Convert alpha channel to mask

General
1

I’m getting icons for extensions and then use this image as drag image. The icon image has an alpha channel but the drag image needs a picture with a mask (bug?). How do I convert an alpha channel to a mask?

First part for getting an icon for an extension:

[code] const extension = “gz”
const ScaleFactor = 1
const size = 256

dim theIcon as IconMBS = new IconMBS("", “”, extension, “”)
dim pic as new Picture(size * ScaleFactor, size * ScaleFactor)
dim thePictureContext as CGBitmapContextMBS = CGBitmapContextMBS.CreateWithPicture(pic)
const DrawNormal = 0
const DrawNoImage = 2
const DrawNoMask = 4
const DrawSelected = &h8000
if theIcon = nil or thePictureContext = nil then
'Return nil
end if
thePictureContext.ClearRect CGRectMBS.Make(0, 0, size * ScaleFactor, size * ScaleFactor)
theIcon.DrawIconCGContext(thePictureContext.Handle, 0, 0, size * ScaleFactor, size * ScaleFactor, 0, 0, DrawNormal, &c000000)
thePictureContext.Flush[/code]

If I use the following code for converting the alpha channel to a mask:

Dim surf As RGBSurface = pic.RGBSurface dim MaskPicture as new Picture(pic.Width, pic.Height) dim masksurf as RGBSurface = MaskPicture.RGBSurface Dim lastX As Integer = pic.Width - 1 Dim lastY As Integer = pic.Height - 1 For y As Integer = 0 To lastY For x As Integer = 0 To lastX dim i as Integer = surf.Pixel(x, y).Alpha masksurf.Pixel(x, y) = RGB(i, i, i) Next Next

then I get a white ring on black. What is wrong here?

Xojo 2016r11. Mac OS 10.11.4.

2

You don’t need to scan the rgbsurface. Just draw the image and copy the mask

dim MaskPicture As new Picture(pic.Width, pic.Height, 32) //32 for mask MaskPicture.Graphics.DrawPicture(pic, 0, 0) MaskPicture.ApplyMask(pic.CopyMask)

3

Thanks, Will. CopyMask for Alpha pictures could have a better name.