ReadGIF

In Class PicGIF

  53 Private Function ReadGIF(ByVal GIFFilename As String) As Boolean
  54 ' Reads a GIF file and retrieves image information
  55 ' [GIFFilename] Name of file to read
  56 ' Return value:
  57 ' True - GIF file was read and information retrieved
  58 ' False - Error or invalid file
  59 
  60 Dim ColorResolution As Integer   ' Number of color bits in the file (1..8)
  61 Dim FileNr As Integer            ' Number of open data file
  62 
  63 StoredFilename = GIFFilename ' Store Filename for later retrieval
  64 FileOK = False               ' Clear the FileOK flag until we have successfully read a valid .gif file
  65 
  66 ' Open the .gif file for binary read access
  67 FileNr = FreeFile
  68 Open GIFFilename For Binary Access Read Lock Write As #FileNr
  69 
  70 If LOF(FileNr) > Len(Signature) + Len(LogicalScreenDescriptor) Then
  71     ' The file size is "enough"
  72     
  73     ' Read 6 GIF signature bytes, which must be either GIF87a or GIF89a in ASCII
  74     Get #FileNr, 1, Signature
  75     If Signature = "GIF87a" Or Signature = "GIF89a" Then
  76         ' Signature bytes OK
  77         
  78         ' Read logical screen descriptor, which contains picture size and color info
  79         Get #FileNr, , LogicalScreenDescriptor
  80         
  81         ' Determine max number of colors
  82         ColorResolution = (LogicalScreenDescriptor.Packed And (64 + 32 + 16)) \ 16 + 1
  83         MaxColors = 2 ^ ColorResolution
  84         
  85         FileOK = True
  86         ReadGIF = True
  87     End If
  88 End If
  89 Close FileNr

    Assigned value not used: FileNr - Integer
  90 FileNr = 0
  91 
  92 End Function
  93 
  94 
  95 

Called by

IPicInfo_ReadFile