Fritz: All Fritz/All Fritz.zip/All Fritz/FILES/DESKHING/PICTURE3.LZH/TXT2.EXE/MANUAL2.TXT

Text File | 1991-12-31 | 56KB | 955 lines

         PICTURETHIS(TM) "SHAREWARE" VERSION

         RELEASE 4.00

         DECEMBER 31, 1991

         USER MANUAL, PART 2 OF 7 PARTS


         Copyright 1988, 1989, 1990, 1991 by Patricia Y. Williams and
           Gregory Williams, All Rights Reserved.

         HortIdeas Publishing, 460 Black Lick Road, Gravel Switch,
           KY 40328 U.S.A.


         9. FINDING ENDPOINTS

           To move the cursor to an endpoint of a previously drawn
         curve, first press the Del key on the numeric keypad (with
         NumLock NOT toggled on and Shift NOT pressed). The cursor
         jumps to the endpoint which was APPROXIMATELY closest to the
         cursor's position when Del was pressed. (The measure of
         "closeness" used by PictureThis here is the sum of the
         horizontal distance and the vertical distance, rather than
         the true distance, for faster program operation.) All of the
         curves having that endpoint become dashed to help you
         distinguish the endpoint at which the cursor is now located
         from other nearby endpoints.
           If you want to move the cursor to another endpoint, press
         Space or + to shift the cursor to the NEXT closest endpoint
         on the screen to the ORIGINAL cursor position when the Del
         key was pressed. Or press - to move the cursor to the
         "previous" endpoint (which at first is the FURTHEST endpoint
         from the ORIGINAL cursor location). Continue pressing Space,
         +, and/or - until the cursor is at the desired endpoint.
           When the cursor is at the desired endpoint, press any key
         except Space, +, -, Enter, or Esc. The cursor remains at the
         selected endpoint, and the operation specified by the
         pressed key is carried out (for example, if F1 was pressed,
         a new curve is started); if a currently invalid key is
         pressed, the speaker beeps. If you prefer to remain at the
         endpoint and NOT start another operation, press Enter. In
         either case, the curves that were dashed become solid again.
           Pressing Esc at any time during the operation moves the
         cursor back to its original position when Del was pressed
         and returns all dashed curves to solid again.
           The cursor can be moved to an endpoint by using this
         operation any time you can move with the cursor keys, except
         when moving along a guideline (see Sections 8.2 and 8.3).
           Because the internal coordinates of the endpoints are
         finer than the screen resolution (see Section 20.3) at all
         screen magnifications except the highest (2400%), the cursor
         can APPEAR to be at an endpoint when it ISN'T -- the screen
         resolution is too low to distinguish "close to" from "at."
         IF YOU WANT TO POSITION THE CURSOR EXACTLY ON AN ENDPOINT,
         USE THE MOVE-TO-ENDPOINT OPERATION TO BE SURE.

         10. SMOOTHING CURVES

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           Using smoothing, you can draw a succession of curves end-
         to-end so that two curves sharing an endpoint also have the
         same direction (are tangent to each other) at the shared
         endpoint. Smoothing can be accessed either manually or
         automatically.

         10.1. MANUAL SMOOTHING

           For manual smoothing, during the drawing of a curve (after
         F1 has been pressed at least once to define an endpoint),
         press S to move the cursor to the endpoint associated with
         the currently selected control point IF ONE OR MORE
         PREVIOUSLY DRAWN CURVES ALSO HAVE THAT ENDPOINT. If NO
         previously drawn curves also have that endpoint, then you
         the speaker beeps (if toggled on) and an error message
         appears (if toggled on); the cursor remains where it is. If
         there is ONE previously drawn curve with ONE end at that
         endpoint, a line tangent to that previously drawn curve at
         the endpoint will appear. If there are TWO OR MORE
         previously drawn curves with that endpoint, or ONE
         previously drawn curve with BOTH of its ends at that
         endpoint, a prompt ("Next: +, Space"/ "Previous: -"/"Select:
         Enter") appears on the left side of the screen, and one of
         the previously drawn curves is dashed to distinguish it. If
         you want to draw the new curve tangent to the dashed curve
         at their shared endpoint, press Enter. A guideline tangent
         to the dashed curve at its endpoint appears. Otherwise, by
         repeatedly pressing Space, +, and/or -you can cause each of
         the previously drawn curves with the selected endpoint to be
         dashed successively. When the curve to which you want the
         new curve being drawn to be tangent at their shared endpoint
         is dashed, press Enter to select it. A guideline tangent to
         the dashed curve at its endpoint appears, unless guidelines
         are toggled off (see Section 10.3). For a previously drawn
         curve with both ends at the endpoint, pressing Enter when
         that curve is dashed causes a guideline tangent to one of
         its ends to appear; if you want to select the tangent to the
         OTHER end, instead press Esc, then S, and then Space, +,
         and/or - (repeatedly) to cycle through the curves until the
         curve with both ends at the selected endpoint again becomes
         dashed. This time when Enter is pressed, a guideline tangent
         to the OTHER end appears, unless guidelines are toggled off
         (see Section 10.3).
           The new curve's control point associated with the shared
         endpoint is constrained to move along the tangent guideline
         (whether visible or not). To move the control point with the
         cursor, first use the cursor key on the numeric keypad
         closest to the guideline direction (away from the previously
         drawn curve). Then use the "opposite" cursor key to move the
         other direction on the guideline (example: first 9, then 1).
         Note: By pressing Ins, you can toggle the cursor to move 1
         or 10 pixels (NOT any other units, regardless of the current
         units) per key press along the guideline. The new curve
         being drawn and the previously drawn curve have the same
         tangent at the endpoint they share: in other words, the two
         curves together form a SMOOTH curve (OR, if you move the
         control point back along the tangent guideline in the
         direction of the previously drawn curve, the two curves form
         a CUSP). Note: To GUARANTEE a truly smooth curve or a true
         cusp, you MUST move the control point of the new curve which

