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JanetTerra
Dec 21, 2009
Getting Image File Information with GDI32
While it is possible to open and read any image file as a sequential file to find the image width and height , it may be easier to use the GDI32 GetObjectA . GetObjectA retrieves information for all bitmaps in memory. Load the image first with GDIPlus with a call to GdipCreateBitmapFromFile . Once the image is loaded, call GetObjectA to retrieve information. This code is based in part upon Alyce Watson's demo Sprite in a Box in the Liberty BASIC Newsletter, Issue #108 . The code also uses Dan Teel's demo Load Any Image with GDIPlus .
Two structs are needed. The first is for the GetObjectA code. The struct holds the bitmap information.
Struct ImageInfo, _The second struct is for the GdipCreateBitmapFromFile code.
imgType as Long, _
imgWidth as Long, _
imgHeight as Long, _
imgWidthBytes as Long, _
imgPlanes as Word, _
imgBitsPixel as Word, _
imgBits as Long
Struct doubleWord, a as uLong
Once the image is loaded and GetObjectA is called, the ImageInfo struct will contain the bitmap. Copy the width and height information from the struct to numeric variables.
imgWidth = ImageInfo.imgWidth.structThe advantages to loading an image with GdipCreateBitmapFromFile and then calling GetObjectA to find the width and height of the image are
imgHeight = ImageInfo.imgHeight.struct
When the image is no longer needed, delete the image from memory with DeleteObject .
Call DeleteObject hImage
Sub DeleteObject hImage
CallDLL #gdi32, "DeleteObject", _
hImage as uLong, _
result as Long
End Sub
Demo to Load an Image with GdipCreateBitmapFromFile and Find Dimensions with GetObjectA
' Extension variable for Filedialog
' Valid image formats are bmp, gif, ico, jpg, png, and tiff
iExt$ = "*.bmp;*.gif;*.ico;*.jpg;*.png;*.tiff"
' Variables to hold the width and height of the image
imageWidth = 0
imageHeight = 0
' Struct necessary for loading an image with GDIPlus
Struct doubleWord, a as uLong
' Struct necessary for returning image file information
Struct ImageInfo, _
imgType as Long, _
imgWidth as Long, _
imgHeight as Long, _
imgWidthBytes as Long, _
imgPlanes as Word, _
imgBitsPixel as Word, _
imgBits as Long
' Design a GUI to host the image
WindowWidth = 800
WindowHeight = 600
UpperLeftX = Int((DisplayWidth - WindowWidth) / 2)
UpperLeftY = Int((DisplayHeight - WindowHeight) / 2)
' Design a graphicbox to display the image
Stylebits #main.g, 0, _WS_BORDER, 0, 0
Graphicbox #main.g, 0, 0, 792, 580
Open "Getting the Image Width and Height with GetObjectA" for Window_nf as #main
#main, "Trapclose [closeApp]"
#main, "Font Verdana 10 Bold"
hMain = hWnd(#main)
hG = hWnd(#main.g)
#main.g, "Down"
' Load an image file
Filedialog "Image to Load", iExt$, imagePathFile$
' Load the image using GDIPlus, hImage is the returned handle to the bitmap in memory
hImage = LoadImgFromFile(imagePathFile$)
' Get the bitmap information using GetObjectA
imageDimen$ = ImageDimensions$(hImage)
imageW = Val(Word$(imageDimen$, 1, Chr$(0)))
imageH = Val(Word$(imageDimen$, 2, Chr$(0)))
' Load the bitmap in memory
Loadbmp "pic", hImage
' Draw the image using native LB command Drawbmp
#main.g, "Drawbmp pic 10 10; Flush"
' Resize the graphicbox to the size of the image
#main.g, "Locate 0 0 ";imageW + 20;" ";imageH + 20
#main, "Refresh"
' Give the width and height of the image
msg$ = "Image Dimensions";Chr$(10);Chr$(13); _
"Width: ";imageW;" pixels";Chr$(10);Chr$(13); _
"Height: ";imageH;" pixels";Chr$(10);Chr$(13)
Notice msg$
Wait
[closeApp]
' Unload the native LB bitmap
Unloadbmp "pic"
' Release memory from GDIPlus loaded image
Call DeleteObject hImage
Close #main
End
Function ImageDimensions$(hImage)
lStruct = Len(ImageInfo.struct)
CallDLL #gdi32, "GetObjectA", _
hImage as uLong, _
lStruct as Long, _
ImageInfo as struct, _
result as Long
imgWidth = ImageInfo.imgWidth.struct
imgHeight = ImageInfo.imgHeight.struct
ImageDimensions$ = Str$(imgWidth);Chr$(0);Str$(imgHeight)
End Function
Function wChar$(string$)
For i = 1 to Len(string$)
wChar$ = wChar$ + Mid$(string$, i, 1) + chr$(0)
Next i
wChar$ = wChar$ + Chr$(0) + Chr$(0)
End Function
Function LoadImgFromFile(picFile$)
Open "gdiplus.dll" for dll as #gdip
gdistart$=Chr$(1)
For i = 1 to 15
gdistart$ = gdistart$ + Chr$(0)
Next i
Calldll #gdip,"GdiplusStartup", _
doubleWord as struct, _
gdistart$ as Ptr, _
status as uLong
token=doubleWord.a.struct
If status <> 0 Then
LoadImgFromFile = 0
Else
wFileLoc$=wChar$(picFile$)
Calldll #gdip,"GdipCreateBitmapFromFile", _
wFileLoc$ as Ptr, _
doubleWord as struct, _
status as uLong
hPic = doubleWord.a.struct
If status <>0 then
LoadImgFromFile=0
Else
CallDLL #gdip,"GdipCreateHBITMAPFromBitmap", _
hPic as uLong, _
doubleWord as struct, _
0 as uLong, _
status as uLong
hImage=doubleWord.a.struct
If status <> 0 Then
LoadImgFromFile = 0
Else
LoadImgFromFile = hImage
End if
CallDLL #gdip,"GdipDisposeImage", _
hPic as uLong, _
result as uLong
End If
CallDLL #gdip,"GdiplusShutdown", _
token as uLong, _
result as uLong
End If
Close #gdip
End Function
Sub DeleteObject hImage
CallDLL #gdi32, "DeleteObject", _
hImage as uLong, _
result as Long
End Sub