<*PRAGMA LL*>A
PaintOp.T is a screen-independent painting operation.
A painting operation op takes a source pixel s and a destination
pixel d and produces a new value op(d, s) for the destination pixel.
A painting operation that ignores the source pixel is called a {\it tint}.
If op is a tint, we just write op(d) instead of op(d, s).
If the effect of a tint is to set the destination pixel to
some fixed value independent of its initial value, then the
tint is said to be {\it opaque}.
The locking level is LL.sup <= VBT.mu for all of the procedures
in this interface.
INTERFACEPaintOp ; TYPE T = RECORD op:INTEGER END; Predefined = [0..16]; CONST Bg = T{0}; Fg = T{1}; Transparent = T{2}; Swap = T{3}; Copy = T{4};
Bg, Fg, Transparent, and Swap are Trestle's four basic tints.
Bg sets the destination pixel to the screen's background color;
Fg sets it to the screen's foreground color; Transparent is the
identity function; Swap is a self-inverting operation that
exchanges the foreground and background pixels. More precisely,
consider a particular screentype and let bgpix and fgpix be the
foreground and background pixel for that screentype. Then for any
pixel d,
Bg(d) = bgpix
Fg(d) = fgpix
Transparent(d) = d
Swap(bgpix) = fgpix
Swap(fgpix) = bgpix
Swap(Swap(d)) = d
Swap(d) # d
The operation Copy copies source to destination:
Copy(d, s) = s
Copy is not a tint, and should be used only when the source pixels
are of the same screentype as the destination pixels (for example,
with VBT.Scroll, or when painting a pixmap of the same type as
the screen).
CONST
BgBg = Bg;
BgFg = T{5};
BgTransparent = T{6};
BgSwap = T{7};
FgFg = Fg;
FgBg = T{8};
FgTransparent = T{9};
FgSwap = T{10};
TransparentTransparent = Transparent;
TransparentBg = T{11};
TransparentFg = T{12};
TransparentSwap = T{13};
SwapSwap = Swap;
SwapBg = T{14};
SwapFg = T{15};
SwapTransparent = T{16};
The sixteen operations above all have names of the form XY,
where X and Y are one of the four basic tints.
They are defined by the rule:
XY(dest, source) =
IF source = 0 THEN X(dest) ELSE Y(dest) END
For example, BgFg can be used to paint a one bit deep source
interpreting zeros as background and ones as foreground.
Obviously these sixteen painting operations should be used only with
one-bit deep sources. However, not all one-bit deep sources are
of the same screentype: for example, different screentypes might
have different rules for representing bitmaps. To accomodate this
unfortunate fact of life, we associate with every screentype st
another screentype st.bits, which is the type of bitmap sources
appropriate for st. The depth of st.bits is always one. If the
depth of st is one, then it is possible (but not certain) that
st.bits = st. When using one of sixteen operations above on a VBT
with screentype st, the source must have type st.bits. You will
be happy to recall that this will be taken care of automatically
if you use screen-independent bitmaps and fonts.
Next there is a procedure for generating colored painting operations.
TYPE
Mode = {Stable, Normal, Accurate};
BW = {UseBg, UseFg, UseIntensity};
PROCEDURE FromRGB(
r, g, b: REAL;
mode := Mode.Normal;
gray := -1.0;
bw := BW.UseIntensity): T;
Return a tint that will set a pixel to the color (r,g,b). The values
r, g, and b should be in the range 0.0 to 1.0;
they represent the fractions of red, green, and blue in the
desired color.
The gray argument controls what the tint will do on a gray-scale
display. If gray is between zero and one, it specifies the
intensity of the tint. If gray is defaulted to -1, then the
tint will use the intensity of the color (r,g,b).
The bw argument controls what the tint will be on a monochrome
display. If bw is UseBg or UseFg, then the tint will be Bg
or Fg, respectively. If bw is UseIntensity, then the tint
will be Fg if r, g, and b are all zero (that is, if the color
is black), and Bg otherwise.
The mode argument is relevant on color and gray-scale displays.
When the total number of pixel colors desired by all of the
applications that are running exceeds the number of available colors,
then some applications' colors will change (usually in an
unpleasantly random way).
To reduce the likelihood that your color will change randomly (at
the cost of fidelity), set mode to Stable. To increase the
fidelity of the pixel to the specified intensities (at the cost of
increased danger of random change), set mode to Accurate. For
example, an icon window should use stable colors; a color editor
should use accurate colors.
PROCEDURE Pair(op0, op1: T): T;
Return an operationopsuch thatop(d,0) = op0(d)andop(d,1) = op1(d).
For example,
Pair(FromRGB(1.0,1.0,1.0), FromRGB(1.0,0.0,0.0))
will paint a bitmap with zeros as white and ones as red.
PROCEDURE SwapPair(op0, op1: T): T;
Return an operation that swaps the pixels painted byop0andop1.
SwapPair requires that op0 and op1 be opaque, that is,
they must set the destination to particular pixels (say, pix0
and pix1). Then the tint op returned by SwapPair satisfies:
op(pix0) = pix1
op(pix1) = pix0
op(op(p)) = p for any pixel p
For example, Swap = SwapPair(Bg, Fg).
Sometimes it is handy to collect several related painting operations into a single object:
TYPE
ColorQuad = OBJECT
bg, fg, bgFg, transparentFg: T
END;
PROCEDURE MakeColorQuad(bg, fg: T): ColorQuad;
Return ColorQuad{bg,fg,Pair(bg,fg),Pair(Transparent,fg)}.
TYPE
ColorScheme = ColorQuad OBJECT
swap, bgTransparent, bgSwap, fgBg, fgTransparent,
fgSwap, transparentBg, transparentSwap,
swapBg, swapFg, swapTransparent: T;
END;
PROCEDURE MakeColorScheme(bg, fg: T): ColorScheme;
Return the fifteen painting operations other thanTransparentthat can be made by combiningbg,fg, andTransparent, usingSwapPairandPair.
In
MakeColorQuad and MakeColorScheme, bg and fg should be
tints.
VAR (*CONST*) bgFg: ColorScheme;This ``variable'' is really a constant for
MakeColorScheme(Bg, Fg).
END PaintOp.