ltk/src/render/clip.rs

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

//! Clip-mask management for [`SoftwareCanvas`]. The partial-redraw
//! path calls `set_clip_rects` before every repaint so only pixels
//! inside the dirty rects are touched. `set_clip_path` installs an
//! arbitrary anti-aliased vector path as the clip (an exact tiny-skia
//! coverage [`Mask`]) for shaped clipping such as a circular avatar.
//! [`interior_clip`] narrows whatever clip is active to a widget's rect, on either backend.

use tiny_skia::{ FillRule, Mask, PathBuilder, Transform };

use crate::types::Rect;

use super::SoftwareCanvas;

/// The active clip `outer` narrowed to `inner`. An empty intersection must still clip everything: an empty rect list would lift the clip.
pub( crate ) fn interior_clip( outer: &[ Rect ], inner: Rect ) -> Vec<Rect>
{
	if outer.is_empty()
	{
		return vec![ inner ];
	}
	let clip: Vec<Rect> = outer.iter()
		.filter_map( |o| rect_intersect( *o, inner ) )
		.collect();
	if clip.is_empty()
	{
		vec![ Rect { x: 0.0, y: 0.0, width: 0.0, height: 0.0 } ]
	} else {
		clip
	}
}

fn rect_intersect( a: Rect, b: Rect ) -> Option<Rect>
{
	let x0 = a.x.max( b.x );
	let y0 = a.y.max( b.y );
	let x1 = ( a.x + a.width  ).min( b.x + b.width  );
	let y1 = ( a.y + a.height ).min( b.y + b.height );
	if x1 > x0 && y1 > y0
	{
		Some( Rect { x: x0, y: y0, width: x1 - x0, height: y1 - y0 } )
	} else {
		None
	}
}

impl SoftwareCanvas
{
	/// Set the active clip region to the union of `rects` (physical pixels).
	pub fn set_clip_rects( &mut self, rects: &[Rect] )
	{
		let w = self.pixmap.width();
		let h = self.pixmap.height();
		let Some( mut mask ) = Mask::new( w, h ) else
		{
			self.clip_mask   = None;
			self.clip_bounds = Vec::new();
			return;
		};
		let mut pb = PathBuilder::new();
		for r in rects
		{
			let x0 = r.x.max( 0.0 ).min( w as f32 );
			let y0 = r.y.max( 0.0 ).min( h as f32 );
			let x1 = ( r.x + r.width  ).max( 0.0 ).min( w as f32 );
			let y1 = ( r.y + r.height ).max( 0.0 ).min( h as f32 );
			if x1 <= x0 || y1 <= y0 { continue; }
			pb.push_rect( tiny_skia::Rect::from_ltrb( x0, y0, x1, y1 )
				.expect( "valid rect" ) );
		}
		if let Some( path ) = pb.finish()
		{
			mask.fill_path( &path, FillRule::Winding, false, Transform::identity() );
			self.clip_mask   = Some( mask );
			self.clip_bounds = rects.to_vec();
		} else if rects.is_empty() {
			self.clip_mask   = None;
			self.clip_bounds = Vec::new();
		} else {
			// Only zero-area rects: clip everything, like the GLES zero scissor.
			self.clip_mask   = Some( mask );
			self.clip_bounds = Vec::new();
		}
	}

	/// Clip subsequent paints to an arbitrary vector path (surface
	/// coordinates), via an anti-aliased tiny-skia coverage mask. The GLES
	/// counterpart composites an offscreen layer through an equivalent
	/// anti-aliased mask; both give a smooth clipped edge.
	pub fn set_clip_path( &mut self, cmds: &[ crate::types::PathCmd ] )
	{
		let w = self.pixmap.width();
		let h = self.pixmap.height();
		let Some( path ) = crate::render::helpers::build_ts_path( cmds ) else
		{
			self.clear_clip();
			return;
		};
		let Some( mut mask ) = Mask::new( w, h ) else
		{
			self.clip_mask   = None;
			self.clip_bounds = Vec::new();
			return;
		};
		mask.fill_path( &path, FillRule::Winding, true, Transform::identity() );
		let b = path.bounds();
		self.clip_mask   = Some( mask );
		self.clip_bounds = vec![ Rect
		{
			x:      b.left(),
			y:      b.top(),
			width:  b.right()  - b.left(),
			height: b.bottom() - b.top(),
		} ];
	}

	/// Remove the active clip so subsequent paints cover the full canvas.
	pub fn clear_clip( &mut self )
	{
		self.clip_mask   = None;
		self.clip_bounds = Vec::new();
	}

	pub ( super ) fn has_clip( &self ) -> bool
	{
		self.clip_mask.is_some()
	}

	/// Snapshot of the active clip bounds (empty when no clip is set).
	pub fn clip_bounds_snapshot( &self ) -> Vec<Rect>
	{
		if self.has_clip() { self.clip_bounds.clone() } else { Vec::new() }
	}

	/// True when a horizontal strip `y` in `[y0, y1]` touches any clip bound.
	pub ( super ) fn strip_intersects_clip( &self, y0: f32, y1: f32 ) -> bool
	{
		if self.clip_bounds.is_empty() { return !self.has_clip(); }
		self.clip_bounds.iter().any( |r|
		{
			y1 > r.y && y0 < r.y + r.height
		} )
	}

	/// Zero the alpha+RGB bytes inside each rect, used by the
	/// partial-redraw path when the surface background is fully
	/// transparent.
	pub fn clear_rects_transparent( &mut self, rects: &[Rect] )
	{
		let pw    = self.pixmap.width()  as i32;
		let ph    = self.pixmap.height() as i32;
		let bytes = self.pixmap.data_mut();
		for r in rects
		{
			let x0 = ( r.x as i32 ).max( 0 );
			let y0 = ( r.y as i32 ).max( 0 );
			let x1 = ( ( r.x + r.width  ).ceil() as i32 ).min( pw );
			let y1 = ( ( r.y + r.height ).ceil() as i32 ).min( ph );
			if x1 <= x0 || y1 <= y0 { continue; }
			for py in y0..y1
			{
				let row_start = ( py * pw + x0 ) as usize * 4;
				let row_end   = ( py * pw + x1 ) as usize * 4;
				bytes[ row_start..row_end ].fill( 0 );
			}
		}
	}
}