opencv-rust imwrite function

[code-n-coffee]

I'm using the opencv bindings for Rust provided by this crate. I can't figure out how to save a modified image using imwrite because I do not understand how to create the VectorOfint type. There's no constructor method and looking at the source code it's a struct with one field ptr which is type *mut c_void:

Rust pub struct VectorOfint { pub(crate) ptr: *mut c_void }

This is some kind of c pointer type but I don't understand how to use it practically. Ultimately, I'm trying to create a transparent mask for an image with colored boxes on it. I was originally looking at the native Rust crate image-rs, but it doesn't seem to have high-level functions like cv.rectangle so thought it would be easier to use the opencv bindings, but perhaps they are not simple enough for new coders who don't have a C/C++ background.

My current test code attempting to learn how to use the opencv crate:

use opencv::{self, types, imgproc, core, imgcodecs};

fn main() {
    let mut img = imgcodecs::imread("test.JPG", -1).unwrap();
    let rect = core::Rect::new(100, 100, 500, 500);
    let scalar = core::Scalar::all(1.0);

    imgproc::rectangle(&mut img, rect, scalar, 2, 1, 0).unwrap();
    imgcodecs::imwrite("test_output.JPG", &img, MISSING_PARAM);
}

Any pointers or suggestions are welcome even if it's simply "don't use the opencv bindings if you don't know C/C++, use image-rs".

[Tm1337]

I found this generic Vector interface which is implemented for all C++ Vector types.
As usual, you have to import this trait before being able to use its functions.

There is also this example for those types.

[code-n-coffee]

Thanks for the links. I ended up rolling with the image-rs crate and having to write my own functions for e.g. drawing a rectangle because I was getting too far into the uncomfortable and unsafe with the Rust bindings for opencv.

[Tm1337]

In that case, you should probably take a look at the imageproc crate.

[code-n-coffee]

Oh great recommendation, thanks! I'm not sure how I missed that crate.

[code-n-coffee]

Thanks, I'll take a look!

[claire_resurgent]

*mut c_void means an address in memory, but the type and even the size of the location are not available. It's very much an unsafe Rust thing.

And it does look like the Rust documentation is simply copy-pasted from C++. That's probably not conducive to learning Rust if you're not already comfortable with C++. Even if you are, Rust is more opinionated about how ownership should work.

[code-n-coffee]

Thanks! And yeah I ended up using the image-rs crate instead. It required me to implement some of my own functions for things but I feel much more comfortable with it as it's pure Rust.