Building Viruscraft planets

The last months have been booked solid with production on various projects, so I’m very behind with blogging. This means that there are a few loose threads that I need to look back on and write about, one of which is the Viruscraft world.

This is a screenshot of the current ‘alpha version’ of viruscraft we tested with the custom tangible interface (more on that soon) during the second game testing workshop. You can read Amber’s report on this workshop here.

It took a while to develop this planet, we started with a more conventional system:

This was a planet modelled in blender, the idea being to create islands and regions for different host species to live. We automatically made zones for different species to live (sea and land mainly but also higher terrain is possible) and then populated this with host organisms. There are two problems with this approach, one is that it’s a static model – we could have a set of variations on planets but e can’t change the terrain. One of the initial obvious references we talked about to the Wellcome Trust was Minecraft – which allows players to modify a procedurally generated terrain. Another problem with this is that if we look at our initial mood board for the project, where we collect artistic references:

There are lots of interesting ideas here, including perhaps using geomtric virus shapes in an interesting way. There is a problem I’ve seen on many games projects where if there isn’t a strong artistic style at the start, a more photorealistic logic takes over and pushes things into less and less interesting territory. So we decided to try something a little stranger and more interesting – could we create worlds built from triangular sections of terrain in the same was as viruses are created from triangular proteins?

There is also a distinct advantage to a procedural technique we can do with modular world building because the shape of the land affects how viruses spread – the number and physical location of population clusters has a big affect on how difficult it is, as a virus – to spread and become successful. The more dynamic and controllable we can make the world, the more interesting the game will be.

We chose a shape called a ‘Pentakis icosidodecahedron‘ – basically an 80 sided sphere built from triangles. One mistake I made with this was to not read the mathematical fine print – it took quite a lot of swearing before I figured out that it’s not regular, some of the triangles are equilaterals and others are isosceles. This means we have to squash and stretch the components to fit precisely, otherwise there are gaps between them.

Once we can arrange the triangles in the right places we need to make sure the terrain edges match up. It turns out there are 8 possible arrangements – from all sea, all land to the 6 varieties of crossings that can occur between the edges of the triangles:

We can also control the probability of a triangle of containing land, and use a slider as a sea level setting. Roughly speaking, the more unified the planet – the less, bigger populations possible and the easier it is for your virus to spread. The more fragmented and diverse the populations, the harder it is.

We’ll be adding more controls here in the future, so you’ll be able to customise your planet quite a bit more. We then made some animated low-poly host creatures to populate the planet. These have receptors for the virus that match the different shaped ligands – they breed and evolve to gain resistance to your virus over time.

In order to place them correctly on the right habitat we created some test ‘flat worlds’ to make sure everything was lined up correctly. It works by calculating barycentric coordinates in each triangle based on the particular terrain section, so we can generate a random location and check if its land or sea.

Another possibility is to have different themed planets, an ice world, urban planet, etc – perhaps rather than creating them you could explore a galaxy planet by planet. One important idea that came from the feedback would be to use the ‘difficulty setting’ that we’ve figured out from the terrain composition to provide tutorial levels that you could work through in increasing difficulty.

Procedural landscape demo on OUYA/Android

A glitchy procedural, infinite-ish landscape demo running on Android and OUYA. Use the left joystick to move around on OUYA, or swiping on Android devices with touchscreens. Here’s the apk, and the source is here.


It’s great to be able to have a single binary that works across all these devices – from OUYA’s TV screen sizes to phones, and using the standard gesture interface at the same time as the OUYA controller.

The graphics are programmed in Jellyfish Lisp, using Perlin noise to create the landscape. The language is probably still a bit too close to the underlying bytecode in places, but the function calling is working and it’s getting easier to write and experiment with the code.

(define terrain
  '(let ((vertex positions-start)
         (flingdamp (vector 0 0 0))
         (world (vector 0 0 0)))

     ;; recycle a triangle which is off the screen
     (define recycle 
       (lambda (dir)         
         ;; shift along x and y coordinates:
         ;; set z to zero for each vertex
         (write! vertex       
                 (+ (*v (read vertex) 
                        (vector 1 1 0)) dir))
         (write! (+ vertex 1) 
                 (+ (*v (read (+ vertex 1)) 
                        (vector 1 1 0)) dir))
         (write! (+ vertex 2) 
                 (+ (*v (read (+ vertex 2)) 
                        (vector 1 1 0)) dir))

         ;; get the perlin noise values for each vertex
         (let ((a (noise (* (- (read vertex) world) 0.2)))
               (b (noise (* (- (read (+ vertex 1)) 
                               world) 0.2)))
               (c (noise (* (- (read (+ vertex 2))
                               world) 0.2))))

           ;; set the z coordinate for height
           (write! vertex 
                   (+ (read vertex) 
                      (+ (*v a (vector 0 0 8)) 
                         (vector 0 0 -4))))
           (write! (+ vertex 1) 
                   (+ (read (+ vertex 1)) 
                      (+ (*v b (vector 0 0 8)) 
                         (vector 0 0 -4))))
           (write! (+ vertex 2) 
                   (+ (read (+ vertex 2)) 
                      (+ (*v c (vector 0 0 8)) 
                         (vector 0 0 -4))))

           ;; recalculate normals
           (define n (normalise 
                      (cross (- (read vertex)
                                (read (+ vertex 2)))
                             (- (read vertex)
                                (read (+ vertex 1))))))

           ;; write to normal data
           (write! (+ vertex 512) n)
           (write! (+ vertex 513) n)
           (write! (+ vertex 514) n)

