Transparent pixels overwrite existing pixels on mlx_put_image_to_window

[42paris]

Transparent pixels overwrite existing pixels on mlx_put_image_to_window

[Rush-iam]

Hello!
Faced same issue while trying to port my cub3D from MacOS to Linux/Windows.
I dived into X11 manuals and found the way to add alpha channel to MLX - by using XRender extension which can blend images.
You can find modified MinilibX Linux on my project page:
https://github.com/Rush-iam/nGragasstein3D-cub3D
May be you need to install required libraries before:
apt install libxrender-dev

To use: function mlx_new_image_alpha() with same arguments as mlx_new_image() - it will create image, which will be blended on top of other images. From my tests there is almost no performance penalty.
I checked work only on WSL2 without SHM, so don't know how it behaves on true Linux environment - will be glad if you'll post any bugs.

Alpha channel in X11 works not the same way as in stock MLX.
255 is fully opaque and 0 is full transparent here (inverted to MLX).
So you need to draw accordingly - set upper bits of color to 0xFF if you want them to be opaque.
(if anybody knows how to invert it on X11 side - I will be grateful)
There is also another issue - if you want to play with semi-transparency - you should premultiply your color relative to alpha value before outputting - X11Render don't do that.

Here is screenshot from my cub3D with semi-transparent weapon glow - just made it to work after few days and now happy))

p.s. I also modified MLX by implementing some kind of double buffer - it now writes image to main buffer only once a frame.
In stock MLX it writes every time you call put_image_to_windows, so it can result in flickering images if there are lot of put_image's per frame.

[paulo-santana]

In the test program, the blowfish sprite is drawn with its transparent pixels as if they were opaque.

[Rakjlou]

Same problem here. Hope it's fixed someday.