/*
* Copyright (c) 2023, MacDue <macdue@dueutil.tech>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Array.h>
#include <AK/Debug.h>
#include <AK/IntegralMath.h>
#include <AK/Types.h>
#include <LibGfx/AntiAliasingPainter.h>
#include <LibGfx/EdgeFlagPathRasterizer.h>
#if defined(AK_COMPILER_GCC)
# pragma GCC optimize("O3")
#endif
// This a pretty naive implementation of edge-flag scanline AA.
// The paper lists many possible optimizations, maybe implement one? (FIXME!)
// https://mlab.taik.fi/~kkallio/antialiasing/EdgeFlagAA.pdf
// This currently implements:
// - The scanline buffer optimization (only allocate one scanline)
// Possible other optimizations according to the paper:
// - Using fixed point numbers
// - Edge tracking
// - Mask tracking
// - Loop unrolling (compilers might handle this better now, the paper is from 2007)
// Optimizations I think we could add:
// - Using fast_u32_fills() for runs of solid colors
// - Clipping the plotted edges earlier
namespace Gfx {
static Vector<Detail::Edge> prepare_edges(ReadonlySpan<FloatLine> lines, unsigned samples_per_pixel, FloatPoint origin)
{
Vector<Detail::Edge> edges;
edges.ensure_capacity(lines.size());
for (auto& line : lines) {
auto p0 = line.a() - origin;
auto p1 = line.b() - origin;
p0.scale_by(1, samples_per_pixel);
p1.scale_by(1, samples_per_pixel);
i8 winding = -1;
if (p0.y() > p1.y()) {
swap(p0, p1);
} else {
winding = 1;
}
if (p0.y() == p1.y())
continue;
auto min_y = static_cast<int>(p0.y());
auto max_y = static_cast<int>(p1.y());
float start_x = p0.x();
float end_x = p1.x();
auto dx = end_x - start_x;
auto dy = max_y - min_y;
auto dxdy = dx / dy;
edges.unchecked_append(Detail::Edge {
start_x,
min_y,
max_y,
dxdy,
winding,
nullptr });
}
return edges;
}
template<unsigned SamplesPerPixel>
EdgeFlagPathRasterizer<SamplesPerPixel>::EdgeFlagPathRasterizer(IntSize size)
: m_size(size.width() + 1, size.height() + 1)
{
m_scanline.resize(m_size.width());
m_edge_table.resize(m_size.height());
}
template<unsigned SamplesPerPixel>
void EdgeFlagPathRasterizer<SamplesPerPixel>::fill(Painter& painter, Path const& path, Color color, Painter::WindingRule winding_rule, FloatPoint offset)
{
fill_internal(painter, path, color, winding_rule, offset);
}
template<unsigned SamplesPerPixel>
void EdgeFlagPathRasterizer<SamplesPerPixel>::fill(Painter& painter, Path const& path, PaintStyle const& style, float opacity, Painter::WindingRule winding_rule, FloatPoint offset)
{
style.paint(enclosing_int_rect(path.bounding_box()), [&](PaintStyle::SamplerFunction sampler) {
if (opacity == 0.0f)
return;
if (opacity != 1.0f) {
return fill_internal(
painter, path, [=, sampler = move(sampler)](IntPoint point) {
return sampler(point).with_opacity(opacity);
},
winding_rule, offset);
}
return fill_internal(painter, path, move(sampler), winding_rule, offset);
});
}
template<unsigned SamplesPerPixel>
void EdgeFlagPathRasterizer<SamplesPerPixel>::fill_internal(Painter& painter, Path const& path, auto color_or_function, Painter::WindingRule winding_rule, FloatPoint offset)
{
// FIXME: Figure out how painter scaling works here...
VERIFY(painter.scale() == 1);
auto bounding_box = enclosing_int_rect(path.bounding_box().translated(offset));
auto dest_rect = bounding_box.translated(painter.translation());
auto origin = bounding_box.top_left().to_type<float>() - offset;
m_blit_origin = dest_rect.top_left();
m_clip = dest_rect.intersected(painter.clip_rect());
if (m_clip.is_empty())
return;
auto& lines = path.split_lines();
if (lines.is_empty())
return;
auto edges = prepare_edges(lines, SamplesPerPixel, origin);
int min_scanline = m_size.height();
int max_scanline = 0;
for (auto& edge : edges) {
int start_scanline = edge.min_y / SamplesPerPixel;
int end_scanline = edge.max_y / SamplesPerPixel;
// Create a linked-list of edges starting on this scanline:
edge.next_edge = m_edge_table[start_scanline];
m_edge_table[start_scanline] = &edge;
min_scanline = min(min_scanline, start_scanline);
max_scanline = max(max_scanline, end_scanline);
}
// FIXME: We could probably clip some of the egde plotting if we know it won't be shown.
