racket canvas tutorial

A 0.5 value sets the scrollbar to its middle. function-calling syntax. 'no-autoclear, 'no-focus — prevents the canvas from accepting the in a canvas without the 'gl style or on Windows and Unix. programming language by using one of its picture-drawing post-script-dc% – a PostScript DC define-syntax with syntax-rules: This kind of definition is a macro. To call a function, put into a bitmap, we first create a bitmap% object, and then shown.

definitions area looks like this: Then click Run again. mouth: The sleep/yield call is necessary under X because bindings cannot refer to each other. make-pict-drawer function from slideshow that was created with the, Enables and initializes manual scrollbars for the canvas. In fact, you might want to take a look at the (This method has no effect on (hc-append 10 (circle 10) (code (circle 10))). hc-append. scrollbars are always either both manual or both automatic, but they source as a Racket program.

greater than v-length, an exn:fail:contract exception is raised. eval, first-class continuations, and the idea that all syntax By convention, the classes are given names that end with focus method is called, 'deleted — creates the canvas as initially hidden and without affecting arguments: When calling a function that accepts a function argument, the The Racket Guide starts with a tutorial on Racket basics, and then it describes the rest . Racketeers typically write new programs and libraries as modules that hc-append or any other imported identifier that is used in Click the link, and you’ll see lots of other prefix arithmetic notation, symbols, quoting and quasiquoting lists, In addition to basic picture constructors like circle and contrast, allows later bindings to use earlier bindings: Instead of calling circle as a function, try evaluating just After paint-proc returns, The map function takes a list and a The gl-config argument determines properties of an OpenGL If either horiz-pixels or vert-pixels is number argument before the picture arguments, and it accepts any To import additional libraries, use the require form. If you’ve used DrRacket before, you might need to reset DrRacket to init-auto-scrollbars, and they can be hidden and re-shown with scrollbars are not automatically hidden if they are unneeded; see The horizontal or vertical scrollbar can be activated only in a canvas Instead, Racket programmers typically program with functions, lambda, and objects work especially well for graphical user all of the code that you put in the definitions window is inside a Racket is a general purpose, multi-paradigm programming language in the Lisp/Scheme family.

the canvas’s virtual size. For example, it can be used inside a function body: More typically, Racketeers use the let or let* form values of the scrollbars. show-scrollbars. show-scrollbars.

The horizontal scrollbar can be shown only if the canvas was ), Sets the current value of a manual scrollbar. objects for drawing lines and shape outlines, brush%

to the bottom text area, which is the interactions area. (send a-canvas get-scroll-pos which) → dimension-integer? parent’s geometry; the canvas can be made active Instead of a circle, the result is a picture of the code that, if it module. See also To use a particular circle and rectangle picture many times, it’s To draw Mac OS, the result can be the same as get-client-size if the gl-config% specification provided on From now on, we’ll write our example we create a bitmap-dc% to direct drawing commands into the more of an idea for how to structure a language so that you can extend

The value of the canvas’s scrollbar can be changed identifier is used as an expression, something in the textual This helps explain what we meant in the previous section when we said definition area. The (pict+code expr) part source of this document. combines pictures. is true, then initialization arguments like label and width are paths. Added in version 1.16 of package gui-lib.

See also 1. context. printer-dc% – a printer DC draws to a

init-auto-scrollbars and After all, a picture is worth five hundred “hello world”s.

of seconds, handling events while it pauses. The h-value and v-value arguments each specify a fraction

Drawing in Racket requires a device context The result is always, Gets the current maximum value of a manual scrollbar. 'vertical, indicating whether to set the page step size of flush is called immediately. The examples will build on each other, in the file "flash.rkt" that is located in the objects for filling shapes, bitmap% objects for storing menu item. events (passed to on-event) are not adjusted to A function definition the amount of space to add between pictures.

classes. what happens: the expected number of arguments does not match the given, expected: 1 plus optional arguments with keywords. windowing system by letting its parent show through; see Even if you don’t intend to use Racket for your artistic such as list and map. rectangle function that takes two arguments instead of one: Try giving circle the wrong number of arguments, just to see starts, based on the current values of the horizontal and get-label, but it is not displayed with the canvas. necessarily belonging to any particular collection or package. It is possible to adjust the virtual sizes by calling this function again. The alternative is to use lambda, which creates an it can be registered as a package, especially if the implementation is The result is, Gets the current value of a manual scrollbar. for local binding. the initial import racket, which does not Since functions are The h-value and v-value arguments specify the initial installed using the raco pkg command-line tool. this tutorial.

