ltk/src/widget/image/mod.rs

// SPDX-License-Identifier: LGPL-2.1-only
// Copyright (C) 2026 Liberux Labs, S. L. <info@liberux.net>

use std::sync::Arc;
use crate::types::{ Length, Rect };
use crate::render::Canvas;

/// A static image widget that renders RGBA pixel data.
///
/// Images are scaled to fill their allocated rect. Alpha blending against the
/// background is handled automatically (straight → premultiplied conversion).
///
/// The pixel buffer is shared via `Arc` so reusing the same image across
/// frames (e.g. a background decoded once at startup) is a cheap pointer
/// copy instead of a full `Vec<u8>` clone.
///
/// ```rust,no_run
/// # use std::sync::Arc;
/// # use ltk::{ img_widget, Element, Length };
/// # #[ derive( Clone ) ] enum Msg {}
/// # fn _ex( rgba_bytes: Arc<Vec<u8>>, width: u32, height: u32 ) -> Element<Msg> {
/// // Display at 40 % of the viewport width by 20 % of its height instead of
/// // the source's intrinsic pixel size — scales across screens with no tweaks.
/// img_widget( rgba_bytes, width, height )
///     .size( Length::vw( 40.0 ), Length::vh( 20.0 ) )
///     .opacity( 0.8 )
/// .into()
/// # }
/// ```
pub struct Image
{
	/// Raw RGBA pixel data (4 bytes per pixel, straight alpha).
	pub( crate ) rgba:    Arc<Vec<u8>>,
	/// Pixel width of the source image.
	pub( crate ) width:   u32,
	/// Pixel height of the source image.
	pub( crate ) height:  u32,
	/// When `true` the image scales to fill the available width (cover mode).
	pub( crate ) cover:   bool,
	/// Optional explicit display size (Length values, resolved at layout time).
	pub( crate ) display_size: Option<( Length, Length )>,
	/// Optional extent along the viewport's **short** side (width in portrait,
	/// height in landscape), with the other axis following the source aspect
	/// ratio. Resolved at layout time. Takes precedence over `display_size`
	/// and `cover`.
	pub( crate ) short_side: Option<Length>,
	/// Opacity multiplier in `[0.0, 1.0]`. Default: `1.0`.
	pub( crate ) opacity: f32,
}

impl Image
{
	/// Create an image from a shared RGBA buffer.
	///
	/// `width` and `height` must match the dimensions of `rgba`.
	pub fn new( rgba: Arc<Vec<u8>>, width: u32, height: u32 ) -> Self
	{
		Self { rgba, width, height, cover: false, display_size: None, short_side: None, opacity: 1.0 }
	}

	/// Load an image from a file path. Supports PNG, JPEG, and other formats
	/// supported by the [`image`](https://crates.io/crates/image) crate.
	pub fn from_path( path: &str ) -> Result<Self, Box<dyn std::error::Error>>
	{
		let img = image::open( path )?.into_rgba8();
		let ( width, height ) = img.dimensions();
		Ok( Self { rgba: Arc::new( img.into_raw() ), width, height, cover: false, display_size: None, short_side: None, opacity: 1.0 } )
	}

	/// Scale the image to fill the available width, preserving aspect ratio (cover mode).
	pub fn cover( mut self ) -> Self
	{
		self.cover = true;
		self
	}

	/// Set an explicit display size. Accepts logical `f32` pixels or any
	/// [`Length`] variant (e.g. `Length::vw(13.0)` for 13 % of viewport width).
	pub fn size( mut self, width: impl Into<Length>, height: impl Into<Length> ) -> Self
	{
		self.display_size = Some( ( width.into(), height.into() ) );
		self
	}

	/// Size the image by its extent along the viewport's **short** side —
	/// the width in portrait, the height in landscape — with the other axis
	/// derived from the source aspect ratio. Pairs with
	/// [`Length::orient`](crate::Length::orient) to express a rule like "40 %
	/// of the width in portrait, 5 % of the height in landscape" in one call:
	/// `img_widget( rgba, w, h ).short_side( Length::orient( 40.0, 5.0 ) )`.
	pub fn short_side( mut self, extent: impl Into<Length> ) -> Self
	{
		self.short_side = Some( extent.into() );
		self
	}

	/// Set the opacity multiplier. Clamped to `[0.0, 1.0]`.
	pub fn opacity( mut self, o: f32 ) -> Self
	{
		self.opacity = o.clamp( 0.0, 1.0 );
		self
	}

	/// Return the preferred `(width, height)` given available `max_width`.
	/// `canvas` is used to resolve viewport-relative [`Length`] values.
	pub fn preferred_size( &self, max_width: f32, canvas: &Canvas ) -> (f32, f32)
	{
		if let Some( extent ) = &self.short_side
		{
			let ( vw, vh ) = canvas.viewport_layout();
			let s          = canvas.resolve_geom( *extent ).max( 0.0 );
			let sw         = self.width  as f32;
			let sh         = self.height as f32;
			if sw <= 0.0 || sh <= 0.0 { return ( s, s ); }
			// Portrait: short side is the width → `s` sets the width.
			// Landscape: short side is the height → `s` sets the height.
			if vw <= vh
			{
				return ( s, s * sh / sw );
			} else {
				return ( s * sw / sh, s );
			}
		}
		if let Some( ( w, h ) ) = &self.display_size
		{
			let rw  = canvas.resolve_geom( *w ).max( 0.0 );
			let rh  = canvas.resolve_geom( *h ).max( 0.0 );
			return ( rw, rh );
		}
		if self.cover
		{
			( max_width, max_width * self.height as f32 / self.width as f32 )
		} else {
			let scale = max_width / self.width as f32;
			( max_width, self.height as f32 * scale )
		}
	}

	/// Draw the image into `canvas` at `rect`.
	pub fn draw( &self, canvas: &mut Canvas, rect: Rect )
	{
		canvas.draw_image_data( &self.rgba[..], self.width, self.height, rect, self.opacity );
	}
}

#[ cfg( test ) ]
mod tests;