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# qwindowsurface_ahigl.cpp Example File
qtopiacore/ahigl/qwindowsurface_ahigl.cpp

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     #include "qwindowsurface_ahigl_p.h"
     #include "qscreenahigl_qws.h"

     #include <qwsdisplay_qws.h>
     #include <QtGui/QPaintDevice>
     #include <QtGui/QWidget>
     #include <QtOpenGL/private/qglpaintdevice_qws_p.h>
     #include <QtOpenGL/private/qgl_p.h>
     #include <GLES/gl.h>

     /*!
       \class QAhiGLWindowSurfacePrivate
       \internal

       \brief The QAhiGLWindowSurfacePrivate class is the private implementation
       class for class QAhiGLWindowSurface.

       This class contains only state variables.
       */
     class QAhiGLWindowSurfacePrivate
     {
     public:
         QAhiGLWindowSurfacePrivate(EGLDisplay eglDisplay,
                                    EGLSurface eglSurface,
                                    EGLContext eglContext);

         QPaintDevice *device;

         int textureWidth;
         int textureHeight;

         GLuint texture;
         GLuint frameBufferObject;
         GLuint depthbuf;

         EGLDisplay display;
         EGLSurface surface;
         EGLContext context;
     };

     /*!
       The construct just sets statwe variables using the ones
       provided.
      */
     QAhiGLWindowSurfacePrivate::QAhiGLWindowSurfacePrivate(EGLDisplay eglDisplay,
                                                            EGLSurface eglSurface,
                                                            EGLContext eglContext)
         : texture(0), frameBufferObject(0), depthbuf(0), display(eglDisplay),
           surface(eglSurface), context(eglContext)
     {
     }

     inline static int nextPowerOfTwo(uint v)
     {
         v--;
         v |= v >> 1;
         v |= v >> 2;
         v |= v >> 4;
         v |= v >> 8;
         v |= v >> 16;
         ++v;
         return v;
     }

     /*!
         \class QAhiGLWindowSurface
         \preliminary
         \internal

         \brief The QAhiGLWindowSurface class provides the drawing area
         for top-level windows using OpenGL for drawing on an ATI handheld
         device.

         In \l {Qtopia Core}, the default behavior for each client is to
         render widgets into an area of memory. The server then displays
         the contents of that memory on the screen. For ATI handheld
         devices using OpenGL, QAhiGLWindowSurface is the window surface
         class that allocates and manages the memory areas in the clients
         and the server.

         When a screen update is required, the server runs through all the
         top-level windows that intersect with the region being updated,
         ensuring that the clients have updated their window surfaces. Then
         the server uses the screen driver to copy the contents of the
         affected window surfaces into its composition and then display the
         composition on the screen.

         \tableofcontents

         \section1 Pure Virtual Functions

         There are two window surface instances for each top-level window.
         One is used by the application when drawing a window, and the
         other is used by the server application to make its copy for
         building a window composition to send to the screen.

         The key() function is implemented to uniquely identify this window
         surface class as "ahigl", and the isValid() function is
         implemented to determine whether the associated window is still
         acceptable for representation by this window surface class.  It
         must either be a window using an \l {QGLWidget} {OpenGL widget},
         or it must be a window whose frame is no bigger than 256 x 256.

         The setGeometry() function is implemented to change the geometry
         of the frame buffer whenever the geometry of the associated
         top-level window changes. The image() function is called by the
         window system when building window compositions to return an image
         of the top-level window.

         The paintDevice() function is implemented to return the appropriate
         paint device.

         \section1 Virtual Functions

         When painting onto the surface, the window system will always call
         the beginPaint() function before any painting operations are
         performed. It ensures that the correct frame buffer will be used
         by the OpenGL library for painting operations. Likewise, the
         endPaint() function is automatically called when the painting is
         done, but it isn't implemented for this example.
     */

     /*!
       This is the client side constructor.
      */
     QAhiGLWindowSurface::QAhiGLWindowSurface(QWidget *widget,
                                              EGLDisplay eglDisplay,
                                              EGLSurface eglSurface,
                                              EGLContext eglContext)
         : QWSGLWindowSurface(widget)
     {
         d_ptr = new QAhiGLWindowSurfacePrivate(eglDisplay, eglSurface, eglContext);
         d_ptr->device = new QWSGLPaintDevice(widget);

         setSurfaceFlags(QWSWindowSurface::Buffered);
     }

     /*!
       This is the server side constructor.
      */
     QAhiGLWindowSurface::QAhiGLWindowSurface(EGLDisplay eglDisplay,
                                              EGLSurface eglSurface,
                                              EGLContext eglContext)
     {
         d_ptr = new QAhiGLWindowSurfacePrivate(eglDisplay, eglSurface, eglContext);
         setSurfaceFlags(QWSWindowSurface::Buffered);
     }

