ltk/src/draw/paint.rs

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

//! Painting a surface's view on its canvas, the same for every backend and renderer. The backend prepares the canvas before and presents it after; see [`crate::platform::Platform`].

use std::collections::HashMap;
use std::sync::Arc;

use crate::event_loop::SurfaceState;
use crate::render::Canvas;
use crate::types::{ Color, Rect };
use crate::widget::Element;

use super::{ build_draw_ctx, commit_draw_ctx, compute_damage, layout_and_draw, DrawCtx };
use super::chrome::{ draw_fallback_banner, draw_titlebar };

/// The canvas in `slot` at `pw × ph`, built by `create` with the theme's fonts and `scale` on first use.
pub( crate ) fn fit_canvas( slot: &mut Option<Canvas>, pw: u32, ph: u32, scale: f32, create: impl FnOnce() -> Canvas ) -> &mut Canvas
{
	let canvas = slot.get_or_insert_with( ||
	{
		let mut c = create();
		c.set_dpi_scale( scale );
		if let Some( reg ) = crate::theme::build_font_registry()
		{
			c.set_font_registry( Arc::new( reg ) );
		}
		c
	} );
	if canvas.size() != ( pw, ph )
	{
		canvas.resize( pw, ph );
		canvas.set_dpi_scale( scale );
	}
	canvas
}

/// Paint `view` over the whole of `canvas`, cleared to transparent, with no focus, hover or press, for a surface that takes no input such as a subsurface. `scroll` and `viewport` keep its sub-canvases between paints.
pub( crate ) fn paint_detached<Msg: Clone>( canvas: &mut Canvas, view: &Element<Msg>, scroll: &mut HashMap<usize, Canvas>, viewport: &mut HashMap<usize, Canvas> )
{
	canvas.clear_clip();
	canvas.clear();
	let ( pw, ph ) = canvas.size();
	let screen_rect = Rect { x: 0.0, y: 0.0, width: pw as f32, height: ph as f32 };
	let mut ctx = DrawCtx
	{
		focused_idx:            None,
		hovered_idx:            None,
		pressed_idx:            None,
		cursor_state:           HashMap::new(),
		selection_anchor:       HashMap::new(),
		text_scroll:            HashMap::new(),
		widget_rects:           Vec::new(),
		debug_layout:           false,
		scroll_offsets:         HashMap::new(),
		scroll_rects:           Vec::new(),
		scroll_canvases:        std::mem::take( scroll ),
		viewport_canvases:      std::mem::take( viewport ),
		viewport_seq:           0,
		scroll_navigable_items: HashMap::new(),
		scroll_clipped:         Vec::new(),
		previous_widget_rects:  Vec::new(),
		accessible_extras:      Vec::new(),
		live_depth:             0,
		origin:                 ( 0.0, 0.0 ),
		blur_regions:           Vec::new(),
	};
	layout_and_draw::<Msg>( view, canvas, screen_rect, &mut ctx, 0 );
	*scroll   = ctx.scroll_canvases;
	*viewport = ctx.viewport_canvases;
}

/// Repaint the whole surface. Returns the rects that changed when `precise_damage` asks for them and the content did not change wholesale, else none, meaning the whole surface.
pub( crate ) fn paint_full<Msg: Clone, S>(
	ss:             &mut SurfaceState<Msg, S>,
	view:           &Element<Msg>,
	bg:             Color,
	debug_layout:   bool,
	precise_damage: bool,
	pw:             u32,
	ph:             u32,
	scale:          f32,
) -> Vec<Rect>
{
	let canvas = ss.canvas.as_mut().expect( "canvas prepared" );
	canvas.clear_clip();
	if bg.a > 0.0 { canvas.fill( bg ); } else { canvas.clear(); }

	let ctx = paint_view( ss, view, debug_layout, pw, ph, scale );

	let damage = if ss.content_dirty || !precise_damage
	{
		Vec::new()
	} else {
		compute_damage(
			&ss.frame.widget_rects,
			&ctx.widget_rects,
			ss.frame.prev_focused,
			ss.frame.prev_hovered,
			ss.frame.prev_pressed,
			ss.focused_idx,
			ss.hovered_idx,
			ss.gesture.pressed_idx,
			pw, ph,
		)
	};

	commit_draw_ctx( &mut ss.frame, ss.focused_idx, ss.hovered_idx, ss.gesture.pressed_idx, ctx );
	ss.content_dirty = false;
	damage
}

