VB.NET: How to save a WebP encoded image to disk

[flora...@gmail.com]

I have the following code:

Private Declare Function WebPEncodeBGRA Lib "libwebp.dll" (ByVal rgba As IntPtr, ByVal width As Integer, ByVal height As Integer, ByVal stride As Integer, ByVal quality_factor As Single, ByRef output As IntPtr) As Integer

Private Declare Function WebPFree Lib "libwebp.dll" (ByVal p As IntPtr) As Integer

Private Sub Encode()
    Dim source As Bitmap = New Bitmap("input.png")
    Dim data As BitmapData = source.LockBits(New Rectangle(0, 0, source.Width, source.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb)
    Dim webp_data As IntPtr
    Dim i As Integer = WebPEncodeBGRA(data.Scan0, source.Width, source.Height, data.Stride, 80, webp_data)

    WebPFree(webp_data)
End Sub

But how can I get the encoded WebP image and save that to disk?

[James Zern]

Hi,

The webp image is stored to webp_data, its size is the return value of WebPEncodeBGRA. In another C# example Marshal.Copy was used to move the unmanaged data (webp_data) to something that the language could work with to store a file.

[James Zern]

+webp-discuss

On Wed, May 9, 2018 at 12:56 PM James Zern <jz...@google.com> wrote:

On Wed, May 2, 2018 at 1:35 AM Floran Felen <flora...@gmail.com> wrote:

Hi,

Thank you for this. The problem is actually a bit broader, I created an SO post with a 150rep bounty: https://stackoverflow.com/questions/50078087/asp-net-libwebp-dll-how-to-save-webp-image-to-disk, maybe you can see what's going on? Others on SO apparently don't.

Also, do you have a link to this other C# that you mention?

Sorry I didn't include the link before. I think the origin of my comment was this thread [1] and the source [2].

 

Thank you in advance!

[1] https://groups.google.com/a/webmproject.org/forum/#!searchin/webp-discuss/C$23|sort:date/webp-discuss/1coeidT0rQU/hvOn09vvCAAJ

[2] https://github.com/JosePineiro/WebP-wrapper/blob/master/WebPTest/WebPWrapper.cs

 

Cheers,

Floran