Note: Tests of successful loading of the image without applying the workaround have been done on various O/S. This patch may not be required on Win7 and above
You probably know that GDI+ is useful for loading various image formats, but GDI+ also has issues with every format it loads. For JPGs specifically, if certain APP markers within the file have zero length data then one of two things can happen: 1) image won't load or 2) image loads, but the size reported by GDI+ is 0x0
The attached txt file is a VB class. After you save it to disk, rename it to .cls
I've also included a JPG with a zero-length APP marker.
So, to play.
1) Download the txt file & rename it .cls
2) Create a new project and add that class to your project
3) On the form, add a commandbutton
4) Paste this code to your form & run project
5) Drag/drop a JPG onto the form
Code:
Option Explicit
Private Declare Function GdipDeleteGraphics Lib "GdiPlus.dll" (ByVal mGraphics As Long) As Long
Private Declare Function GdipDrawImageRectRectI Lib "GdiPlus.dll" (ByVal hGraphics As Long, ByVal hImage As Long, ByVal dstX As Long, ByVal dstY As Long, ByVal dstWidth As Long, ByVal dstHeight As Long, ByVal srcX As Long, ByVal srcY As Long, ByVal srcWidth As Long, ByVal srcHeight As Long, ByVal srcUnit As Long, ByVal imageAttributes As Long, ByVal Callback As Long, ByVal callbackData As Long) As Long
Private Declare Function GdipCreateFromHDC Lib "GdiPlus.dll" (ByVal hDC As Long, hGraphics As Long) As Long
Private Declare Sub GdiplusShutdown Lib "gdiplus" (ByVal Token As Long)
Private Declare Function GdiplusStartup Lib "gdiplus" (Token As Long, inputbuf As Any, Optional ByVal outputbuf As Long = 0) As Long
Private Type GdiplusStartupInput
GdiplusVersion As Long
DebugEventCallback As Long
SuppressBackgroundThread As Long
SuppressExternalCodecs As Long
End Type
Private m_Token As Long
Private m_JPG As cJPGreader
Private Sub Form_Load()
Call pvCreateToken
If m_Token = 0 Or m_Token = -1 Then
Me.Show
DoEvents
MsgBox "Failed to start up GDI+", vbExclamation + vbOKOnly
Unload Me
Exit Sub
End If
Set m_JPG = New cJPGreader
Me.Move (Screen.Width - 10245) \ 2, (Screen.Height - 6585) \ 2, 10245, 6585
Me.ScaleMode = vbPixels
Me.Command1.Move 0, 0
Me.Command1.Caption = "Refresh"
Me.OLEDropMode = vbOLEDropManual
End Sub
Private Sub Form_Unload(Cancel As Integer)
Set m_JPG = Nothing
If Not (m_Token = 0& Or m_Token = -1&) Then pvDestroyToken
End Sub
Private Function pvCreateToken() As Boolean
Dim GSI As GdiplusStartupInput
On Error Resume Next
If Not m_Token = -1 Then
GSI.GdiplusVersion = 1&
Call GdiplusStartup(m_Token, GSI)
If m_Token = 0 Then
m_Token = -1&
Else
pvCreateToken = True
End If
End If
End Function
Private Sub pvDestroyToken()
If Not (m_Token = 0 Or m_Token = -1) Then GdiplusShutdown m_Token
m_Token = 0&
End Sub
Private Sub Command1_Click()
Call pvRenderImage
End Sub
Private Sub pvRenderImage()
If Not m_JPG.Handle = 0& Then
Dim hGraphics As Long, w As Long, h As Long, sngRatio As Single
Dim x As Long, Y As Long, cx As Long, cy As Long
Const UnitPixel As Long = 2&
w = m_JPG.Width
h = m_JPG.Height
cy = Me.ScaleHeight - Command1.Height
If Me.ScaleWidth / w > cy / h Then
sngRatio = cy / h
Else
sngRatio = Me.ScaleWidth / w
End If
If sngRatio > 1! Then sngRatio = 1&
cx = w * sngRatio
cy = h * sngRatio
x = (Me.ScaleWidth - cx) \ 2
Y = ((Me.ScaleHeight - Command1.Height) - cy) \ 2 + Command1.Height
Me.Cls
GdipCreateFromHDC Me.hDC, hGraphics
GdipDrawImageRectRectI hGraphics, m_JPG.Handle, x, Y, cx, cy, 0, 0, w, h, UnitPixel, 0, 0, 0
GdipDeleteGraphics hGraphics
End If
End Sub
Private Sub Form_OLEDragDrop(Data As DataObject, Effect As Long, Button As Integer, Shift As Integer, x As Single, Y As Single)
If Data.Files.Count Then
m_JPG.FileName = Data.Files.Item(1)
Call pvRenderImage
End If
End Sub
Okay, this might be annoying - but FYI, on Win 7, GDI+ loads the problematic JPEG without any trouble. I'm afraid I don't have Vista to test v1.1 there, but it looks like Microsoft put some work into fixing some of these issues somewhere between XP and Win 7. Good for them, I guess??
Not exactly shocked. Many of these GDI+ shortcomings were discussed in hundreds of forums and MS received hundreds of bug reports from coders. For my purposes of creating an image control, it is even more annoying for me. Depending on the target O/S, some shortfalls are still active while others are not. And it's not like the workarounds are simple one-liners either. This will be something I'll have to think about: without relying on the O/S version, identifying whether a workaround is needed and set on/off switches to apply them if needed.
Thanx for the Win7/Win8 results for the various posts I put up. I do have Win7 on a laptop, but don't have access to it on a regular basis. I have no Win8 access.
Insomnia is just a byproduct of, "It can't be done"
Just a little clarification, GDIplus loads a JPEG alright when it is with an empty marker, if Length field is not entered with "2". It would accept it if Length field is entered "0".
I've checked that the file you uploaded is a perfectly valid one; although it has an empty marker, its Lengh entry is correctly entered. Thus the conclusion to be drawn appears to be:
(i) GDIplus would reject a JPEG with an empty marker when its Length field is correctly entered as "2".
(ii) GDIplus would accept a JPEG with an empty marker if its Length field is incorrectly entered as "0". This is true even on Win 7.
Attached ZIP contains a JPEG, modified from yours (the only modification is to change Length entry from "2" to "0"), you would be able to load it without a problem, albeit its Length field entry is not a proper one.
Last edited by Brenker; Feb 16th, 2015 at 03:05 PM.
Reason: Add a remark to "ii"
I said what I said because I had already tested it on both Vista and Win 7.
The screenshot shows the specific path of GDIplus used on Vista (not designated by my program), and its actual version No. Because both are long, hence screenshot.
The above is just for a bit of fun, and to highlight the funny behaviour of GDIplus concerning the subject file. Removal of the empty marker is preferred, if one bothers.
And I wouldn't have made the claim if I didn't experience it... Look at the screen shot, the property sheet on the left is the jpg loaded with pure GDI+, the one the right is loaded by VB's LoadPicture. Note that the image did load in GDI+, it reported 0x0 dimensions and therefore does not render with GDI+. It depends on what version happens to be on the system... When manifested, that GDI+ version won't even load the JPG.
Last edited by LaVolpe; Feb 16th, 2015 at 11:08 PM.
Insomnia is just a byproduct of, "It can't be done"