path: root/src/lib/evas/Evas.h
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   @page evas_main Evas

   @date 2000 (created)

   @section toc Table of Contents

   @li @ref evas_main_intro
   @li @ref evas_main_work
   @li @ref evas_main_compiling
   @li @ref evas_main_next_steps
   @li @ref evas_main_intro_example

   @section evas_main_intro Introduction

   Evas is a clean display canvas API for several target display systems
   that can draw anti-aliased text, smooth super and sub-sampled scaled
   images, alpha-blend objects and much more.

   It abstracts any need to know much about what the characteristics of
   your display system are or what graphics calls are used to draw them
   and how. It deals on an object level where all you do is create and
   manipulate objects in a canvas, set their properties, and the rest is
   done for you.

   Evas optimises the rendering pipeline to minimise effort in redrawing
   changes made to the canvas and so takes this work out of the
   programmers hand, saving a lot of time and energy.

   It's small and lean, designed to work on embedded systems all the way
   to large and powerful multi-cpu workstations. It can be compiled to
   only have the features you need for your target platform if you so
   wish, thus keeping it small and lean. It has several display
   back-ends, letting it display on several display systems, making it
   portable for cross-device and cross-platform development.

   @subsection evas_main_intro_not_evas What Evas is not?

   Evas is not a widget set or widget toolkit, however it is their
   base. See Elementary (
   for a toolkit based on Evas, Edje, @ref Ecore and other Enlightenment

   It is not dependent or aware of main loops, input or output
   systems. Input should be polled from various sources and fed to
   Evas. Similarly, it will not create windows or report windows updates
   to your system, rather just drawing the pixels and reporting to the
   user the areas that were changed. Of course these operations are quite
   common and thus they are ready to use in @ref Ecore, particularly in
   @ref Ecore_Evas_Group.

   @section evas_main_work How does Evas work?

   Evas is a canvas display library. This is markedly different from most
   display and windowing systems as a canvas is structural and is also a
   state engine, whereas most display and windowing systems are immediate
   mode display targets. Evas handles the logic between a structural
   display via its state engine, and controls the target windowing system
   in order to produce rendered results of the current canvas' state on
   the display.

   Immediate mode display systems retain very little, or no state. A
   program will execute a series of commands, as in the pseudo code:

   draw line from position (0, 0) to position (100, 200);

   draw rectangle from position (10, 30) to position (50, 500);

   bitmap_handle = create_bitmap();
   scale bitmap_handle to size 100 x 100;
   draw image bitmap_handle at position (10, 30);

   The series of commands is executed by the windowing system and the
   results are displayed on the screen (normally). Once the commands are
   executed the display system has little or no idea of how to reproduce
   this image again, and so has to be instructed by the application how
   to redraw sections of the screen whenever needed. Each successive
   command will be executed as instructed by the application and either
   emulated by software or sent to the graphics hardware on the device to
   be performed.

   The advantage of such a system is that it is simple, and gives a
   program tight control over how something looks and is drawn. Given the
   increasing complexity of displays and demands by users to have better
   looking interfaces, more and more work is needing to be done at this
   level by the internals of widget sets, custom display widgets and
   other programs. This means more and more logic and display rendering
   code needs to be written time and time again, each time the
   application needs to figure out how to minimise redraws so that
   display is fast and interactive, and keep track of redraw logic. The
   power comes at a high-price, lots of extra code and work.  Programmers
   not very familiar with graphics programming will often make mistakes
   at this level and produce code that is sub optimal. Those familiar
   with this kind of programming will simply get bored by writing the
   same code again and again.

   For example, if in the above scene, the windowing system requires the
   application to redraw the area from 0, 0 to 50, 50 (also referred as
   "expose event"), then the programmer must calculate manually the
   updates and repaint it again:

   Redraw from position (0, 0) to position (50, 50):

   // what was in area (0, 0, 50, 50)?

   // 1. intersection part of line (0, 0) to (100, 200)?
      draw line from position (0, 0) to position (25, 50);

   // 2. intersection part of rectangle (10, 30) to (50, 500)?
      draw rectangle from position (10, 30) to position (50, 50)

   // 3. intersection part of image at (10, 30), size 100 x 100?
      bitmap_subimage = subregion from position (0, 0) to position (40, 20)
      draw image bitmap_subimage at position (10, 30);

   The clever reader might have noticed that, if all elements in the
   above scene are opaque, then the system is doing useless paints: part
   of the line is behind the rectangle, and part of the rectangle is
   behind the image. These useless paints tend to be very costly, as
   pixels tend to be 4 bytes in size, thus an overlapping region of 100 x
   100 pixels is around 40000 useless writes! The developer could write
   code to calculate the overlapping areas and avoid painting then, but
   then it should be mixed with the "expose event" handling mentioned
   above and quickly one realizes the initially simpler method became
   really complex.