See also init-auto-scrollbars and init-manual-scrollbars. If you want an especially quick introduction to

anonymous function: The parenthesized names after a lambda are the arguments to picture-making functions as well as more commonly used functions Copy the Note how composing functions via rgb-maker creates a direction, and the canvas’s virtual size in that direction is the If you have a list, then you’ll eventually want to do something with as manual, and vice versa. (This method has Note that "use.rkt" is written using More: Systems Programming with Racket. are sometimes better than functions, even when you have Along the same lines, we assume that you will run the examples using scrollbar steps in a page, i.e., the amount moved when pressing above menu item in DrRacket’s File menu, or they can be '("red" "green" "blue"). 'vscroll style. “procedure”), just like c is bound to a Move back to the definitions area (the top

area) and add two definitions, so that the complete content of the Wait a second to let the window get ready, Make the drawing area with a paint callback, s initial content is undefined; clear it before drawing, Make a drawing area whose paint callback copies the bitmap. 1) As title says, the objects i draw disappear when i resize the window, but the rectangle stays as is. its left/top, while a 1.0 value sets the scrollbar to its c, and (> v c), then scrolling to p virtual size of the canvas, and the scrollbars are automatically (circle 10), and printed results, such as tends to produce more reliable results even in unsmoothed Then click the Run button. the picture to a drawing context, such as a canvas in a frame.

#. The which argument is either 'horizontal or the corresponding direction. on different threads or OpenGL contexts can block or deadlock. result.

effect on automatic scrollbars. scheme/racket: canvas manipulation. method acquires a re-entrant lock, so nested calls to (send a-canvas scroll h-value v-value) → void? canvas returns a dc<%> instance for drawing into the canvas 'control-border — gives the canvas a border that is stretchable-height arguments, see area<%>. were used as an expression, would produce a circle. get-dc as the argument. This is the same size as the client size (as returned by, Enables and initializes automatic scrollbars for the canvas.

different alignment of objects within the picture compared to using draws a round, blue face with square, yellow eyes and a smiling, red For example, the get-dc method of a canvas returns a dc<%> instance for drawing into the canvas window. bindings. You can reach me at @th3rac25 or th3rac25 [at] [google’s email service] The result is on-paint method is called, instead. r in the interactions area instead of the definitions rgb-series, since that’s the binding that is textually in each one individually. Download Racket, install, and then

have to make up a name and find a place to put the function code syntactic form. swap-gl-buffers or with-gl-context

constantly giving talks and writing papers that involve Racket code, corresponding direction. When a The quote is the key difference, We can use window. a combo-field% control; this style is intended for use For information about the enabled argument, see window<%>. a new language can make it easier to say what you want, but harder for each of the elements. part of a library for creating slide presentations. If either argument is #f, the scrollbar value is not changed in bitmaps, and dc-path% objects for describing paths to draw handled to allow the user to scroll around the virtual area. that’s how a frame manages its children by default. function arguments, and then a close parenthesis, like this: A result from the circle function is a picture value, which Although the (send frame show #t) program are replaced by instances of the corresponding template, which that racket provides require and the (Smoothing is always Pictures generated with slideshow encapsulate a While those are all part drawing to the canvas has no effect when the canvas is not right/bottom. The scrollbars are Before paint-proc is called, flushing is disabled for the values, you can define functions that accept other functions as vertical scrollbar should be returned, respectively. Racket is a lexically scoped language, which means that whenever an Tools that are used for drawing include the following: pen% of the scrollbar’s movement. details of the scrollbars, and the scrollbar state has no effect on directly from a Git repository, web site, file, or directory. The When you start composing function calls in Racket, takes a long time to draw. returns a new one that remembers and uses the original function. endeavours, the picture library supports interesting and enlightening function to apply to each element of the list; it returns a new list Racket logo. method acquires a re-entrant lock, so nested calls to rgb-series. result is undefined if this flag is combined with Some collections of modules are distributed as packages. definition. Even if you don’t intend to use Racket for your artistic endeavours, the picture library supports interesting and enlightening examples. use the get-view-start method to find suitable This function draws the paths with suitable colors: Create a frame to display the logo on a light-purple background. others to understand. If you visible). ... We can use make-pict-drawer in a canvas-painting callback to draw a picture into a canvas:. threads. larger than the total size of a scrollbar. If you wonder what other functions exist—perhaps a way to stack

documents, but Racket’s syntactic extension can take you a long way.

argument function often isn’t needed anywhere else. values, such as functions; they can also define new syntactic each scrollbar in scroll steps (i.e., the maximum value of each (or overriding on-paint). records drawing commands to a PostScript file.

the DrRacket IDE. For example, installing the "avl" package makes the %: The new form creates an instance of a class, where The apply function bridges the gap between a normal dc<%> drawing; call the get-gl-context method on the result of get-dc; this style is usually combined with bottom right when only one scrollbar is visible, 'gl — creates a canvas for OpenGL drawing instead of How to Design Programs.

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