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LibWeb: Layout SVG <text> elements during layout (not while painting)

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Previously, all SVG <text> elements were zero-sized boxes, that were
only actually positioned and sized during painting. This led to a number
of problems, the most visible of which being that text could not be
scaled based on the viewBox.

Which this patch, <text> elements get a correctly sized layout box,
that can be hit-tested and respects the SVG viewBox.

To share code with SVGGeometryElement's the PathData (from the prior
commit) has been split into a computed path and computed transforms.
The computed path is specific to geometry elements, but the computed
transforms are shared between all SVG graphics elements.
This commit is contained in:
MacDue 2023-10-29 19:11:46 +00:00 • committed by Alexander Kalenik
parent dc9cb449b1
commit c93d367d95
16 changed files with 209 additions and 173 deletions
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109
Userland/Libraries/LibWeb/Layout/SVGFormattingContext.cpp
View file

@ -135,8 +135,6 @@ static ViewBoxTransform scale_and_align_viewbox_content(SVG::PreserveAspectRatio
static bool should_ensure_creation_of_paintable(Node const& node)
{
if (is<SVGTextBox>(node))
return true;
if (is<SVGGraphicsBox>(node))
return true;
if (node.dom_node()) {
@ -166,46 +164,87 @@ void SVGFormattingContext::run(Box const& box, LayoutMode layout_mode, Available
return IterationDecision::Continue;
});
auto compute_viewbox_transform = [&](auto const& viewbox) -> Gfx::AffineTransform {
if (!viewbox.has_value())
return {};
// FIXME: This should allow just one of width or height to be specified.
// E.g. We should be able to layout <svg width="100%"> where height is unspecified/auto.
if (!svg_box_state.has_definite_width() || !svg_box_state.has_definite_height()) {
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Attempting to layout indefinitely sized SVG with a viewbox -- this likely won't work!");
}
auto scale_width = svg_box_state.has_definite_width() ? svg_box_state.content_width() / viewbox->width : 1;
auto scale_height = svg_box_state.has_definite_height() ? svg_box_state.content_height() / viewbox->height : 1;
// The initial value for preserveAspectRatio is xMidYMid meet.
auto preserve_aspect_ratio = svg_svg_element.preserve_aspect_ratio().value_or(SVG::PreserveAspectRatio {});
auto viewbox_offset_and_scale = scale_and_align_viewbox_content(preserve_aspect_ratio, *viewbox, { scale_width, scale_height }, svg_box_state);
CSSPixelPoint offset = viewbox_offset_and_scale.offset;
return Gfx::AffineTransform {}.translate(offset.to_type<float>()).scale(viewbox_offset_and_scale.scale_factor, viewbox_offset_and_scale.scale_factor).translate({ -viewbox->min_x, -viewbox->min_y });
};
box.for_each_in_subtree([&](Node const& descendant) {
if (is<SVGGeometryBox>(descendant)) {
auto const& geometry_box = static_cast<SVGGeometryBox const&>(descendant);
auto& geometry_box_state = m_state.get_mutable(geometry_box);
auto& dom_node = const_cast<SVGGeometryBox&>(geometry_box).dom_node();
if (is<SVGGraphicsBox>(descendant)) {
auto const& graphics_box = static_cast<SVGGraphicsBox const&>(descendant);
auto& graphics_box_state = m_state.get_mutable(graphics_box);
auto& dom_node = const_cast<SVGGraphicsBox&>(graphics_box).dom_node();
auto& path = dom_node.get_path();
auto svg_transform = dom_node.get_transform();
Gfx::AffineTransform viewbox_transform;
Gfx::AffineTransform viewbox_transform = compute_viewbox_transform(dom_node.view_box());
graphics_box_state.set_computed_svg_transforms(Painting::SVGGraphicsPaintable::ComputedTransforms(viewbox_transform, svg_transform));
auto to_css_pixels_transform = Gfx::AffineTransform {}.multiply(viewbox_transform).multiply(svg_transform);
double viewbox_scale = 1;
auto maybe_view_box = dom_node.view_box();
if (maybe_view_box.has_value()) {
// FIXME: This should allow just one of width or height to be specified.
// E.g. We should be able to layout <svg width="100%"> where height is unspecified/auto.
if (!svg_box_state.has_definite_width() || !svg_box_state.has_definite_height()) {
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Attempting to layout indefinitely sized SVG with a viewbox -- this likely won't work!");
if (is<SVGGeometryBox>(descendant)) {
