RGBCube/serenity
1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-05-15 09:24:57 +00:00
Code Issues Activity Actions
serenity/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
Aliaksandr Kalenik 063e66cae9 LibWeb: Introduce RecordingPainter to serialize painting commands 
This modification introduces a new layer to the painting process. The
stacking context traversal no longer immediately calls the
Gfx::Painter methods. Instead, it writes serialized painting commands
into newly introduced RecordingPainter. Created list of commands is
executed later to produce resulting bitmap.

Producing painting command list will make it easier to add new
optimizations:
- It's simpler to check if the painting result is not visible in the
  viewport at the command level rather than during stacking context
  traversal.
- Run painting in a separate thread. The painting thread can process
  serialized painting commands, while the main thread can work on the
  next paintable tree and safely invalidate the previous one.
- As we consider GPU-accelerated painting support, it would be easier
  to back each painting command rather than constructing an alternative
  for the entire Gfx::Painter API.
2023-10-18 10:58:42 +02:00

554 lines
27 KiB
C++
Raw Blame History

/*
* Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Debug.h>
#include <AK/ExtraMathConstants.h>
#include <AK/QuickSort.h>
#include <AK/StringBuilder.h>
#include <LibGfx/AffineTransform.h>
#include <LibGfx/Matrix4x4.h>
#include <LibGfx/Rect.h>
#include <LibWeb/CSS/ComputedValues.h>
#include <LibWeb/CSS/StyleValues/TransformationStyleValue.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/ReplacedBox.h>
#include <LibWeb/Layout/Viewport.h>
#include <LibWeb/Painting/PaintableBox.h>
#include <LibWeb/Painting/SVGPaintable.h>
#include <LibWeb/Painting/StackingContext.h>
#include <LibWeb/Painting/TableBordersPainting.h>
#include <LibWeb/SVG/SVGMaskElement.h>
namespace Web::Painting {
static void paint_node(Paintable const& paintable, PaintContext& context, PaintPhase phase)
{
paintable.before_paint(context, phase);
paintable.paint(context, phase);
paintable.after_paint(context, phase);
}
StackingContext::StackingContext(PaintableBox& paintable_box, StackingContext* parent, size_t index_in_tree_order)
: m_paintable_box(paintable_box)
, m_transform(combine_transformations(paintable_box.computed_values().transformations()))
, m_transform_origin(compute_transform_origin())
, m_parent(parent)
, m_index_in_tree_order(index_in_tree_order)
{
VERIFY(m_parent != this);
if (m_parent)
m_parent->m_children.append(this);
}
void StackingContext::sort()
{
quick_sort(m_children, [](auto& a, auto& b) {
auto a_z_index = a->paintable_box().computed_values().z_index().value_or(0);
auto b_z_index = b->paintable_box().computed_values().z_index().value_or(0);
if (a_z_index == b_z_index)
return a->m_index_in_tree_order < b->m_index_in_tree_order;
return a_z_index < b_z_index;
});
for (auto* child : m_children)
child->sort();
}
static PaintPhase to_paint_phase(StackingContext::StackingContextPaintPhase phase)
{
// There are not a fully correct mapping since some stacking context phases are combined.
switch (phase) {
case StackingContext::StackingContextPaintPhase::Floats:
case StackingContext::StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced:
case StackingContext::StackingContextPaintPhase::BackgroundAndBorders:
return PaintPhase::Background;
case StackingContext::StackingContextPaintPhase::Foreground:
return PaintPhase::Foreground;
case StackingContext::StackingContextPaintPhase::FocusAndOverlay:
return PaintPhase::Overlay;
default:
VERIFY_NOT_REACHED();
}
}
void StackingContext::paint_node_as_stacking_context(Paintable const& paintable, PaintContext& context)
{
paint_node(paintable, context, PaintPhase::Background);
paint_node(paintable, context, PaintPhase::Border);
paint_descendants(context, paintable, StackingContextPaintPhase::BackgroundAndBorders);
paint_descendants(context, paintable, StackingContextPaintPhase::Floats);
paint_descendants(context, paintable, StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(paintable, context, PaintPhase::Foreground);
paint_descendants(context, paintable, StackingContextPaintPhase::Foreground);
paint_node(paintable, context, PaintPhase::Outline);
paint_node(paintable, context, PaintPhase::Overlay);
paint_descendants(context, paintable, StackingContextPaintPhase::FocusAndOverlay);
}
void StackingContext::paint_descendants(PaintContext& context, Paintable const& paintable, StackingContextPaintPhase phase)
{
paintable.before_children_paint(context, to_paint_phase(phase));
paintable.apply_clip_overflow_rect(context, to_paint_phase(phase));
paintable.for_each_child([&context, phase](auto& child) {
auto* stacking_context = child.stacking_context_rooted_here();
if (child.is_positioned()) {
// If `child` is positioned with a z-index of `0` or `auto`, skip over it.
