This class is responsible to create one texture with desktop image. The RGB buffer with screenshot of desktop is obtained with ScreenCapture class. The background image texture is created with 25% transparency. It is achieved with glPixelTransferf() before texture loading. glPixelTransferf is used to provide scale factor of Red, Green Blue channels.

Screenshot of Zoom Text display.

Zoom Text dislayed at center of dialog, with current zoom factor. This text is displayed in a semi transparent way. Hide and Show are very smooth, which is implemented by blending feature of OpenGL. When drawing new object, new object and old object[already drawn object] are combined and create a transparent look of new object. Alpha value is started from 0.0, and increased 0.1 during each frame, and get get smooth appearance. When hide, Alpha value is decreased from 1.0 to 0.0, and getting a smooth disappearance effect.

Translation:

LButtonDown and MouseMove messages are tracked in ImageArea, and find out the translation required in X and Y direction.When drawing the image texture, ImageArea::Draw() will apply translation with OpenGL translate function glTranslatef. 

    // Y value is -ve, only becouse opengl Y coordinate is increasing from bottom to top,
    // But Y direction mouse movement received in Dialog is decreasing from bottom to top.
    glTranslatef( m_fXTranslation, -m_fYTranslation, 0.0 );

3. BottomWindows. 

This class is responsible for drawing and message handling of buttons displayed at the bottom of PicZoom.

There are 9 buttons displayed at bottom of PicZoom, which will help to explore different image files in the current folder, zoom, and rotation of image.

Screenshot of BottomWindows.

GLButton is designed to handle all operations related to one button. Bottomwindows creates 9 instances of GLButton, and hold in a list, and all commands are passed to the button list.

/*
This class handles all operations related to a Button.
The drawing and mouse message handling is handled in this class.
The resource ID of bitmap is provided to this class, and ID of Message
to send to parentWindow( PicZoomDlg) is also provide to this class.
Whenever user press the button, this class will send message to PicZoomDlg.
*/
class GLButton : public GLWindowBase
{
public:

    GLButton( HWND hParentWindow_i );
    virtual ~GLButton();
    virtual void SetRegion( const int nLeft_i, const int nTop_i,
                    const int nWidth_i, const int nHeight_i );
    virtual void SetImage( const int nResourceID_i );
    virtual bool SetupButton();
    virtual void SetLButtonMessage( const int nMessageToParent_i );
    virtual bool OnMouseMove( const int nX_i, const int nY_i, const int nFlags_i );
    virtual bool OnLButtonDown( const int nX_i, const int nY_i, const int nFlags_i );
    virtual bool OnLButtonUp( const int nX_i, const int nY_i, const int nFlags_i );
    virtual bool IsWithinRegion( const int nX_i, const int nY_i );
    void SetTransparency( const float fTransparency_i );
    virtual bool Draw();
}; <span class="Apple-style-span" style="font-size: 14.4px; "> </span>

The initialization of a GLButton is very simple. Three items are required to initialize a GLButton. The resource ID, region of display and the Message ID.  The resource ID of bitmap is used to create button image. The alpha channels of each pixel determine the transparency of button. When alpha values of a pixel is 0.0, then that pixel will not displayed in button image.  When user clicks the button, the message will send to the parent window(PicZoomDlg). 

The transparent behaviour of each button is achieved by the alpha blending technique. The bitmaps are created in RGBA format( one 8 bit channel for alpha component). GLTexture class is modified to create RGB8, RGBA8, textures. The bitmaps required for bottom windows are added as resource of PixZoom, and that bitmaps are loaded with BMPLoader, and create GLTexture with RGBA data.

// The texture and vertex buffer for rendering are setup in this function.
bool GLButton::SetupButton()
{
    // Create Vertex buffer.
    m_pVertexBuffer = new GLVertexBuffer;
    if( 0 == m_pVertexBuffer )
    {
        return false;
    }
    // Create Vertex buffer for rendering Quad image.
    m_pVertexBuffer->CreateQuadVertexBuffer();

    UpdateVertexBuffer();

    // Setup Texture from Bitmap resource ID.
    m_pTexture = new GLTexture;
    int nWidth = 0;
    int nHeight = 0;
    BYTE* pbyARGBImage = 0;
    BMPLoader LoadImage;
    // Load Alpha enabled texture.
    LoadImage.LoadBMP( m_nResourceID, nWidth, nHeight, pbyARGBImage, true );
    // Create RGBA format texture.
    m_pTexture->Create( nWidth, nHeight, pbyARGBImage, GL_RGBA, GL_RGBA8 );
    return (GL_NO_ERROR == glGetError());
} 

The mouse over effect of buttons is implemented in a tricky way. When displaying, the blending feature of texel( texture color) with current colour(glColor) is enabled. Then set low color( glColor4f(0.75f, 0.75f, 0.75f, 0.75f) while diplaying button in normal scenario. While displaying button with mouse over high color is applied glColor4f(1.0, 1.0, 1.0, 1.0 ).

bool GLButton::Draw()
{
    if( m_bMouseOver )
    {
        // After drawing, pixelstore biasing is changed.
        //glColor4f( 1.0, 1.0, 1.0, 1.0 );
        glColor4f( m_fTransparency, m_fTransparency, m_fTransparency, m_fTransparency );
    }
    else
    {
        // After drawing, pixelstore biasing is changed.
        //glColor4f( 0.75, 0.75, 0.75, 1.0 );
        glColor4f( 0.75 * m_fTransparency, 0.75 * m_fTransparency, 0.75 * m_fTransparency, 0.75 * m_fTransparency );
    }
    m_pVertexBuffer->DrawVertexBuffer( GL_QUADS );
    return true;
} 

Displaying functionality of current button. 