auto path = static_cast<SVG::SVGGeometryElement&>(dom_node).get_path();
auto path_bounding_box = to_css_pixels_transform.map(path.bounding_box()).to_type<CSSPixels>();
// Stroke increases the path's size by stroke_width/2 per side.
CSSPixels stroke_width = CSSPixels::nearest_value_for(graphics_box.dom_node().visible_stroke_width() * viewbox_transform.x_scale());
path_bounding_box.inflate(stroke_width, stroke_width);
graphics_box_state.set_content_offset(path_bounding_box.top_left());
graphics_box_state.set_content_width(path_bounding_box.width());
graphics_box_state.set_content_height(path_bounding_box.height());
graphics_box_state.set_computed_svg_path(move(path));
} else if (is<SVGTextBox>(descendant)) {
auto& text_element = static_cast<SVG::SVGTextPositioningElement&>(dom_node);
// FIXME: Support arbitrary path transforms for fonts.
// FIMXE: This assumes transform->x_scale() == transform->y_scale().
auto& scaled_font = graphics_box.scaled_font(to_css_pixels_transform.x_scale());
auto text_contents = text_element.text_contents();
auto text_offset = text_element.get_offset().transformed(to_css_pixels_transform).to_type<CSSPixels>();
auto text_width = CSSPixels::nearest_value_for(scaled_font.width(Utf8View { text_contents }));
// https://svgwg.org/svg2-draft/text.html#TextAnchoringProperties
switch (text_element.text_anchor().value_or(SVG::TextAnchor::Start)) {
case SVG::TextAnchor::Start:
// The rendered characters are aligned such that the start of the resulting rendered text is at the initial
// current text position.
break;
case SVG::TextAnchor::Middle: {
// The rendered characters are shifted such that the geometric middle of the resulting rendered text
// (determined from the initial and final current text position before applying the text-anchor property)
// is at the initial current text position.
text_offset.translate_by(-text_width / 2, 0);
break;
}
case SVG::TextAnchor::End: {
// The rendered characters are shifted such that the end of the resulting rendered text (final current text
// position before applying the text-anchor property) is at the initial current text position.
text_offset.translate_by(-text_width, 0);
break;
}
default:
VERIFY_NOT_REACHED();
}
auto view_box = maybe_view_box.value();
auto scale_width = svg_box_state.has_definite_width() ? svg_box_state.content_width() / view_box.width : 1;
auto scale_height = svg_box_state.has_definite_height() ? svg_box_state.content_height() / view_box.height : 1;
// The initial value for preserveAspectRatio is xMidYMid meet.
auto preserve_aspect_ratio = svg_svg_element.preserve_aspect_ratio().value_or(SVG::PreserveAspectRatio {});
auto viewbox_offset_and_scale = scale_and_align_viewbox_content(preserve_aspect_ratio, view_box, { scale_width, scale_height }, svg_box_state);
viewbox_transform = Gfx::AffineTransform {}.translate(viewbox_offset_and_scale.offset.to_type<float>()).scale(viewbox_offset_and_scale.scale_factor, viewbox_offset_and_scale.scale_factor).translate({ -view_box.min_x, -view_box.min_y });
viewbox_scale = viewbox_offset_and_scale.scale_factor;
auto text_height = CSSPixels::nearest_value_for(scaled_font.pixel_size());
graphics_box_state.set_content_offset(text_offset.translated(0, -text_height));
graphics_box_state.set_content_width(text_width);
graphics_box_state.set_content_height(text_height);
}
// Stroke increases the path's size by stroke_width/2 per side.
auto path_transform = Gfx::AffineTransform {}.multiply(viewbox_transform).multiply(svg_transform);
auto path_bounding_box = path_transform.map(path.bounding_box()).to_type<CSSPixels>();
CSSPixels stroke_width = CSSPixels::nearest_value_for(static_cast<double>(geometry_box.dom_node().visible_stroke_width()) * viewbox_scale);
path_bounding_box.inflate(stroke_width, stroke_width);
geometry_box_state.set_content_offset(path_bounding_box.top_left());
geometry_box_state.set_content_width(path_bounding_box.width());
geometry_box_state.set_content_height(path_bounding_box.height());
geometry_box_state.set_svg_path_data(Painting::SVGGeometryPaintable::PathData(path, viewbox_transform, svg_transform));
} else if (is<SVGSVGBox>(descendant)) {
SVGFormattingContext nested_context(m_state, static_cast<SVGSVGBox const&>(descendant), this);
nested_context.run(static_cast<SVGSVGBox const&>(descendant), layout_mode, available_space);