Skip to content

Snap markers to subpixels instead of whole ones #32108

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
QuLogic wants to merge 2 commits into
base: main
Choose a base branch
from
+106 −92
Draft

Snap markers to subpixels instead of whole ones #32108

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
24851a7
Agg: De-duplicate loop for marker rendering
QuLogic Jul 23, 2026
f98d6c2
Snap markers to subpixels instead of whole ones
QuLogic Jul 23, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
198 changes: 106 additions & 92 deletions src/_backend_agg.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -480,21 +480,6 @@ inline void RendererAgg::draw_markers(GCAgg &gc,
trans *= agg::trans_affine_scaling(1.0, -1.0);
trans *= agg::trans_affine_translation(0.5, (double)height + 0.5);

auto marker_path_transformed = agg::conv_transform{marker_path, marker_trans};
auto marker_path_nan_removed = PathNanRemover{
marker_path_transformed, true, marker_path.has_codes()};
auto marker_path_snapped = PathSnapper{
marker_path_nan_removed,
gc.snap_mode, marker_path.total_vertices(), points_to_pixels(gc.linewidth)};
auto marker_path_curve = agg::conv_curve{marker_path_snapped};

if (!marker_path_snapped.is_snapping()) {
// If the path snapper isn't in effect, at least make sure the marker
// at (0, 0) is in the center of a pixel. This, importantly, makes
// the circle markers look centered around the point they refer to.
marker_trans *= agg::trans_affine_translation(0.5, 0.5);
}

auto path_transformed = agg::conv_transform{path, trans};
auto path_nan_removed = PathNanRemover{path_transformed, false, false};
auto path_snapped = PathSnapper{
Expand All @@ -507,118 +492,147 @@ inline void RendererAgg::draw_markers(GCAgg &gc,
face = color;
}

// maxim's suggestions for cached scanlines
agg::scanline_storage_aa8 scanlines;
struct CachedMarker {
std::vector<agg::int8u> fillBuffer;
std::vector<agg::int8u> strokeBuffer;
agg::rect_d clipping_rect;
};

// TODO: Pixel markers *must* be drawn snapped.
auto const& is_pixel_marker = false;
// py_eq(marker_path, PIXEL_MARKER.attr("get_path")())
// && marker_trans == PIXEL_MARKER.attr("get_transform")().cast<agg::trans_affine>();
Comment on lines +501 to +504

@QuLogic QuLogic Jul 23, 2026

Copy link
Copy Markdown
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

mplcairo special-cases the pixel marker; I have not checked how that turns out or whether that is necessary.

auto const& simplify_threshold = is_pixel_marker ? 0 : path.simplify_threshold();
auto const& n_vertices = path.total_vertices();
auto marker_cache = std::vector<CachedMarker>{};
auto n_subpix = // NOTE: Arbitrary limit of 1/16.
simplify_threshold >= 1. / 16 ? int(std::ceil(1 / simplify_threshold)) : 0;
if (!(n_subpix && n_subpix * n_subpix < n_vertices)) {
n_subpix = 1;
}
marker_cache.resize(n_subpix * n_subpix);

theRasterizer.reset();
theRasterizer.reset_clipping();
rendererBase.reset_clipping(true);
agg::rect_i marker_size(0x7FFFFFFF, 0x7FFFFFFF, -0x7FFFFFFF, -0x7FFFFFFF);

try
{
std::vector<agg::int8u> fillBuffer;
if (face) {
theRasterizer.add_path(marker_path_curve);
agg::render_scanlines(theRasterizer, slineP8, scanlines);
fillBuffer.resize(scanlines.byte_size());
scanlines.serialize(fillBuffer.data());
marker_size = agg::rect_i(scanlines.min_x(),
scanlines.min_y(),
scanlines.max_x(),
scanlines.max_y());
}
for (auto i = 0; i < n_subpix; ++i) {
for (auto j = 0; j < n_subpix; ++j) {
auto subpix_marker_trans =
marker_trans *
agg::trans_affine_translation(
double(i) / n_subpix,
double(j) / n_subpix);
auto marker_path_transformed = agg::conv_transform{
marker_path, subpix_marker_trans};
auto marker_path_nan_removed = PathNanRemover{
marker_path_transformed, true, marker_path.has_codes()};
auto marker_path_snapped = PathSnapper{
marker_path_nan_removed,
gc.snap_mode, marker_path.total_vertices(),
points_to_pixels(gc.linewidth)};
Comment on lines +532 to +535

@QuLogic QuLogic Jul 23, 2026

Copy link
Copy Markdown
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I'm not 100% certain we should be snapping here for each of the cached subpixel markers. It affects a lot more test images if we drop this though.

auto marker_path_curve = agg::conv_curve{marker_path_snapped};

if (!marker_path_snapped.is_snapping()) {
// If the path snapper isn't in effect, at least make sure the marker
// at (0, 0) is in the center of a pixel. This, importantly, makes
// the circle markers look centered around the point they refer to.
subpix_marker_trans *= agg::trans_affine_translation(0.5, 0.5);
}

auto stroke = agg::conv_stroke{marker_path_curve};
stroke.width(points_to_pixels(gc.linewidth));
stroke.line_cap(gc.cap);
stroke.line_join(gc.join);
stroke.miter_limit(points_to_pixels(gc.linewidth));
theRasterizer.reset();
theRasterizer.add_path(stroke);
agg::render_scanlines(theRasterizer, slineP8, scanlines);
std::vector<agg::int8u> strokeBuffer(scanlines.byte_size());
scanlines.serialize(strokeBuffer.data());
marker_size = agg::rect_i(std::min(marker_size.x1, scanlines.min_x()),
std::min(marker_size.y1, scanlines.min_y()),
std::max(marker_size.x2, scanlines.max_x()),
std::max(marker_size.y2, scanlines.max_y()));
// maxim's suggestions for cached scanlines
agg::scanline_storage_aa8 scanlines;
auto marker_size = agg::rect_i{
0x7FFFFFFF, 0x7FFFFFFF, -0x7FFFFFFF, -0x7FFFFFFF};