// Though care would have to be taken to ensure the active edges are correct at the first drawn scaline.
auto for_each_sample = [&](Detail::Edge& edge, int start_subpixel_y, int end_subpixel_y, auto callback) {
for (int y = start_subpixel_y; y < end_subpixel_y; y++) {
int xi = static_cast<int>(edge.x + SubpixelSample::nrooks_subpixel_offsets[y]);
if (xi < 0 || xi >= (int)m_scanline.size()) {
// FIXME: For very low dxdy values, floating point error can push the sample outside the scanline.
// This does not seem to make a visible difference most of the time (and is more likely from generated
// paths, such as this 3D canvas demo: https://www.kevs3d.co.uk/dev/html5logo/).
dbgln_if(FILL_PATH_DEBUG, "fill_path: Sample out of bounds: {} not in [0, {})", xi, m_scanline.size());
return;
}
SampleType sample = 1 << y;
callback(xi, y, sample);
edge.x += edge.dxdy;
}
};
Detail::Edge* active_edges = nullptr;
if (winding_rule == Painter::WindingRule::EvenOdd) {
auto plot_edge = [&](Detail::Edge& edge, int start_subpixel_y, int end_subpixel_y) {
for_each_sample(edge, start_subpixel_y, end_subpixel_y, [&](int xi, int, SampleType sample) {
m_scanline[xi] ^= sample;
});
};
for (int scanline = min_scanline; scanline <= max_scanline; scanline++) {
active_edges = plot_edges_for_scanline(scanline, plot_edge, active_edges);
accumulate_even_odd_scanline(painter, scanline, color_or_function);
}
} else {
VERIFY(winding_rule == Painter::WindingRule::Nonzero);
// Only allocate the winding buffer if needed.
// NOTE: non-zero fills are a fair bit less efficient. So if you can do an even-odd fill do that :^)
if (m_windings.is_empty())
m_windings.resize(m_size.width());
auto plot_edge = [&](Detail::Edge& edge, int start_subpixel_y, int end_subpixel_y) {
for_each_sample(edge, start_subpixel_y, end_subpixel_y, [&](int xi, int y, SampleType sample) {
m_scanline[xi] |= sample;
m_windings[xi].counts[y] += edge.winding;
});
};
for (int scanline = min_scanline; scanline <= max_scanline; scanline++) {
active_edges = plot_edges_for_scanline(scanline, plot_edge, active_edges);
accumulate_non_zero_scanline(painter, scanline, color_or_function);
}
}
}
template<unsigned SamplesPerPixel>
Color EdgeFlagPathRasterizer<SamplesPerPixel>::scanline_color(int scanline, int offset, u8 alpha, auto& color_or_function)
{
using ColorOrFunction = decltype(color_or_function);
constexpr bool has_constant_color = IsSame<RemoveCVReference<ColorOrFunction>, Color>;
auto color = [&] {
if constexpr (has_constant_color) {
return color_or_function;
} else {
return color_or_function({ offset, scanline });
}
}();
return color.with_alpha(color.alpha() * alpha / 255);
}
template<unsigned SamplesPerPixel>
Detail::Edge* EdgeFlagPathRasterizer<SamplesPerPixel>::plot_edges_for_scanline(int scanline, auto plot_edge, Detail::Edge* active_edges)
{
auto y_subpixel = [](int y) {
return y & (SamplesPerPixel - 1);
};
auto* current_edge = active_edges;
Detail::Edge* prev_edge = nullptr;
// First iterate over the edge in the active edge table, these are edges added on earlier scanlines,
// that have not yet reached their end scanline.
while (current_edge) {
int end_scanline = current_edge->max_y / SamplesPerPixel;
if (scanline == end_scanline) {
// This edge ends this scanline.
plot_edge(*current_edge, 0, y_subpixel(current_edge->max_y));
// Remove this edge from the AET
current_edge = current_edge->next_edge;
if (prev_edge)
prev_edge->next_edge = current_edge;
else
active_edges = current_edge;
} else {
// This egde sticks around for a few more scanlines.
plot_edge(*current_edge, 0, SamplesPerPixel);
prev_edge = current_edge;
current_edge = current_edge->next_edge;
}
}
// Next, iterate over new edges for this line. If active_edges was null this also becomes the new
// AET. Edges new will be appended here.
current_edge = m_edge_table[scanline];
while (current_edge) {
int end_scanline = current_edge->max_y / SamplesPerPixel;
if (scanline == end_scanline) {
// This edge will end this scanlines (no need to add to AET).
plot_edge(*current_edge, y_subpixel(current_edge->min_y), y_subpixel(current_edge->max_y));
} else {
// This edge will live on for a few more scanlines.
