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Messing with Godot

My early experience in working on a toy platformer game.

I recently downloaded Godot, a game engine and game development environment. I never did much with games, so I figured I might mess about. So far I’ve been playing around with the 2D stuff, something that could be a platformer-style game.

Godot does a decent job of making concepts clear, though as with any new effort, searching is your friend. Most hurdles have been in figuring out the math to use for custom physics, and even there the engine provides a lot of the basics.

One of the hardest challenges in any program is keeping organized and picking up the right way to implement things. There are places I know I should use custom signals, but I don’t quite understand exactly how to wire them up the right way, so I’m relying on direct calls. My tile map places overlapping tiles. Or places where I know I should be processing velocity changes in the frame process function, but I’m modifying the velocity directly, which means I have to make sure it doesn’t get eaten by a collision.

Eaten by a collision? If you run into a wall, that wall eats your velocity in the direction it opposes. Godot provides collision checking which you can use in custom physics, but it’s up to you to decide how to handle collisions because you might want to bounce, or some collisions might break blocks or teleport you or whatever you want them to do. In my case, the collisions should eat the velocity:

func collide_normal(vel, nnorm):
    var out_vel = Vector2(vel.x, vel.y)
    var dot_product = vel.x * nnorm.x + vel.y * nnorm.y
    if sign(vel.x) != sign(nnorm.x):
        out_vel.x -= dot_product * nnorm.x
    if sign(vel.y) != sign(nnorm.y):
        out_vel.y -= dot_product * nnorm.y

    return out_vel

This function takes a velocity (with an X component and a Y component for how much the object moves frame-to-frame, which together also tells you what direction, like the slope of a line) and a normal vector. A normal vector also has an X and a Y, but if you remember the unit circle from trigonometry, it’s normalized so that it has a length of one, and it points away from the face of an object.

Given those two components, the function negates the velocity that is pointed against the given normal vector. In my case it also has two conditional checks that are used in case either of the components happen to agree in sign (same as direction). Without those, the function would just as happily negate the part of a velocity that points the same way as the normal vector.

But that’s the kind of thing you have to do if you’re poking around and not taking time to do it properly inside the frame process function. Otherwise the bouncy spring you added will sometimes behave like a wall, if the signal of your collision with it happens to come right before the frame process checks if you collided with anything and decides to cancel the bounce.


One of the other things I’m considering is experimenting with a “ghost” player. Godot has its own built-in physics, which is usually applied to inanimate objects, but not to controlled objects and, depending, on animate enemies. But it looks like there are times that it might be handy to ride on the built-in physics, so I believe I can create an invisible player surrogate that will respond to the built-in physics, and for limited uses that might save some code and allow for cool things with limited effort.

I haven’t tried to do any fancy graphics yet (e.g., animations and particles), nor tried anything in 3D, but it’s still fun to mess around with my bouncy springs and gravity fields.

Numerical Step Function in Python

Technical article about creating an interval/range in Python.

The classic range() (and in 2.* series, xrange()) is useful for getting an iterator of numbers. Its full signature is: range(start, stop[, step]).

So you can do, e.g., range(5, 10) = [5, 6, 7, 8, 9].

Or you can do, e.g., range(6, 13, 3) = [6, 9, 12].

But as far as I know there’s not an easy, built-in way to iterate over a range-like set of integers defined both by the range and a number of parts desired.

An example: you want five evenly-distributed numbers starting with 1 and ending with 10. So something like [3, 5, 6, 8, 10].

In my case, I had two similar use-cases. The first was the example above: a semi-arbitrary set of values in a range. I didn’t need to strictly include the endpoints in the values, but wanted a decent distribution of the values between start and end.

The second case was a little different, in that I wanted the range to always include the ends (it was a case of covering a whole range), but I also wanted to know how much each “step” over the range amounted to.

In the naïve version of this case, you don’t need the magnitude, as you could cheat and throw an extra piece in to account for slight differences (e.g., 11 / 3 => 1, 4, 7, 10 with the last piece being 10 through 11).

But there’s a nice way to evenly distribute the extra pieces: using rounding of the fractional value to distribute the extras.

Example:

10 / 4 = 2.5
0 * 2.5 = 0.0
1 * 2.5 = 2.5; round(2.5) = 2
2 * 2.5 = 5.0
3 * 2.5 = 7.5; round(7.5) = 8
[0, 2, 5, 8]

(In Python, round(number[, ndigits]) of n.5 goes to the even side (when using ndigits=0 or with a single argument).)

In this case, the caller could buffer the previous value and calculate the gap/step itself, but this is Python, so we might as well give it a mode to get that itself.