The above screenshot displaying the behavior of description text display.  GLText is created for displaying a text with smooth show and hide. Here also, alpha blending is used to make smooth appearance and smooth hide. 

void GLText::Draw(const int nX_i, const int nY_i)
{
    if( m_StringTimerHide.IsEnabled())
    {
        // Hide old string. Here fColorComponent will decrease
        // after each frame.
        int nRemTime = m_StringTimerHide.GetRemainingTime();
        float fColorComponent = ( nRemTime / 20.0 );
        glEnable( GL_BLEND );
        glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
        glColor4f( 1.0, 1.0, 1.0, fColorComponent );
        // Drawing text to screen.
        m_pFontEngine->DrawText( nX_i, nY_i, m_csDisplayString.GetBuffer( 0 ) );
        glDisable( GL_BLEND );
        glColor4f( 1.0, 1.0, 1.0, 1.0 );
        m_StringTimerHide.ElapseTime();
    }
    else
    {
        m_csDisplayString = m_csDisplayStringNew;
        // Show New string. Here fColorComponent will 
        // increase during each frame, then reach the maximum value.
        int nRemTime = 20 - m_StringTimerShow.GetRemainingTime();
        float fColorComponent = ( nRemTime / 20.0 );
        glEnable( GL_BLEND );
        glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
        glColor4f( 1.0, 1.0, 1.0, fColorComponent );
        // Drawing text to screen.
        m_pFontEngine->DrawText( nX_i, nY_i, m_csDisplayString.GetBuffer( 0 ) );
        glDisable( GL_BLEND );
        glColor4f( 1.0, 1.0, 1.0, 1.0 );
        m_StringTimerShow.ElapseTime();
    }
} 

4. CloseButton.

CloseButton is derived from GLButton, in order to implement some additional functionalities in CloseButton. The circular shape of close button is implemented by setting alpha channels to outer region of circle to 0.0 and 1.0 to the inner region of circle. The mouse cursor changing is also based on the circle region.  

bool CloseButton::IsWithinRegion( const int nX_i, const int nY_i )
{
    if( GLButton::IsWithinRegion( nX_i, nY_i ))
    {
        // Here check the bottom left corner of circle.
        // If mouse move is not within the semi-circle, then return false.
        int nXDiff = nX_i - GLWindowBase::m_nWidth;
        int nYDiff = nY_i;
        int nRadius = sqrt( (float)nXDiff * nXDiff + (float)nYDiff * nYDiff );
        if( nRadius < 45 )
        {
            return true;
        }
    }
    return false;
} 

One work around is also included in CloseButton to create smooth edges of semi circle.  When semicircle is texture mapped, the edges will not be smooth. Therefore one GLCircle will draw a circle with 50% transparency. Therefore edges of close button will be smooth.

bool CloseButton::Draw()
{
    GLButton::Draw();
    // CloseBoundry draws the outline of cirle in 50% transparency.
    m_CloseBoundary.Draw();
    return true;
} 

Slideshow functionality

Slideshow is also implemetend with alpha blending functionality. Two textures are created with bitmap data of two image files. Transition from first image to second is created by blending first and texture texels. When starting slide show, the window size is changed to full desktop size, then hides all other windows( BottomWindows, CloseButton etc).  

void SlideShow::Display()
{ 
   // glColor3f is used to make small amount of texture display.
    // This color factor is multiplied with texel color and get a shading effect.
    glColor4f( fColorFactor, fColorFactor, fColorFactor, fColorFactor );
    m_pTexture1->Enable();
    // Apply zoom1.
    glScalef( m_fZoom1, m_fZoom1, 0.0 );
    m_pVertexBuffer1->DrawVertexBuffer( GL_QUADS );
    glPopMatrix();

    if( nRemTime < 100 )
    {
        glPushMatrix();
        // When transparent display of second texture is required.
        float fTex2Color = 1.0 - fColorFactor;
        glColor4f( fTex2Color, fTex2Color, fTex2Color, fTex2Color );
        m_pTexture2->Enable();
        // Apply Zoom 2.
        glScalef( m_fZoom2, m_fZoom2, 0.0 );
        m_pVertexBuffer2->DrawVertexBuffer( GL_QUADS );
        glPopMatrix();
    } 
}  

Installer. 

PicZoomInstaller is created to modify the registry entries, which are required to add context menu in windows explorer. When right click a file, the following context menu will be appeared. 

The following registry modification is required for creating a context menu in Windows Explorer.

Create a new key “OpenWith PicZoom” under HKEY_CLASSES_ROOT\*\Shell\.

RegistryHandler::RegisterForAllFiles() is responsible for creating a OpenWith PicZoom entry in HKEY_CLASSES_ROOT\*\Shell\. 

PicZoomInstaller Some other registry modification is also implemented, inorder to create a new application entry(PicZoom) in open with list.  

The registry modification is identified by trial and error method. I selected new program(PicZoom.exe) as default application for opening a bmp file. Then searched registry and find out the registry location to create an application in open with list. I don’t know any other method to do the same.

The registry entries are created for open with list in bmp, jpg, png, and tga files.

// HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.jpg
// HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.bmp
// HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.png
// HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.tga 

RegistryHandler::AddApplicationName() is responsible for creating PicZoom in open with list of different image files. 

Points of Interest

When retrieving the width and height of a character with GetGlyphOutline(), I got a GDI_ERROR. Debug mode works fine, but release mode cause a GDI_ERROR. At last I found its reason from some forums. The transformation matrix provided to GetGlyphOutline(), should be initialised with idendity matrix. 

Projection Matrix. 

 Since there is no 3D related operation, here we can use orthographic projection. Orthographic projection area is same as the window coordinate, and simply overcame -1 to +1 mapping method of perspective projection.      

History 

16-Jan-2011: Initial version.