<![CDATA[GravityLoops, my gravity simulator in Interlisp and LOOPS, can finally show something on the screen. The program now animates a body of mass like the Moon interacting under gravity with a body of mass like the Earth. The dots in the simulation window here are the bodies after 180 days of simulated time, with the Earth at left. Watch the full run. Screenshot of a still frame of a simulation of a body like the Earth and one like the Moon interacting under the muatal gravity. Well, that's not much. But the code confirms the simulation loop with an offscreen buffer works well. After putting in place some infrastructure, to get there I wrote the simulation loop, tweaked a few methods, wrote a demo function that sets up the simulation, and fixed a few bugs. There's a lot more to do. I need to make the graphics of the body markers more complete and explanatory, control the speed of the animation, fix more bugs, and refactor to decouple some interclass dependencies. And, of course, GravityLoops will also have a user interface to control the simulation and enter the parameters. #GravityLoops #Interlisp #Lisp a href="https://remark.as/p/journal.paoloamoroso.com/early-simulations-with-gravityloops"Discuss.../a Email | Reply @[email protected] !--emailsub--]]>

<![CDATA[I started working on the class Universe of GravityLoops, my gravity simulator in Interlisp and LOOPS. I defined the class itself and the main methods, Universe.Register and Universe.Simulate. The class represents a collection of bodies and manages the parameters and state of the simulation. Universe.Register adds a body to a universe, Universe.Simulate runs the simulation. In the C++ code of the article my design draws inspiration from, an instance variable of the class UNIVERSE holds a pool of bodies in an array, with the most recently added body indexed by another instance variable. In GravityLoops the corresponding instance variable bodyPool is a list which, as the article notes, is more versatile and doesn't need the index. Universe.Simulate, just a stub for now, is the core method. It will update the state of the simulation, display the bodies in a graphical window along with status information, and check whether the user interrupts the simulation. The C++ program runs the simulation until the user presses a specific key and GravityLoops will have a similar feature. I'll also have the program accept a number of time ticks to step the simulation through. For Universe.Simulate I'll mostly follow the C++ code. But I plan to revisit the decision after I have something running to experiment with. I may want to split the simulation functionality into more than one method to separate the simulation itself from output, or redesign control around LOOPS' active values. #GravityLoops #Interlisp #Lisp a href="https://remark.as/p/journal.paoloamoroso.com/representing-the-universe-of-gravityloops"Discuss.../a Email | Reply @[email protected] !--emailsub--]]>

<![CDATA[I started working on GravityLoops, a software that simulates a collection of bodies interacting under the mutual gravity. I develop it on Medley in Interlisp and its object extension LOOPS, the Lisp Object-Oriented Programming System. GravityLoops will show an animation of the bodies and their motions, along with facilities for defining the parameters of the system and controlling the simulation. Motivation I've been meaning to do a LOOPS learning project but none of the ideas I initially came up with clicked. I wanted something more complex than a toy but easy enough to implement with reasonable effort. The project should also incorporate naturally the features of LOOPS, such as the gauges library of graphical meters and dials for displaying quantities. I finally stumbled upon the gravity simulator described in the article Force-Based Simulations by Todd King in the September, 1989 issue of Dr. Dobbs Journal. It's just perfect. I'm adapting to LOOPS the design of the sample C++ code that comes with the article. It's nice as it reads like an object-oriented domain specific language for simulation. The code is so short and clean I can fully understand it despite my minimal C++. I never thought I would say that of C++. There is much to like of King's program starting from its domain, astronomy and physics, which overlaps with some of my passions. The project is period accurate too as when Dr. Dobb's Journal published the article LOOPS was still under development. And, along with window systems, simulation was among the killer applications object-oriented programming proponents pointed to. The program comprises only two, hierarchically unrelated classes, a shallow inheritance design more in line with the later evolution of object-oriented programming. But the application does offer other potential classes that are a good fit for LOOPS. For example, I plan to specialize the LOOPS class Window to represent the simulaton window. I will likely need more classes for the GUI, such as dialogs for entering the simulation parameters. LOOPS is one of the subsystems best integrated with the Interlisp environment and comes with good documentation. I want to experience this high integration, the ability of combining tools designed to work together that comes natural once you're familiar with the environment. Adapting King's program to the Interlisp environment is also an opportunity to employ useful programming techniques like screen buffering to improve animation fluidity. Plus, anything that draws pretty graphics is fun. Design To adapt Todd's design to LOOPS I create matching classes with similar instance variables and methods, named according to the LOOPS style. I will rename a few confusing methods, such as UNIVERSE::service() to register a body with a universe which I'll call Universe.Register, and UNIVERSE::big_bang() to run the simulation which will become Universe.Simulate. The C++ code represents a 2D vector as a struct that I map to an Interlisp record. A class seems overkill. Todd's program outputs to the MS-DOS text console via the conio library. GravityLoops instead will draw graphics in a window. So far the code implements the Body class that represents a body. I'm about to start working on the Universe class that holds a collection of bodies and manages the parameters and state of the simulation. Once the core classes are in place I will turn to implementing the animated simulation. #GravityLoops #Interlisp #Lisp a href="https://remark.as/p/journal.paoloamoroso.com/gravityloops-a-gravity-simulator-in-interlisp-and-loops"Discuss.../a Email | Reply @[email protected] !--emailsub--]]>

<![CDATA[Insphex adds the Hexdump item to the File Browser menu to view the hex dump of the selected files. The initial implementation called the public API for adding commands at the top level of the menu. To later move the item to the See sumbenu that groups various file viewing commands I resorted to list surgery, as the API doesn't support submenus. The problem is internal system details can and do change, which happened to the File Browser menu and led to an Insphex load error. I fixed the issue by reverting the public API call and now the item is back at the top level of the menu. Insphex is a hex dump tool similar to the Linux command hexdump. I wrote it in Common Lisp on Medley Interlisp. #insphex #CommonLisp #Interlisp #Lisp a href="https://remark.as/p/journal.paoloamoroso.com/rearranging-the-file-browser-menu-for-insphex"Discuss.../a Email | Reply @[email protected] !--emailsub--]]>