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LibGfx: Implement box sampling image scaling

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Box sampling is a scaling algorithm that averages all the pixels that
form the source for the target pixel. For example, if you would resize a
9x9 image to 3x3, each target pixel would encompass a 3x3 pixel area in
the source image.

Box sampling is a near perfect scaling algorithm for downscaling. When
upscaling with this algorithm, the result is similar to nearest neighbor
or smooth pixels.
This commit is contained in:
Jelle Raaijmakers 2023-05-19 00:26:34 +02:00 • committed by Andreas Kling
parent 4944b16bd5
commit eb418bec32
2 changed files with 60 additions and 0 deletions
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59
Userland/Libraries/LibGfx/Painter.cpp
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@ -1180,6 +1180,59 @@ ALWAYS_INLINE static void do_draw_integer_scaled_bitmap(Gfx::Bitmap& target, Int
}
}
template<bool has_alpha_channel, typename GetPixel>
ALWAYS_INLINE static void do_draw_box_sampled_scaled_bitmap(Gfx::Bitmap& target, IntRect const& dst_rect, IntRect const& clipped_rect, Gfx::Bitmap const& source, FloatRect const& src_rect, GetPixel get_pixel, float opacity)
{
float source_pixel_width = src_rect.width() / dst_rect.width();
float source_pixel_height = src_rect.height() / dst_rect.height();
float source_pixel_area = source_pixel_width * source_pixel_height;
for (int y = clipped_rect.top(); y <= clipped_rect.bottom(); ++y) {
auto* scanline = reinterpret_cast<Color*>(target.scanline(y));
for (int x = clipped_rect.left(); x <= clipped_rect.right(); ++x) {
// Project the destination pixel in the source image
FloatRect source_box = {
src_rect.left() + (x - dst_rect.x()) * source_pixel_width,
src_rect.top() + (y - dst_rect.y()) * source_pixel_height,
source_pixel_width,
source_pixel_height,
};
IntRect enclosing_source_box = enclosing_int_rect(source_box).intersected(source.rect());
// Sum the contribution of all source pixels inside the projected pixel
float red_accumulator = 0.f;
float green_accumulator = 0.f;
float blue_accumulator = 0.f;
float total_area = 0.f;
for (int sy = enclosing_source_box.y(); sy <= enclosing_source_box.bottom(); ++sy) {
for (int sx = enclosing_source_box.x(); sx <= enclosing_source_box.right(); ++sx) {
float area = source_box.intersected({ static_cast<float>(sx), static_cast<float>(sy), 1.f, 1.f }).size().area();
auto pixel = get_pixel(source, sx, sy);
area *= pixel.alpha() / 255.f;
red_accumulator += pixel.red() * area;
green_accumulator += pixel.green() * area;
blue_accumulator += pixel.blue() * area;
total_area += area;
}
}
Color src_pixel = {
round_to<u8>(min(red_accumulator / total_area, 255.f)),
round_to<u8>(min(green_accumulator / total_area, 255.f)),
round_to<u8>(min(blue_accumulator / total_area, 255.f)),
round_to<u8>(min(total_area * 255.f / source_pixel_area * opacity, 255.f)),
};
if constexpr (has_alpha_channel)
scanline[x] = scanline[x].blend(src_pixel);
else
scanline[x] = src_pixel;
}
}
}
template<bool has_alpha_channel, Painter::ScalingMode scaling_mode, typename GetPixel>
ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, IntRect const& dst_rect, IntRect const& clipped_rect, Gfx::Bitmap const& source, FloatRect const& src_rect, GetPixel get_pixel, float opacity)
{
@ -1208,6 +1261,9 @@ ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, IntRect con
}
}
if constexpr (scaling_mode == Painter::ScalingMode::BoxSampling)
return do_draw_box_sampled_scaled_bitmap<has_alpha_channel>(target, dst_rect, clipped_rect, source, src_rect, get_pixel, opacity);
bool has_opacity = opacity != 1.f;
i64 shift = (i64)1 << 32;
i64 fractional_mask = shift - (u64)1;
@ -1307,6 +1363,9 @@ ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, IntRect con
case Painter::ScalingMode::BilinearBlend:
do_draw_scaled_bitmap<has_alpha_channel, Painter::ScalingMode::BilinearBlend>(target, dst_rect, clipped_rect, source, src_rect, get_pixel, opacity);
break;
case Painter::ScalingMode::BoxSampling:
do_draw_scaled_bitmap<has_alpha_channel, Painter::ScalingMode::BoxSampling>(target, dst_rect, clipped_rect, source, src_rect, get_pixel, opacity);
break;
case Painter::ScalingMode::None:
do_draw_scaled_bitmap<has_alpha_channel, Painter::ScalingMode::None>(target, dst_rect, clipped_rect, source, src_rect, get_pixel, opacity);
break;