     /*!
       The destructor deletes the OpenGL structures held by the
       private implementation class, and then it deletes the
       private implementation class.
      */
     QAhiGLWindowSurface::~QAhiGLWindowSurface()
     {
         if (d_ptr->texture)
             glDeleteTextures(1, &d_ptr->texture);
         if (d_ptr->depthbuf)
             glDeleteRenderbuffersOES(1, &d_ptr->depthbuf);
         if (d_ptr->frameBufferObject)
             glDeleteFramebuffersOES(1, &d_ptr->frameBufferObject);

         delete d_ptr;
     }

     /*!
       This function changes the geometry of the frame buffer
       to the geometry in \a rect. It is called whenever the
       geometry of the associated top-level window changes. It
       also rebuilds the window surface's texture and binds
       the OpenGL identifier to the texture for use by the
       OpenGL library.
      */
     void QAhiGLWindowSurface::setGeometry(const QRect &rect)
     {
         QSize size = rect.size();

         const QWidget *w = window();
         if (w && !w->mask().isEmpty()) {
             const QRegion region = w->mask()
                                    & rect.translated(-w->geometry().topLeft());
             size = region.boundingRect().size();
         }

         if (geometry().size() != size) {

             // Driver specific limitations:
             //   FBO maximimum size of 256x256
             //   Depth buffer required

             d_ptr->textureWidth = qMin(256, nextPowerOfTwo(size.width()));
             d_ptr->textureHeight = qMin(256, nextPowerOfTwo(size.height()));

             glGenTextures(1, &d_ptr->texture);
             glBindTexture(GL_TEXTURE_2D, d_ptr->texture);

             glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
             glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
             glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
             glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

             const int bufSize = d_ptr->textureWidth * d_ptr->textureHeight * 2;
             GLshort buf[bufSize];
             memset(buf, 0, sizeof(GLshort) * bufSize);

             glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, d_ptr->textureWidth,
                          d_ptr->textureHeight, 0,
                          GL_RGBA, GL_UNSIGNED_BYTE, buf);

             glGenRenderbuffersOES(1, &d_ptr->depthbuf);
             glBindRenderbufferOES(GL_RENDERBUFFER_EXT, d_ptr->depthbuf);
             glRenderbufferStorageOES(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT16,
                                      d_ptr->textureWidth, d_ptr->textureHeight);

             glGenFramebuffersOES(1, &d_ptr->frameBufferObject);
             glBindFramebufferOES(GL_FRAMEBUFFER_EXT, d_ptr->frameBufferObject);

             glFramebufferTexture2DOES(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
                                       GL_TEXTURE_2D, d_ptr->texture, 0);
             glFramebufferRenderbufferOES(GL_FRAMEBUFFER_EXT,
                                          GL_DEPTH_ATTACHMENT_EXT,
                                          GL_RENDERBUFFER_EXT, d_ptr->depthbuf);
             glBindFramebufferOES(GL_FRAMEBUFFER_EXT, 0);
         }

         QWSGLWindowSurface::setGeometry(rect);
     }

     /*!
       Returns the window  surface's texture as a QByteArray.
      */
     QByteArray QAhiGLWindowSurface::permanentState() const
     {
         QByteArray array;
         array.resize(sizeof(GLuint));

         char *ptr = array.data();
         reinterpret_cast<GLuint*>(ptr)[0] = textureId();
         return array;
     }

     /*!
       Sets the window surface's texture to \a data.
      */
     void QAhiGLWindowSurface::setPermanentState(const QByteArray &data)
     {
         const char *ptr = data.constData();
         d_ptr->texture = reinterpret_cast<const GLuint*>(ptr)[0];
     }

     /*!
       Returns the paint device being used for this window surface.
      */
     QPaintDevice *QAhiGLWindowSurface::paintDevice()
     {
         return d_ptr->device;
     }

     /*!
       Returns the window surface's texture.
      */
     GLuint QAhiGLWindowSurface::textureId() const
     {
         return d_ptr->texture;
     }

     /*!
       The \l {QWSServer} {window system} always calls this function
       before any painting operations begin for this window surface.
       It ensures that the correct frame buffer will be used by the
       OpenGL library for painting operations.
      */
     void QAhiGLWindowSurface::beginPaint(const QRegion &region)
     {
         QWSGLWindowSurface::beginPaint(region);

         if (d_ptr->frameBufferObject)
             glBindFramebufferOES(GL_FRAMEBUFFER_EXT, d_ptr->frameBufferObject);
     }

     /*!
       This function returns true if the window associated with
       this window surface can still rendered using this window
       surface class. Either the window's top-level widget must
       be an \l {QGLWidget} {OpenGL widget}, or the window's
       frame must be no bigger than 256 x 256.
      */
     bool QAhiGLWindowSurface::isValid() const
     {
         if (!qobject_cast<QGLWidget*>(window())) {
             const QRect r = window()->frameGeometry();
             if (r.width() > 256 || r.height() > 256)
                 return false;
         }
         return true;
     }