diff --git a/legacy/evas/src/lib/Evas.h b/legacy/evas/src/lib/Evas.h index 162c306435..498c9bfac4 100644 --- a/legacy/evas/src/lib/Evas.h +++ b/legacy/evas/src/lib/Evas.h @@ -45,25 +45,26 @@ @section intro What is Evas? -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 much and more. +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. +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. +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. +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 intro_not_evas What Evas is not? @@ -73,7 +74,7 @@ for a toolkit based on Evas, Edje, Ecore and other Enlightenment technologies. It is not dependent or aware of main loops, input or output -systems. Input should be polled from various sources and feed them to +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 @@ -84,14 +85,15 @@ Ecore_Evas (http://docs.enlightenment.org/auto/ecore/). @section 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 canvases state on the display. +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: +Immediate mode display systems retain very little, or no state. A +program will execute a series of commands, as in the pseudo code: @verbatim draw line from position (0, 0) to position (100, 200); @@ -103,27 +105,29 @@ scale bitmap_handle to size 100 x 100; draw image bitmap_handle at position (10, 30); @endverbatim -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 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. +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 @@ -149,7 +153,7 @@ Redraw from position (0, 0) to position (50, 50): 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 tends to be very costly, as +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 @@ -157,10 +161,10 @@ 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. +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: @@ -182,32 +186,34 @@ show bitmap_handle; render scene; @endverbatim -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 they -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 he canvas and its contents to reflect the current state, -and then it can go off and do the actual drawing of the canvas. +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 display on different display -systems with very little work. +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. +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 compiling How to compile using Evas ? -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 @p pkg-config script outputs. For example: +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 +example: Compiling C or C++ files into object files: @@ -221,18 +227,19 @@ Linking object files into a binary executable: gcc -o my_application main.o `pkg-config --libs evas` @endverbatim -You simply have to make sure that pkg-config is in your shell's PATH (see -the manual page for your appropriate shell) and evas.pc in /usr/lib/pkgconfig -or its path is in the PKG_CONFIG_PATH environment variable. It's that simple -to link and use Evas once you have written your code to use it. +You simply have to make sure that @c pkg-config is in your shell's @c +PATH (see the manual page for your appropriate shell) and @c evas.pc +in @c /usr/lib/pkgconfig or its path in the @c PKG_CONFIG_PATH +environment variable. It's that simple to link and use Evas once you +have written your code to use it. -Since the program is linked to Evas, it is now able to use any advertised -API calls to display graphics in a canvas managed by Evas, as well as use -the API calls provided to manage data as well. +Since the program is linked to Evas, it is now able to use any +advertised API calls to display graphics in a canvas managed by it, as +well as use the API calls provided to manage data. You should make sure you add any extra compile and link flags to your -compile commands that your application may need as well. The above example -is only guaranteed to make Evas add it's own requirements. +compile commands that your application may need as well. The above +example is only guaranteed to make Evas add it's own requirements. @section install How is it installed? @@ -259,17 +266,22 @@ you tons of work compared to using just Evas directly. Recommended reading: -@li @ref Evas_Object_Group -@li @ref Evas_Object_Rectangle -@li @ref Evas_Object_Image -@li @ref Evas_Object_Text -@li @ref Evas_Smart_Object_Group and @ref Evas_Smart_Group to define - an object that provides custom functions to handle clipping, - hiding, moving, resizing, setting the color and more. These could +@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_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_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). These smart objects can implement what - ends to be a widget, providing some intelligence (thus the name), - like a button or check box. + 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 intro_example Introductory Example