           ;; write the z height as texture coordinates
           (write! (+ vertex 1536) 
                   (*v (swizzle zzz a) (vector 0 5 0)))          
           (write! (+ vertex 1537) 
                   (*v (swizzle zzz b) (vector 0 5 0)))          
           (write! (+ vertex 1538) 
                   (*v (swizzle zzz c) (vector 0 5 0))))))

     ;; forever
     (loop 1
       ;; add inertia to the fling/gamepad joystick input
       (set! flingdamp (+ (* flingdamp 0.99)
                           (read reg-fling)
                           (vector 0.01 -0.01 0))))

       (define vel (* flingdamp 0.002))
       ;; update the world coordinates
       (set! world (+ world vel))

       ;; for each vertex
       (loop (< vertex positions-end)         

         ;; update the vertex position
         (write! vertex (+ (read vertex) vel))
         (write! (+ vertex 1) (+ (read (+ vertex 1)) vel))
         (write! (+ vertex 2) (+ (read (+ vertex 2)) vel))

         ;; check for out of area polygons to recycle 
          ((> (read vertex) 5.0)
           (recycle (vector -10 0 0)))         
          ((< (read vertex) -5.0)
           (recycle (vector 10 0 0))))
          ((> (swizzle yzz (read vertex)) 4.0)
           (recycle (vector 0 -8 0)))
          ((< (swizzle yzz (read vertex)) -4.0)
           (recycle (vector 0 8 0))))

         (set! vertex (+ vertex 3)))
       (set! vertex positions-start))))

This lisp program compiles to 362 vectors of bytecode at startup, and runs well even on my cheap Android tablet. The speed seems close enough to native C++ to be worth the effort, and it’s much more flexible (i.e. future livecoding/JIT compilation possibilities). The memory layout is shown below, it’s packing executable instructions and model data into the same address space and doesn’t use any memory allocation while it’s running (no garbage collection and not even any C mallocs). The memory size is configurable but the nature of the system is such that it would be possible to put executable data into unused graphics sections (eg. normals or vertex colours), if appropriate.


Ouya development experiments

The Ouya is a tiny game console which is designed for promoting indy games rather than traditional high budget productions. It’s cheap compared to standard games hardware, and all the games are free to play at least in demo form. It’s very easy to start making games with as it’s based on Android – you can just plug in a USB cable and treat it just the same as any other Android device. You also don’t need to sign anything to start building stuff – it’s just a case of adding one line to your AndroidManifest.xml to tell the Ouya that the program is a game:

 <category android:name="tv.ouya.intent.category.GAME"/>

and adding a 732×412 icon in “res/drawable-xhdpi/ouya_icon.png” so it shows up on the menu.


There is a lot to like about the Ouya’s philosophy, so I tried out some graphics experiments with it to get better acquainted:

This program was made using Jellyfish, part of my increasingly odd rendering stack which started out as a port of Fluxus to PS2. It’s a type of microcode written inside TinyScheme and running in a separate virtual machine that makes it possible to process a lot of geometry without garbage collection overheads. At some point I might write a compiler for this, but writing the code longhand at the moment means I can tweak the instruction set and get a better understanding of how to use it. Here is the microcode for the ribbons above, they run at 20,000 cycles per frame each (so about 1.2MHz):

;; register section
   8 20000 0 ;; control (pc, cycles, stack)
   mdl-size prim-tristrip 1 ;; graphics (size, primtype, renderhints)
   0 0 0 ;; pos
   0 0 0 ;; sensor addr

   ;; program data section
   mdl-start 0 0     ;; 4 address of current vertex
   mdl-start 0 0     ;; 5 address of accum vertex (loop)
   0 0 0             ;; 6 influence
   0 0 0             ;; temp

   ;; code section 
   ;; add up differences with every other vertex
   ldi  4  0         ;; load current vertex
   ldi  5  0         ;; load accum vertex
   sub  0  0         ;; get the difference
   lda  6  0         ;; load the accumulation
   add  0  0         ;; accumulate
   nrm  0  0         ;; normalise
   sta  6  0         ;; store accumulation
   add.x 5 1         ;; inc accum address

   ;; accumulation iteration 
   lda  5  0         ;; load accum address
   ldl  mdl-end 0    ;; load end address
   jlt  2  0         ;; exit if greater than model end (relative address)
   jmp  8  0         ;; return to accum-loop

   ;; end accum loop
   ;; push away from other verts
   lda  6  0         ;; load accum
   ldl -0.1 0        ;; reverse & make smaller
   mul 0 0

   ;; attract to next vertex
   ldi 4 0           ;; load current
   ldi 4 1           ;; load next
   sub 0 0           ;; get the difference
   ldl 0.4 0
   mul 0 0           ;; make smaller
   add 0 0           ;; add to accum result

   ;; do the animation
   ldi 4 0           ;; load current vertex
   add 0 0           ;; add the accumulation
   sti 4 0           ;; write to model data

   ;; reset the outer loop
   ldl 0 0           ;; load zero
   sta 6 0           ;; reset accum
   ldl mdl-start 0   
   sta 5 0           ;; reset accum address

   add.x 4 1         ;; inc vertex address
   lda 4  0          ;; load vertex address
   ldl mdl-end 0     ;; load end address
   jlt 2  0          ;; if greater than model (relative address)
   jmp 8  0          ;; do next vertex

   ;; end: reset current vertex back to start
   ldl mdl-start 0
   sta 4 0

   ;; waggle around the last point a bit
   lda mdl-end 0     ;; load vertex pos
   rnd 0 0           ;; load random vert
   ldl 0.5 0         
   mul 0 0           ;; make it smaller
   add 0 0           ;; add to vertex pos
   sta mdl-end 0     ;; write to model

   jmp 8 0