include	"draw.m";
draw := load Draw Draw->PATH;

# compositing operators
SinD:   con 1<<3;
DinS:   con 1<<2;
SoutD:  con 1<<1;
DoutS:  con 1<<0;

S:      con SinD|SoutD;
SoverD: con SinD|SoutD|DoutS;
SatopD: con SinD|DoutS;
SxorD:  con SoutD|DoutS;

D:      con DinS|DoutS;
DoverS: con DinS|DoutS|SoutD;
DatopS: con DinS|SoutD;
DxorS:  con DoutS|SoutD;

Clear:  con 0;

Image: adt
{
    r:          Rect;
    clipr:      Rect;
    chans:      Chans;
    depth:      int;
    repl:       int;

    display:    ref Display;
    screen:     ref Screen;

    draw:       fn(dst: self ref Image, r: Rect, src: ref Image,
                   mask: ref Image, p: Point);
    drawop:       fn(dst: self ref Image, r: Rect, src: ref Image,
                   mask: ref Image, p: Point, op: int);
    gendraw:    fn(dst: self ref Image, r: Rect, src: ref Image,
                   p0: Point, mask: ref Image, p1: Point);
    gendrawop:    fn(dst: self ref Image, r: Rect, src: ref Image,
                   p0: Point, mask: ref Image, p1: Point, op: int);
    line:       fn(dst: self ref Image, p0,p1: Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point);
    lineop:       fn(dst: self ref Image, p0,p1: Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point, op: int);
    poly:       fn(dst: self ref Image, p: array of Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point);
    polyop:       fn(dst: self ref Image, p: array of Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point, op: int);
    bezspline:  fn(dst: self ref Image, p: array of Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point);
    bezsplineop:  fn(dst: self ref Image, p: array of Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point, op: int);
    fillpoly:   fn(dst: self ref Image, p: array of Point,
                   wind: int, src: ref Image, sp: Point);
    fillpolyop:   fn(dst: self ref Image, p: array of Point,
                   wind: int, src: ref Image, sp: Point, op: int);
    fillbezspline: fn(dst: self ref Image, p: array of Point,
                   wind: int, src: ref Image, sp: Point);
    fillbezsplineop: fn(dst: self ref Image, p: array of Point,
                   wind: int, src: ref Image, sp: Point, op: int);
    ellipse:    fn(dst: self ref Image, c: Point, a, b,
                   thick: int, src: ref Image, sp: Point);
    ellipseop:    fn(dst: self ref Image, c: Point, a, b,
                   thick: int, src: ref Image, sp: Point, op: int);
    fillellipse:fn(dst: self ref Image, c: Point, a, b: int,
                   src: ref Image, sp: Point);
    fillellipseop:fn(dst: self ref Image, c: Point, a, b: int,
                   src: ref Image, sp: Point, op: int);
    arc:        fn(dst: self ref Image, c: Point, a, b, thick: int,
                   src: ref Image, sp: Point, alpha, phi: int);
    arcop:      fn(dst: self ref Image, c: Point, a, b, thick: int,
                   src: ref Image, sp: Point,
                   alpha, phi: int, op: int);
    fillarc:    fn(dst: self ref Image, c: Point, a, b: int,
                   src: ref Image, sp: Point, alpha, phi: int);
    fillarcop:  fn(dst: self ref Image, c: Point, a, b: int,
                   src: ref Image, sp: Point,
                   alpha, phi: int, op: int);
    bezier:     fn(dst: self ref Image, a,b,c,d: Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point);
    bezierop:     fn(dst: self ref Image, a,b,c,d: Point,
                   end0,end1,thick: int,
                   src: ref Image, sp: Point, op: int);
    fillbezier: fn(dst: self ref Image, a,b,c,d: Point, wind:int,
                   src: ref Image, sp: Point);
    fillbezierop: fn(dst: self ref Image, a,b,c,d: Point, wind:int,
                   src: ref Image, sp: Point, op: int);
    arrow:      fn(a,b,c: int): int;
    text:       fn(dst: self ref Image, p: Point, src: ref Image,
                   sp: Point, font: ref Font, str: string): Point;
    textop:       fn(dst: self ref Image, p: Point, src: ref Image,
                   sp: Point, font: ref Font, str: string,
                   op: int): Point;
    textbg:     fn(dst: self ref Image, p: Point, src: ref Image,
                   sp: Point, font: ref Font, str: string,
                   bg: ref Image, bgp: Point): Point;
    textbgop:     fn(dst: self ref Image, p: Point, src: ref Image,
                   sp: Point, font: ref Font, str: string,
                   bg: ref Image, bgp: Point, op: int): Point;
    border:     fn(dst: self ref Image, r: Rect, i: int,
                   src: ref Image, sp: Point);
    borderop:     fn(dst: self ref Image, r: Rect, i: int,
                   src: ref Image, sp: Point, op: int);

