Mouse click and drag

This is a little bugger I coped with recently. In Windows forms dragging (holding a mouse button and moving the mouse) produces mouse click event after the mouse button is released. That's OK when a program is interested in only drag or click events but when it has to handle both events, each with different logic then there has to be a way to differentiate between those two events. Let's start with simple case where only mouse click is needed (C#-ish and .Net-ish code):

void init(){
    control.MouseClick.Add(clickHandler);
}

void clickHandler(object sender, EventArgs e)
{
    // Click logic
}

Now let see simple drag handler:

Point lastPos = null;
 
void init(){
    control.MouseMove.Add(moveHandler);
}

void moveHandler(object sender, MouseEventArgs e)
{
    if (lastPos == null)
        lastPos = e.Location;

    if (e.Button.HasFlag(MouseButtons.Left))
    {
        Point change = (e.Location - lastPos);
 
        // Drag logic
    }

    lastPos = e.Location;
} 

There is no need to handle the situations when mouse leaves or enters control's area because once mouse is pressed over some control, only that control will receive mouse related events. That greatly simplifies the code for handling the mouse movement. Only overhead is checking if last position has been initialized. I hope it work the same on Linux and Mac OS with Mono.

If those two pieces of code were combined, mouse drag that ends inside starting control will trigger click handler. One solution is to simply track how far was mouse dragged:

Point? lastPos = null;
double dragDist = 0;
 
void init(){
    control.MouseClick.Add(clickHandler);
    control.MouseMove.Add(moveHandler);
}

void clickHandler(object sender, EventArgs e)
{
    if (dragDist > 0)
        return;

    // Click logic
} 

void moveHandler(object sender, MouseEventArgs e)
{
    if (!lastPos.HasValue)
        lastPos = e.Location;

    if (e.Button.HasFlag(MouseButtons.Left))
    {
        Point change = (e.Location - (Size)lastPos.Value);
        dragDist += Math.Abs(change.X) + Math.Abs(change.Y);

        // Drag logic
    }
    else
        dragDist = 0;

    lastPos = e.Location;
}

Well, Euclidean distance would do too. I used Manhattan distance because the line of code is narrower and has less chance of being broken to multiple lines in your browser. Neat thing about this solutions is that border between click and drag can be adjusted to tolerate some mouse movement.

Coco/R and parsing strings

Writing a parser for Stareater with Coco/R as parser generator was easy. Despite requiring slightly different way of thinking (all terminals "return void" so output is done through method parameters with keyword out) overhead imposed by Coco/R was minimal. And then I wanted to test the parser. I figured unit tests would be appropriate and while writing first unit test I got stuck at scanner constructor. The scanner is the part that converts input to tokens (lexeme) and default Coco/R scanner can be constructed either by providing a file name (or relative path) string or the Stream object. The problem was my parser was intended for in-memory strings.

Quick googling showed that string can written to memory stream with few lines[1]. If you want to be quick and don't mind bloat you can stop reading, here your solution:

var stream = new MemoryStream(Encoding.UTF8.GetBytes(text));

Parser parser = new Parser(new Scanner(stream);

Why do I call this bloated? Because:

Under the hood default scanner implementation wraps stream with buffer. The buffer does what the name says, buffering, plus conversion of bytes to characters. I'm not going to discuss their design decisions like why didn't they use BufferedStream. When implementing IKON reader for .Net I opted for TextReader as a base class for input because conversion form input to characters is guarantied by interface and there StreamReader and StringReader classes that implement TextReader and can read from any stream or from in-memory string. Maybe they had some reason to insist on the Stream but that is not the point of this post. What is the point is that I was talking about default Coco/R scanner.

Both Coco/R parser and scanner are based upon a frame file. Those files are sort of blueprints, a C# code interleaved with placeholders for generated code. When generating parser and scanner, command line tool must be supplied with those files along with grammar specification file though they don't have to be explicitly named if they are in the same folder as grammar file. By customizing scanner's frame file parsing bloat can be reduced. Below are steps for making a frame for a scanner that only accepts string as input.

