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66 lines
3 KiB
C++
66 lines
3 KiB
C++
/*
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* Copyright (c) 2023, Tim Ledbetter <timledbetter@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <LibGfx/Bitmap.h>
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#include <LibGfx/Painter.h>
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#include <LibTest/TestCase.h>
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// Scaling modes which use linear interpolation should use premultiplied alpha.
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// This prevents colors from changing hue unexpectedly when there is a change in opacity.
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// This test uses an image that transitions from a completely opaque pixel in the top left to a completely transparent background.
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// We ensure that premultipled alpha is used by checking that the RGB values of the interpolated pixels do not change, just the alpha values.
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TEST_CASE(test_painter_scaling_uses_premultiplied_alpha)
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{
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auto test_scaling_mode = [](auto scaling_mode) {
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auto src_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 2, 2 }));
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src_bitmap->fill(Color::Transparent);
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src_bitmap->set_pixel({ 0, 0 }, Color::White);
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auto scaled_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 5, 5 }));
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scaled_bitmap->fill(Color::Transparent);
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Gfx::Painter painter(scaled_bitmap);
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painter.draw_scaled_bitmap(scaled_bitmap->rect(), src_bitmap, src_bitmap->rect(), 1.0f, scaling_mode);
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auto top_left_pixel = scaled_bitmap->get_pixel(0, 0);
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EXPECT_EQ(top_left_pixel, Color::White);
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auto center_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().center());
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EXPECT(center_pixel.alpha() > 0);
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EXPECT(center_pixel.alpha() < 255);
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EXPECT_EQ(center_pixel.with_alpha(0), Color(Color::White).with_alpha(0));
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auto bottom_right_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().bottom_right().translated(-1));
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EXPECT_EQ(bottom_right_pixel, Color::Transparent);
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};
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test_scaling_mode(Gfx::ScalingMode::BilinearBlend);
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// FIXME: Include ScalingMode::SmoothPixels as part of this test
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// This mode does not currently pass this test, as it behave according to the spec
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// defined here: https://drafts.csswg.org/css-images/#valdef-image-rendering-pixelated
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// test_scaling_mode(Gfx::ScalingMode::SmoothPixels);
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}
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TEST_CASE(test_bitmap_scaling_uses_premultiplied_alpha)
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{
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auto src_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 2, 2 }));
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src_bitmap->fill(Color::Transparent);
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src_bitmap->set_pixel({ 0, 0 }, Color::White);
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auto scaled_bitmap = MUST(src_bitmap->scaled(2.5f, 2.5f));
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EXPECT_EQ(scaled_bitmap->width(), 5);
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EXPECT_EQ(scaled_bitmap->height(), 5);
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auto top_left_pixel = scaled_bitmap->get_pixel(0, 0);
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EXPECT_EQ(top_left_pixel, Color::White);
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auto center_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().center());
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EXPECT(center_pixel.alpha() > 0);
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EXPECT(center_pixel.alpha() < 255);
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EXPECT_EQ(center_pixel.with_alpha(0), Color(Color::White).with_alpha(0));
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auto bottom_right_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().bottom_right().translated(-1));
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EXPECT_EQ(bottom_right_pixel, Color::Transparent);
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}
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