auto &cached = marker_cache[i * n_subpix + j];
if (face) {
theRasterizer.reset();
theRasterizer.add_path(marker_path_curve);
agg::render_scanlines(theRasterizer, slineP8, scanlines);
cached.fillBuffer.resize(scanlines.byte_size());
scanlines.serialize(cached.fillBuffer.data());
marker_size = {scanlines.min_x(), scanlines.min_y(),
scanlines.max_x(), scanlines.max_y()};
}

auto stroke = agg::conv_stroke{marker_path_curve};
stroke.width(points_to_pixels(gc.linewidth));
stroke.line_cap(gc.cap);
stroke.line_join(gc.join);
stroke.miter_limit(points_to_pixels(gc.linewidth));
theRasterizer.reset();
theRasterizer.add_path(stroke);
agg::render_scanlines(theRasterizer, slineP8, scanlines);
cached.strokeBuffer.resize(scanlines.byte_size());
scanlines.serialize(cached.strokeBuffer.data());
marker_size = {
std::min(marker_size.x1, scanlines.min_x()),
std::min(marker_size.y1, scanlines.min_y()),
std::max(marker_size.x2, scanlines.max_x()),
std::max(marker_size.y2, scanlines.max_y()),
};

cached.clipping_rect = {
-1.0 - marker_size.x2, -1.0 - marker_size.y2,
1.0 + width - marker_size.x1, 1.0 + height - marker_size.y1};

}
}

theRasterizer.reset_clipping();
rendererBase.reset_clipping(true);
set_clipbox(gc.cliprect, rendererBase);
bool has_clippath = render_clippath(gc.clippath.path, gc.clippath.trans, gc.snap_mode);

double x, y;

agg::serialized_scanlines_adaptor_aa8 sa;
agg::serialized_scanlines_adaptor_aa8::embedded_scanline sl;
auto _render_markers = [&]<typename R>(R ren) {
agg::serialized_scanlines_adaptor_aa8 sa;
agg::serialized_scanlines_adaptor_aa8::embedded_scanline sl;
double x, y;

agg::rect_d clipping_rect(-1.0 - marker_size.x2,
-1.0 - marker_size.y2,
1.0 + width - marker_size.x1,
1.0 + height - marker_size.y1);

if (has_clippath) {
while (path_curve.vertex(&x, &y) != agg::path_cmd_stop) {
if (!(std::isfinite(x) && std::isfinite(y))) {
continue;
}

/* These values are correctly snapped above -- so we don't want
to round here, we really only want to truncate */
x = floor(x);
y = floor(y);
auto const& i_target_x = std::floor(x);
auto const& i_target_y = std::floor(y);
auto const& f_target_x = x - i_target_x;
auto const& f_target_y = y - i_target_y;
auto const& idx =
int(n_subpix * f_target_x) * n_subpix + int(n_subpix * f_target_y);
auto const& cached = marker_cache[idx];

// Cull points outside the boundary of the image.
// Values that are too large may overflow and create
// segfaults.
// http://sourceforge.net/tracker/?func=detail&aid=2865490&group_id=80706&atid=560720
if (!clipping_rect.hit_test(x, y)) {
if (!cached.clipping_rect.hit_test(x, y)) {
continue;
}

auto pfa = agg::pixfmt_amask_adaptor{pixFmt, alphaMask};
auto r = agg::renderer_base{pfa};
auto ren = agg::renderer_scanline_aa_solid{r};

if (face) {
ren.color(*face);
sa.init(fillBuffer.data(), fillBuffer.size(), x, y);
sa.init(cached.fillBuffer.data(), cached.fillBuffer.size(),
i_target_x, i_target_y);
agg::render_scanlines(sa, sl, ren);
}
ren.color(gc.color);
sa.init(strokeBuffer.data(), strokeBuffer.size(), x, y);
sa.init(cached.strokeBuffer.data(), cached.strokeBuffer.size(),
i_target_x, i_target_y);
agg::render_scanlines(sa, sl, ren);
}
} else {
while (path_curve.vertex(&x, &y) != agg::path_cmd_stop) {
if (!(std::isfinite(x) && std::isfinite(y))) {
continue;
}

/* These values are correctly snapped above -- so we don't want
to round here, we really only want to truncate */
x = floor(x);
y = floor(y);

// Cull points outside the boundary of the image.
// Values that are too large may overflow and create
// segfaults.
// http://sourceforge.net/tracker/?func=detail&aid=2865490&group_id=80706&atid=560720
if (!clipping_rect.hit_test(x, y)) {
continue;
}

if (face) {
rendererAA.color(*face);
sa.init(fillBuffer.data(), fillBuffer.size(), x, y);
agg::render_scanlines(sa, sl, rendererAA);
}
};

rendererAA.color(gc.color);
sa.init(strokeBuffer.data(), strokeBuffer.size(), x, y);
agg::render_scanlines(sa, sl, rendererAA);
}
if (has_clippath) {
auto pfa = agg::pixfmt_amask_adaptor{pixFmt, alphaMask};
auto r = agg::renderer_base{pfa};
auto ren = agg::renderer_scanline_aa_solid{r};
_render_markers(ren);
} else {
_render_markers(rendererAA);
}
}
catch (...)
Expand Down
Loading