Canvas

Package draw2d is a pure go 2D vector graphics library with support for multiple output devices such as images (draw2d), pdf documents (draw2dpdf) and opengl (draw2dgl), which can also be used on the google app engine. It can be used as a pure go Cairo alternative. draw2d is released under the BSD license. Operations in draw2d include stroking and filling polygons, arcs, Bézier curves, drawing images and text rendering with truetype fonts. All drawing operations can be transformed by affine transformations (scale, rotation, translation). Package draw2d follows the conventions of http://www.w3.org/TR/2dcontext for coordinate system, angles, etc... To install or update the package draw2d on your system, run: Package draw2d itself provides a graphic context that can draw vector graphics and text on an image canvas. The following Go code generates a simple drawing and saves it to an image file: There are more examples here: https://github.com/llgcode/draw2d/tree/master/samples Drawing on pdf documents is provided by the draw2dpdf package. Drawing on opengl is provided by the draw2dgl package. See subdirectories at the bottom of this page. The samples are run as tests from the root package folder `draw2d` by: Or if you want to run with test coverage: This will generate output by the different backends in the output folder. Laurent Le Goff wrote this library, inspired by Postscript and HTML5 canvas. He implemented the image and opengl backend with the freetype-go package. Also he created a pure go Postscript interpreter, which can read postscript images and draw to a draw2d graphic context (https://github.com/llgcode/ps). Stani Michiels implemented the pdf backend with the gofpdf package. - https://github.com/llgcode/ps: Postscript interpreter written in Go - https://github.com/gonum/plot: drawing plots in Go - https://github.com/muesli/smartcrop: content aware image cropping - https://github.com/peterhellberg/karta: drawing Voronoi diagrams - https://github.com/vdobler/chart: basic charts in Go

Package giocanvas is a 2D canvas API built on gio

Package canvas communicates with an HTML canvas in a web browser via WebSocket. The server program sends draw commands to the canvas and the canvas sends mouse and keyboard events to the server.

Package dom provides GopherJS bindings for the JavaScript DOM APIs. This package is an in progress effort of providing idiomatic Go bindings for the DOM, wrapping the JavaScript DOM APIs. The API is neither complete nor frozen yet, but a great amount of the DOM is already useable. While the package tries to be idiomatic Go, it also tries to stick closely to the JavaScript APIs, so that one does not need to learn a new set of APIs if one is already familiar with it. One decision that hasn't been made yet is what parts exactly should be part of this package. It is, for example, possible that the canvas APIs will live in a separate package. On the other hand, types such as StorageEvent (the event that gets fired when the HTML5 storage area changes) will be part of this package, simply due to how the DOM is structured – even if the actual storage APIs might live in a separate package. This might require special care to avoid circular dependencies. The documentation for some of the identifiers is based on the MDN Web Docs by Mozilla Contributors (https://developer.mozilla.org/en-US/docs/Web/API), licensed under CC-BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5/). The usual entry point of using the dom package is by using the GetWindow() function which will return a Window, from which you can get things such as the current Document. The DOM has a big amount of different element and event types, but they all follow three interfaces. All functions that work on or return generic elements/events will return one of the three interfaces Element, HTMLElement or Event. In these interface values there will be concrete implementations, such as HTMLParagraphElement or FocusEvent. It's also not unusual that values of type Element also implement HTMLElement. In all cases, type assertions can be used. Example: Several functions in the JavaScript DOM return "live" collections of elements, that is collections that will be automatically updated when elements get removed or added to the DOM. Our bindings, however, return static slices of elements that, once created, will not automatically reflect updates to the DOM. This is primarily done so that slices can actually be used, as opposed to a form of iterator, but also because we think that magically changing data isn't Go's nature and that snapshots of state are a lot easier to reason about. This does not, however, mean that all objects are snapshots. Elements, events and generally objects that aren't slices or maps are simple wrappers around JavaScript objects, and as such attributes as well as method calls will always return the most current data. To reflect this behaviour, these bindings use pointers to make the semantics clear. Consider the following example: The above example will print `true`. Some objects in the JS API have two versions of attributes, one that returns a string and one that returns a DOMTokenList to ease manipulation of string-delimited lists. Some other objects only provide DOMTokenList, sometimes DOMSettableTokenList. To simplify these bindings, only the DOMTokenList variant will be made available, by the type TokenList. In cases where the string attribute was the only way to completely replace the value, our TokenList will provide Set([]string) and SetString(string) methods, which will be able to accomplish the same. Additionally, our TokenList will provide methods to convert it to strings and slices. This package has a relatively stable API. However, there will be backwards incompatible changes from time to time. This is because the package isn't complete yet, as well as because the DOM is a moving target, and APIs do change sometimes. While an attempt is made to reduce changing function signatures to a minimum, it can't always be guaranteed. Sometimes mistakes in the bindings are found that require changing arguments or return values. Interfaces defined in this package may also change on a semi-regular basis, as new methods are added to them. This happens because the bindings aren't complete and can never really be, as new features are added to the DOM.