    readpixels: fn(src: self ref Image, r: Rect,
                   data: array of byte): int;
    writepixels:fn(dst: self ref Image, r: Rect,
                   data: array of byte): int;
    name:       fn(im: self ref Image, s: string, in: int): int;
    top:        fn(win: self ref Image);
    bottom:     fn(win: self ref Image);
    flush:      fn(win: self ref Image, func: int);
    origin:     fn(win: self ref Image, log, scr: Point): int;
};

An Image has a pixel channel structure as described in colour(6), represented by a value of the Chans adt, defined in draw-display(2). The channel structure of an image is fixed when the image is allocated.

Image has the following components:

display

Tells on which display the image resides.

screen

If the image is a window on a Screen (see draw-screen(2)), this field refers to that screen; otherwise it is nil.

r

The coordinates of the rectangle in the plane for which the Image has defined pixel values. It should not be modified after the image is created.

clipr

The clipping rectangle: operations that read or write the image will not access pixels outside clipr. Frequently, clipr is the same as Image.r, but it may differ; see in particular the discussion of Image.repl. The clipping region may be modified dynamically.

chans

The pixel channel structure of the image; the value should not be modified after the image is created.

depth

The number of bits per pixel in the picture: it is simply a convenience since it is necessarily equal to chans.depth(), and it should not be modified after the image is created.

repl

A boolean value specifying whether the image is tiled to cover the plane when used as a source for a drawing operation. If Image.repl is zero, operations are restricted to the intersection of Image.r and Image.clipr. If Image.repl is set, Image.r defines the tile to be replicated and Image.clipr defines the portion of the plane covered by the tiling, in other words, Image.r is replicated to cover Image.clipr; in such cases Image.r and Image.clipr are independent.

For example, a replicated image with Image.r set to ((0, 0), (1, 1)) and Image.clipr set to ((0, 0), (100, 100)), with the single pixel of Image.r set to blue, behaves identically to an image with Image.r and Image.clipr both set to ((0, 0), (100, 100)) and all pixels set to blue. However, the first image requires far less memory. The replication flag may be modified dynamically along with the clipping rectangle.

dst.draw(r, src, mask, p)

dst.drawop(r, src, mask, p, op)

Draw is the standard drawing function. Only those pixels within the intersection of dst.r and dst.clipr will be affected; draw ignores dst.repl. The operation proceeds as follows (this is a description of the behavior, not the implementation):

1.

If repl is set in src or mask, replicate their contents to fill their clip rectangles.

2.

Translate src and mask so p is aligned with r.min.

3.

Set r to the intersection of r and dst.r.

4.

Intersect r with src.clipr. If src.repl is false, also intersect r with src.r.

5.

Intersect r with mask.clipr. If mask.repl is false, also intersect r with mask.r.

6.

For each location in r, combine the dst pixel using the alpha value corresponding to the mask pixel. If the mask has an explicit alpha channel, the alpha value corresponding to the mask pixel is simply that pixel's alpha channel. Otherwise, the alpha value is the NTSC greyscale equivalent of the colour value, with white meaning opaque and black transparent.

In terms of the Porter-Duff compositing algebra, draw replaces the dst pixels with (src in mask) over dst. Drawop is almost identical, but applies the compositing operation op instead: (src in mask) op dst.

