pixels: CEDAR DEFINITIONS

~ BEGIN

Type Definitions

BYTE: TYPE ~ Basics.BYTE; -- parts of a pixel will not exceed 8 bits in the forseeable future

Extent: TYPE ~ RECORD[x, y, w, h: NAT];

SampleSet: TYPE ~ SampleMapOps.Buffer;

REF RECORD [length: NAT, samples: SEQUENCE maxLength: NAT OF CARDINAL];;

SampleSetSequence: TYPE ~ RECORD[SEQUENCE length: NAT OF SampleSet];

SubMap: TYPE ~ RECORD[ subMap: SampleMapOps.SubMap, df: NAT ← 1];

extended SubMap, df is distance (in samples) between samples

SubMapSequence: TYPE ~ RECORD[SEQUENCE length: NAT OF SubMap];

PixelBuffer: TYPE ~ RECORD[

width: NAT ← 0, -- width, in pixels, of pixel grid

height: NAT ← 0, -- height, in pixels, of pixel grid

samplesPerPixel: NAT ← 0, -- number of samples representing each pixel (eg. RGB)

pixels: REF SubMapSequence ← NIL, -- The bits. Each SubMap represents one sample from a pixel. Where an alpha buffer or depth buffer is used, its location is stored in the props under $Alpha or $Depth.

props: Atom.PropList ← NIL

];

PixelsError: SIGNAL [reason: ErrorDesc];

ErrorDesc: TYPE ~ RECORD [code: ATOM, explanation: Rope.ROPE];

Utility Procedures

XfmMapPlace: PROC [ map: SubMap, x, y: INTEGER ] RETURNS [newX, newY: INTEGER];

ByteAvrgWgtd: PROC[ b1, b2, wgt: BYTE ] RETURNS[ bOut: BYTE ];

SumLessProd: PROC[ b1, b2: BYTE ] RETURNS[ bOut: BYTE ];

GetSampleSet: PROC[size: NAT] RETURNS[SampleSet];

Creation Operations

Create: PROC [width, height: NAT, pixelSizes: SampleSet]
RETURNS[PixelBuffer];

Allocates bits and builds PixelBuffer record with default procedures. PixelSizes allows arbitrary collections of bits to be used as pixels

GetFromImagerContext: PROC [context: Imager.Context, alpha, depth: BOOLEAN]
RETURNS[PixelBuffer, Imager.Rectangle];

Forces pixel buffer onto Imager context in those circumstances where it is possible, stores REF to imager context on PixelBuffer.props

GetFromTerminal: PROC [vt: Terminal.Virtual, alpha, depth: BOOLEAN]
RETURNS[PixelBuffer];

Makes pixel buffer out of terminal color display, if there is one

PixelBuffer Operations

TerminalFromBuffer: PROC [buf: PixelBuffer] RETURNS[vt: Terminal.Virtual];

For getting terminal when needed for locking, etc.

ImagerContextFromBuffer: PROC [buf: PixelBuffer, type: ATOM ← NIL]
RETURNS[ctx: Imager.Context];

Allows imager calls to act on your pixels understood types are: $Dithered, $Mapped, $Grey, $Dorado24

Fill: PROC [buf: PixelBuffer, pixel: SampleSet ← NIL];

Fill pixels with specified pixel value, default pixel value (pixel = NIL) clears to zero

Transfer: PROC [dstBuf, srcBuf: PixelBuffer];

Copies one PixelBuffer into another, doing the "right thing" about non-visible buffers

Copy: PROC [ destination, source: PixelBuffer, destArea, srcArea: Extent,
op: ATOM ← $Write ];

Copies using the specified source and destination rectangles

ShowOnImagerContext: PROC [context: Imager.Context, buf: PixelBuffer];

Puts pixels from displayMemory onto supplied context using Imager calls

Pixel operations

In the following, a SampleSet is assumed to map one byte into one SubMap.

GetPixel: PROC [buf: PixelBuffer, x, y: NAT, pixel: SampleSet ← NIL]
RETURNS[ SampleSet ];

Those in a hurry can avoid allocates by caching "pixel" (the 4th argument)

PutPixel: PROC [ buf: PixelBuffer, x, y: NAT, pixel: SampleSet ];

GetScanSeg: PROC [buf: PixelBuffer, x, y, length: NAT, pixels: REF SampleSetSequence ← NIL]
RETURNS[ REF SampleSetSequence ];

PutScanSeg: PROC [ buf: PixelBuffer, x, y, length: NAT,
pixels: REF SampleSetSequence, op: ATOM ← $Write ];

PixelOp: PROC [ buf: PixelBuffer, area: Extent, pixel: SampleSet,
op: ATOM ← $Write ];

Standard ops include:

$AND = bitwise AND

$OR = bitwise OR

$XOR = bitwise XOR

$Write = replace previous contents with new pixel (default)

$WriteUnder = blend behind previously written pixels (using alpha buffer)

$WriteOver = blend in front of previously written pixels (using alpha buffer)

Visible value operations

In the following, the Client specifies which submap is targeted, and gains speed thereby.

GetValue: PROC [buf: PixelBuffer, x, y: NAT, map: NAT ← 0] RETURNS[ value: CARDINAL ];

PutValue: PROC [ buf: PixelBuffer, x, y: NAT, value: CARDINAL, map: NAT ← 0 ];

ValueOp: PROC [ buf: PixelBuffer, area: Extent, value: CARDINAL, map: NAT ← 0,
op: ATOM ← $Write ];

Standard ops are:

$AND = bitwise AND

$OR = bitwise OR

$XOR = bitwise XOR

$Write = replace previous contents with new pixel (default)

END.