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         is associated with the shared endpoint AT LEAST ONE pixel
         along the tangent guideline.
           On a tangent guideline, control point position is
         indicated by a "missing" (background-colored) pixel. Move
         between the two control points of the new curve by pressing
         F2. A control point not constrained to move along a tangent
         line is moved by pressing the numeric keypad number keys, as
         usual. Note that BOTH control points of a new curve can be
         constrained by smoothing, if both of the new curve's
         endpoints are located at endpoints of previously drawn
         curves (press S when one of the control points is selected,
         select a previously drawn curve for smoothing, then press F2
         to choose the other control point, press S again, and select
         another previously drawn curve for smoothing). After shaping
         the new curve as you desire by positioning its control
         points, press F3 to set it; this also erases tangent
         guidelines.
           While drawing with smoothing, pressing Esc when the cursor
         is at the control point associated with an endpoint WITH a
         tangent constraint causes the tangent guideline to be erased
         and leaves the cursor at the same position; then that
         control point can be moved WITHOUT constraint by the numeric
         keypad number keys. Pressing Esc when the cursor is at the
         control point associated with an endpoint WITHOUT a tangent
         constraint erases any tangent guidelines, and provides the
         usual escape from drawing a curve.

         10.2. AUTOMATIC SMOOTHING

           For quick drawing of a succession of continuous smooth
         curves, you can toggle automatic smoothing on by pressing A.
         Pressing A again toggles automatic smoothing off and results
         in the cursor returning to the FIRST endpoint of a curve,
         instead of the second endpoint, when the curve is set.
         Pressing A yet again results in the cursor returning to the
         second endpoint of a curve when the curve is set, with
         automatic smoothing toggled off. This three-way toggling can
         be done almost any time a menu does not appear at the top of
         the screen, and the toggled state remains in effect until
         you toggle again. The automatic smoothing indicator in the
         status box reads "A " when automatic smoothing is off and
         the cursor returns to the second endpoint when a curve is
         set, "A+" when automatic smoothing is on and the cursor
         returns to the second endpoint when a curve is set, and "A-"
         when automatic smoothing is off and the cursor returns to
         the first endpoint when a curve is set.
           With automatic smoothing ON, just after you have finished
         drawing a curve (F3 has been pressed and the cursor is
         positioned at the second endpoint of the curve), if you
         press F1 to start drawing a new curve with its first
         endpoint at the second endpoint of the curve just drawn, a
         guideline tangent to the curve just drawn appears at its
         second endpoint (if guidelines are toggled on; see Section
         10.3). Proceed by defining a second endpoint for the new
         curve as usual (move the cursor with the numeric keypad
         number keys and press F1 again). The control point
         associated with the first endpoint of the new curve (which
         is also the second endpoint of the curve just drawn) is
         constrained to move along the tangent guideline. Other
         details are as given above with manual smoothing selected.

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         10.3. REMOVING GUIDELINES

           If you don't want to see tangent guidelines during
         smoothing, or if you don't want the guidelines visible when
         drawing a circle, oval, or square (perhaps for a better view
         of an area of a drawing having many curves close together),
         press E. This is a toggle; pressing it a second time
         restores the guidelines to view. "Invisible" guidelines
         still constrain cursor movement during smoothing or drawing
         a square or an oval. The guideline erase indicator in the
         status box reads "E-" if the guidelines are visible, "E+" if
         they are invisible.

         11. CUTTING CURVES

           Curves can be connected to each other with precision ONLY
         at shared endpoints (see Section 9) -- but you CAN attach
         new curves to arbitrary points on previously drawn curves.
         How? By "cutting" a previously drawn curve into TWO smoothly
         connected curves, which together very closely approximate
         the original curve. These two curves share a NEW endpoint
         which results from the cutting operation.
           To begin cutting a curve, press F5. The state changes to
         "CUT" and the cursor moves to the nearest endpoint; all
         curves associated with that endpoint are dashed, just as if
         you had pressed Del (see Section 9). Now press Space, +,
         and/or - (repeatedly) until the cursor is on one of the
         endpoints of the curve you wish to cut. Press Enter to
         select that endpoint. If only one curve is associated with
         the selected endpoint, it becomes dashed. If two or more
         curves are associated with the selected endpoint, dash the
         curve you want to cut by pressing Space, +, and/or -, and
         select it with Enter. The selected curve does NOT have to be
         entirely on the visible screen.
           Next, move the cursor ALONG the curve with the cursor
         keys. Ins can be used to switch the cursor movement
         increment between 1 and 10 pixels. (Note: If the curve goes
         off the edge of the screen and then back onto the screen,
         the moving cursor will jump from where the curve leaves the
         screen to where it reenters the screen.) When the cursor is
         located where you want a new endpoint, press F3. A new
         endpoint and two new curves replace the original curve, and
         the state is "FREE." The new curves have the same line
         parameters as the original curve (see Sections 12 and 15).
         These new curves are automatically inserted into the trail
         of which the original curve was part, in place of the
         original curve (see Section 14).

