tests/unit_tests/runtime/scroll_participant_test.cpp

/*
 * Copyright 2026 Rive
 */

// A scroll registers itself on each child provider and each child runs it from
// its own updateConstraints. A participant provides through its
// LayoutParticipant child, so the host is not a provider and neither half
// happened for it — participants sat still while layout children scrolled.
// Mirrors rive_core/test/scroll_participant_test.dart.

#include "rive/artboard.hpp"
#include "rive/constraints/scrolling/scroll_constraint.hpp"
#include "rive/layout/layout_participant.hpp"
#include "rive/layout_component.hpp"
#include "rive/shapes/shape.hpp"
#include "rive_file_reader.hpp"
#include "rive_testing.hpp"
#include <catch.hpp>

using namespace rive;

// Asset generated by rive_core/test/layout_participant_export_test.dart: a
// 100-tall viewport over 300-tall content whose only child is a participating
// shape, so nothing else can carry the scroll for it.
TEST_CASE("a scroll constraint moves a participating child", "[layoutscroll]")
{
    auto file = ReadRiveFile("assets/layout/scroll_participant.riv");
    auto artboard = file->artboard();
    REQUIRE(artboard != nullptr);
    artboard->advance(0.0f);

    // By type, not by name: the exporter keeps only the artboard's name, so
    // this asset carries none for its children.
    auto shapes = artboard->find<Shape>();
    REQUIRE(shapes.size() == 1);
    auto* shape = shapes[0];
    REQUIRE(shape->isParticipatingInLayout());

    REQUIRE(artboard->find<ScrollConstraint>().size() == 1);
    auto* scroll = artboard->find<ScrollConstraint>()[0];

    // There is room to scroll, so the offset below is not clamped away.
    REQUIRE(scroll->maxOffsetY() <= -50.0f);

    const float before = shape->worldTransform()[5];
    scroll->scrollOffsetY(-50.0f);
    artboard->advance(0.0f);

    REQUIRE(shape->worldTransform()[5] - before == Approx(-50.0f));
}