Learning PostScript   ~ Part 3 ~   By Peter Goed   || 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||   Graphics  As we have already seen, a PostScript page description is built up by applying paint to graphics and text with the 'stroke', 'fill', and 'show' operators. Paint can be applied in black, white, or any shade of grey; or in any colour, for PostScript devi ces that handle colour. We can modify the elements of the current graphics state in a similar fashion to an artist changing a brush or paint colour before rendering text and graphic elements on your page. PostScript interpreters remember the current graphics state parameters, any of which may be modified either temporarily or permanently at any point in a page description to affect just a small specified area or the entire page. In part one of these tutorials you learned to initialize and to modify two of the most fundamental graphics state parameters: the current point and the current path. In part two you learned to select the graphics shapes or characters that define the current font. In this session we will examine two graphics state parameters that are used to change the appearance of graphics or text: the width of the line produced by the 'stroke' operator and the colour of the graphic produced by the painting operators 'stroke', 'fill', and 'show'.  Colour  Because very few people have access to colour PostScript output devices, I will limit this section to cover black, white and grey shades only. Let us begin with the following small page description. 0 0 moveto 612 0 rlineto 0 792 rlineto -612 0 rlineto closepath fill /Times-BoldItalic findfont 24 scalefont setfont 306 100 moveto 1 setgray (Amiga Forever ...) show showpage This page description constructs a rectangle the full size of the page (612 by 792) and fills it with the default colour black, we then selected a font and showed the text string (Amiga Forever ...) at the specified place on the page.  setgray  The 1 'setgray' instruction caused the text to be painted white. This technique is commonly referred to as a reverse, because it reverses the natural order of printing black characters on a white page. The 'setgray' operator is one of the simplest in the PostScript vocabulary. In addition to reversing the natural order of black on white, it can also be used to create the illusion of depth or of a three dimensional aspect by altering background and fo reground colours, and by shading some graphic elements in relationship to others. The 'setgray' operator requires only one operand, ranging from 0 for black to 1 for white (no colour), or any intermediate value representing a percentage of black and white. For example, .1 is 10 percent white - in other words dark grey; .5 is equal a mounts of black and white - medium grey; and .99 is nearly all white - very light grey. The following page description will give you an impression of text ranging from black to white in 10 steps. /Times-Bold findfont 30 scalefont setfont 144 720 moveto 0 setgray (PostScript) show 144 648 moveto .1 setgray (PostScript) show 144 576 moveto .2 setgray (PostScript) show 144 504 moveto .3 setgray (PostScript) show 144 432 moveto .4 setgray (PostScript) show 144 360 moveto .5 setgray (PostScript) show 144 288 moveto .6 setgray (PostScript) show 144 216 moveto .7 setgray (PostScript) show 144 144 moveto .8 setgray (PostScript) show 144 72 moveto .9 setgray (PostScript) show 144 0 moveto 1 setgray % which being white, will not be seen. (PostScript) show showpage  Layering  The order in which the 'setgray' operator applies text and graphics to the page, using black, white and various shades of grey, is important. In the following page description, the shadowing effect of the text produced by the .9 'setgray' instruction must be applied before the black text produced by the 0 'setgray' instruction, or the shadow would be on top of the solid black text, instead of underneath it. /Helvetica-Bold findfont 72 scalefont setfont .9 setgray % Grey first 200 400 moveto (Stand) show 225 325 moveto (Out) show 0 setgray % Black secondly 220 425 moveto (Stand) show 245 350 moveto (Out) show showpage This technique of applying paint to text and graphics in a certain order is known as "layering".  Shadowing  The rectangle constructed by the code below, appears to be a solid white box, outlined with a black line, and with a black shadow underneath that causes the box to stand out from the page. It is the shadow that gives the illusion of depth to the box. If you study the following instructions you will see that the illusion is in fact constructed from three separate boxes; a filled black box on the bottom, a white filled box, slightly offset on top of the black box, and a third box which is outlined with the stroke operator. % Box 1 -- a filled black box 120 400 moveto 200 0 rlineto 0 300 rlineto -200 0 rlineto closepath fill % Box 2 -- a filled white box - offset by 15 points from box 1 1 setgray 100 400 moveto 200 0 rlineto 0 300 rlineto -200 0 rlineto closepath fill % Box 3 -- a stroked box outline - offset as box 2 0 setgray 100 400 moveto 200 0 rlineto 0 300 rlineto -200 0 rlineto closepath stroke showpage  gsave and grestore  The following instructions will create the previous example but in a slightly different way, to show the "save" and "restore" graphics state parameters to temporarily change one or more of the parameters. In this example we use the 'gsave' operator to save the default black colour used to paint the solid black in box 1, then issue the "1 setgray" instruction that sets the colour for box 2. The 'grestore' instruction then restores the black colour that was saved before we issued the "1 setgray" instruction. There is now no need for a "0 setgray" instruction for the black outline of box 3. % Box 1 -- solid black 115 385 moveto 200 0 rlineto 0 300 rlineto -200 0 rlineto closepath fill % Box 2 -- white gsave 1 setgray 100 400 moveto 200 0 rlineto 0 300 rlineto -200 0 rlineto closepath fill grestore % Box 3 -- black outline -- 0 setgray not needed 2 setlinewidth 100 400 moveto 200 0 rlineto 0 300 rlineto -200 0 rlineto closepath stroke showpage  setlinewidth  In the previous example we added the instruction "2 setlinewidth" to thicken the black outline stroked around the white box. In the following example we use the 'setlinewidth' operator in place of filling a rectangle, as we did in the example in part 2 last month, for underlined text. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) show 0 -27 rmoveto 72 621 lineto 18 setlinewidth stroke showpage Instead of constructing and filling a rectangular box 18 points high, and underlining the string "Your Text" as in the example in part 2, the same object is achieved by stroking a line with the same 18 point thickness. NOTE: The 'setlinewidth' operator strokes equally on either side of the current path, hence the necessity to set the current path at 18 points plus half the linewidth of the 18 point line (9) equalling 27 points. The 'setlinewidth' operator is capable of rendering both text and lines at below the default of 1 point. There are often times that you will find that a linewidth of .5 can give an attractive appearance to outlined text. On the other hand there will be times when you will want to display outlined text with a bolder appearance. The instructions below cover both aspects discussed here. /Times-BoldItalic findfont 72 scalefont setfont 72 504 moveto (Your Text) true charpath .5 setlinewidth % Ultra thin text stroke 72 654 moveto (Your Text) true charpath 12 setlinewidth % This will give you an outline % of 6 points either side of the % 1 point default character outline. % To make the characters look more % attractive, you would normally add % the following instructions to only % give you the outside 6 points of % the character as your outline. stroke 72 654 moveto 1 setgray % Turn on white (Your Text) show % This will dump the normal text in % white, on top of the inside % 6 points of the outline you made, % filling the characters with white. showpage You can use this principle to advantage in creating fancy looking text such as in the following instructions. /Times-BoldItalic findfont 72 scalefont setfont 72 360 moveto (Your Text) true charpath fill % This will give you normal black text 72 360 moveto (Your Text) true charpath 3 setlinewidth stroke % This will give you a thicker outline % stroked around the previous text 72 360 moveto (Your Text) true charpath 1 setlinewidth 1 setgray % This will give you a white outline stroke % around and on top of the first text % but inside the outline used above % and will result in fancy looking text. showpage Using what we have learned so far in this month's episode, let us now construct something that will be useful in many applications. Fancy Text within a Shadow Box. % Shadow box 46 566 moveto 540 0 rlineto 0 100 rlineto -540 0 rlineto closepath fill % Step one is to lay down the % black box for the background shadow % Background box gsave 36 576 moveto 1 setgray 540 0 rlineto 0 100 rlineto -540 0 rlineto closepath fill % Step two is to lay the offset white grestore % box on top of the step one black box % Outline box 36 576 moveto 2 setlinewidth 540 0 rlineto 0 100 rlineto -540 0 rlineto closepath stroke % Step three is to lay the black outline % box on top of the white box in step 2 /Times-BoldItalic findfont 108 scalefont setfont 140 590 moveto (TITLE) true charpath % Step four fill % This lays solid black text on top of % the outline box in step three 140 590 moveto (TITLE) true charpath 3 setlinewidth % Step five stroke % This lays a 3 point outline text on % top of the smaller text from step 4. 140 590 moveto (TITLE) true charpath 1 setlinewidth % Step Six 1 setgray % Lays a one point white outline text stroke % on top of the outline text of step 5. showpage These layers must be created in the order given above for the whole show to work properly and give the desired result.  Shaded Box with Shadow Text  Using the example we just created but changing a small amount of the code we can get another nice effect of shadow text within a shaded and shadowed box. % Shadow box 46 566 moveto 540 0 rlineto 0 100 rlineto -540 0 rlineto closepath fill % Background box gsave 36 576 moveto .9 setgray % Here we change from 1 to .9 (white to grey) 540 0 rlineto 0 100 rlineto -540 0 rlineto closepath fill grestore % Outline box 36 576 moveto 2 setlinewidth 540 0 rlineto 0 100 rlineto -540 0 rlineto closepath stroke % Step three is to lay the black outline % box on top of the white box in step 2 /Times-BoldItalic findfont 108 scalefont setfont 90 587 moveto % The instructions here are changed (T I T L E) show % Paint solid black characters gsave % Save graphic state 1 setgray % Set white 87 590 moveto % Offset 3 points left and 3 points up (T I T L E) show % Paint solid white characters grestore % Restore graphic state .5 setlinewidth 87 590 moveto % Offset 3 points left (T I T L E) true Charpath % Paint a .5 point line in black stroke % around the characters, thus allowing % us to more easily see the break % between the white text and grey box showpage That brings us to the end of this month's lesson. For homework this time, I will make it easy for you. Using the two previous examples, create a page description that will give us a black box in the same position as in the last example. Make this box 550 by 110 points and draw a white box that is 10 points smaller in height and width than the black box, but central within it. Now Central to this place the word TITLE in it using the 'ashow' operator to give a spacing of 24 points between characters. If you can handle this exercise comfortably, then you are with us, if you are having problems, I suggest that some revision of parts one and two will get you back on track again. Good Luck!  || 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||| 33 ||