         12. MODIFYING CURVES

           To alter a previously drawn curve, press F4. The state
         becomes "CURMOD." The cursor automatically jumps to the
         closest endpoint and any curves associated with that
         endpoint are dashed (as if you pressed Del). Press Space, +,
         and/or - repeatedly (see Section 9) until the cursor is on
         one of the endpoints of the curve you want to modify. Then
         press Enter. If there is only one curve with the selected
         endpoint, it is dashed, and a menu box (described below)
         appears. If there are two or more curves with the selected
         endpoint, a box with instructions ("Next: +,

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         Space"/"Previous: -" /"Select: Enter") appears, and one
         curve with the selected endpoint is dashed. If you want to
         alter the dashed curve, press Enter; otherwise, by pressing
         Space, +, and/or -repeatedly, you can cause any of the
         curves with the endpoint to be dashed successively. When the
         curve you want to modify is dashed, press Enter; a menu box
         appears, with three options: Erase, Change, and Line.
         Pressing Esc backs out to the "FREE" state.

         12.1. ERASING A CURVE

           While in the "CURMOD" state, the Erase option is accessed
         by pressing E. This places a prompt in the menu box ("Erase
         selected curve (Y/N)"), and sets the state to "ERASE." If
         you want to erase the curve, press Y. This erases the dashed
         curve. The cursor remains at the originally selected end
         point, the menu box disappears, and the state returns to
         "FREE." Any other key will not erase the curve, and returns
         you to the curve modification menu and state "CURMOD."
           You cannot erase a curve bounding a filled area unless you
         first change the fill to none (-1) (see Section 14.3). If
         you try to erase such a curve, an error message appears, the
         curve modification menu reappears, and the state returns to
         "CURMOD."

         12.2. CHANGING A CURVE

           While in the "CURMOD" state, the Change option is accessed
         by pressing C. IF both endpoints of the selected curve are
         on the screen, the curve is dashed and a straight line
         appears between the curve's endpoints. The state is now
         "CHANGE." (If one of the selected curve's endpoints is not
         on the screen, you hear a beep (and see an error message if
         toggled on) and return to the "FREE" state.)
           Now you can alter the shape of the replacement curve, but
         NOT the placement of its endpoints) via the F2, cursor, and
         F3 keys, as described above in Section 7.2. You also can
         smooth the curve, as described in Section 10. Throughout the
         alteration process, the original curve is dashed; this
         dashed curve disappears when F3 is pressed to end the
         process. Note: during the changing procedure, if Esc is
         pressed, the original curve becomes undashed, with the
         cursor at the curve's starting endpoint, and the state
         returns to "FREE."

         12.3. CHANGING A CURVE'S LINE PARAMETERS

           Each curve has four line parameters associated with it:
         line weight ("thickness"), line gray percentage (the gray
         shading of the curve, ranging from white to black), linecap
         (the style of the ends of the curve), and dash pattern. Each
         newly drawn curve is assigned the current "GLOBAL" values
         for these parameters. When PictureThis is first loaded, the
         values for the global parameters are as follows: line
         weight, 1 PostScript point (EXACTLY 1/72 inch; NOT equal to
         1 traditional printer's point, which is only APPROXIMATELY
         1/72 inch); line gray, 100% (black; 0% corresponds to
         white); dash, solid (that is, no dash at all); linecap,
         round. These GLOBAL line parameters may be changed at any
         time (see Section 15). The following procedures will change

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         a SELECTED curve's line parameters ("LOCALLY"), from the
         "CURMOD" menu.
           The Line option is accessed by pressing L. This allows
         changes in line weight, line gray percentage, linecap, and
         dash pattern. The state changes to "THISLN," and a line
         parameter change menu appears. The top line of the menu
         lists items which can be altered (Weight, Gray, Linecap, and
         Dash) and the word Keep. The second line of the menu
         displays current values of these parameters for the selected
         curve (shown dashed).

         12.3.1. CHANGING LINE WEIGHT

           To change the weight of the selected curve, press W when
         the line parameter menu is showing. A line weight prompt
         appears. Its first line displays the current line weight in
         PostScript points (one PostScript point = EXACTLY 1/72
         inch). The second line requests that you enter a new line
         weight in points. If you are satisfied with the current line
         weight, press Enter or Esc; this takes you back to the line
         parameter menu with no change in line weight of the selected
         curve. If you want to change the line weight, key in a
         number between -0 and 327.00 and then press Enter. If you
         set the line weight between .01 and 327.00, the weight of
         the curve on the Quickshow screen (see Section 13) and the
         PostScript output equals that value (as close as the output
         device allows). If you set the weight to 0, the curve's
         thickness is "hairline," the least thickness available on
         the particular output device used (quite thin on 300 dpi
         laser printers; almost invisible on 1270 and 2540 dpi
         imagesetters). If you set the weight to a negative number,
         it is stored as -1. In PictureThis, -1 line weight means
         that the curve is a "construction" or "blue" curve; that is,
         it does not appear on the output at all, but is used only as
         a reference curve, or is part of a trail filled with a gray
         shade, but doesn't show (see Section 14.3). A curve with a
         line weight of -1 is shown as dotted on the drawing screen
         of PictureThis, and it does not appear at all on the
         Quickshow screen (see Section 13) or the Viewscreen (see
         Section 25.1).
           An invalid input results in an error message (and a chance
         to try again).
           After you have entered a valid line weight, the line
         parameter menu reappears with the line weight in the second
         line changed to the new line weight.

