OpenEuphoria

Re: win32lib printing

• Posted by ghaberek (admin) Dec 23, 2014
• 1343 views

I did some testing and I realized that queryDevice() in Win32Lib calls CreateIC to create an information context and returns only 96 DPI for the Printer.

According to the GetDeviceCaps documentation, it appears that 96 DPI is the "default" when it cannot figure out the actual DPI...

The trick then, is to just call GetDeviceCaps directly and provide it the proper device context using getDC() instead. Here is a function that will return one or more device values.

public function getDeviceCaps( integer device, object index ) 
     
    object result 
    atom dc = getDC( device ) 
     
    if atom( index ) then 
         
        -- just return one value 
        result = w32Func( xGetDeviceCaps, {dc,index} ) 
         
    else 
         
        -- look up each value and return the list 
        result = repeat( 0, length(index) ) 
        for i = 1 to length(index) do 
            result[i] = w32Func( xGetDeviceCaps, {dc,index[i]} ) 
        end for 
         
    end if 
     
    return result 
end function 

And now that we can get the DPI for any device, we can scale from one device to another, so an image appears the same size on both.

public function scaleDPI( sequence size, integer fromDevice, integer toDevice, atom factor = 1.0 ) 
-- use 'factor' to provide additional scaling if required 
     
    -- get the DPI for each device 
    sequence fromDPI = getDeviceCaps( fromDevice, {LOGPIXELSX,LOGPIXELSY} ) 
    sequence toDPI   = getDeviceCaps( toDevice,   {LOGPIXELSX,LOGPIXELSY} ) 
     
    -- calculate the scale ratio 
    sequence scale = (toDPI / fromDPI) 
     
    -- return the scaled size 
    return floor( size * scale * factor ) 
end function 

Now my click event handler looks like this. Notice I am taking nothing for granted and the bitmap appears the correct size on the page.

procedure myButton_OnClick( integer self, integer event, sequence params ) 
     
    sequence result = getPrinter() 
    if length( result ) = 0 then 
        -- user cancelled 
        return 
    end if 
     
    -- get the printer DPI values 
    sequence printerDPI = getDeviceCaps( Printer, {LOGPIXELSX,LOGPIXELSY} ) 
     
    if startDoc( "Test" ) then 
         
        if startPage() then 
             
            atom bmp = loadBitmapFromFile( "space.bmp" ) 
             
            -- original bitmap size in pixels 
            sequence screenSize = getCtlSize( bmp ) 
             
            -- scale the bitmap from screen DPI to printer DPI (e.g. 96-to-600) 
            sequence printSize = scaleDPI( screenSize, Screen, Printer ) 
             
            -- calculate a decent page margin (1/2 inch) 
            sequence margins = floor( printerDPI * 0.5 ) 
             
            stretchBlt( 
                Printer,        -- dest device 
                margins[1],     -- dest x 
                margins[2],     -- dest y 
                printSize[1],   -- dest width 
                printSize[2],   -- dest height 
                bmp,            -- src bitmap 
                0,              -- src x 
                0,              -- src y 
                screenSize[1],  -- src width 
                screenSize[2],  -- src height 
                SRCCOPY         -- operation 
            ) 
             
            endPage() 
             
        end if 
         
        endDoc() 
         
    end if 
     
    releasePrinter() 
     
end procedure 

-Greg