Buffers can be ditched altogether since in-memory string is already buffered and converted to collection of characters. Feel free to completle delete Buffer and UTF8Buffer classes from scanner's frame but keep in mind that generated scanner's code depends on Buffer.EOF constant. I prefer to hide it as static private nested class inside Scanner class even but it's valid to just leave original Buffer as is.

static class Buffer
{
  public const int EOF = char.MaxValue + 1;
}


Next, make an reference to input string and initialize it in constructor.


public string input; // scanner input
public Scanner (string input) {
    this.input = input;
    Init();
}


Than clean up Init method. Aside form initialization, that method detect whether the stream is encoded in ASCII or UTF-8. Since new scanner works directly with characters, encoding detection can be omitted.


void Init() {
    pos = -1; line = 1; col = 0; charPos = -1;
    oldEols = 0;
    NextCh();
    pt = tokens = new Token();  // first token is a dummy
}


And finally modify NextCh method to raise "end of file" when end of string is reached.


    void NextCh() {
        if (oldEols > 0) { ch = EOL; oldEols--; }
        else {
            pos = charPos;
            charPos++;

            if (charPos >= input.Length)
                ch = Buffer.EOF;
            else
            {
                ch = input[charPos]; col++;
                // replace isolated '\r' by '\n' in order to make
                // eol handling uniform across Windows, Unix and Mac
                if (ch == '\r' && input.Length > charPos + 1 && input[charPos + 1] != '\n') ch = EOL;
                if (ch == EOL) { line++; col = 0; }
            }
        }
-->casing1
    }


That's it! In case you want to support both strings and streams you could do similar modifications with TextReader instead of string. I haven't tried that yet since the idea occurred to me while writing this post.

Binary Domain and C-evo

It was almost to months since I wanted to write about this and there was always something in the way. I've seen first impressions of Binary Domain video game on Cynical Brit's YouTube channel and although the guy on the channel was not impressed by the game, a friend told me it was good and I was intrigued by the plot. I downloaded the demo version and what should have been fun was an agony. The controls were disaster! You'd understand my shock if I told you that I do not and never had owned a console and the game was ported from console meaning, among the other things, it was designed for a game pad instead of mouse and keyboard. On top of that I played quite a number of first person shooter on desktop computer back in '00 when they were blossoming genre there. My expectations were WASD movement, space for jump, shift for sprint, C or control for crouch, E for interaction, R for reload and mouse for aiming and shooting. Binary Domain being console port did this it's own way, WASD was there but space was kind of everything else button, sprint was some random letter (F or something like that), shift just turned character's facing direction to the left. That looked silly :). To rebind the keys you had to exit the game and use separate application. All of that would be bearable if there wasn't a lot bigger issue, aiming with mouse. When I moved mouse slowly aim kind of jumped few degrees at the time making it hard to "aim for a head", when I tried to make sharp turn, fast mouse movement was dampened to slow turn. Shooters are known to have an issue with mouse acceleration but this was opposite, mouse deceleration. Why??? Was it just on my machine or are there more players that think the game was never tested with mouse? I tried to find a quick workaround but except "use gamepad instead mouse" there was nothing. That's preposterous measure that I'm never going to take to just play a game.

After I stepped back from computer to calm down and eat lunch I figured that only reason why I wanted to play that game was a story and what is natural medium for story telling? In this case it's video and there are a few "let's plays" on the Internet for this game. "Let's plays" are something that big companies don't like and they may even be legal issue if they are monetized. But why people demand such content if video games are there to provide fun in the first place? Some games fail to deliver a fun, some games are broken, some cost more than they are worth and some people are plain lazy so they want somebody to play a game for them :). Binary Domain is broken and probably kind of game that is one time experience, once you play it through that's it, no more new stuff to do. Basically a 25€ movie, thereby it more fun to watch it than play it. What games aren't one time experience? I'd say most strategies (especially grand strategies such as Civilization series) and every game with healthy multiplayer. Out side the world of video games, chess and poker are great examples. It basically boils down to having big enough uncertainty factor and allowing player(s) to influence the outcome.

Watching a video didn't exactly fulfilled my need for interactive fun so I browsed through my good old library and decided to play a game of C-evo. C-evo is polar opposite of Binary Domain, it's PC native, can't be played without the mouse, it's turn based strategy and as most grand strategies has high replay value. I had that game for a few years and played it through about couple dozen times. It occurred to me that I never experimented much with the map size in C-evo. In grand strategies large maps tend to prolong the gameplay while not really adding to the experience, small maps on the other hand tend to be more aggressive. Peaceful expansion is concluded much sooner so wars start sooner. I opted for the smallest map, about half the size (1/4 of area) of normal map with a little bit more land. The game turned out to be easy, there were only two tiles I had to fortify in order to prevent other player from peeking and colonizing my territory and during the second session I had enough technological advantage to steam roll opponents. But the game didn't end there, oh no, it was the time form something more. It took me at least five more session to complete my plan. I could have achieved victory condition with very little effort but instead I chose to something else, something I've tried to do but never managed to pull off before, to cultivate whole planet. Since the map was small and I had almost hundred engineers (special units that can cultivate land) due to disbanding poorly placed AI's cities, it was doable. A little tedious but not to much.