         12.3.2. CHANGING LINE GRAY

           To change the selected curve's gray shade, press G when
         the line parameter menu is showing. A line gray prompt will
         appear. The first line of this prompt indicates the current
         line gray, from 0% (white) to 100% (black). The second line
         requests that you enter a new line gray percentage. If you
         are satisfied with the current gray, press Enter or Esc, and
         the line parameter menu reappears with an unchanged line
         gray percentage. If you want to change the line gray
         percentage, enter a number between 0 (white) and 100
         (black). An invalid entry results in an error message (and a
         chance to try again). When you have entered a legal line
         gray percentage, the line parameter menu reappears with the

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         line gray percentage in the second line changed to the new
         line gray percentage.

         12.3.3. CHANGING THE LINECAP

           To change the selected curve's linecap, press L when the
         line parameter menu is showing. A linecap menu appears. The
         first line of the menu shows the current linecap. The second
         line allows you to change the cap to Butt, Round, or Square.
         Pressing Esc returns to the line parameter menu without
         changing the linecap. Pressing B, R, or S changes the
         linecap to butt, round, or square, respectively, and returns
         to the line parameter menu with the new linecap displayed in
         the second line.
           For thin curves, the linecap has little importance, since
         it is barely visible; for thick curves, the linecap can be
         very significant. A butt cap is a straight line oriented
         perpendicular to a curve, located at the curve's endpoint. A
         round cap is a semicircle with radius equal to one-half of
         the line width, centered on the curve's endpoint (so it
         extends beyond the endpoint). A square cap is a straight
         line oriented perpendicular to the end of the curve, located
         beyond the curve's endpoint a distance equal to one-half of
         the line width. To see the differences among these linecaps,
         draw three horizontal lines on the screen with the same
         large line weight (say, 100 points), and choose a different
         linecap for each line, then view the lines on the Quickshow
         screen (see Section 13).

         12.3.4. CHANGING THE DASH PATTERN

           To change the selected curve's dash pattern, press D when
         the line parameter menu is showing. A dash pattern menu
         appears. The current dash pattern is shown on the second
         line of the menu. You can choose a new dash pattern from six
         user-settable dash patterns (see Section 15.2) plus the
         (default) solid setting. Each dash pattern has a number,
         shown in parentheses at the right of the second line of the
         menu. Solid is 0; the user-settable patterns are 1 through
         6. Press Spacebar, +, and/or - repeatedly to cycle through
         the dash patterns; notice that, for each dash pattern,
         information is provided about its current settings (see
         Section 15.2 for details on these settings). If you want to
         change the Offset setting (between 0.0 and 25.5 points; see
         Section 15.2) for the dash pattern shown, press O; you're
         shown the current offset setting and prompted to key in a
         new one (press Esc to return to the dash pattern menu
         without changing the offset setting). At the dash pattern
         menu, press K (for "Keep") or Enter to use the dash pattern
         shown, or press Esc to use the old dash pattern (with its
         old offset setting); in either case, the line parameter menu
         reappears.

         12.3.5. SAVING THE LINE PARAMETERS

           To save the line parameters displayed on the second line
         of the line parameter menu, press K (for "Keep") or Enter.
         This saves the line parameters for the selected curve and
         returns to the "FREE" state. If you press Esc while the line
         parameter menu is on the screen, any changes which you made

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         to the weight, gray percentage, linecap, and/or dash pattern
         are NOT saved. You can change any of the line parameters any
         number of times before you press K or Enter; only the final
         values are saved.

         13. QUICKSHOW SCREEN

           The Quickshow screen allows you to see a quickly drawn
         screen representation corresponding to "showpage" in the
         PostScript language -- in other words, a representation of
         what the hard copy output will look like. To see the
         Quickshow screen for the current drawing screen (only in the
         "FREE" state), press Q.
           The Quickshow screen can be accessed at any magnification,
         and it can be zoomed or scrolled (see Section 6). The
         Quickshow screen "clips" curves (stops drawing them) at the
         current frame boundaries, shows approximations for proper
         line weights, line gray percentages, and linecaps (see
         Section 12.3), and shows dashed curves as dashed (though NOT
         with approximations to their individual dash patterns). It
         also shows joins and fills of trails (see Section 14) and
         layering of objects (see Section 16.4). Of course, the low
         resolution of the screen makes accurate representation of
         fine lines impossible, some curves have the "jaggies," and
         the grays are VERY approximate -- still, the Quickshow
         screen is a good way to predict how the PostScript output
         will appear.
           Note: PostScript hard copy output does NOT show dots
         (drawn by pressing F1 and then F3, without moving the cursor
         in between) with non-solid dash patterns or with square or
         butt linecaps, so such dots also are NOT shown on the
         Quickshow screen. Dots with dash setting 0 (see Section
         15.2) and round linecaps (see Section 12.3.3) -- the
         defaults in PictureThis -- are shown as circles with a
         diameter equal to the line weight on both the hard-copy
         output and on the Quickshow screen.
           When the Quickshow screen has finished drawing, pressing
         Esc returns the state to "FREE" and restores the drawing
         screen to reflect what was last on the Quickshow screen.
           Pressing Esc while the Quickshow screen is drawing stops
         the drawing. Pressing Esc again returns to the "FREE" state.
           Very wide curves appear rather slowly on the Quickshow
         screen when drawn with the highest possible precision
         (especially if you have a slow computer). For this reason,
         there is a user-settable "flatness" parameter that allows a
         trade-off between the speed and precision of such curves on
         the Quickshow screen. To set this parameter, press F9. The
         state changes to "MISC," and the miscellaneous operations
         menu will appear. To change the flatness parameter, press F.
         A Flatness menu appears, and you can choose between flat
         (faster) curves (by pressing F) or round (more accurate)
         curves (by pressing R). The default setting for the flatness
         parameter is flat (faster). If they are very wide, flat
         curves are indeed "flatter" than round curves on the
         Quickshow screen, but not on the PostScript output.
           At high magnifications, sometimes there are errors in the
         ways extremely wide lines are shown on the Quickshow screen.
         This happens very rarely (due to an overflow) and is
         essentially harmless, so we decided not to correct it (an
         undertaking which would make the program run significantly