   Evas is a structural system in which the programmer creates and
   manages display objects and their properties, and as a result of this
   higher level state management, the canvas is able to redraw the set of
   objects when needed to represent the current state of the canvas.

   For example, the pseudo code:

   line_handle = create_line();
   set line_handle from position (0, 0) to position (100, 200);
   show line_handle;

   rectangle_handle = create_rectangle();
   move rectangle_handle to position (10, 30);
   resize rectangle_handle to size 40 x 470;
   show rectangle_handle;

   bitmap_handle = create_bitmap();
   scale bitmap_handle to size 100 x 100;
   move bitmap_handle to position (10, 30);
   show bitmap_handle;

   render scene;

   This may look longer, but when the display needs to be refreshed or
   updated, the programmer only moves, resizes, shows, hides etc. the
   objects that need to change. The programmer simply thinks at the
   object logic level, and the canvas software does the rest of the work
   for them, figuring out what actually changed in the canvas since it
   was last drawn, how to most efficiently redraw the canvas and its
   contents to reflect the current state, and then it can go off and do
   the actual drawing of the canvas.

   This lets the programmer think in a more natural way when dealing with
   a display, and saves time and effort of working out how to load and
   display images, render given the current display system etc. Since
   Evas also is portable across different display systems, this also
   gives the programmer the ability to have their code ported and
   displayed on different display systems with very little work.

   Evas can be seen as a display system that stands somewhere between a
   widget set and an immediate mode display system. It retains basic
   display logic, but does very little high-level logic such as
   scrollbars, sliders, push buttons etc.

   @section evas_main_compiling How to compile

   Evas is a library your application links to. The procedure for this is
   very simple. You simply have to compile your application with the
   appropriate compiler flags that the @c pkg-config script outputs. For

   Compiling C or C++ files into object files:

   gcc -c -o main.o main.c `pkg-config --cflags evas`

   Linking object files into a binary executable:

   gcc -o my_application main.o `pkg-config --libs evas`

   See @ref pkgconfig

   @section evas_main_next_steps Next Steps

   After you understood what Evas is and installed it in your system
   you should proceed understanding the programming interface for all
   objects, then see the specific for the most used elements. We'd
   recommend you to take a while to learn @ref Ecore, @ref Edje and
   Elementary ( as they
   will likely save you tons of work compared to using just Evas

   Recommended reading:

   @li @ref Evas_Object_Group, where you'll get how to basically
    manipulate generic objects lying on an Evas canvas, handle canvas
    and object events, etc.
   @li @ref Evas_Object_Rectangle, to learn about the most basic object
    type on Evas -- the rectangle.
   @li @ref Evas_Object_Polygon, to learn how to create polygon elements
    on the canvas.
   @li @ref Evas_Line_Group, to learn how to create line elements on the
   @li @ref Evas_Object_Image, to learn about image objects, over which
    Evas can do a plethora of operations.
   @li @ref Evas_Object_Text, to learn how to create textual elements on
    the canvas.
   @li @ref Evas_Object_Textblock, to learn how to create multiline
    textual elements on the canvas.
   @li @ref Evas_Smart_Object_Group and @ref Evas_Smart_Group, to define
    new objects that provide @b custom functions to handle clipping,
    hiding, moving, resizing, color setting and more. These could
    be as simple as a group of objects that move together (see @ref
    Evas_Smart_Object_Clipped) up to implementations of what
    ends to be a widget, providing some intelligence (thus the name)
    to Evas objects -- like a button or check box, for example.

   @section evas_main_intro_example Introductory Example

   @include evas-buffer-simple.c

   More examples can be found at @ref evas_examples.


#ifndef _EVAS_H
#define _EVAS_H

#include <Efl_Config.h>

#include <time.h>

#include <Eina.h>

/* This include has been added to support Eo in Evas */
#include <Eo.h>

#include <Evas_Loader.h>

#ifdef EAPI
# undef EAPI

#ifdef _WIN32
#  ifdef DLL_EXPORT
#   define EAPI __declspec(dllexport)
#  else
#   define EAPI
#  endif /* ! DLL_EXPORT */
# else
#  define EAPI __declspec(dllimport)
# endif /* ! EFL_EVAS_BUILD */
# ifdef __GNUC__
#  if __GNUC__ >= 4
#   define EAPI __attribute__ ((visibility("default")))
#  else
#   define EAPI
#  endif
# else
#  define EAPI
# endif
#endif /* ! _WIN32 */

#ifdef __cplusplus
extern "C" {

#include <Evas_Common.h>
#include <Evas_Legacy.h>
#include <Evas_Eo.h>

#ifdef __cplusplus