February 2020 Summary

This month I continued to work on SDL Shooter, which is a space shooter written in SDL and C.  This game started as a presentation demo for the December 2019 Knoxville Game Design meeting.  The project source code is available on my GitHub account.  I’m hoping to release it on more platforms when it gets to a point where I feel that it is complete.  Right now I’m just having fun adding new types of enemies.


  • Foxtrot – Moves a few units either vertically or horizontally, pauses, and then moves in a new direction.
  • Golf – Snake type enemy that has a random number of tail links.  Each link of the tail must be damaged before the head can be damaged.  Moves in a sine wave at variable rates.
  • Hotel – Stationary enemy that constantly fires projectiles in a radial fashion.
  • India – Large enemy that explodes into four smaller enemies when damaged.  When the four smaller enemies are damaged they explode into eight even smaller enemies.  I need to make the explosion angles random, instead of the standard 90/180/270 and 45/90,135, etc angles.
  • Juliett – Hopper enemy that jumps in a parabola one to three units horizontally.  One issue is two of these enemies can jump to the same spot and overlap.  This could be solved by adding a target location variable for each enemy, and determine if another enemy has claimed that spot before jumping there.  I would also like to have the enemy attack the player’s ship in some way.  Either charge the player’s ship when it is aligned vertically, or shoot webs at the player’s ship to slow it down like in Zekkou no Tomodachi.
  • Kilo – A random number is displayed on top, and the player must shoot the correct binary sequence to defeat this enemy.  Added the current “attack value” below the target value, which makes completing the binary sequence a little easier.  The enemy has between 3 and 5 bits, so the maximum value for a 3 bit enemy is 7 and the maximum for a 5 bit enemy is 31.
  • Lima – A bat type enemy that starts sleeping, and then awakes and chases the player when the ship is near.  The enemy is only vulnerable when it is not sleeping.  The amount of time that it takes for the enemy to wake up is random.  The second level enemy moves faster and takes more damage to defeat.
  • Mike – Color orb enemy.  Three small orbs revolve around the center, which are either red, green, or blue.  The player must shoot the correct revolving orb to match the center.  If the center is yellow, cyan, or magenta, then it takes the correct two orb combination to defeat the enemy (such as cyan = green and blue).  Shooting an incorrect orb will make the orbs revolve faster for a short period of time and the enemy will shoot at the player’s ship.

I checked my Microsoft developer dashboard today to see if the XBox One Creators Program was still running.  I noticed that Kitty’s Adventure has now passed 50,000 acquisitions between XBox One and Windows Store.  It is by far the most popular game that I’ve released to this day.

Also this month, we had a great turnout for the online Knoxville Game Design Meeting.  This month’s topic was Java Game Development.

I spent some time updating my two college work pages for Georgia Tech and the University of Tennessee.  Links to those two pages are now displayed on the main menu on my site under Education.  I also found more of my old websites, which I uploaded and linked on my wiki page under Historical Pages.  I uploaded the source code for some projects that were missing, such as the Predator database projects.

Blender Simulation of Liquid Filling a Cocktail Glass

I finally resolved a problem that has plagued me for years, which is simulating liquid filling in a cocktail glass. It seems like this could be solved with a simple scale in the upward direction in Unity, but it’s a lot more complex. My cocktail glass model has two meshes, one for the glass which remains static and another for the fluid which increases in size as the glass is filled. The fluid mesh is an upsidedown cone with a flattened top. Simply scaling the fluid mesh will result in the fluid mesh not correctly filling the glass.

Simple scale of entire fluid mesh gives incorrect fill of cocktail glass
Simple scale of entire fluid mesh gives incorrect fill of cocktail glass

When I created the original fluid mesh in Blender , I believe I used the boolean difference modifier, but it’s been years since I created it so I could have possibly used some other method. For the animation, I used an armature in Blender with two bones. A bottom bone for controlling the ring of vertexes at the bottom of the fluid mesh and a top bone for controlling the ring of vertexes at the top of the mesh.

The new 2.80 version of Blender has significant changes for weight painting. I created the following infographic to show the process I use for weight painting a mesh. For my fuild mesh, I set full wieght of the top vertexes to the top bone, and the full weight of the bottom vertexes to the bottom bone.