                                        24

         slower).
           Saving and retrieving drawing files can be done while on
         the Quickshow screen (see Sections 19.1 and 19.2).
           To change the background color of the CGA Quickshow
         screen, press B repeatedly to cycle through the 16
         possibilities. The default is light gray. This is especially
         useful if running in CGA mode on a VGA screen.

         14. TRAILS, FILLS, AND JOINS

           A trail is a group of curves. Trails are useful because
         they can bound areas filled with gray shades, and because
         the points where the curves in a trail meet can be made to
         join neatly (important for wide curves). (Note: Trails are
         similar but NOT identical to the "paths" defined in the
         PostScript language.)
           The most common trails are continuously connected curves.
         If you draw a curve, then draw a second curve connected so
         that its first endpoint is the same as the first curve's
         second endpoint, (that is, you press F1 for the first
         endpoint of the second curve WITHOUT moving the cursor after
         pressing F3 to establish the first curve), you have drawn a
         trail of two curves. As long as you continue to connect the
         curves in this manner ("head-to-tail," so to speak), they
         are all automatically in one trail. If you connect the
         second endpoint of the final curve in your trail to the
         first endpoint of the first curve, you have made a closed
         trail. Closed trails can be filled with a gray shade.
         (Actually, open trails can be filled too, but this usually
         isn't desirable. When you fill an open trail, a construction
         (weight: -1) line automatically connects the beginning and
         end of the set of curves, to make a closed boundary suitable
         for filling.) Boxes (see Section 8.1), squares (Section
         8.2), circles (Section 8.3), and ovals (ellipses) (Section
         8.4) all are automatically made into closed trails when they
         are drawn.
           Most of the time while drawing in PictureThis, you need
         not be concerned about trails. They are automatically made
         for you as you draw curves. Every curve is placed in a
         trail, as noted above (some trails contain only one curve),
         and no curve is in more than one trail. However, if you want
         to fill an area that is enclosed by curves which weren't
         continuously drawn, or if you want to manipulate only part
         of an existing trail, you can still do so by defining a new
         trail (see Section 14.1). You also can define trails which
         are made of two or more unconnected subtrails; these are
         useful for doing "fancy" fills, especially for making holes
         in filled areas (see Section 14.3).
           To define or modify existing trails, access the trail menu
         by pressing F6. The state is changed to "TRAIL," and the
         trail menu appears. This menu allows you to define a new
         trail, or erase, fill, or change the line parameters for an
         existing trail. It also allows you to copy an object
         (defined in Section 16) to one or more endpoints of a trail,
         as described in Section 17.7.

         14.1. DEFINING A TRAIL

           You can define a trail composed of any previously drawn
         curves. To begin this operation while in the "TRAIL" state,

                                        25

         press D. The state changes to "DEFTRL," the cursor jumps to
         the nearest endpoint, and any curves with that endpoint are
         dashed (just as if you had pressed Del). Press Space, +,
         and/or - repeatedly until the cursor is on the endpoint
         where you want to BEGIN a new trail. Next, press Enter. A
         box with instructions ("Next curve: +, Space"/"Select curve:
         Enter"/"Next endpoint: Del"/"Done: D") appears on the left
         side of the screen, and one curve with the selected endpoint
         is dashed to distinguish it. If you want to start the trail
         with the dashed curve, press Enter. Otherwise, by pressing
         Space, +, and/or - repeatedly, you can cause each of the
         curves with the endpoint to be dashed successively. When the
         curve with which you want to start the trail is dashed,
         press Enter. This curve is dashed-and-dotted to show that it
         has been chosen as part of your trail, and the cursor moves
         to the other endpoint of the curve, where you can again
         select any curve (except ones already selected for the
         trail) to be the next curve in the trail. Continue with this
         process until the final curve which you want in the trail is
         selected. Then press D. Your trail is established.
           Alternatively, if your trail is to be made of disjoint
         subtrails (see Section 14.3.2 for why you might want to do
         this), with the cursor at any endpoint, instead of
         immediately selecting an associated curve, move the cursor
         to a different endpoint to start a new subtrail by pressing
         Del, followed by Space, +, and/or - repeatedly, and finally
         Enter to select a new endpoint as usual. Then you can
         continue, as above, selecting curves for your subtrail. You
         can make as many subtrails as you want. When the entire
         trail is complete, press D to establish it. (Note: In the
         process of defining the trail, if you reach an endpoint for
         which all associated curves have already been chosen for the
         trail, you have a choice only between pressing D to
         establish the trail and Del to start another subtrail.)
           If at any time during the trail definition process you
         press Esc, the selected curves are returned to normal, the
         state becomes "TRAIL," and the trail menu reappears.
           When your trail has been established, it remains "dashed-
         and-dotted" while two prompts appear successively, allowing
         the specification of a fill percentage and changed line
         parameters for (ALL curves in) the newly defined trail. The
         first prompt asks for a gray fill percentage; it is
         identical to the prompt described in Section 14.3.1. (Note:
         Once a new trail has been established by pressing D, you
         CANNOT "back out" to the trail defining process. Pressing
         Esc while at the fill prompt just continues with the next
         prompt and leaves the defined trail with NO (-1;
         transparent) fill.) The next prompt states: "Change
         parameters of ALL curves (Y/N)?" If you answer Y, a line
         parameter menu identical to the one described in Section
         14.4 appears, and you can change the line parameters of ALL
         curves in the trail to be identical and set the join
         parameter (see Section 14.4.2) for the trail. When these two
         prompts have been answered, the new trail is again solid and
         the state returns to "FREE."
           What happens to the previously defined trails that
         contained curves now in the newly defined trail? PictureThis
         automatically takes care of this in one of two ways. If a
         curve was in a trail which had a fill, or was part of an
         object (see Section 16), the curve is duplicated

