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A programming language for animated turtle graphics
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Rose - a programming language for temporal turtle graphics INTRODUCTION A Rose program produces an animation drawn by a number of "turtles" moving around on a canvas. Each turtle has the following state: - Position (x and y) - Direction - Pen size - Color index, called "tint" - Random number generator state. Unless specific otherwise, all numeric values in Rose are 16.16 bits fixed-point values. The position and direction are available as global variables x, y and dir. SYNTAX Rose is whitespace-agnostic: line breaks can be inserted or omitted anywhere between tokens. Comments start with # and extend to the end of the line. Just for the fun of it, and because I enjoy using a thesaurus, all keywords in Rose have four letters. A Rose program consists of a number of top-level declarations. Except where noted, these are all optional and can appear in any order. The various kinds of declarations are described in the following: A part declaration includes the declarations from another file at the point of the part declaration. The path of the file to be included is relative to the file into which it is included. - part <filename> Where <filename> is the name of the file to be included, in double quotes. A form declaration has four numbers which specify the width and height in pixels, the number of layers, and the number of colors in each layer, respectively: - form <expression> <expression> <expression> <expression> The tints are distributed over the layers, so if, for instance, there are 4 colors per layer, tints 0-3 are in the first (backmost) layer, tints 4-7 are in the next layer and so on. A program can contain at most one form declaration. If no form declaration is given, the resolution will be 352x280 (full overscan), and there will be 1 layer with 4 colors. A fact declaration defines a global constant: - fact <identifier> = <expression> The expression cannot contain variables, but the defined fact can be used in all expressions in the program, even ones that cannot contain variables. A fact can refer to other facts, but only ones declared earlier in the program. A plan declaration, along with any number of look declarations, define the color script: - plan <event>* - look <identifier> <event>* where <event> is one of: - wait <expression> Wait a number of frames. The expression cannot contain variables. - fade <expression> Fade over a number of frames. The expression cannot contain variables. - <tint>:<color> Set the given tint (integer) to the given color (three-digit hex value). - <identifier> Insert the events from the look with the given name. The first tint in each layer except the first is transparent, showing the layers behind it. Thus, the colors for these tints are ignored. A procedure declaration defines executable code: - proc <name> <param>* <statement>* where <name> and <param> are identifiers, and <statement> is one of: - move <expression> Move forward a number of pixels. - jump <expression> <expression> Jump to a pixel coordinate position. - turn <expression> Turn a number of 256-on-a-circle degrees clockwise. - face <expression> Turn to a number of 256-on-a-circle degrees clockwise from horizontal right. - size <expression> Set pen radius in pixels (rounded to nearest integer-and-a-half). - tint <expression> Set the current tint (rounded down to an integer). - draw Draw a circular dot at the current position. - plot Draw a square dot at the current position. - wait <expression> Wait a number of frames. - fork <procedure> <expression>* Branch off a new turtle with a copy of this turtle's state, running the given procedure with the given arguments. The old turtle continues executing the rest of the current procedure in parallel. - temp <variable> = <expression> Assign a value to a local variable. - wire <variable> = <expression> Assign a value to a global variable whose value is inherited through forks. - seed <expression> Seed the random number generator. - when <expression> <statement>* done Run the block of statements if the expression evaluates to non-zero. - when <expression> <statement>* else <statement>* done Run the first block of statements if the expression evaluates to non-zero, or the second block of statements otherwise. - defy Suppress all warnings for the current source line. An <expression> is one of: - <digit>+[.<digit>+] Constant value. - $<hexdigit>+ Constant value in hexadecimal. The value is used directly as the 32-bit fixed-point representation, i.e. the last four digits are implicitly fractional. - <name> Procedure or value of parameter, temporary variable or global variable. - <expression> op <expression> Binary operation, where op can be (precedence from strongest to weakest): * / multiplication, division (do fixed-point adjustment to match fixed-point multiplication and division), << >> >>> ><< >>< shift left, shift right, unsigned shift right, rotate left, rotate right (shift value is 6 least significant integer part bits of second operand), + - addition, subtraction, == != < <= > >= comparisons, & bitwise and, | bitwise or. - ~ <expression> Negate value. Used instead of - to enable airy, delimiter-sparse syntax. - sine ( <expression> ) Computes the sine of 2pi * argument. - rand Produces a random number between 0 and 1. - <expression> ? <expression> : <expression> If the first expression evaulates to non-zero, evaluate the second expression, otherwise evaluate the third expression. - ( <expression> ) For grouping. Procedures can be assigned to temporaries and passed as arguments to procedures. The procedure part of a fork statement can refer directly to a procedure or to a parameter or local variable containing a procedure. A Rose program must contain at least one procedure. The first procedure in the program is the main procedure, which is the entry point (a single turtle running this procedure is created at time 0). And just to mention it one more time, because this could be a common pitfall: Remember to use ~ and not - for negation, including for writing negative numbers! THE VISUALIZER Run the visualizer with these arguments: rose <filename> [<scale>] [<framerate> [<music>]] where <filename> is the name of a file containing a Rose program, <scale> is a scale factor for the visualizer window (with an 'x' in front, i.e. 'x3' for a scaling factor of 3), <framerate> is the frame rate in frames per second (default 50) and <music> is a 16-bit stereo WAV file containing the music to play to the animation. The total number of frames for the animation will be inferred from the length of the music, or set to 10000 if no music is specified. The visualizer will continuously monitor the file and reload it whenever its modification time changes. Keyboard shortcuts: - SPACE: start/stop animation. - RIGHT/LEFT: Step one frame forward/backward. - PGDOWN/PGUP: Step 50 frames forward/backward. - BACKSPACE: Go back to frame animation was last started. - HOME: Go to first frame. - TAB: Toggle statistics overlay. - ESCAPE: Quit the visualizer. Clicking or holding the left mouse button sets the time proportionally to the mouse X position within the window, up to the total number of frames.