auto const& z_index = child.computed_values().z_index();
if (!z_index.has_value() || z_index.value() == 0)
return;
// Skip positioned children with stacking contexts, these are handled in paint_internal().
if (stacking_context)
return;
}
if (stacking_context) {
// FIXME: This may not be fully correct with respect to the paint phases.
if (phase == StackingContextPaintPhase::Foreground)
paint_child(context, *stacking_context);
// Note: Don't further recuse into descendants as paint_child() will do that.
return;
}
// NOTE: Grid specification https://www.w3.org/TR/css-grid-2/#z-order says that grid items should be treated
// the same way as CSS2 defines for inline-blocks:
// "For each one of these, treat the element as if it created a new stacking context, but any positioned
// descendants and descendants which actually create a new stacking context should be considered part of
// the parent stacking context, not this new one."
auto should_be_treated_as_stacking_context = child.layout_node().is_grid_item();
if (should_be_treated_as_stacking_context) {
// FIXME: This may not be fully correct with respect to the paint phases.
if (phase == StackingContextPaintPhase::Foreground)
paint_node_as_stacking_context(child, context);
return;
}
bool child_is_inline_or_replaced = child.is_inline() || is<Layout::ReplacedBox>(child);
switch (phase) {
case StackingContextPaintPhase::BackgroundAndBorders:
if (!child_is_inline_or_replaced && !child.is_floating()) {
paint_node(child, context, PaintPhase::Background);
bool is_table_with_collapsed_borders = child.display().is_table_inside() && child.computed_values().border_collapse() == CSS::BorderCollapse::Collapse;
if (!child.display().is_table_cell() && !is_table_with_collapsed_borders)
paint_node(child, context, PaintPhase::Border);
paint_descendants(context, child, phase);
if (child.display().is_table_inside() || child.computed_values().border_collapse() == CSS::BorderCollapse::Collapse) {
paint_table_borders(context, verify_cast<PaintableBox>(child));
}
}
break;
case StackingContextPaintPhase::Floats:
if (child.is_floating()) {
paint_node(child, context, PaintPhase::Background);
paint_node(child, context, PaintPhase::Border);
paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
}
paint_descendants(context, child, phase);
break;
case StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced:
if (child_is_inline_or_replaced) {
paint_node(child, context, PaintPhase::Background);
paint_node(child, context, PaintPhase::Border);
if (child.display().is_table_inside() && child.computed_values().border_collapse() == CSS::BorderCollapse::Separate)
paint_table_borders(context, verify_cast<PaintableBox>(child));
paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
}
paint_descendants(context, child, phase);
break;
case StackingContextPaintPhase::Foreground:
paint_node(child, context, PaintPhase::Foreground);
paint_descendants(context, child, phase);
break;
case StackingContextPaintPhase::FocusAndOverlay:
paint_node(child, context, PaintPhase::Outline);
paint_node(child, context, PaintPhase::Overlay);
paint_descendants(context, child, phase);
break;
}
});
paintable.clear_clip_overflow_rect(context, to_paint_phase(phase));
paintable.after_children_paint(context, to_paint_phase(phase));
}
void StackingContext::paint_child(PaintContext& context, StackingContext const& child)
{
auto parent_paintable = child.paintable_box().parent();
if (parent_paintable)
parent_paintable->before_children_paint(context, PaintPhase::Foreground);
auto containing_block = child.paintable_box().containing_block();
auto* containing_block_paintable = containing_block ? containing_block->paintable() : nullptr;
if (containing_block_paintable)
containing_block_paintable->apply_clip_overflow_rect(context, PaintPhase::Foreground);
child.paint(context);
if (parent_paintable)
parent_paintable->after_children_paint(context, PaintPhase::Foreground);
if (containing_block_paintable)
containing_block_paintable->clear_clip_overflow_rect(context, PaintPhase::Foreground);
}
void StackingContext::paint_internal(PaintContext& context) const
{
// For a more elaborate description of the algorithm, see CSS 2.1 Appendix E
// Draw the background and borders for the context root (steps 1, 2)
paint_node(paintable_box(), context, PaintPhase::Background);
