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/*
* Copyright (c) 2023, Tim Ledbetter <timledbetter@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibGfx/Bitmap.h>
#include <LibGfx/Painter.h>
#include <LibTest/TestCase.h>
// Scaling modes which use linear interpolation should use premultiplied alpha.
// This prevents colors from changing hue unexpectedly when there is a change in opacity.
// This test uses an image that transitions from a completely opaque pixel in the top left to a completely transparent background.
// We ensure that premultipled alpha is used by checking that the RGB values of the interpolated pixels do not change, just the alpha values.
TEST_CASE(test_painter_scaling_uses_premultiplied_alpha)
{
auto test_scaling_mode = [](auto scaling_mode) {
auto src_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 2, 2 }));
src_bitmap->fill(Color::Transparent);
src_bitmap->set_pixel({ 0, 0 }, Color::White);
auto scaled_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 5, 5 }));
scaled_bitmap->fill(Color::Transparent);
Gfx::Painter painter(scaled_bitmap);
painter.draw_scaled_bitmap(scaled_bitmap->rect(), src_bitmap, src_bitmap->rect(), 1.0f, scaling_mode);
auto top_left_pixel = scaled_bitmap->get_pixel(0, 0);
EXPECT_EQ(top_left_pixel, Color::White);
auto center_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().center());
EXPECT(center_pixel.alpha() > 0);
EXPECT(center_pixel.alpha() < 255);
EXPECT_EQ(center_pixel.with_alpha(0), Color(Color::White).with_alpha(0));
auto bottom_right_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().bottom_right());
EXPECT_EQ(bottom_right_pixel, Color::Transparent);
};
test_scaling_mode(Gfx::Painter::ScalingMode::BilinearBlend);
// FIXME: Include ScalingMode::SmoothPixels as part of this test
// This mode does not currently pass this test, as it behave according to the spec
// defined here: https://drafts.csswg.org/css-images/#valdef-image-rendering-pixelated
// test_scaling_mode(Gfx::Painter::ScalingMode::SmoothPixels);
}
TEST_CASE(test_bitmap_scaling_uses_premultiplied_alpha)
{
auto src_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 2, 2 }));
src_bitmap->fill(Color::Transparent);
src_bitmap->set_pixel({ 0, 0 }, Color::White);
auto scaled_bitmap = MUST(src_bitmap->scaled(2.5f, 2.5f));
EXPECT_EQ(scaled_bitmap->width(), 5);
EXPECT_EQ(scaled_bitmap->height(), 5);
auto top_left_pixel = scaled_bitmap->get_pixel(0, 0);
EXPECT_EQ(top_left_pixel, Color::White);
auto center_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().center());
EXPECT(center_pixel.alpha() > 0);
EXPECT(center_pixel.alpha() < 255);
EXPECT_EQ(center_pixel.with_alpha(0), Color(Color::White).with_alpha(0));
auto bottom_right_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().bottom_right());
EXPECT_EQ(bottom_right_pixel, Color::Transparent);
}
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