Without further ado, this is what I came up with:

def equal_parts(start, end, parts, include_step=False):
    part_size = (end - start) / float(parts)
    for i in range(parts):
        part = start + round(part_size * i)
        step = start + round(part_size * (i + 1)) - part
        if include_step:
            yield (part, step)
        else:
            yield chunk

It’s messier than it needs to be, due to its dual-use nature. It’s arguably cleaner to have a second function that would handle the include_step=False case:

def equal_parts_only(start, end, parts):
    for part, step in equal_parts(start, end, parts):
        yield step + part

That function would remove the conditional business at the end of the original equal_parts:

def equal_parts(start, end, parts):
    part_size = (end - start) / float(parts)
    for i in range(parts):
        part = start + round(part_size * i)
        step = start + round(part_size * (i + 1)) - part
        yield (part, step)

In the stepless version, it’s got another nice property: what if you do equal_parts(0, 10, 11)? You get: [1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 10]. That’s a nice property: getting more parts than integers in the range.

I wrote a GIMP plugin to create stepped (or random) gaussian blurs on an image. The stepless version lets me create the set of blur levels, while the step-including version lets me properly select (mostly-)even parts of the image.

Here’s an image that used this plugin containing a dual use of this function: Sample image of gaussian blur in sections

If anyone wants a copy of the plugin, let me know and I’ll put it on Github or such.

Future Software

A look at some ideas for better computers.

Occasionally you read interesting ideas for the future of software. Here are a few to ponder.

docopt

docopt is basically a domain-specific language. The language is the standard Usage output of a command-line program. By simply documenting a program’s usage, it aims to provide the functionality of parsing the program’s invocation.

This is a great step forward in finding ways to reduce duplicated effort in an elegant way. Before, you might programmatically add or modify the argument handler, and that might generate the Usage. But it was still tedious, as it required keeping what was a messy bit of code as clean as you could. Messy because you had to do a lot of thinking about the basic form of your command line API, and then translate it to code.

Instead, with docopt you should be able to purely focus on the form of the Usage.

I think that this will be a common theme for future computing, without relying on more complex systems like SOAP.

Why do we need modules at all?

Erlang.org: Erlang-Questions: 24 May 2011: Joe Armstrong: Why do we need modules at all? was an interesting post I remember reading a few years back. It questions the basic assumption of building software hierarchically and statically.

This is akin to the age-old (at least since birth of UNIX) desire to have programming be a set of pipes thrown together at will, with the elegance and wisdom of a seasoned hacker behind it.

What it really seems to suggest though is a move toward a way to let computers program themselves. The desire to let evolution play a key and direct role in how a computing system operates. If some given function is replaced by a more efficient function, all software depending can be faster. If you have some chain of functions A->B->...->ZZ, and someone writes a better chain, the whole can be replaced.

We already get some of this with packages/modules and dynamic linking, so the question (short-/mid-term) is really whether a kind of function-level alternative would replace modules/packages, or work alongside them.

Why do we need GUIs at all?

This is a spin on the previous. It’s the basic question of whether larger elements of the GUI can be easily reused. At present the basic unit of the GUI is the widget. The widget is some semi-small piece of the GUI, like a button or a text input.

If you want a more complex GUI, it’s a matter of assembling widgets together. This is equally true for a native application as it is for a webpage or web application.

Reuse is dependent upon some human brain recognizing the opportunity, and wiring the whole thing up for reuse. That’s opposed to something like the hypothetical functions database above, which in theory would have enough metadata to be able to say, “takes in a list, outputs a sorted list, stable, memory use, complexity.”

But if you can do it with functions (which seems likely enough), you can do it with larger pieces, including GUIs. So you can have a GUI that’s designed separately from the consuming code, and it can say, “presents a list, allows reordering, sorting, adding, deleting,” and you might specify some constraints on the adding/editing portion, so it could select another GUI component (“unique (name, number) pair”, or “unique name, non-unique number pair”, or whatever).

The initial versions of this can probably be written off of docopt, where by the same magic of parsing Usage a GUI could be created for any command line API. This is a project I’ve been meaning to work on, but haven’t done it yet.

Common theme

The common idea is reducing duplication of work, increasing productivity, removing friction to create. Making the computer figure out more of the work. Automating more. Instead of having to spend so much time doing analysis of tradeoffs and pondering why something broke when it shouldn’t, we should be building more.

That leads to the last one: moving away from pure-text programming. That doesn’t mean we write it out to binary; the text layer can persist. But it does mean that to some extent we stop doing everything as text. We can already extract interaction diagrams from text, but we currently do the editing in text and only get the diagrams when we want a conceptual view.

It will take some time before we see these last sorts of changes take place. But it’s likely that they will, if for no other reason than the benefits are there. I’d rather write the Usage once and know everything was wired up for me, just like I’d rather not muck about with every last bit of CSS and markup every time I want to add something to an application.

And as fun as it is to find the extra comma and find out that I wrote it correctly except for that typo, I’d rather that footgun go away entirely.