Why is my canvas not transparent on MacOS?

[Julia_Truchsess]

I know there are many many posts here complaining about canvas transparency issues, but it seems they’re all about a lack of transparency under Windows. I have the opposite problem - under Windows it looks great but under MacOS not so much.

My canvas is painting an 8-bit RGB PNG image. The white background of the image has been removed in Photoshop (checkerboard shows) and it looks right in the Xojo IDE.

Under Windows 10 or 11 I see only the colored parts of the image - the rest is exactly the color of the window on which the canvas sits, which is the desired result.

Under MacOS, the canvas has a visible background darker than the window, giving it a “dirty” look:

Xojo 2021r2.1, MacOS Monterey.

[Greg_O]

Are you sure that the background is 100% transparent?

Oh, and make sure you call ClearRect before drawing.

[Julia_Truchsess]

@Greg_O

make sure you call ClearRect before drawing

That did the trick, thanks!

[Eric_Williams]

Wait, why does this work? The Canvas has some random color filling it that doesn’t match the window background color?

[Julia_Truchsess]

I was a little surprised, too.