Rendering +to an RWindow Tutorial

Procedure

You must get and initialize +the EGLDisplay prior to calling most other EGL or client +API functions. You only need to do this once.
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY); +eglInitialize(display, NULL, NULL); +
EGL has the concept +of current rendering API. To make one of the EGL client APIs the current +rendering API for the thread, call eglBindAPI() passing EGL_OPENVG_API or EGL_OPENGLES_API as +required. For example:
// Set OpenGL ES as the current rendering API for the thread +eglBindAPI(EGL_OPENGLES_API); +
Use the eglChooseConfig() method to get the EGLConfig that +matches a list of attributes. In order to render to an RWindow, +these must include the EGL_WINDOW_BIT.
// List of attributes to pass to eglChooseConfig. +const EGLint KColorRGB565AttribList[] = + { + EGL_RED_SIZE, 5, + EGL_GREEN_SIZE, 6, + EGL_BLUE_SIZE, 5, + EGL_SURFACE_TYPE, EGL_WINDOW_BIT, + EGL_RENDERABLE_TYPE, EGL_OPENGL_ES_BIT, + EGL_NONE + }; + +EGLint numConfigs; +EGLConfig chosenConfig = 0; + +// Get the config to use. +eglChooseConfig(display, KColorRGB565AttribList, &chosenConfig, 1, &numConfigs); + +if (numConfigs == 0) + { + RDebug::Printf("No matching configs found"); + User::Leave(KErrNotSupported); + }
Note: By default the EGL_SURFACE_TYPE has +the EGL_SWAP_BEHAVIOR_PRESERVED_BIT set for window surfaces +in order to support the preserve buffer option. You can set this explicitly +like this:
EGL_SURFACE_TYPE, EGL_WINDOW_BIT|EGL_SWAP_BEHAVIOR_PRESERVED_BIT,
To create an on-screen +rendering surface, you first need to create a Symbian Window Server window +(RWindow). This window is then passed as the third argument +to eglCreateWindowSurface() along with an EGLConfig that +has the EGL_WINDOW_BIT set.
// Create a window surface to draw to. +winSurface = eglCreateWindowSurface(display, chosenConfig, &iWindow, NULL);
Set the surface attribute EGL_SWAP_BEHAVIOR +to EGL_BUFFER_PRESERVED. This step is only required if you want to +enable the preserve buffer option.
EGLBoolean queryResult = eglSurfaceAttrib(display, winSurface, EGL_SWAP_BEHAVIOR, EGL_BUFFER_PRESERVED);
To create a rendering +context for the current rendering API, call the eglCreateContext() with +the share_context parameter set to EGL_NO_CONTEXT. +If this method succeeds, it initializes the context to the initial state defined +for the current rendering API, and returns a handle to it.
// Create a context to store the current rendering API settings. +contextGL = eglCreateContext(display, chosenConfig, EGL_NO_CONTEXT, NULL);
In order to allow the +context to render to a given surface, you need to call eglMakeCurrent(). +After doing this you can call EGL client functions, which need a current surface +and context.
// Make the context current on the surface and the display +eglMakeCurrent(display, winSurface, winSurface, contextGL); +
You are now ready to +perform your OpenGL ES drawing commands.

The main thing to understand +is that the EGL window surface is double-buffered. This means that the drawing +commands are drawn into a back buffer and you need to call eglSwapBuffers() in +order to make the drawing appear on the screen in the window. This mechanism +has the advantage that it stops flicker.
eglSwapBuffers(display, winSurface);
Because you enabled the preserve buffer option in step 5, the eglSwapBuffers() promotes +the back buffer to the front for display as usual, and also copies the content +to the new back buffer. This means the client application can provide incremental +drawing commands instead of creating the entire new scene.
To release the current +context and surface without assigning a new one, set the context parameter +to EGL_NO_CONTEXT and set the draw and read surfaces to EGL_NO_SURFACE. +This flushes the current context for the current rendering API and marks it +as no longer current. The current rendering API does not have a current context +after eglMakeCurrent() returns.
eglMakeCurrent(display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
You destroy the rendering +context by calling eglDestroyContext(). All resources associated +with the context are marked for deletion as soon as possible. If the context +is current to any thread, resources are not actually released while the context +remains current.
eglDestroyContext(display, contextGL); +
You destroy the EGLSurface by +calling eglDestroySurface(). All resources associated with +the surface are marked for deletion as soon as possible. If the surface is +current to any thread, the resources are not actually released while the surface +remains current.
eglDestroySurface(display, winSurface); +
Perform final cleanup +by first terminating the EGLDisplay using eglTerminate() and +then releasing any resources still held by EGL by calling eglReleaseThread().
eglTerminate(display); +eglReleaseThread();