paint_node(paintable_box(), context, PaintPhase::Border);
// Stacking contexts formed by positioned descendants with negative z-indices (excluding 0) in z-index order
// (most negative first) then tree order. (step 3)
for (auto* child : m_children) {
if (!child->paintable_box().is_positioned())
continue;
if (child->paintable_box().computed_values().z_index().has_value() && child->paintable_box().computed_values().z_index().value() < 0)
paint_child(context, *child);
}
// Draw the background and borders for block-level children (step 4)
paint_descendants(context, paintable_box(), StackingContextPaintPhase::BackgroundAndBorders);
// Draw the non-positioned floats (step 5)
paint_descendants(context, paintable_box(), StackingContextPaintPhase::Floats);
// Draw inline content, replaced content, etc. (steps 6, 7)
paint_descendants(context, paintable_box(), StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(paintable_box(), context, PaintPhase::Foreground);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::Foreground);
// Draw positioned descendants with z-index `0` or `auto` in tree order. (step 8)
// FIXME: There's more to this step that we have yet to understand and implement.
paintable_box().for_each_in_subtree([&context](Paintable const& paintable) {
auto const& z_index = paintable.computed_values().z_index();
if (!paintable.is_positioned() || (z_index.has_value() && z_index.value() != 0)) {
return paintable.stacking_context_rooted_here()
? TraversalDecision::SkipChildrenAndContinue
: TraversalDecision::Continue;
}
// At this point, `paintable_box` is a positioned descendant with z-index: auto.
// FIXME: This is basically duplicating logic found elsewhere in this same function. Find a way to make this more elegant.
auto exit_decision = TraversalDecision::Continue;
auto* parent_paintable = paintable.parent();
if (parent_paintable)
parent_paintable->before_children_paint(context, PaintPhase::Foreground);
auto containing_block = paintable.containing_block();
auto* containing_block_paintable = containing_block ? containing_block->paintable() : nullptr;
if (containing_block_paintable)
containing_block_paintable->apply_clip_overflow_rect(context, PaintPhase::Foreground);
if (auto* child = paintable.stacking_context_rooted_here()) {
paint_child(context, *child);
exit_decision = TraversalDecision::SkipChildrenAndContinue;
} else {
paint_node_as_stacking_context(paintable, context);
}
if (parent_paintable)
parent_paintable->after_children_paint(context, PaintPhase::Foreground);
if (containing_block_paintable)
containing_block_paintable->clear_clip_overflow_rect(context, PaintPhase::Foreground);
return exit_decision;
});
// Stacking contexts formed by positioned descendants with z-indices greater than or equal to 1 in z-index order
// (smallest first) then tree order. (Step 9)
for (auto* child : m_children) {
if (!child->paintable_box().is_positioned())
continue;
if (child->paintable_box().computed_values().z_index().has_value() && child->paintable_box().computed_values().z_index().value() >= 1)
paint_child(context, *child);
}
paint_node(paintable_box(), context, PaintPhase::Outline);
paint_node(paintable_box(), context, PaintPhase::Overlay);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::FocusAndOverlay);
}
Gfx::FloatMatrix4x4 StackingContext::combine_transformations(Vector<CSS::Transformation> const& transformations) const
{
auto matrix = Gfx::FloatMatrix4x4::identity();
for (auto const& transform : transformations)
matrix = matrix * transform.to_matrix(paintable_box());
return matrix;
}
// FIXME: This extracts the affine 2D part of the full transformation matrix.
// Use the whole matrix when we get better transformation support in LibGfx or use LibGL for drawing the bitmap
Gfx::AffineTransform StackingContext::affine_transform_matrix() const
{
auto* m = m_transform.elements();
return Gfx::AffineTransform(m[0][0], m[1][0], m[0][1], m[1][1], m[0][3], m[1][3]);
}
void StackingContext::paint(PaintContext& context) const
{
RecordingPainterStateSaver saver(context.painter());
auto opacity = paintable_box().computed_values().opacity();
if (opacity == 0.0f)
return;
if (auto masking_area = paintable_box().get_masking_area(); masking_area.has_value()) {
// TODO: Support masks and CSS transforms at the same time.
