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Technical details of my small programs



Articles documenting my tiny graphics programs, best read in order (for Linux) to see progression.

Most release names are taken from the Star Control world, one of my favorite adventure game !
Sources can be found here.




A pseudorandom number generator might be useful early on, check out this thread about tiny PRNG, another good source is this, i used this one early on in my Linux programs, on modern x86 (~2012) RDRAND instruction is also available, good enough random numbers can also be sourced from RAM etc. sometimes.

LCG (MCG especially) are probably the smallest ones, they just require an addition and multiply if the moduli is a power of two, there is also Xorshift.

A naive and primitive one i used on Halite is just using a 8 bits register and an addition (can hardly call that a RNG but it was good enough for me) : r = (r + 159) & 255

Here is an okay 2^16 moduli 16 bits MCG (taken from here with multiplier value likely found from this tool) : r = (r * 47989) & 65535

Linux (x86, framebuffer)









RISC OS / RPI / Acorn Archimedes (ARM)


DOS (x86, MCGA / VGA)



JavaScript / p5js code that i published on my Twitter account, no definite size goal but generally less than 256 characters.

Code of this category is not very well size optimized, they are more to show interesting short algorithms that i discovered on my own or intro effect that i replicated, made them with accessibility in mind so not much arcane code stuff and it use as few as possible p5js stuff and lib stuff (software rendering) to be ported / understood easily.

Rotating Ortho. Cube (2023, ~230 characters)

no polygons, all integers orthographic cube render


The idea is to show off the algorithm of many intros (i believe) which render pseudo 3d iso / ortho objects such as cubes in very small code, these objects can be built easily without going the usual way by iterating on an area with center 0,0 and applying a transform to the x,y; this produce a shape which can be extruded down (with an additional loop), this method also works with any complex shapes eg. a labyrinth or a text as long as you generate them and extrude them.

using logical operators

The shading can be done by using the extrusion loop value and more fancy shading such as per face shading is also easily possible by either doing it as a single pass or on a second pass by rendering the cube into a buffer and using the buffer to isolate face from pixel color / horizontal position. (or a combination)

fancy texturing / shading ! (logical operators, also note the lighting fakery)

composition, stacking and scrolling, almost like the cool 256b intro Pixel Town by Digimind, note here that the shading is only on the side faces, could also be applied on the upper face which would appear as a cheap roof

The rendering of multiple objects is also easy with a second pass, it can be pretty fast also since it is just a bitmap that is copied over. :)

multiple objects

2d map made of tiny patterns rendered with isometric projection and with highly extruded ortho objects, wave is just a shading trick, still fairly small

The best way to map the cubes to the screen is to use this coordinates transform : x = (x - y) and y = (x + y) / 2

To go full 3D from this is not difficult, it will still stay tiny and fast, just adds 2D rotation to the coordinates, this will be equivalent to a forward mapping affine renderer (you might have to downscale the result to remove sampling holes, this can be done quite easily with scaling; a right arithmetic shift) and for perspective just add 3D rotation (with pitch component), texture mapping can also be added easily with the x and y coordinates and you will get a simple quad forward mapping 3D renderer at this point, 4-point quadrilaterals can also be made by adjusting the loop endpoints which would end up being comparable to a Sega Saturn / 3DO style rasterizer although they also go further with algorithms to fill the sampling holes, it will be a bit tricky compared to a triangles based rasterizer but it might do the job in size limited context or if you don't care about optimal performances.

Black filled circle (2024, ~122 characters)


A way to draw a filled circle with the simplest arithmetic operations (no multiplication, only addition, subtraction and bit shifting), this use an integer variant of Minsky circle algorithm (HAKMEM 149) with adjustment outside the loop to fill the circle (make it "unstable"), downscale is used to cover the gaps, the circle fill is noisy if there is no downscale.

This method is quite tailored to early x86/ARM CPU instructions because the core Minsky circle algorithm and even the downscale can be implemented in few instructions with movsx trick (this explain the shift by 8), shift and conditional is great on early ARM due to the single instruction add/sub + barrel shifter (shift) and conditional instructions so this can be implemented in few instructions on these CPU.

It is of course inefficient (slow) and has the downside that multiple pixels will be revisited if not cared for.

Can also be done without the conditional by replacing the conditional code with : y -= y >> 8

The cool thing is that a variable thickness circle (outward or inward; just a matter of sign) can be done with the exact same code by just moving the line above in the loop (and a spiral can even be done if the shift is small !) :

let x = 6e4
let y = 0
for (let i = 0; i < 1e4; i += 1) {
  x += y >> 8
  y -= x >> 8
  y -= y >> 16 // perturb the orbit by very small amount, the shift adjust the thickness, downscaling may be needed to fill the gaps

Note that the usual way of drawing a filled circle (see below) is already quite small by looping over a rectangular portion of the screen and checking if the current point is inside or outside the circle (or doing it by spans) but it require multiplication.

Here is a more conventional way (but still tiny !) to draw a filled circle, color (c) is based on distance from center so not uniform, s2 is half radius and sl is a shift value that control the circle radius (shortcut to avoid more operations; only works with power of two radius), circle radius can of course be controlled in a finer way by replacing the shift with a division or a mul and the two loops could be broken into a single one :

for (let y = 0; y < s; y += 1) {
  for (let x = 0; x < s; x += 1) {
    let cx = x - s2
    let cy = y - s2
    let c = (cx * cx + cy * cy) >> sl
    let i = (x + (y << 9)) << 2 // 512x512 canvas (= explain the shifts)
    // full white there means that the point lie outside the circle radius (so just needs a conditional + constant for an uniform color circle)
    // could be done with single conditional instruction like a cmov on x86 CPU
    pixels[i + 0] = c
    pixels[i + 1] = c
    pixels[i + 2] = c

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