Cannot create a single channel image

[jice-nospam]

Description

When using a single channel image, the pixel function should return a (f32) which is as far as I understand simplified into f32 by the compiler. This results in a compilation error :

the trait bound `f32: IntoRecursive` is not satisfied

Reproducing

let channels = SpecificChannels::build()
        .with_channel("H")
        .with_pixel_fn(|_| {
            (0.0f32)
        });

Environment

• Windows 10
• EXRS Version 1.5.2

[johannesvollmer]

thanks for taking the time :)
yes, this is probably a design issue in exrs. I think this is an edge case that was never tested. should be rather simple to fix

[johannesvollmer]

If you need a workaround, there are multiple options.

You could add a second optional channel and ignore it (very dirty)

You can also use dynamic channels, which loads all the channels without the need to specify them, and then you can extract the channel you are interested in.

exrs/examples/3b_read_all_channels_with_metadata.rs

Line 13 in 49fece0

.largest_resolution_level().all_channels().all_layers().all_attributes()

[jice-nospam]

I'm actually trying to write a single channel file (used as a heightmap). For now I'm adding a second channel filled with zeroes :)

[johannesvollmer]

Oh yeah, oopsie. In either case, there is another option: use a custom struct that knows your image data, and make it implement WritableChannels. You can pass your struct into a layer, instead of using SpecificChannels, like in this example:

exrs/examples/5a_write_multiple_layers.rs

Line 28 in 49fece0

SpecificChannels::rgba(|_pos| (0.8_f32, 0.5_f32, 0.1_f32, 1.0_f32)),

[jice-nospam]

I tried this way but it seems very complex for what I need, I'll keep my empty channel for now.
Also using globally the exr prelude breaks all the code because you redefine Result. You shouldn't do that!

[johannesvollmer]

Yes, if the second channel workaround works for you, it's definitely the nicest code

[johannesvollmer]

Would it solve the other issue to export a type alias ExrResult in the prelude, but keep the original type name Result internally?

[jice-nospam]

yes I think it would fix the issue

[johannesvollmer]

Have you tried using the tuple syntax for creating tuples with one value? The Syntax looks like this:
let tuple = (value,)

let channels = SpecificChannels::build()
        .with_channel("H")
        .with_pixel_fn(|_| {
            (0.0f32,)
        });

[jice-nospam]

oh yes it works ! thanks I didn't know this syntax !

[johannesvollmer]

Nice to have it working - but let's keep the issue open, because exrs can be improved nevertheless. IntoRecursive should be implemented for f32.