Graphic Twist

Shiva toolkit becoming more comfortable

Just today, Shiva (cross-platform vector GLUT-based GUI toolkit) has got some new features, that make it more comfortable to use. Some of them, in fact, break the boundaries of standard C++ coding, however, not in a way to dispose the standards, but instead to provide a more comfortable alternative. I always try to retain “backward-compatibility” with well-accepted standards, but I don’t hesitate to import some new concepts, that I find to make the coding easier. So, let’s go straight to the basic features it supports.

Feature #1: The very concept of Shiva’s GUI drawing and building

There’s no “Widget->onDraw” events to be responded to. Each Widget is just a sub-class that inherits all the properties of it’s two base classes: Drawable and Drawing. Drawable is the very base class, which is supposed to represent everything that can be drawn. This includes typical geometry objects like Point, Curve, Rectangle, Ellipse etc. They are drawn with their Draw() member function. Drawing is an object that holds many Drawables and draws them upon calling it’s Draw() function. Obviously Drawing is also a Drawable. Now, Widget is nothing else then a Drawing with respond-to-user functionality. It’s a sub-class of Drawable and Drawing. This means that it can include pure graphic objects (Drawables), but can also hold other Widgets and so the standard parent-child widget hierarchy is implemented.

When one want’s to define the visual appearance of a widget, the basic Drawables are to be added to a Widget by it’s add() member function. Since a Widget is a Drawing, it contains sort of a “drawing-stack” on which all it’s children are placed. When a Widget needs redraw, they are automatically drawn in the order of the stack, from the first added to the last added. Of course the order can be easily rearranged through member functions, that I’m going to add during the development of this toolkit.

Feature #2: Smart-pointers

If you look at the code at the end of this article, you’ll see there’s no *s and &s for pointers. Just the bare variable names and the standard arrows between members. It’s because they are all pointers, just like in C# or Java. Variables are automatically deleted from memory when not referenced by any pointer, just like in C# or Java. Objects are copied with ->clone() functions and compared by value with ->equals() functions, just like in C# or Java. We don’t have to bother with annoying pointers and their deletion, because it all happens automatically. In short words: Shiva is now a C++ toolkit, that retains the speed of C++ because of it’s native OS binary, but also offers some much appreciated comfort that higher-level programming languages usually have.

But what’s best: if one wants, normal pointers can still be used for low-level operations, without any limitations. Even the Shiva classes, can be used without smart pointers if one so prefers. This is possible, because of how the memory management is designed. Instead of providing a general “garbage collector” that affects all the allocated memory, reference to objects is counted with a pair of two key classes: SmartObj and SmartPtr. SmartObj is an object, pointed to by a member of SmartPtr and SmartPtr overloads the -> operator in order to provide immediate access to the members of the object it points to. When a SmartPtr is pointed on a SmartObj it raises the reference count of the latter and lowers the reference count of the object it previously pointed to. This means that using SmartObj as base-class of another class, gives the latter the ability to be memory-managed, but doesn’t yet force this functionality. The object is really managed only when pointed to by smart pointers.

This design gives the space for the managed and unmanaged memory to easily coexist in an application. When memory management is not welcome, SmartObj-ects can be pointed to by normal pointers and everything works just as fine.

Feature #3: Namespaces and lightweight feel

Well, this is actually a matter of personal taste, but I believe many would agree that a simple-looking code, split into smaller portions is more pleasant to write and look at. That’s why I stick to this rule when writing Shiva’s code. First, I separated it into namespaces, which is for now most noticeable in the base OpenCC classes and functions. This way a programmer can write functions with a namespace prefix, but can also get rid of it by invoking a “using namespace xxx” directive. For example: string class can be used as OCC::Data::String, just Data::String or even just String. The same holds for OCC::Memory::SmartPtr etc.).

Second, I try to use as simple sintax as possible. All member variable and function names are written with lower-case first letter (like in Java) in order to make code more plain-looking. This way the functions also more homogeneous with the member variables (e.g. rect->x, rect->y, rect->w, rect->h, rect->right(), rect->bottom(), rect->center(), …). The only ones that use capital letters are namespaces, class names, and static member functions (Shiva, Rectangle, Application::Start(), …).

Here’s a piece of Shiva code that draws a rectangle and 10 filled circles around:

#include \"OpenCC/OpenCC.h\"
using namespace OCC;
using namespace OCC::Data;
using namespace OCC::Memory;
	
#include \"Shiva/Shiva.h\"
using namespace Shiva;
	
int main(int argc, char *argv[])
{
	Widget main = Application::CreateMainWindow(\"test\", 400, 300, 32, WindowMode::WINDOWED);
	
	//Draw central rectangle
	Rectangle rcmain = new CRectangle(0,0,400,300);
	Rectangle rc = new CRectangle(rcmain->center(), 100,100);
	rc->fill->color->set(0,200,0);
	main->add(rc);
	
	//Create a Pen
	Pen ptpen = new CPen();
	ptpen->color->set(50,100,200);
	ptpen->width = 32.0f;
	
	//Draw dots around rectangle
	for (int i=0; i<10; i++)
	{
		float angle = i * (2*PI)/10.0f;
		Point pt = new CPoint(cos(angle)*120, sin(angle)*120);
		pt->offset(rcmain->center()->x, rcmain->center()->y);
		pt->pen = ptpen;
		main->add(pt);
	}
	
	Application::Start();
}

And this is the result. Though the code uses only Point, Rectangle and Pen classes, the pen width makes points look like filled circles. Notice the antialiasing on the edges

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