New kitty image backend (#74)

* Initial attempt at supporting new backend for kitty images

* it's almost working !!

* it almost basically works

* yaaayyyy it works

* Use github kittage

* Uhhhh various improvements from kittage and psx-shm

* Remove logging

* incorporate recovering from deleted images

* Make it work correctly with ghostty image eviction too

* fall back to stdout if shms don't work

* Make help page work again

* zooming basically does what you'd expect now

* yay zooming woohoo

* clean up top and bottom rendering

* Only allow zooming in kitty

* Add debug logging and fix cursor placement after image display

* yaaaay zooming out once you're already zoomed in and respecting kitty's limits for how big of an image to display

* mmmm maybe it's finally ready to merge...

* Update deps

* Switch around list of items on changelog

* fmt

* Small fixes to avoid panic and allow zooming back in after zooming out

src/lib.rs

@@ -3,12 +3,57 @@ use std::num::NonZeroUsize;
 #[global_allocator]
 static ALLOC: mimalloc::MiMalloc = mimalloc::MiMalloc;
 
+#[derive(PartialEq)]
 pub enum PrerenderLimit {
 	All,
 	Limited(NonZeroUsize)
 }
 
 pub mod converter;
+pub mod kitty;
 pub mod renderer;
 pub mod skip;
 pub mod tui;
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum FitOrFill {
+	Fit,
+	Fill
+}
+
+pub struct ScaledResult {
+	width: f32,
+	height: f32,
+	scale_factor: f32
+}
+
+pub fn scale_img_for_area(
+	(img_width, img_height): (f32, f32),
+	(area_width, area_height): (f32, f32),
+	fit_or_fill: FitOrFill
+) -> ScaledResult {
+	// and get its aspect ratio
+	let img_aspect_ratio = img_width / img_height;
+
+	// Then we get the full pixel dimensions of the area provided to us, and the aspect ratio
+	// of that area
+	let area_aspect_ratio = area_width / area_height;
+
+	// and get the ratio that this page would have to be scaled by to fit perfectly within the
+	// area provided to us.
+	// we do this first by comparing the aspec ratio of the page with the aspect ratio of the
+	// area to fit it within. If the aspect ratio of the page is larger, then we need to scale
+	// the width of the page to fill perfectly within the height of the area. Otherwise, we
+	// scale the height to fit perfectly. The dimension that _is not_ scaled to fit perfectly
+	// is scaled by the same factor as the dimension that _is_ scaled perfectly.
+	let scale_factor = match (img_aspect_ratio > area_aspect_ratio, fit_or_fill) {
+		(true, FitOrFill::Fit) | (false, FitOrFill::Fill) => area_width / img_width,
+		(false, FitOrFill::Fit) | (true, FitOrFill::Fill) => area_height / img_height
+	};
+
+	ScaledResult {
+		width: img_width * scale_factor,
+		height: img_height * scale_factor,
+		scale_factor
+	}
+}