// Note: Currently only SVG masking is implemented (which does not use CSS transforms anyway).
if (masking_area->is_empty())
return;
auto paint_rect = context.enclosing_device_rect(*masking_area);
context.painter().push_stacking_context_with_mask(paint_rect);
paint_internal(context);
auto mask_bitmap = paintable_box().calculate_mask(context, *masking_area);
auto mask_type = paintable_box().get_mask_type();
context.painter().pop_stacking_context_with_mask(mask_bitmap, *mask_type, paint_rect, opacity);
return;
}
auto affine_transform = affine_transform_matrix();
auto translation = context.rounded_device_point(affine_transform.translation().to_type<CSSPixels>()).to_type<int>().to_type<float>();
affine_transform.set_translation(translation);
auto transform_origin = this->transform_origin();
auto source_rect = context.enclosing_device_rect(paintable_box().absolute_paint_rect()).to_type<int>().to_type<float>().translated(-transform_origin);
auto transformed_destination_rect = affine_transform.map(source_rect).translated(transform_origin);
auto destination_rect = transformed_destination_rect.to_rounded<int>();
RecordingPainter::PushStackingContextParams push_stacking_context_params {
.semitransparent_or_has_non_identity_transform = false,
.has_fixed_position = false,
.opacity = opacity,
.source_rect = source_rect,
.transformed_destination_rect = transformed_destination_rect,
.painter_location = context.rounded_device_point(-paintable_box().absolute_paint_rect().location())
};
RecordingPainter::PopStackingContextParams pop_stacking_context_params {
.semitransparent_or_has_non_identity_transform = false,
.scaling_mode = CSS::to_gfx_scaling_mode(paintable_box().computed_values().image_rendering(), destination_rect, destination_rect)
};
if (paintable_box().is_fixed_position()) {
push_stacking_context_params.has_fixed_position = true;
}
if (opacity < 1.0f || !affine_transform.is_identity_or_translation()) {
push_stacking_context_params.semitransparent_or_has_non_identity_transform = true;
pop_stacking_context_params.semitransparent_or_has_non_identity_transform = true;
context.painter().push_stacking_context(push_stacking_context_params);
paint_internal(context);
context.painter().pop_stacking_context(pop_stacking_context_params);
} else {
context.painter().push_stacking_context(push_stacking_context_params);
context.painter().translate(affine_transform.translation().to_rounded<int>());
paint_internal(context);
context.painter().pop_stacking_context(pop_stacking_context_params);
}
}
Gfx::FloatPoint StackingContext::compute_transform_origin() const
{
auto style_value = paintable_box().computed_values().transform_origin();
// FIXME: respect transform-box property
auto reference_box = paintable_box().absolute_border_box_rect();
auto x = reference_box.left() + style_value.x.to_px(paintable_box().layout_node(), reference_box.width());
auto y = reference_box.top() + style_value.y.to_px(paintable_box().layout_node(), reference_box.height());
return { x.to_float(), y.to_float() };
}
template<typename U, typename Callback>
static TraversalDecision for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
if (paintable.stacking_context_rooted_here()) {
// Note: Include the stacking context (so we can hit test it), but don't recurse into it.
if (auto decision = callback(static_cast<U const&>(paintable)); decision != TraversalDecision::Continue)
return decision;
return TraversalDecision::SkipChildrenAndContinue;
}
for (auto* child = paintable.last_child(); child; child = child->previous_sibling()) {
if (for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse<U>(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
if (is<U>(paintable)) {
if (auto decision = callback(static_cast<U const&>(paintable)); decision != TraversalDecision::Continue)
return decision;
}
return TraversalDecision::Continue;
}
template<typename U, typename Callback>
static TraversalDecision for_each_in_subtree_of_type_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
for (auto* child = paintable.last_child(); child; child = child->previous_sibling()) {
if (for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse<U>(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
return TraversalDecision::Continue;
}
Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTestType type) const
{
if (!paintable_box().is_visible())
return {};
auto transform_origin = this->transform_origin().to_type<CSSPixels>();
// NOTE: This CSSPixels -> Float -> CSSPixels conversion is because we can't AffineTransform::map() a CSSPixelPoint.
