Book Image

Opa Application Development

By : Li Wenbo
Book Image

Opa Application Development

By: Li Wenbo

Overview of this book

Opa is a full-stack Open Source web development framework for JavaScript that lets you write secure and scalable web applications. It generates standard Node.js/MongoDB applications, natively supports HTML5 and CSS and automates many aspects of modern web application programming. It handles all aspects of web programming written in one consistent language and compiled to web standards.Opa Application Development is a practical,hands-on guide that provides you with a number of step-by-step exercises. It covers almost all aspects of developing a web application with Opa, which will help you take advantage of the real power of Opa, as well as building a secure, powerful web application rapidly.Opa Application Development dives into all concepts and components required to build a web application with Opa. The first half of this book shows you all of the basic building blocks that you will need to develop an Opa application, including the syntax of Opa, web development aspects, client and server communication and slicing, plugin, database, and so on. By the end of the book you will have yourself created a complete web application along with a game: Pacman!
Table of Contents (18 chapters)
Opa Application Development
About the Author
About the Reviewers

Drawing an image

To display an image on HTML5 Canvas in Opa, we can use the Canvas.draw_image function that requires an image object and a destination point. Since the draw_image method requires an image object, we must first create an image and wait for it to load before we can draw it on the canvas. In our game, we will preload all images and sounds at the beginning of the game as you will see later. The Canvas.draw_image function is declared as follows:

void draw_image(Canvas.context ctx, Canvas.image img, int x, int y)

The first argument that we pass to draw_image is the canvas context that we retrieved. The second argument is the image object of type Canvas.image. The Canvas.image type is declared as:

type Canvas.image = {Image.image   image} 
                 or {Canvas.canvas canvas} 
                 or {   video}

Image.image is an external type. It is identical to the image type that we created in JavaScript with the new Image() code.

We preload the images when the game starts...