The various pixel channel formats involved need not be identical. If the channels involved are smaller than 8-bits, they will be promoted before the calculation by replicating the extant bits; after the calculation, they will be truncated to their proper sizes. For draw and gendraw only, if mask is nil, no mask is used.

dst.gendraw(r, src, p0, mask, p1)

dst.gendrawop(r, src, p0, mask, p1, op)

Similar to draw() except that it aligns the source and mask differently: src is aligned so p0 corresponds to r.min and mask is aligned so p1 corresponds to r.min. For most purposes with simple masks and source images, draw is sufficient, but gendraw is the general operator and the one the other drawing primitives are built upon.

dst.line(p0, p1, end0, end1, thick, src, sp)

dst.lineop(p0, p1, end0, end1, thick, src, sp, op)

Line draws in dst a line of width 1+2*thick pixels joining points p0 and p1. The line is drawn using pixels from the src image aligned so sp in the source corresponds to p0 in the destination. The line touches both p0 and p1, and end0 and end1 specify how the ends of the line are drawn. Draw->Endsquare terminates the line perpendicularly to the direction of the line; a thick line with Endsquare on both ends will be a rectangle. Draw->Enddisc terminates the line by drawing a disc of diameter 1+2*thick centered on the end point. Draw->Endarrow terminates the line with an arrowhead whose tip touches the endpoint. See the description of arrow for more information.

Line and the other geometrical operators are equivalent to calls to gendraw using a mask produced by the geometric procedure.

dst.poly(p, end0, end1, thick, src, sp)

dst.polyop(p, end0, end1, thick, src, sp, op)

Poly draws a general polygon; it is equivalent to a series of calls to line joining adjacent points in the array of Points p. The ends of the polygon are specified as in line; interior lines are terminated with Enddisc to make smooth joins. The source is aligned so sp corresponds to p[0].

dst.bezspline(p, end0, end1, thick, src, sp)

dst.bezsplineop(p, end0, end1, thick, src, sp, op)

Bezspline takes the same arguments as poly but draws a quadratic B-spline (despite its name) rather than a polygon. If the first and last points in p are equal, the spline has periodic end conditions.

dst.fillpoly(p, wind, src, sp)

dst.fillpolyop(p, wind, src, sp, op)

Fillpoly is like poly but fills in the resulting polygon rather than outlining it. The source is aligned so sp corresponds to p[0]. The winding rule parameter wind resolves ambiguities about what to fill if the polygon is self-intersecting. If wind is ~0, a pixel is inside the polygon if the polygon's winding number about the point is non-zero. If wind is 1, a pixel is inside if the winding number is odd. Complementary values (0 or ~1) cause outside pixels to be filled. The meaning of other values is undefined. The polygon is closed with a line if necessary.

dst.fillbezspline(p, wind, src, sp)

dst.fillbezsplineop(p, wind, src, sp, op)

Fillbezspline is like fillpoly but fills the quadratic B-spline rather than the polygon outlined by p. The spline is closed with a line if necessary.

dst.ellipse(c, a, b, thick, src, sp)

dst.ellipseop(c, a, b, thick, src, sp, op)

Ellipse draws in dst an ellipse centered on c with horizontal and vertical semiaxes a and b. The source is aligned so sp in src corresponds to c in dst. The ellipse is drawn with thickness 1+2*thick.

dst.fillellipse(c, a, b, src, sp)

dst.fillellipseop(c, a, b, src, sp, op)

Fillellipse is like ellipse but fills the ellipse rather than outlining it.

dst.arc(c, a, b, thick, src, sp, alpha, phi)

dst.arcop(c, a, b, thick, src, sp, alpha, phi, op)

Arc is like ellipse, but draws only that portion of the ellipse starting at angle alpha and extending through an angle of phi. The angles are measured in degrees counterclockwise from the positive x axis.

dst.fillarc(c, a, b, src, sp, alpha, phi)

dst.fillarcop(c, a, b, src, sp, alpha, phi, op)

Fillarc is like arc, but fills the sector with the source color.

dst.bezier(a, b, c, d, end0, end1, thick, src, sp)

dst.bezierop(a, b, c, d, end0, end1, thick, src, sp, op)

Bezier draws the cubic Bezier curve defined by Points a, b, c, and d. The end styles are determined by end0 and end1; the thickness of the curve is 1+2*thick. The source is aligned so sp in src corresponds to a in dst.

dst.fillbezier(a, b, c, d, wind, src, sp)

dst.fillbezierop(a, b, c, d, wind, src, sp, op)

Fillbezier is to bezier as fillpoly is to poly.

arrow(a, b, c)

Arrow is a function to describe general arrowheads; its result is passed as end parameters to line, poly, etc. If all three parameters are zero, it produces the default arrowhead, otherwise, a sets the distance along line from end of the regular line to tip, b sets the distance along line from the barb to the tip, and c sets the distance perpendicular to the line from edge of line to the tip of the barb, all in pixels.