That's what I expect from a game, to be a medium that can surprise and please more than once, to be significantly different experience over multiple playthroughs and to allow experimentation.

ANTLR, second chance and rivals

This post continues the story from the introduction and first impression.

It has been long month and it took me quite a while to gather the material for this post. Long story short ANTLR is no go for C#, it's rival in alpha stage is lacking and the third option finally proved worthy. Now the long story:

Last time I tried ANTLR with separate files for lexer, parser and tree processor grammars which produced "mouth feeding" process in the user code using those grammars. This time i tried ANTLR with combined grammar file, basically all three grammars in one file.

grammar MyLogoCombined;

options {
language=CSharp3;
output=AST;
}

@header {
using System;
}

fragment SIGN
: '+' | '-';
fragment SPACE
: ' ' | '\t';

NUMBER : '0' | SIGN? '1'..'9' '0'..'9'*;
FORWARD : 'FD';
ROTATE : 'RT';

NEWLINE : ('\r'? '\n')+ { Skip(); };
WHITESPACE
: SPACE+ { Skip(); };

public script : statement* EOF!;

statement
: FORWARD v=NUMBER {
double length = toDouble($v);
angle = Math.PI * this.angle / 180;
x += Math.Cos(angle) * length;
y += Math.Sin(angle) * length;
Console.WriteLine("Moved to {0}, {1}", x.ToString("0.#"), y.ToString("0.#"));
}
| ROTATE v=NUMBER {
angle += toDouble($v);
Console.WriteLine("Facing {0}°", angle.ToString("0.#"));
};

It doesn't look bad or crammed and generated code is better too. Generated classes are lexer and merged parser and tree processor. As an effect a user code required to utilize those classes got considerably simpler.

static void CombinedLogo()
{
using (var input = new StreamReader("input.txt")) {
MyLogoCombinedLexer lexer = new MyLogoCombinedLexer(new ANTLRReaderStream(input));
MyLogoCombinedParser parser = new MyLogoCombinedParser(new CommonTokenStream(lexer));
parser.script();
}
}

Now we have something usable. But I wasn't satisfied, generated code requires 100 kB run-time library (may look weird compared to executable weighting 30 kB) and is riddled with comments mentioning full path to original grammar file. And there is no way to generate code without those comments. Well, not exactly critical issues, more like unnecessary vice. There is another issue I haven't mentioned earlier, documentation is not quite there. It exists, that's good, there are a lot of examples, that's good too but you won't get your question answered on the single page. You'll have to look in the official docs, unofficial examples and still do a few experiments to get definite answers.

Irony.Net

On the Stack Overflow webpage that led me to ANTLR next recommended thing was Irony.Net. It's the project hosted on CodePlex with professional looking home page. I've downloaded source code and started looking around. The nicest thing about Irony.Net is the way of defining a grammar, there is no code generations from specially formatted text file, it's defined as ordinary C# class. I usually post code as plain text but for the sake of presentation you'll get an image this time.

That's as awesome as ANTLR's state diagram for grammar rules. Operator overloading is usually syntax evil but in some cases it's OK thing to do and Irony.Net has found one. As you can see plus and bitwise OR operators are overloaded to operate on non-terminals so the grammar rules can resemble BNF notation as closely as possible. At the same time the image presents three issues with the Irony.Net: piece of code commented out, first parameter of MakeStarRule method and lack of rule attributes (tree processor actions).

Commented out code is left on purpose to demonstrate the existence of various flags and properties. While trying to make it work I read somewhere that I should explicitly specify creation of abstract syntax tree which is usually normal process in parsers so I added that line. It turned out that Irony.Net creates syntax tree by default and that flag actually confuses it. Alright, it confused me too because it didn't work with educational material, it required extra information that I couldn't figure out within the time I had at the moment. I figured it is supposed to indicate that custom tree node objects are being used and that creation of those objects is mysterious art.

That leads us to the lack of rule attributes problem. In order to process the tree you have to either traverse the tree on your own or use the mysterious art. I really tried to figure out the mysterious art but the lack of education materials and limited time bested me (a year later after writing this post I did learn how to use visitor pattern but still, there better ways). The biggest problem with Irony.Net is the lack of documentation. It has so many features and only way to figure them out is to dig in their source code.