/// Repaint only under `dirty_rects`, keeping the rest of the previous frame's pixels, and return them as the damage.
pub( crate ) fn paint_partial<Msg: Clone, S>(
	ss:          &mut SurfaceState<Msg, S>,
	view:        &Element<Msg>,
	bg:          Color,
	dirty_rects: Vec<Rect>,
	pw:          u32,
	ph:          u32,
	scale:       f32,
) -> Vec<Rect>
{
	let canvas = ss.canvas.as_mut().expect( "canvas prepared" );
	canvas.set_clip_rects( &dirty_rects );
	// Start the dirty rects from the background rather than the previous widget's pixels.
	if bg.a > 0.0 { canvas.fill( bg ); } else { canvas.clear_rects_transparent( &dirty_rects ); }

	let ctx = paint_view( ss, view, false, pw, ph, scale );

	if let Some( canvas ) = ss.canvas.as_mut() { canvas.clear_clip(); }
	commit_draw_ctx( &mut ss.frame, ss.focused_idx, ss.hovered_idx, ss.gesture.pressed_idx, ctx );
	ss.content_dirty = false;
	dirty_rects
}

/// The title bar, the widget tree and what the runtime draws over it, on a canvas already cleared where needed.
fn paint_view<Msg: Clone, S>(
	ss:           &mut SurfaceState<Msg, S>,
	view:         &Element<Msg>,
	debug_layout: bool,
	pw:           u32,
	ph:           u32,
	scale:        f32,
) -> DrawCtx<Msg>
{
	let canvas      = ss.canvas.as_mut().expect( "canvas prepared" );
	let sf          = scale;
	let tb_h        = ss.titlebar_height * sf;
	let inset       = ss.insets;
	let osk_h       = crate::event_loop::osk::place_osk( &mut ss.osk, pw, ph, sf, inset );
	let top         = tb_h + inset.top * sf;
	let screen_rect = Rect
	{
		x:      inset.left * sf,
		y:      top,
		width:  ( pw as f32 - ( inset.left + inset.right ) * sf ).max( 0.0 ),
		height: ( ph as f32 - top - osk_h - inset.bottom * sf ).max( 0.0 ),
	};

	ss.titlebar_close_rect = draw_titlebar( canvas, &ss.titlebar_title, pw, tb_h, sf );

	// A text field draws its cursor when focused however the focus came.
	let drawn_focus = ss.focused_idx.filter( |&idx| ss.focus_visible || crate::tree::find_handlers( &ss.frame.widget_rects, idx ).is_some_and( |h| h.is_text_input() ) );
	let mut ctx = build_draw_ctx( &mut ss.frame, drawn_focus, ss.hovered_idx, ss.gesture.pressed_idx, debug_layout );
	layout_and_draw::<Msg>( view, canvas, screen_rect, &mut ctx, 0 );

	if ctx.debug_layout
	{
		for w in &ctx.widget_rects
		{
			canvas.stroke_rect( w.rect, Color::rgb( 1.0, 0.0, 0.0 ), 1.5, 0.0 );
		}
	}

	if let Some( panel ) = ss.osk.as_mut() { panel.draw( canvas ); }
	if let Some( ref menu ) = ss.context_menu
	{
		super::draw_context_menu( canvas, menu );
	}

	// Last, so it sits over every widget. Outside a partial repaint's clip the previous frame's banner stays.
	draw_fallback_banner( canvas, pw, sf );
	ctx
}