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LibGfx: Make Painter::fill_rect_with_checkerboard() faster

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We now divide each scanline into prologue, aligned run, and epilogue.
Basically, we draw enough pixels one-by-one until we reach a grid
intersection. Then we draw full grid cell slices using fast memory
fills. Finally we go back to one-by-one for the epilogue.

This is roughly 2.5x faster in a microbenchmark and no longer dominates
the ImageViewer and PixelPaint resizing profiles.
This commit is contained in:
Andreas Kling 2021-07-06 11:50:27 +02:00
parent 7e4bc04057
commit e7b8f6fe48
1 changed files with 28 additions and 4 deletions
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32
Userland/Libraries/LibGfx/Painter.cpp
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@ -177,14 +177,38 @@ void Painter::fill_rect_with_checkerboard(const IntRect& a_rect, const IntSize&
RGBA32* dst = m_target->scanline(rect.top()) + rect.left();
const size_t dst_skip = m_target->pitch() / sizeof(RGBA32);
int first_cell_column = rect.x() / cell_size.width();
int prologue_length = cell_size.width() - (rect.x() % cell_size.width());
int number_of_aligned_strips = ((rect.width() - prologue_length) / cell_size.width());
for (int i = 0; i < rect.height(); ++i) {
int y = rect.y() + i;
int cell_row = y / cell_size.height();
for (int j = 0; j < rect.width(); ++j) {
int x = rect.x() + j;
int cell_col = x / cell_size.width();
dst[j] = ((cell_row % 2) ^ (cell_col % 2)) ? color_light.value() : color_dark.value();
bool odd_row = cell_row & 1;
// Prologue: Paint the unaligned part up to the first intersection.
int j = 0;
int cell_column = first_cell_column;
for (int p = 0; p < prologue_length; ++p) {
dst[j] = (odd_row ^ (cell_column % 2)) ? color_light.value() : color_dark.value();
++j;
}
// Aligned run: Paint the maximum number of aligned cell strips.
for (int strip = 0; strip < number_of_aligned_strips; ++strip) {
++cell_column;
bool odd_cell = cell_column & 1;
auto color = (odd_row ^ odd_cell) ? color_light.value() : color_dark.value();
fast_u32_fill(&dst[j], color, cell_size.width());
j += cell_size.width();
}
// Epilogue: Paint the unaligned part until the end of the rect.
++cell_column;
for (; j < rect.width(); ++j) {
dst[j] = (odd_row ^ (cell_column % 2)) ? color_light.value() : color_dark.value();
}
dst += dst_skip;
}
}