The weirdness of MakeStarRule method may not be obvious but why does it require destination non-terminal and why is it class member? In my opinion it should be static and have only one mandatory parameter, the repeatable BNF term. The reason why it requires destination non-terminal is because it secretly modifies the rule instead of just building the BNF term. The reason it is non-static is because it uses certain flag from the grammar object. That is actually OK because the grammar object is used to build the "language" object, not for direct parsing.

Now that I mentioned it, using the grammar is quite simple, build parser using the grammar, feed the input and get the tree:


Parser parser = new Parser(new IronyLogo());
ParseTree tree;
using (var input = new StreamReader("input.txt"))
tree = parser.Parse(input.ReadToEnd());

For processing the tree I opted for no mysterious art approach, doing it in the user code and it's not a big hassle:

double x = 0, y = 0, angle = 0;

foreach (ParseTreeNode statement in tree.Root.ChildNodes) {
ParseTreeNode node = statement.ChildNodes[0];
int value = (int)node.ChildNodes[1].Token.Value;

switch (node.Term.Name) {
case "forward":
x += value * Math.Cos(angle);
y += value * Math.Sin(angle);
break;

case "rotate":
angle += Math.PI * value / 180.0;
break;
}

Console.WriteLine("Turtle at {0}, {1}", x.ToString("0.#"), y.ToString("0.#"));
}

Neat thing is that NumberLiteral type of literals handles string to number conversion on it's own. In fact Irony.Net has a lot of features for building programming languages, custom literals for number and identifiers, methods for defining operator precedence to name a few.

So why is Irony.Net on go for C#? If you are building a compiler or interpreter, it's good but if you are build parser for domain specific language it's simply not the right tool. You can chop wood with hammer but using an axe would be more practical. First of all it requires 160 kB of run-time library, that's more than ANTLR, doesn't have elegant grammar attributes and is undocumented. Oh my God, it is so undocumented that I have to involve the God to the issue. Author himself claims that source code is enough and is unwilling to write decent documentation (well, the project is still in alpha phase so I can forgive him) and sometimes doesn't give an answer beyond "look in the code of a certain example shipped with Irony". There is a moderate number of examples included with Irony.Net source code but they are either grammars without attributes or proofs of concept (such as fully featured interpreter with a lot of layers between grammar and attributes) that are hard to follow while learning stuff.

Coco/R

Goggling for third solution led me back to Stack Overflow but to a different page this time. Answers on that page presented various new solutions and I've checked the first one (actually the second one because the first is for F#), Coco/R. The link led me to a clean black on white page where I've quickly found my way to the tutorial that hooked me up. At first I was skeptical, zip file with 5 years old Powerpoint presentation but after skipping language processing theory, presentation arrived at very simple example describing whole process, from writing a grammar to running the parser. Few slides further presented grammar attributes and gimmicks such as how to ignore new line characters, make grammar case insensitive and so on. The post is already long, but heck, I'll publish my first class Logo grammar anyway:

COMPILER Logo
double turtleX = 0, turtleY = 0, angle = 0;

IGNORECASE

CHARACTERS
digit = "0123456789".

TOKENS
number = digit {digit}.

IGNORE '\t' + '\r' + '\n'

PRODUCTIONS
Logo = {Statement}.
Statement = Forward | Rotate.

Forward (. double length; .)
= "fd" Parameter<out length>
(. turtleX += Math.Cos(angle) * length;
turtleY += Math.Sin(angle) * length;
Console.WriteLine("Turtle at {0}, {1}", 
turtleX.ToString("0.#"), 
turtleY.ToString("0.#"));
.)
.

Rotate (. double ang; .)
= "rt" Parameter<out ang>
(. angle += Math.PI * ang / 180; .)
.

Parameter<out double n>
= number (. n = Convert.ToDouble(t.val); .)


.
END Logo.

You've already seen something similar with ANTLR grammar, lexical tokens, extenden BNF production, c# header and attributed code. This one has a period character after almost everything. One thing I should point out is that parts of definition have to strictly follow an order of appearance. For instance IGNORE part can't appear before TOKENS or CHARACTERS blocks. Correct order of appearance can be found in the documentation that exists and is informative. Before I start praising it's documentation, let's conclude the usage of Coco/R. This is what user code looks like:

static void Main(string[] args)
{
Scanner scanner = new Scanner("input.txt");
Parser parser = new Parser(scanner);
parser.Parse();
}

As simple as that. Scanner can also accept Stream object instead of file name, for those insisting on abstraction (which is good requirement).

Conclusion

Unlike ANTLR or Irony.Net, Coco/R didn't catch me with nasty surprises, it's simple, it works, requires no run-time files and it is well documented. Though it doesn't have fancy grammar editor or grammar visualisation it's a tool that I would use in my projects.