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         automatically, so identical curves are in BOTH the old and
         new trails. (Remember, a curve cannot be in more than one
         trail at a time.) Otherwise, the curve is removed from its
         old trail. (If all curves are removed from a trail, the
         trail becomes undefined.)
           The process of defining a trail sounds rather complicated
         in words, but it is actually quite simple for the most
         common class of trails (simple closed trails) -- and it
         isn't very difficult for even quite complex trails.
         PictureThis automatically does most of the work for you.
         Just try it and check your results with the Quickshow
         screen. Also, if you are careful to draw curves
         continuously, as described above, you will only rarely have
         to define a trail.

         14.2. ERASING A TRAIL

           An entire trail can be erased, whether filled or not. At
         the trail menu, press E. The state changes to "ERASE," the
         cursor jumps to the closest initial point of a trail, and
         the entire trail is dashed. (The initial point of a trail is
         the first endpoint of the first curve drawn for
         automatically defined trails, or the first endpoint selected
         for manually defined trails.) A box with instructions
         appears on the left side of the screen ("Next: +, Space"/
         "Previous: -"/"Select: Enter"). If the dashed trail is the
         one you want to erase, press Enter. If you want to select a
         different trail, press Space, +, and/or - repeatedly until
         the trail you want to erase is dashed, then press Enter. If
         only one trail's initial point is on-screen, it is selected
         automatically, and the instruction box does not appear. (If
         you press Esc during this process, the trail menu reappears,
         and the state returns to "TRAIL.")
           A prompt appears: "Erase selected trail? (Y/N)." If you
         want to erase the dashed trail, press Y; the trail is erased
         and the state returns to "FREE." Otherwise, press any other
         key; the trail menu reappears and the state returns to
         "TRAIL."

         14.3. FILLING A TRAIL

           An already existing trail (either automatically or
         manually defined) can be filled with a gray shade.

         14.3.1. SPECIFYING A FILL GRAY PERCENTAGE

           While in the "TRAIL" state, to fill an unfilled trail, or
         to change the gray percentage of (or "unfill") a previously
         filled trail, press F. The state changes to "FILL," the
         cursor jumps to the closest initial point of a trail, and
         that trail is dashed. (The initial point of a trail is the
         first endpoint of the first curve drawn for automatically
         defined trails, or the first endpoint selected for manually
         defined trails.) A box with instructions will appear on the
         left side of the screen ("Next: +, Space"/ "Previous: -"
         /"Select: Enter"). If the dashed trail is the one you want
         to fill, press Enter. If you want to select a different
         trail, press Space, +, and/or - repeatedly until the trail
         you want to fill is dashed, then press Enter. If only one
         trail has its initial point on-screen, it is selected

                                        27

         automatically, and the instruction box does not appear. (If
         you press Esc during this process, the trail menu reappears,
         and the state returns to "TRAIL.")
           A fill prompt appears. The first line of the prompt gives
         the current fill percentage, from 0% (white) to 100%
         (black). A fill percentage of -1% means that the trail is
         not filled; it is transparent, NOT opaque. The second line
         requests that you enter a gray percentage. If you are
         satisfied with the current fill gray percentage, just press
         Enter and it is not changed. If you want to "unfill" the
         trail, enter a -1 at the prompt. Otherwise, enter a number
         between 0 (white) and 100 (black). Upon your valid entry,
         the trail is filled and the state returns to "FREE." (If you
         press Esc instead of entering a fill, the state returns to
         "TRAIL," and the trail menu reappears.)
           The Quickshow screen shows approximate grays as 33
         gradually darkening patterns. Actual grays on PostScript
         output devices vary considerably. You will have to
         experiment with the grays on the particular printer you are
         using to find the most appropriate ones for your drawings.

