LibWeb: Implement CanvasRenderingContext2D.createPattern()

This is a first pass at implementing CRC2D.createPattern() and the
associated CanvasPattern object. This implementation only works for a
few of the required image sources [like CRC2D.drawImage()], and does
not yet support transforms. Other than that it supports everything
else (which is mainly the various repeat modes).

Userland/Libraries/LibWeb/HTML/CanvasPattern.cpp

@@ -0,0 +1,144 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibGfx/Bitmap.h>
+#include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/HTML/CanvasPattern.h>
+#include <LibWeb/HTML/CanvasRenderingContext2D.h>
+
+namespace Web::HTML {
+
+void CanvasPatternPaintStyle::paint(Gfx::IntRect physical_bounding_box, PaintFunction paint) const
+{
+    // 1. Create an infinite transparent black bitmap.
+    // *waves magic wand 🪄*
+    // Done!
+
+    // 2. Place a copy of the image on the bitmap, anchored such that its top left corner
+    // is at the origin of the coordinate space, with one coordinate space unit per CSS pixel of the image,
+    // then place repeated copies of this image horizontally to the left and right, if the repetition behavior
+    // is "repeat-x", or vertically up and down, if the repetition behavior is "repeat-y", or in all four directions
+    // all over the bitmap, if the repetition behavior is "repeat".
+
+    // FIMXE: If the original image data is a bitmap image, then the value painted at a point in the area of
+    // the repetitions is computed by filtering the original image data. When scaling up, if the imageSmoothingEnabled
+    // attribute is set to false, then the image must be rendered using nearest-neighbor interpolation.
+    // Otherwise, the user agent may use any filtering algorithm (for example bilinear interpolation or nearest-neighbor).
+    // User agents which support multiple filtering algorithms may use the value of the imageSmoothingQuality attribute
+    // to guide the choice of filtering algorithm. When such a filtering algorithm requires a pixel value from outside
+    // the original image data, it must instead use the value from wrapping the pixel's coordinates to the original
+    // image's dimensions. (That is, the filter uses 'repeat' behavior, regardless of the value of the pattern's repetition behavior.)
+
+    // FIXME: 3. Transform the resulting bitmap according to the pattern's transformation matrix.
+
+    // FIXME: 4. Transform the resulting bitmap again, this time according to the current transformation matrix.
+
+    // 5. Replace any part of the image outside the area in which the pattern is to be rendered with transparent black.
+
+    // 6. The resulting bitmap is what is to be rendered, with the same origin and same scale.
+
+    auto const bitmap_width = m_bitmap->width();
+    auto const bitmap_height = m_bitmap->height();
+
+    paint([=, this](auto point) {
+        point.translate_by(physical_bounding_box.location());
+        point = [&]() -> Gfx::IntPoint {
+            switch (m_repetition) {
+            case Repetition::NoRepeat: {
+                return point;
+            }
+            case Repetition::Repeat: {
+                return {
+                    point.x() % bitmap_width,
+                    point.y() % bitmap_height
+                };
+            }
+            case Repetition::RepeatX: {
+                return {
+                    point.x() % bitmap_width,
+                    point.y()
+                };
+            }
+            case Repetition::RepeatY: {
+                return {
+                    point.x(),
+                    point.y() % bitmap_height
+                };
+            }
+            default:
+                VERIFY_NOT_REACHED();
+            }
+        }();
+        if (m_bitmap->rect().contains(point))
+            return m_bitmap->get_pixel(point);
+        return Gfx::Color();
+    });
+}
+
+CanvasPattern::CanvasPattern(JS::Realm& realm, CanvasPatternPaintStyle& pattern)
+    : PlatformObject(realm)
+    , m_pattern(pattern)
+{
+}
+
+CanvasPattern::~CanvasPattern() = default;
+
+// https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-createpattern
+WebIDL::ExceptionOr<JS::GCPtr<CanvasPattern>> CanvasPattern::create(JS::Realm& realm, CanvasImageSource const& image, StringView repetition)
+{
+    auto parse_repetition = [&](auto repetition) -> Optional<CanvasPatternPaintStyle::Repetition> {
+        if (repetition == "repeat"sv)
+            return CanvasPatternPaintStyle::Repetition::Repeat;
+        if (repetition == "repeat-x"sv)
+            return CanvasPatternPaintStyle::Repetition::RepeatX;
+        if (repetition == "repeat-y"sv)
+            return CanvasPatternPaintStyle::Repetition::RepeatY;
+        if (repetition == "no-repeat"sv)
+            return CanvasPatternPaintStyle::Repetition::NoRepeat;
+        return {};
+    };
+
+    // 1. Let usability be the result of checking the usability of image.
+    auto usability = TRY(check_usability_of_image(image));
+
+    // 2. If usability is bad, then return null.
+    if (usability == CanvasImageSourceUsability::Bad)
+        return JS::GCPtr<CanvasPattern> {};
+
+    // 3. Assert: usability is good.
+    VERIFY(usability == CanvasImageSourceUsability::Good);
+
+    // 4. If repetition is the empty string, then set it to "repeat".
+    if (repetition.is_empty())
+        repetition = "repeat"sv;
+
+    // 5. If repetition is not identical to one of "repeat", "repeat-x", "repeat-y", or "no-repeat",
+    // then throw a "SyntaxError" DOMException.
+    auto repetition_value = parse_repetition(repetition);
+    if (!repetition_value.has_value())
+        return WebIDL::SyntaxError::create(realm, "Repetition value is not valid");
+
+    // Note: Bitmap won't be null here, as if it were it would have "bad" usability.
+    auto const& bitmap = *image.visit([](auto const& source) -> Gfx::Bitmap const* { return source->bitmap(); });
+
+    // 6. Let pattern be a new CanvasPattern object with the image image and the repetition behavior given by repetition.
+    auto pattern = CanvasPatternPaintStyle::create(bitmap, *repetition_value);
+
+    // FIXME: 7. If image is not origin-clean, then mark pattern as not origin-clean.
+
+    // 8. Return pattern.
+    return MUST_OR_THROW_OOM(realm.heap().allocate<CanvasPattern>(realm, realm, *pattern));
+}
+
+JS::ThrowCompletionOr<void> CanvasPattern::initialize(JS::Realm& realm)
+{
+    MUST_OR_THROW_OOM(Base::initialize(realm));
+    set_prototype(&Bindings::ensure_web_prototype<Bindings::CanvasPatternPrototype>(realm, "CanvasPattern"));
+
+    return {};
+}
+
+}