TestScalingFunctions.cpp 3.0 KB

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  1. /*
  2. * Copyright (c) 2023, Tim Ledbetter <timledbetter@gmail.com>
  3. *
  4. * SPDX-License-Identifier: BSD-2-Clause
  5. */
  6. #include <LibGfx/Bitmap.h>
  7. #include <LibGfx/Painter.h>
  8. #include <LibTest/TestCase.h>
  9. // Scaling modes which use linear interpolation should use premultiplied alpha.
  10. // This prevents colors from changing hue unexpectedly when there is a change in opacity.
  11. // This test uses an image that transitions from a completely opaque pixel in the top left to a completely transparent background.
  12. // We ensure that premultipled alpha is used by checking that the RGB values of the interpolated pixels do not change, just the alpha values.
  13. TEST_CASE(test_painter_scaling_uses_premultiplied_alpha)
  14. {
  15. auto test_scaling_mode = [](auto scaling_mode) {
  16. auto src_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 2, 2 }));
  17. src_bitmap->fill(Color::Transparent);
  18. src_bitmap->set_pixel({ 0, 0 }, Color::White);
  19. auto scaled_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 5, 5 }));
  20. scaled_bitmap->fill(Color::Transparent);
  21. Gfx::Painter painter(scaled_bitmap);
  22. painter.draw_scaled_bitmap(scaled_bitmap->rect(), src_bitmap, src_bitmap->rect(), 1.0f, scaling_mode);
  23. auto top_left_pixel = scaled_bitmap->get_pixel(0, 0);
  24. EXPECT_EQ(top_left_pixel, Color::White);
  25. auto center_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().center());
  26. EXPECT(center_pixel.alpha() > 0);
  27. EXPECT(center_pixel.alpha() < 255);
  28. EXPECT_EQ(center_pixel.with_alpha(0), Color(Color::White).with_alpha(0));
  29. auto bottom_right_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().bottom_right().translated(-1));
  30. EXPECT_EQ(bottom_right_pixel, Color::Transparent);
  31. };
  32. test_scaling_mode(Gfx::Painter::ScalingMode::BilinearBlend);
  33. // FIXME: Include ScalingMode::SmoothPixels as part of this test
  34. // This mode does not currently pass this test, as it behave according to the spec
  35. // defined here: https://drafts.csswg.org/css-images/#valdef-image-rendering-pixelated
  36. // test_scaling_mode(Gfx::Painter::ScalingMode::SmoothPixels);
  37. }
  38. TEST_CASE(test_bitmap_scaling_uses_premultiplied_alpha)
  39. {
  40. auto src_bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, { 2, 2 }));
  41. src_bitmap->fill(Color::Transparent);
  42. src_bitmap->set_pixel({ 0, 0 }, Color::White);
  43. auto scaled_bitmap = MUST(src_bitmap->scaled(2.5f, 2.5f));
  44. EXPECT_EQ(scaled_bitmap->width(), 5);
  45. EXPECT_EQ(scaled_bitmap->height(), 5);
  46. auto top_left_pixel = scaled_bitmap->get_pixel(0, 0);
  47. EXPECT_EQ(top_left_pixel, Color::White);
  48. auto center_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().center());
  49. EXPECT(center_pixel.alpha() > 0);
  50. EXPECT(center_pixel.alpha() < 255);
  51. EXPECT_EQ(center_pixel.with_alpha(0), Color(Color::White).with_alpha(0));
  52. auto bottom_right_pixel = scaled_bitmap->get_pixel(scaled_bitmap->rect().bottom_right().translated(-1));
  53. EXPECT_EQ(bottom_right_pixel, Color::Transparent);
  54. }