mrgameeng/tests/MrGameEng.Graphics.Tests/CameraMathTests.cs

using Microsoft.Xna.Framework;
using MrGameEng.Graphics;
using Xunit;

namespace MrGameEng.Graphics.Tests;

public class CameraMathTests
{
    private static void AssertVector(Vector2 expected, Vector2 actual, float tolerance = 0.001f)
    {
        Assert.InRange(actual.X, expected.X - tolerance, expected.X + tolerance);
        Assert.InRange(actual.Y, expected.Y - tolerance, expected.Y + tolerance);
    }

    [Fact]
    public void CameraPosition_MapsToScreenCenter()
    {
        var camera = new Camera(new Vector2(500f, 300f), zoom: 2f, rotation: 0.7f);

        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);

        AssertVector(new Vector2(400f, 300f), state.WorldToScreen(camera.Position));
    }

    [Fact]
    public void ScreenToWorld_RoundTripsWithWorldToScreen()
    {
        var camera = new Camera(new Vector2(123f, -45f), zoom: 1.5f, rotation: 0.3f);
        var state = CameraMath.Compute(
            camera,
            1280,
            720,
            new ViewportMapping(new Vector2(0f, 60f), 1.5f)
        );

        var screen = new Vector2(200f, 500f);
        var world = state.ScreenToWorld(screen);

        AssertVector(screen, state.WorldToScreen(world));
    }

    [Fact]
    public void Zoom_ShrinksCullRect()
    {
        var camera = new Camera(Vector2.Zero, zoom: 2f);

        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);

        Assert.Equal(400f, state.CullRect.Width, 1);
        Assert.Equal(300f, state.CullRect.Height, 1);
        AssertVector(Vector2.Zero, state.CullRect.Center);
    }

    [Fact]
    public void Rotation_ExpandsCullRectToCoverRotatedView()
    {
        var straight = CameraMath.Compute(
            new Camera(Vector2.Zero),
            800,
            600,
            ViewportMapping.Identity
        );
        var rotated = CameraMath.Compute(
            new Camera(Vector2.Zero, rotation: MathF.PI / 4f),
            800,
            600,
            ViewportMapping.Identity
        );

        Assert.True(rotated.CullRect.Width > straight.CullRect.Width);
        Assert.True(rotated.CullRect.Height > straight.CullRect.Height);
    }

    [Fact]
    public void Bounds_ClampCameraToWorldEdges()
    {
        var bounds = new RectF(0f, 0f, 2000f, 1000f);
        var camera = new Camera(new Vector2(-500f, 500f), bounds: bounds);

        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);

        // Camera should be clamped so the view's left edge sits at the world's left edge.
        AssertVector(new Vector2(0f, 200f), state.ScreenToWorld(Vector2.Zero));
    }

    [Fact]
    public void WorldCenter_EqualsUnclampedCameraPosition()
    {
        var camera = new Camera(new Vector2(640f, 360f), zoom: 2f);

        var state = CameraMath.Compute(camera, 1280, 720, ViewportMapping.Identity);

        AssertVector(camera.Position, state.WorldCenter);
    }

    [Fact]
    public void WorldCenter_ReflectsBoundsClamp_UnlikeRawPosition()
    {
        var bounds = new RectF(0f, 0f, 2000f, 1000f);
        var camera = new Camera(new Vector2(-500f, 500f), bounds: bounds);

        var state = CameraMath.Compute(camera, 800, 600, ViewportMapping.Identity);

        // Raw position is (-500, 500); only X clamps (to half-width 400 from the left world edge),
        // Y (500) is already inside [300, 700]. The effective centre the view is built around is (400, 500).
        AssertVector(new Vector2(400f, 500f), state.WorldCenter);
    }

    [Fact]
    public void Mapping_CentersVirtualResolutionInWiderWindow()
    {
        var mapping = CameraMath.ComputeMapping(1920, 1080, 640, 360);

        Assert.Equal(3f, mapping.Scale);
        Assert.Equal(Vector2.Zero, mapping.Offset);

        var letterboxed = CameraMath.ComputeMapping(1920, 1200, 640, 360);
        Assert.Equal(3f, letterboxed.Scale);
        Assert.Equal(new Vector2(0f, 60f), letterboxed.Offset);
    }
}