Mechapoint: dissection of a presentation program
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Chapter 3. How Mechapoint uses Evas

Using Evas in Mechapoint was a fairly obvious decision - it gives me a solid graphical functionality to build the application, instead of making me worry about having to load images, or use Freetype to render anti-aliased TrueType text, or writing code to perform potentially millions of transparency calculations a second. However, Evas doesn't give all the needed functionality - there was still some work for me to do. This is an overview of some of the functionality that I've added on top of Evas for Mechapoint.

3.1. C++ Wrapper Classes

While a lot of people cringe at the thought of C++, and while I'll admit that it does have it's problems, on the whole I personally find it a much nicer language to work with than pure C. Regardless of whether you're working in an OO manner or not, C++ has a bunch of features that come in very handy such as default function arguments, function overloading, and (gasp!) high-level string and container classes. How many C libraries or other projects include their own linked list implementation? The answer is plenty, and Evas is one such project.

Anyway, ranting aside, C++ seemed like the best language for Mechapoint, and while Evas's C API is nice and clean, I'm not a fan of verbose C APIs, so I decided to implement a simple C++ wrapper. This makes the syntax a little bit cleaner, as you can see in the examples below.

Example 3-1. Snippet of code using Evas C API


void setup(void)
{
    Evas_Object bg;
    Evas_Object text;

    bg = evas_add_rectangle(evas);
    evas_move(evas, bg, 0, 0);
    evas_resize(evas, bg, 400, 400);
    evas_set_color(evas, bg, 255, 255, 255, 255);
    evas_show(evas, bg);

    text = evas_add_text(evas, "Arial", 20, "This is foo!");
    evas_move(evas, text, 50, 50);
    evas_set_color(evas, text, 255, 0, 0, 255);
	  evas_show(evas, text);
}

Example 3-2. Snippet of code using C++ wrapper


void setup(void)
{
    EvasObject* bg;
    EvasObject* text;

    bg = new EvasRectangle(evas, 0, 0, 400, 400);
    bg->set_color(255, 255, 255, 255);
    bg->show();

    text = new EvasText(evas, "Arial", 20, "This is foo!");
    text->move(50, 50);
    text->set_color(255, 0, 0, 255);
	  text->show();
}

As you can see, the changes aren't drastic, but the C++ wrapper does make a slight reduction to the amount of code used. However, for me at least, it makes things much clearer, because the C++ object syntax shows quite clearly which object each of the operations is being applied to.

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