Weight Painting in Blender 2.80

To solve the liquid filling problem, the bottom set of vertexes must remain unchanged, while the top vertexes move upward and scale outward. The fluid mesh is modeled with the glass filled. Therefore, in Blender the default pose is the last frame in the animation. I used 60 frames for this animation, so I set the keyframe for the 60th frame with the default pose. It is important to set the keying mode to location, rotation, and scale. In most of my games, I only set the key mode to location and rotation, since game objects are rarely ever scaled.

To create the filling effect, in Animation mode I set the frame in the timeline to the first frame. Then I select the top bone and scale it inward (on the X and Y axes) so that it matches the same diameter as the bottom of the glass (and same diameter as the ring of bottom vertexes). Then I translate the top bone downward, until it exactly overlaps with the bottom ring of vertexes. Then I add a keyframe for the first frame. Pressing play will show the simulated liquid starting from the bottom of the glass and filling to the rim of the glass.

Correct cocktail glass fill animation using two armature bones
Correct cocktail glass fill animation using two armature bones

I plan to use this new liquid fill animation technique to update Bartender Game in the near future.


Unity Version Tool

The latest updates and documentation can be found on the Unity Build Tool wiki page.

One of the biggest problems with having 59 Unity projects is keeping them all up to date.  I knew many of my Unity projects were out of date and needed to be updated to the latest version of Unity, but I didn’t have a good method for detecting which ones.  I had previously developed build and upload scripts in Ruby to create Windows BAT files to compile a project for Windows, MacOS and Linux and upload those builds to Itchio using Butler.  However, those BAT files could not make Unity WebGL builds.

The Unity Version Tool that I developed solves these problems.  It was developed in Ruby using the GTK+3 graphical libraries.

Unity Version Tool

  • Pressing Scan Projects will check all subfolders in the specified project directory for Unity projects.
  • If a project does not match the current version of Unity or PlayMaker, then the project will be highlighted in red.  Default version values can be set in the unity_version.config file.  The version number of the project is checked from ProjectSettings/ProjectVersion.txt and files ending with the .csproj extension.
  • Pressing Update Version will attempt to read the current version of Unity installed on the system (<User Profile>/AppData/Local/Unity/Editor/Editor.log) and store it in the unity_version.config file.  The PlayMaker version information is read from Assets/PlayMaker/Editor/PlayMakerWelcomeWindow.cs.
  • Individual projects can be selected by checking the boxes next to the project names, or all projects can be selected or deselected using the checkbox in the header row.
  • Builds for the selected projects can be compiled for Windows, MacOS, Linux, or WebGL.
  • WebGL builds require a script to be generated from the included template, which is embedded into the project for compilation, since there is not a Unity command line option for making WebGL builds.  It uses the “-executeMethod” command line parameter to execute project script.
  • All builds for a project can be deleted by pressing Clear build folder.
  • By default, the Unity editor will start on compilation.  I may add “-batchmode” as an option in the future to compile without starting the Unity editor, but I’ve noticed issues lately with using the “-batchmode” Unity parameter.  If a project is compiled and it is not using the latest version, then Unity will prompt to update the project.  Therefore, it is advisable to update the projects (which are highlighted in red) by opening them before selecting the compile option.
  • Note that while updating the Unity project to the latest version, there may be multiple .csproj files that still return an old version of Unity.  I’ve found that the .csproj files (such as Assembly-CSharp.csproj, Assembly-CSharp-Editor.csproj, and <project>.csproj) can be safely deleted in most cases, and Unity should create new versions of those files the next time a script is accessed in the Unity editor.  Hopefully, I will add an option to remove old .csproj files.
  • After updating a Unity project, it may be necessary to make a change (such as moving a GameObject in the Hierarchy and moving it back) in order for the ProjectSettings/ProjectVersion.txt to be updated.  I don’t know if there are any drawbacks to manually updating the version number in that file, so I wouldn’t advise doing it.

Using this tool, it is possible to compile multiple project for a selected platform at once.  This is a process that had previously taken me hours or days for WebGL projects, since each project would need to be opened, updated, platform setting changed, and then compiled.  It still takes a long time, but at least now I can kick it off before going to bed and just let it run.

Download the Unity Version Tool  (Ruby and GTK+3 required to be installed on system, which is not included)