Gfx::FloatPoint offset_position {
(position.x() - transform_origin.x()).to_float(),
(position.y() - transform_origin.y()).to_float()
};
auto transformed_position = affine_transform_matrix().inverse().value_or({}).map(offset_position).to_type<CSSPixels>() + transform_origin;
if (paintable_box().is_fixed_position()) {
auto scroll_offset = paintable_box().document().navigable()->viewport_scroll_offset();
transformed_position.translate_by(-scroll_offset);
}
// FIXME: Support more overflow variations.
if (paintable_box().computed_values().overflow_x() == CSS::Overflow::Hidden && paintable_box().computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paintable_box().absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
return {};
}
// NOTE: Hit testing basically happens in reverse painting order.
// https://www.w3.org/TR/CSS22/visuren.html#z-index
// 7. the child stacking contexts with positive stack levels (least positive first).
// NOTE: Hit testing follows reverse painting order, that's why the conditions here are reversed.
for (ssize_t i = m_children.size() - 1; i >= 0; --i) {
auto const& child = *m_children[i];
if (child.paintable_box().computed_values().z_index().value_or(0) <= 0)
break;
auto result = child.hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
Optional<HitTestResult> result;
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable_box(), [&](PaintableBox const& paintable_box) {
// FIXME: Support more overflow variations.
if (paintable_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paintable_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paintable_box.absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
return TraversalDecision::SkipChildrenAndContinue;
}
auto const& z_index = paintable_box.computed_values().z_index();
if (z_index.value_or(0) == 0 && paintable_box.is_positioned() && !paintable_box.stacking_context()) {
auto candidate = paintable_box.hit_test(transformed_position, type);
if (candidate.has_value() && candidate->paintable->visible_for_hit_testing()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
if (paintable_box.stacking_context()) {
if (z_index.value_or(0) == 0) {
auto candidate = paintable_box.stacking_context()->hit_test(transformed_position, type);
if (candidate.has_value() && candidate->paintable->visible_for_hit_testing()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
}
return TraversalDecision::Continue;
});
if (result.has_value())
return result;
// 5. the in-flow, inline-level, non-positioned descendants, including inline tables and inline blocks.
if (paintable_box().layout_box().children_are_inline() && is<Layout::BlockContainer>(paintable_box().layout_box())) {
auto result = paintable_box().hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 4. the non-positioned floats.
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable_box(), [&](PaintableBox const& paintable_box) {
// FIXME: Support more overflow variations.
if (paintable_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paintable_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paintable_box.absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
return TraversalDecision::SkipChildrenAndContinue;
}
if (paintable_box.is_floating()) {
if (auto candidate = paintable_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
// 3. the in-flow, non-inline-level, non-positioned descendants.
if (!paintable_box().layout_box().children_are_inline()) {
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable_box(), [&](PaintableBox const& paintable_box) {
// FIXME: Support more overflow variations.
if (paintable_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paintable_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paintable_box.absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
return TraversalDecision::SkipChildrenAndContinue;
}
if (!paintable_box.is_absolutely_positioned() && !paintable_box.is_floating()) {
if (auto candidate = paintable_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 2. the child stacking contexts with negative stack levels (most negative first).
// NOTE: Hit testing follows reverse painting order, that's why the conditions here are reversed.
for (ssize_t i = m_children.size() - 1; i >= 0; --i) {
auto const& child = *m_children[i];
if (child.paintable_box().computed_values().z_index().value_or(0) >= 0)
break;
auto result = child.hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 1. the background and borders of the element forming the stacking context.
if (paintable_box().absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y())) {
return HitTestResult {
.paintable = const_cast<PaintableBox&>(paintable_box()),
};
}
return {};
}
void StackingContext::dump(int indent) const
{
StringBuilder builder;
for (int i = 0; i < indent; ++i)
builder.append(' ');
builder.appendff("SC for {} {} [children: {}] (z-index: ", paintable_box().layout_box().debug_description(), paintable_box().absolute_rect(), m_children.size());
if (paintable_box().computed_values().z_index().has_value())
builder.appendff("{}", paintable_box().computed_values().z_index().value());
else
builder.append("auto"sv);
builder.append(')');
auto affine_transform = affine_transform_matrix();
if (!affine_transform.is_identity()) {
builder.appendff(", transform: {}", affine_transform);
}
dbgln("{}", builder.string_view());
for (auto& child : m_children)
child->dump(indent + 1);
}
}
Reference in a new issue View git blame Copy permalink