Add height/width swap for SharedPixelBuffer

[guimath]

Hi I'm writing an image gallery where the images are the same size but sometimes in landscape, sometimes in portrait.

Basically the idea is to only create a SharedPixelBuffer at the initialization and then directly change the data depending on the image to display. The issue is when the orientation changes, AFAIK I then have to re create a SharedPixelBuffer, even though the data size has not changed.

A work around I have tested is adding a swap_width_height function to SharedPixelBuffer like so :

impl<Pixel> SharedPixelBuffer<Pixel> {
    ...
    /// swaps width and height without changing the data
    pub fn swap_width_height(&mut self) {
        std::mem::swap(&mut self.width, &mut self.height);
    }
}

Was wondering if such a function would be a good addition or if there's another way of going about it.

[tronical]

I'm not sure that function would be a good fit, but perhaps we could add a these two functions like in the image crate: https://docs.rs/image/latest/image/struct.ImageBuffer.html#method.from_vec (but shared_vector in the name).

@ogoffart what do you think?

[ogoffart]

Yes, having a way to sonstruct from a slint::SharedVector seems like a good idea.

[guimath]

So something like:

/// Creates an SharedPixelBuffer out of an existing buffer. Returns None if the buffer is not big enough.
pub fn from_shared_pixel_buffer(
    width: u32,
    height: u32,
    buf: SharedPixelBuffer<Pixel>,
) -> Option<SharedPixelBuffer<Pixel>> {
    if width * height != buf.width * buf.height {
        return None;
    }
    Some(Self { width, height, data: buf.data })
}

[tronical]

Not quite, more like this:

fn as_vec(&self) -> &SharedVector<Pixel> { &self.data }
fn from_vec(width: u32, height: u32, data: SharedVector<Pixel>) -> Result<Self, XXXNeedAnErrorTypeHere> { todo!() }

(in theory we could also make the fields public, but then it's easier to create an image buffer with invalid size)

[guimath]

But in that case wouldn't be easier to have a reshape function that takes a width and height as arguments and returns an error if the size is bigger then the buffer, and Ok otherwise like:

pub fn reshape(&mut self, width:u32, height:u32) -> Result<(), XXXNeedAnErrorTypeHere>

It's just that the other way seems like it will be a bit verbose imo