yay zooming woohoo

src/lib.rs

@@ -3,6 +3,7 @@ use std::num::NonZeroUsize;
 #[global_allocator]
 static ALLOC: mimalloc::MiMalloc = mimalloc::MiMalloc;
 
+#[derive(PartialEq)]
 pub enum PrerenderLimit {
 	All,
 	Limited(NonZeroUsize)
@@ -13,3 +14,46 @@ 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
+	}
+}