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LibWeb: Add BorderRadiusCornerClipper

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This is a helper class for clipping the corners off a element.

This works in a similar way to how (outline) borders are painted.

The steps are:
  1. A small bitmap that fits only the corners is allocated
  2. The corners are painted into the bitmap
  3. The existing pixels (where the corners will be painted)
     are copied using the (inverse) corner bitmap as a mask
     (done before the element is painted)
  4. The element is painted
  5. The areas outside the corner radii are restored

Like with the borders, this only requires allocation on the first
paint.
This commit is contained in:
MacDue 2022-06-15 21:15:29 +01:00 • committed by Linus Groh
parent 4dfbbd5965
commit 830632407f
3 changed files with 155 additions and 0 deletions
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51
Userland/Libraries/LibWeb/Painting/BorderRadiusCornerClipper.h Normal file
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/*
* Copyright (c) 2022, MacDue <macdue@dueutil.tech>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <LibGfx/AntiAliasingPainter.h>
#include <LibWeb/Painting/BorderPainting.h>
namespace Web::Painting {
class BorderRadiusCornerClipper {
public:
static ErrorOr<BorderRadiusCornerClipper> create(Gfx::IntRect const& border_rect, BorderRadiiData const& border_radii);
void sample_under_corners(Gfx::Painter& page_painter);
void blit_corner_clipping(Gfx::Painter& page_painter);
private:
using CornerRadius = Gfx::AntiAliasingPainter::CornerRadius;
struct CornerData {
struct CornerRadii {
CornerRadius top_left;
CornerRadius top_right;
CornerRadius bottom_right;
CornerRadius bottom_left;
} corner_radii;
struct CornerLocations {
Gfx::IntPoint top_left;
Gfx::IntPoint top_right;
Gfx::IntPoint bottom_right;
Gfx::IntPoint bottom_left;
};
CornerLocations page_locations;
CornerLocations bitmap_locations;
Gfx::IntSize corner_bitmap_size;
} m_data;
NonnullRefPtr<Gfx::Bitmap> m_corner_bitmap;
bool m_has_sampled { false };
BorderRadiusCornerClipper(CornerData corner_data, NonnullRefPtr<Gfx::Bitmap> corner_bitmap)
: m_data(move(corner_data))
, m_corner_bitmap(corner_bitmap)
{
}
};
}