Package dom provides Go bindings for the JavaScript DOM APIs. This package is an in progress effort of providing idiomatic Go bindings for the DOM, wrapping the JavaScript DOM APIs. The API is neither complete nor frozen yet, but a great amount of the DOM is already usable. While the package tries to be idiomatic Go, it also tries to stick closely to the JavaScript APIs, so that one does not need to learn a new set of APIs if one is already familiar with it. One decision that hasn't been made yet is what parts exactly should be part of this package. It is, for example, possible that the canvas APIs will live in a separate package. On the other hand, types such as StorageEvent (the event that gets fired when the HTML5 storage area changes) will be part of this package, simply due to how the DOM is structured – even if the actual storage APIs might live in a separate package. This might require special care to avoid circular dependencies. The documentation for some of the identifiers is based on the MDN Web Docs by Mozilla Contributors (https://developer.mozilla.org/en-US/docs/Web/API), licensed under CC-BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5/). The usual entry point of using the dom package is by using the GetWindow() function which will return a Window, from which you can get things such as the current Document. The DOM has a big amount of different element and event types, but they all follow three interfaces. All functions that work on or return generic elements/events will return one of the three interfaces Element, HTMLElement or Event. In these interface values there will be concrete implementations, such as HTMLParagraphElement or FocusEvent. It's also not unusual that values of type Element also implement HTMLElement. In all cases, type assertions can be used. Example: Several functions in the JavaScript DOM return "live" collections of elements, that is collections that will be automatically updated when elements get removed or added to the DOM. Our bindings, however, return static slices of elements that, once created, will not automatically reflect updates to the DOM. This is primarily done so that slices can actually be used, as opposed to a form of iterator, but also because we think that magically changing data isn't Go's nature and that snapshots of state are a lot easier to reason about. This does not, however, mean that all objects are snapshots. Elements, events and generally objects that aren't slices or maps are simple wrappers around JavaScript objects, and as such attributes as well as method calls will always return the most current data. To reflect this behavior, these bindings use pointers to make the semantics clear. Consider the following example: The above example will print `true`. Some objects in the JS API have two versions of attributes, one that returns a string and one that returns a DOMTokenList to ease manipulation of string-delimited lists. Some other objects only provide DOMTokenList, sometimes DOMSettableTokenList. To simplify these bindings, only the DOMTokenList variant will be made available, by the type TokenList. In cases where the string attribute was the only way to completely replace the value, our TokenList will provide Set([]string) and SetString(string) methods, which will be able to accomplish the same. Additionally, our TokenList will provide methods to convert it to strings and slices. This package has a relatively stable API. However, there will be backwards incompatible changes from time to time. This is because the package isn't complete yet, as well as because the DOM is a moving target, and APIs do change sometimes. While an attempt is made to reduce changing function signatures to a minimum, it can't always be guaranteed. Sometimes mistakes in the bindings are found that require changing arguments or return values. Interfaces defined in this package may also change on a semi-regular basis, as new methods are added to them. This happens because the bindings aren't complete and can never really be, as new features are added to the DOM.

Package glfw experimentally provides a glfw-like API with desktop (via glfw) and browser (via HTML5 canvas) backends. It is used for creating a GL context and receiving events. Note: This package is currently in development. The API is incomplete and may change.

Package openvg is a wrapper to a C library of high-level 2D graphics operations built on OpenVG 1.1 The typical "hello world" program looks like this: The Init function provides the necessary graphics subsystem initialization and the dimensions of the whole canvas. The Init() call must be paired with a corresponding Finish() call, which performs an orderly shutdown. Typically a "drawing" begins with the Start() call, and ends with End(). A program can have an arbitrary set of Start()/End() pairs. The coordinate system uses float64 coordinates, with the origin at the lower left, with x increasing to the right, and y increasing upwards. Currently, the library provides no mouse or keyboard events, other than those provided by the base operating system. It is typical to pause for user input between drawings by reading standard input. The library's functionally includes shapes, attributes, transformations, text, images, and convenince functions. Shape functions include Polygon, Polyline, Cbezier, Qbezier, Rect, Roundrect, Line, Elipse, Circle, and Arc. Transformation functions are: Translate, Rotate, Shear, and Scale. For displaying and measuring text: Text, TextMid, TextEnd, and TextWidth. The attribute functions are StrokeColor, StrokeRGB, StrokeWidth, and FillRGB, FillColor, FillLinearGradient, and FillRadialGradient. Colors are specfied with RGB triples (0-255) with alpha values (0.0-1.0), or named colors as specified by the SVG standard. Convenience functions are used to set the Background color, start the drawing with a background color, and save the raster to a file. The input terminal may be set/restored to/from raw and cooked mode. Package openvg is a high-level 2D vector graphics library built on OpenVG