         14.3.2. RESULTS OF FILLING A TRAIL

           PictureThis (and PostScript) fills are NOT like those of
         "paint" programs, in which a fill "paints" the interior of a
         simple closed boundary. There are three main differences:
           1. PictureThis fills (except "no fill," -1) are "opaque."
         If one trail overlaps another trail, and the trail "in
         front" is filled, the portions of the second trail which are
         "behind" (or "under") the first trail are not visible on the
         Quickshow screen or on the PostScript output. Try this by
         drawing a circle and filling it with some shade of gray.
         Then draw a box that overlaps the circle and fill it with a
         different shade of gray. Now look at it on the Quickshow
         screen. Part of the circle is entirely covered by the box.
         You actually can see the circle draw and then see the box
         cover it. It is as if the objects were cut out and pasted on
         the drawing, in order. The order in which trails are
         "pasted" on the Quickshow screen (and the PostScript output)
         initially is determined by the order in which they are drawn
         or defined (the earliest drawn/defined are "pasted on"
         first), but the order can be changed easily (see Section
         16.4).
           2. PictureThis trails which form simple closed boundaries,
         such as boxes or circles, are filled exactly as you would
         expect: their interiors are filled with the selected shade
         of gray. (This is the most useful type of trail to fill and
         should suffice for most purposes.) But trails are not at all
         limited to simple closed boundaries. A single trail can
         cross itself many times, and can have many disjoint
         subtrails. How does PictureThis determine which parts of a
         complex trail will be inside the trail, and thus filled? It
         uses the "non-zero winding number rule." This means that
         starting at any point, it (conceptually) draws a line from
         that point in any direction to infinity, examining each
         curve of the path the line crosses. Starting with a count of
         zero, it adds one each time a curve crosses the line from
         left to right and subtracts one each time a curve crosses
         the line from right to left. When it has completed crossing
         all the curves in the trail along the line, if the count is

                                        28

         zero, the starting point is outside the trail and will not
         be colored gray; otherwise, the point is inside the trail
         and will be colored.
           In practice, that means that the directions in which
         trails are drawn or defined is important for complex trails.
         However, you'll probably need to worry about the direction
         of trails only very rarely. It's fun to draw or define
         complex trails with many crossings and subpaths and then
         fill them and view them on the Quickshow screen. However,
         complex trails aren't very useful in most "real" drawings.
         There is one notable exception, however: occasionally, you
         might want to create a "window" or "hole" through a trail,
         to let what is behind the trail show through. This is very
         simple to accomplish. As an example, try this. Draw two
         boxes, one with its boundaries totally inside the other,
         like a window in a door. Now define a new trail consisting
         of two subtrails (the two boxes) as follows: Press F6 to
         access the trail menu. Press D to define a trail. Press +
         until the cursor is on the lower left endpoint of the outer
         box, and then press Enter. Press + and Enter or just Enter
         to select the left side of the box. The left side of the box
         is dashed-and-dotted, indicating that it is part of the
         trail, and the cursor jumps to the top left corner of the
         outer box. Press Enter three more times, selecting the top,
         right, and bottom sides of the outer box. The cursor should
         now be at the lower left corner of the outer box again, and
         the outer box should be all dashed-and-dotted. Now press Del
         followed by + repeatedly until the cursor is on the lower
         left corner of the inner box. Then press Enter. Select the
         bottom of the inner box and press Enter. Press Enter three
         more times to select the right, top, and left sides of the
         inner box. Notice that you defined the subtrail of the inner
         box in the direction OPPOSITE that of the subtrail of the
         outer box. (The DIFFERENCE IN DIRECTIONS OF THE SUBTRAILS is
         what is important, not which endpoint you start with, or
         which direction you initially choose.) Now press D to
         establish the trail. At the fill prompt, enter some shade of
         gray and press any key except Y to answer the query about
         changing the parameters of all curves in the trail. Now
         press Q to see the Quickshow screen. Your screen should show
         you a box with a box-shaped "window" in it. Anything behind
         the trail will show through the "window." This procedure
         generalizes to much more complex shapes in the obvious way;
         just be sure that the inner trail is defined in the opposite
         direction to the outer trail, if you want a "window." (If
         the inner and outer trails are defined in the SAME
         direction, the window will be FILLED.)
           3. PictureThis can fill trails which are not closed. It
         does this by drawing a straight line with line weight -1
         (that is, a construction line) from the final endpoint of
         each subtrail to the first point of that subtrail, and then
         filling the resulting trail. Try it. Draw a trail of two
         curves on the screen (with the second endpoint of the second
         curve NOT the same as the first endpoint of the first curve)
         and then fill it. PictureThis automatically connects the end
         of the trail with the beginning of the trail and fills the
         resulting trail. (You'll probably find that this feature is
         useful only occasionally.)