plot_edge(*current_edge, y_subpixel(current_edge->min_y), SamplesPerPixel);
// Add this edge to the AET
if (prev_edge)
prev_edge->next_edge = current_edge;
else
active_edges = current_edge;
prev_edge = current_edge;
}
current_edge = current_edge->next_edge;
}
if (prev_edge)
prev_edge->next_edge = nullptr;
m_edge_table[scanline] = nullptr;
return active_edges;
}
template<unsigned SamplesPerPixel>
void EdgeFlagPathRasterizer<SamplesPerPixel>::write_pixel(Painter& painter, int scanline, int offset, SampleType sample, auto& color_or_function)
{
auto dest = IntPoint { offset, scanline } + m_blit_origin;
if (!m_clip.contains_horizontally(dest.x()))
return;
// FIXME: We could detect runs of full coverage and use fast_u32_fills for those rather than many set_pixel() calls.
auto coverage = SubpixelSample::compute_coverage(sample);
if (coverage) {
auto paint_color = scanline_color(scanline, offset, coverage_to_alpha(coverage), color_or_function);
painter.set_physical_pixel(dest, paint_color, true);
}
}
template<unsigned SamplesPerPixel>
void EdgeFlagPathRasterizer<SamplesPerPixel>::accumulate_even_odd_scanline(Painter& painter, int scanline, auto& color_or_function)
{
auto dest_y = m_blit_origin.y() + scanline;
if (!m_clip.contains_vertically(dest_y)) {
// FIXME: This memset only really needs to be done on transition from clipped to not clipped,
// or not at all if we properly clipped egde plotting.
memset(m_scanline.data(), 0, sizeof(SampleType) * m_scanline.size());
return;
}
SampleType sample = 0;
for (int x = 0; x < m_size.width(); x += 1) {
sample ^= m_scanline[x];
write_pixel(painter, scanline, x, sample, color_or_function);
m_scanline[x] = 0;
}
}
template<unsigned SamplesPerPixel>
void EdgeFlagPathRasterizer<SamplesPerPixel>::accumulate_non_zero_scanline(Painter& painter, int scanline, auto& color_or_function)
{
// NOTE: Same FIXMEs apply from accumulate_even_odd_scanline()
auto dest_y = m_blit_origin.y() + scanline;
if (!m_clip.contains_vertically(dest_y)) {
memset(m_scanline.data(), 0, sizeof(SampleType) * m_scanline.size());
memset(m_windings.data(), 0, sizeof(WindingCounts) * m_windings.size());
return;
}
SampleType sample = 0;
WindingCounts sum_winding = {};
for (int x = 0; x < m_size.width(); x += 1) {
if (auto edges = m_scanline[x]) {
// We only need to process the windings when we hit some edges.
for (auto y_sub = 0u; y_sub < SamplesPerPixel; y_sub++) {
auto subpixel_bit = 1 << y_sub;
if (edges & subpixel_bit) {
auto winding = m_windings[x].counts[y_sub];
auto previous_winding_count = sum_winding.counts[y_sub];
sum_winding.counts[y_sub] += winding;
// Toggle fill on change to/from zero
if ((previous_winding_count == 0 && sum_winding.counts[y_sub] != 0)
|| (sum_winding.counts[y_sub] == 0 && previous_winding_count != 0)) {
sample ^= subpixel_bit;
}
}
}
}
write_pixel(painter, scanline, x, sample, color_or_function);
m_scanline[x] = 0;
m_windings[x] = {};
}
}
static IntSize path_bounds(Gfx::Path const& path)
{
return enclosing_int_rect(path.bounding_box()).size();
}
// Note: The AntiAliasingPainter and Painter now perform the same antialiasing,
// since it would be harder to turn it off for the standard painter.
// The samples are reduced to 8 for Gfx::Painter though as a "speedy" option.
void Painter::fill_path(Path const& path, Color color, WindingRule winding_rule)
{
EdgeFlagPathRasterizer<8> rasterizer(path_bounds(path));
rasterizer.fill(*this, path, color, winding_rule);
}
void Painter::fill_path(Path const& path, PaintStyle const& paint_style, float opacity, Painter::WindingRule winding_rule)
{
EdgeFlagPathRasterizer<8> rasterizer(path_bounds(path));
rasterizer.fill(*this, path, paint_style, opacity, winding_rule);
}
void AntiAliasingPainter::fill_path(Path const& path, Color color, Painter::WindingRule winding_rule)
{
EdgeFlagPathRasterizer<32> rasterizer(path_bounds(path));
rasterizer.fill(m_underlying_painter, path, color, winding_rule, m_transform.translation());
}
void AntiAliasingPainter::fill_path(Path const& path, PaintStyle const& paint_style, float opacity, Painter::WindingRule winding_rule)
{
EdgeFlagPathRasterizer<32> rasterizer(path_bounds(path));
rasterizer.fill(m_underlying_painter, path, paint_style, opacity, winding_rule, m_transform.translation());
}
template class EdgeFlagPathRasterizer<8>;
template class EdgeFlagPathRasterizer<16>;
template class EdgeFlagPathRasterizer<32>;
}