Transparent for Pictures with alpha channel

General
1

Hello, before the new pictures, to change the white of an image in transparent I made
thepicture.transparent = 1
I searched in the documentation and in the forum without finding, how do we do now?
Thanks
Marc

2

create a mask

3

But in the Dev Center I read :
In the Picture class, support for alpha channels means that the use of masks is no longer required

4

Yes, but transparent works only on the old picture type, which means pictures with a mask – see the LR.
You can convert your picture to an old type – say you have a picture with alpha channel named pic:

Dim oldPic As New Picture (pic.width, pic.height, 32) oldPic.Graphics.DrawPicture pic, 0,0 oldPic.Transparent = 1

5

With an alpha channel, you specify transparency in the color. &cRRGGBBAA, where AA is the alpha (transparency) value. 00 is opaque, FF is fully transparent.

6

Tim, how would you set ‘transparency in the color’?

oldPic.graphics.forecolor = &cFFFFFFFF
7

I have an picture, read or built in xojo, and I just want to make the white transparent (or not), as before.
And not turning it into an old format …

8

So either use the conversion like written above and then convert it back to a picture with alpha channel the same way or use RGBSurface, loop through the pixel data and create another picture from it, replacing each white pixel with a transparent color.
I would guess the first version is faster, but I have not tested it.

9

I played with both ; copying the picture to a 32 bit depth and applying transparent is WAY faster.

10

Yes, it works, many thanks - but not with a resolution other than 72
This code creates an image 4 times too small if the original image has a resolution of 300dpi :

dim oldPic As New Picture (pic.width, pic.height, 32)
oldPic.HorizontalResolution = pic.HorizontalResolution
oldPic.VerticalResolution = pic.VerticalResolution
oldPic.Graphics.DrawPicture pic, 0,0
oldPic.Transparent = 1

11

Yes, the code was a bit sloppy, not taking different resolutions into account.
Extend the line before the last:

oldPic.Graphics.DrawPicture pic, 0, 0, pic.Width, pic.Height, 0, 0, oldpic.Width, oldpic.Height
12

it’s ok !

But, I am surprised that the new picture format does not allow a function as simple as the previous one …