First commit. Version 0.1.0

src/render/clip.rs

@@ -0,0 +1,100 @@
+// 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.
+
+use tiny_skia::{ FillRule, Mask, PathBuilder, Transform };
+
+use crate::types::Rect;
+
+use super::SoftwareCanvas;
+
+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 {
+			self.clip_mask   = None;
+			self.clip_bounds = Vec::new();
+		}
+	}
+
+	/// 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 );
+			}
+		}
+	}
+}