dst.border(r, i, src, sp)

dst.borderop(r, i, src, sp, op)

Border draws in dst an outline of rectangle r in the given src colour. The outline has width i; if positive, the border goes inside the rectangle; negative, outside. The source is aligned so sp corresponds to r.min.

dst.text(p, src, sp, font, str)

dst.textop(p, src, sp, font, str, op)

dst.textbg(p, src, sp, font, str, bg, bgp)

dst.textbgop(p, src, sp, font, str, bg, bgp, op)

Text draws in dst characters specified by the string str and font font; it is equivalent to a series of calls to gendraw using source src and masks determined by the character shapes. The text is positioned with the left of the first character at p.x and the top of the line of text at p.y. The source is positioned so sp in src corresponds to p in dst. Text returns a Point that is the position of the next character that would be drawn if the string were longer.

For characters with undefined or zero-width images in the font, the character at font position 0 (NUL) is drawn.

Text draws the text leaving the background intact. Textbg draws the background colour bg behind the characters, with the alignment specified by point bgp; it is otherwise the same as text.

src.readpixels(r, data)

Readpixels fills the data array with pixels from the specified rectangle of the src image. The pixels are presented one horizontal line at a time, starting with the top-left pixel of r. Each scan line starts with a new byte in the array, leaving the last byte of the previous line partially empty, if necessary. Pixels are packed as tightly as possible within data, regardless of the rectangle being extracted. Bytes are filled from most to least significant bit order, as the x coordinate increases, aligned so x=0 would appear as the leftmost pixel of its byte. Thus, for a 1-bit deep greyscale image, the pixel at x offset 165 within the rectangle will be in a data byte with mask value 16r04 regardless of the overall rectangle: 165 mod 8 equals 5, and 16r80 >> 5 equals 16r04. It is an error to call readpixels with an array that is too small to hold the rectangle's pixels. The return value is the number of bytes copied. The arrangement of pixels in arrays of bytes is described in image(6).

dst.writepixels(r, data)

Writepixels copies pixel values from the data array to the specified rectangle in the dst image. The format of the data is that produced by readpixels. The return value is the number of bytes copied. It is an error to call writepixels with an array that is too small to fill the rectangle.

im.name(s,in)

Publish the image im on its display under name s, if in is non-zero; otherwise, s must be an already published name and it is withdrawn from publication. A published image can be retrieved using Display.namedimage (see draw-display(2)). This function returns -1 on error, typically because the name is already in use (for in non-zero), or does not exist (for in zero).

win.top()

If the image win is a window, top pulls it to the ``top'' of the stack of windows on its Screen, perhaps obscuring other images. If win is not a window, top has no effect.

win.bottom()

If the image win is a window, bottom pulls it to the ``bottom'' of the stack of windows on its Screen, perhaps obscuring it. If win is not a window, bottom has no effect.

image.flush(flag)

The connection to a display has a buffer used to gather graphics requests generated by calls to the draw library. By default, the library flushes the buffer at the conclusion of any call that affects the visible display image itself. The flush routine allows finer control of buffer management. The flag has three possible values: Flushoff turns off all automatic flushing caused by writes to image, typically a window or the display image itself (buffers may still be written when they fill or when other objects on the display are modified); Flushnow causes the buffer to be flushed immediately; and Flushon restores the default behaviour.

win.origin(log, scr)

When a window is created (see draw-screen(2)), the coordinate system within the window is identical to that of the screen: the upper left corner of the window rectangle is its physical location on the display, not for example (0, 0). This symmetry may be broken, however: origin allows control of the location of the window on the display and the coordinate system used by programs drawing on the window. The first argument, log, sets the upper left corner of the logical (in-window) coordinate system without changing the position of the window on the screen. The second argument, scr, sets the upper left corner of physical (on-screen) coordinate system, that is, the window's location on the display, without changing the internal coordinate system. Therefore, changing scr without changing log moves the window without requiring the client using it to be notified of the change; changing log without changing scr allows the client to set up a private coordinate system regardless of the window's location. It is permissible for values of scr to move some or all of the window off screen. Origin returns -1 if the image is not a window or, in the case of changes to scr, if there are insufficient resources available to move the window; otherwise it returns 1.

T. Porter, T. Duff. ``Compositing Digital Images'', Computer Graphics (Proc. SIGGRAPH), 18:3, pp. 253-259, 1984.