This is README for QLogo.

Downloading

I am not providing compiled versions of QLogo at this time.

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QLogo is an interpreter for the Logo language written in C++ using Qt. It mimics (as much as I find reasonable) the UCBLogo interpreter developed by Brian Harvey at U.C. Berkeley.

Copyright (C) 2017-2024 Jason Sikes

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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The help files included in this package derive from UCBLogo under terms of the GNU General Public License as published by the Free Software Foundation, version 3.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.

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You can find the UCBLogo Manual here:

http://people.eecs.berkeley.edu/~bh/usermanual

The differences between QLogo and UCBLogo are described in the nuances section below. There aren't many.

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Compiling

Building QLogo requires Qt6.5 and CMake.

To build in MacOS and Windows:

Simply open the CMakeLists.txt file in QtCreator and build within there.

To build in Linux:

If you have qtcreator, you can use qtcreator in Linux in the same manner as in Windows and MacOS described above.

Otherwise, you can follow the standard CMake build procedure. First, create a build directory somewhere outside of the QLogo source directory.

In my case, since I keep my projects in a "Projects" directory under my home directory, my QLogo directory can be found at "~/Projects/QLogo". Thus, one place to create my "build" would be adjacent to my QLogo directory, "~/Projects/build".

Then have CMake create the build structure.

$ cd ~/Projects
$ mkdir build
$ cmake -S QLogo -B build

Then enter into your build directory and issue make, and, optionally, if all goes well (it will) you can run make install

$ cd build
$ make
$ sudo make install

This will give you two executables:

1. "qlogo": this is the Logo interpreter that can be run from a script or command line.

2. "QLogo-GUI": this is the graphical user interface that will run qlogo and provides the turtle and editor.

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Here are the nuances (they're mostly insignificant, I think):

• Colors can be specified in one of four ways:

  1. as a palette index (0 to 100), same as UCBLogo

  2. as a list of three percentages, one for each of red, green, blue [0 0 0] is black, [100 100 100] is white, also same as UCBLogo.

  3. as a list of four percentages, similar to Option 2 above, with the fourth value being "alpha". 100 is fully opaque, and 0 means fully transparent.

  4. as a named color from the X Color Database, e.g. white or lemonchiffon. The X Color database can be found here: https://en.wikipedia.org/wiki/X11_color_names

• Changes in font properties (size, color, family) do not affect characters already printed. This enables multiple colors and fonts on the same console.

• The entire Logo standard library is loaded internally and buried. There is no library directory at this time.

• QLogo does not look for nor automatically load STARTUP.LG.

• If ERRACT is set and its size is greater than zero, then any errors execute PAUSE. This was necessary because I couldn't find a reliable way to prevent infinite loops during error handling.

• Garbage collection is on-the-fly, meaning that memory is freed the moment a word/list/array is no longer needed. GC and .SETSEGMENTSIZE are no-ops.

• No scunching. UCBLogo provided a scrunch to compensate for older CRT screens with non-square pixels. This enabled turtle operations to maintain consistent physical height-width. SCRUNCH and SETSCRUNCH are no-ops.

• SAVEPICT saves a copy of the canvas in the format given by the filename's extension. For example: SAVEPICT "MY_PICTURE.PNG will save in PNG format. QLogo can save an image in the following formats: BMP, JPG/JPEG, PNG, PPM, XBM, and XPM

• There is no facility yet for translation/internationalization. Yet.

The following commands are not implemented:

SETMARGINS:

The original purpose of the command was to enable text to be visible on projectors which cut off outer boundaries of a computer screen. Projectors and monitors produced in the last few years show all of the computer screen. In addition, QLogo is a windowed application so an instructor or presentor can move the window to a different position.

FILL:

Two reasons: One of the user interface principles for QLogo is that the canvas should be device resolution-independent. That means when the QLogo window is resized or the separator between the text and the graphics is moved the graphics will be redrawn with the new dimensions. The Flood Fill algorithm depends on specific pixels which means that the display can change dramatically depending on the size of the canvas. The other reason is that the Flood Fill algorithm can slow down window resizing. FILLED is still available.

EPSPICT:

This is replaced by SVGPICT.

CSLSLOAD:

Not implemented yet.

SETCSLSLOC:

Not implemented yet.

SETEDITOR:

The QLogo GUI has its own built-in editor. If you run the logo program from a command line, such as in a terminal, no editor is available.

SETLIBLOC:

The QLogo library is stored internally.

SETHELPLOC:

Not implemented. QLogo uses a SQLite database to store help text.

SETTEMPLOC:

QLogo doesn't create temporary files at this time.

The following variables have no special meaning:

COMMANDLINE:

Not implemented yet.

REDEFP:

Qt has strong support for internationalization, but QLogo is not designed at this time to take advantage of that. Internationalization will be supported soon.

USEALTERNATENAMES:

Ditto.

The following commands are NEW:

SVGPICT has been added and is a replacement for EPSPICT. SVGPICT will save the image on the canvas in Scalable Vector Graphics format.

ALLFONTS:

Returns a list of all the fonts available on your system.

TIME:

This is mostly for debugging and my own curiosity. TIME will take one parameter, a list, which it will execute. A timer will start when the list is executed and then stop when the list is finished. The total running time of the list will be printed. The output will be whatever the list outputs.

MARK:

This is for debugging memory management. MARK will take one parameter, set a flag on it, and output that parameter. At the moment it is marked, a debugging message will be printed out. Later, if/when the item is deleted, another debugging message will be printed.

CURSORINSERT:

Sets cursor to insert mode in QLogo. This is the default.

CURSOROVERWRITE:

Sets cursor to overwrite mode in QLogo.

CURSORMODE:

Outputs either INSERT or OVERWRITE.

STANDOUT:

This works in the QLogo GUI by switching the font's foreground and background colors. It isn't implemented for text terminals.

SETBOUNDS:

The drawing canvas in the QLogo GUI is designed to be device and resolution independent. The user can stretch and resize the GUI window and its components without needing interaction or permission from the QLogo program. Therefore, the best way for the programmer to have control and the GUI to have responsiveness is to set the bounds programatically. The GUI then can squeeze or stretch the canvas to fit the window as needed.

The coordinate system of the drawing canvas is Cartesian: the Origin [0,0] is always in the center. The range of the X-coordinate is between -boundX and boundX. The range of the Y-coordinate is between -boundY and boundY. For example, a bound set at [350 150] means that the turtle is visible if its X-coordinate is between -350 and 350 and its Y-coordinate is between -150 and 150. See also BOUNDS.

BOUNDS:

Outputs a list of two numbers giving the maximum bounds (x,y) of the canvas. See SETBOUNDS.