         14.4. CHANGING THE LINE PARAMETERS OF A TRAIL

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           PictureThis allows you to change the line parameters for
         ALL of the curves in a trail at one time. Trails are made up
         of curves with various line weights, line gray percentages,
         linecaps, and dash patterns. (This is where trails differ
         from PostScript-language "paths," each of the latter made up
         of curves which all have the same line weight, line gray
         percentage, dash, and linecap.) It is often (but not always)
         best for all of the curves in a trail to have the same line
         parameters (see Section 14.4.3), making the trail equivalent
         to a PostScript "path." To change the line parameters for
         all of the curves in a trail, while in the "TRAIL" state
         press L. The state changes to "TRLNS," the cursor jumps to
         the closest on-screen initial point of a trail, and that
         trail is dashed. (The initial point of a trail is the first
         endpoint of the first curve drawn for automatically defined
         trails, or the first endpoint selected for manually defined
         trails.) A box with instructions appears on the left side of
         the screen ("Next: +, Space"/ "Previous: -"/"Select:
         Enter"). If you want to change the line parameters of the
         dashed trail, press Enter. If you want to select a different
         trail, press Space, +, and/or - repeatedly until the trail
         you want to change is dashed, then press Enter. If only one
         trail is on-screen, it is selected automatically, and the
         instruction box does not appear. (If you press Esc during
         this process, the trail menu reappears, and the state
         returns to "TRAIL.")
           A line parameter menu appears, similar but not identical
         to the line parameter menu for single curves (see Section
         12.3). The top line of this menu shows the items which can
         be changed ("Weight," "Gray," "Linecap," and "Dash," as in
         the line parameter for single curves, and a new item:
         "Join"), plus the word "Keep." The second line of the menu
         displays the current values of these parameters for the
         selected trail. If any of these parameters have different
         values for different curves in the trail, the word "MIXED"
         appears under that parameter.

         14.4.1. CHANGING THE LINE WEIGHT, LINE GRAY, LINECAP, OR
                 DASH PATTERN FOR ALL CURVES IN A TRAIL

           To change the line weight, line gray percentage, linecaps,
         or dash for all the curves in a trail, press W, G, L, or D
         respectively, and proceed exactly as for a single curve (see
         Section 12.3). (Note: You subsequently can change the line
         parameters of any individual curve in the trail to any
         value.)

         14.4.2. CHANGING THE JOIN FOR A TRAIL

           The word "Join" in the top line of the menu refers to the
         manner in which the curves in a trail are connected together
         where they join at endpoints. Like linecaps, linejoins are
         insignificant for thin lines, but important for thick lines.
           To change the linejoin of a trail, press J. The join menu
         appears. The first line shows the current linejoin. The
         second line requests that you enter a new linejoin. The
         three possible linejoins are mitered, rounded, and beveled.
         For mitered joins, the outside edges of the curves are
         extended in straight lines until they meet, and filled in.
         For rounded joins, the curves are connected by a rounded

                                        30

         end, formed by a circle with diameter equal to the line
         width. For beveled joins, the curves are connected with butt
         linecaps and filled in to form a bevel. If a mitered join is
         specified for a join where two curves meet at a small angle
         (anything less than approximately 11 degrees), the join is
         beveled to prevent the join from being too long.
           When a trail is drawn or defined, the join parameter for
         that trail is set to the current global linejoin. The
         initial setting for the global join in PictureThis is
         rounded, but this can be changed at any time (see Section
         15.1). Boxes always are given mitered joins (square corners)
         initially, no matter what the global join value, but a box's
         join can be changed later.
           To set the join for a trail, press M, R, or B for mitered,
         rounded, or beveled linejoins, respectively. Pressing Esc
         backs out without changing the current linejoin. In all of
         these cases, the line parameters menu reappears. When you
         are satisfied with all the line parameters, press K (for
         "Keep") or Enter; the line parameters for all of the curves
         in the trail and the trail's join are changed, and the state
         returns to "FREE." (If you press Esc, the parameters are not
         changed, the state returns to "TRAIL," and the trail menu
         reappears.)
           A good way to see the different types of linejoins is to
         set the global line weight to some high value, say 100
         points (see Section 15.1), draw three similar trails having
         at least two curves which meet at an angle, set the linejoin
         values differently for each of the trails, and view their
         joins on the Quickshow screen. Also try drawing a box with
         thick lines and changing its linejoin value.

         14.4.3. TRAILS MADE OF CURVES WITH DIFFERENT LINE PARAMETERS

           If a trail is made of curves all of which have the same
         line weight and line gray percentage, the joins at all
         endpoints are set by the linejoin specified for the trail.
         If the trail is closed (or subtrails are closed), even the
         final join of the trail (or subtrail) where the final curve
         connects to the initial curve are as specified. If the trail
         (or subtrail) is not closed, the linecaps at BOTH ends of
         the trail (or subtrail) are whatever linecap type is
         specified for the LAST curve of the trail (or subtrail).
           If a trail is made of curves of different line weights,
         different line gray percentages, or different dash patterns,
         each time there is a change in one or more of the three
         parameters along the trail, PictureThis treats it as a the
         beginning of a new subtrail (even if the last curve is
         connected to the current one). That is, as long as the
         weight, gray, and dash pattern are the same for each
         successive curve, the joins are the specified join, but if
         the next curve has a different weight, gray, and/or dash
         pattern the "subtrail" ends with a linecap which is the same
         as that of the last curve before the change (its first
         linecap is the same, too). Then the next curve starts with a
         linecap. NO JOIN IS MADE. If there are any changes in
         weight, gray, or dash pattern along a closed trail, the
         final join is NOT joined, even if the last curve is the same
         line weight, gray, and dash pattern as the first curve. If
         you are in doubt as to which linecaps and joins will appear
         on a particular trail, check it on the Quickshow screen, at

                                        31

         large magnification if necessary.
           As you can see, it is generally desirable to have trails
         with curves all of one line weight and gray, but there are
         times when you want to fill an area bounded by curves of
         different grays or line weights. This is perfectly legal,
         and, if you are careful, the places where two linecaps meet
         can look perfectly acceptable (see Section 27.4).

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