KSP-Conformal-Decals/Source/ConformalDecals/ProjectionTarget.cs

using UnityEngine;
using UnityEngine.Rendering;

namespace ConformalDecals {
    public class ProjectionTarget {
        // Target object data
        public readonly Transform target;

        private readonly Renderer _targetRenderer;
        private readonly Mesh     _targetMesh;
        private          bool     _projectionEnabled;

        // property block
        private readonly MaterialPropertyBlock _decalMPB;

        public ProjectionTarget(MeshRenderer targetRenderer, Mesh targetMesh) {
            target = targetRenderer.transform;
            _targetRenderer = targetRenderer;
            _targetMesh = targetMesh;
            _decalMPB = new MaterialPropertyBlock();
        }

        public void Project(Matrix4x4 orthoMatrix, Transform projector, bool useBaseNormal) {
            _projectionEnabled = true;

            var targetMaterial = _targetRenderer.sharedMaterial;
            var projectorToTargetMatrix = target.worldToLocalMatrix * projector.localToWorldMatrix;

            var projectionMatrix = orthoMatrix * projectorToTargetMatrix.inverse;
            var decalNormal = projectorToTargetMatrix.MultiplyVector(Vector3.back).normalized;
            var decalTangent = projectorToTargetMatrix.MultiplyVector(Vector3.right).normalized;

            _decalMPB.SetMatrix(DecalPropertyIDs._ProjectionMatrix, projectionMatrix);
            _decalMPB.SetVector(DecalPropertyIDs._DecalNormal, decalNormal);
            _decalMPB.SetVector(DecalPropertyIDs._DecalTangent, decalTangent);

            if (useBaseNormal && targetMaterial.HasProperty(DecalPropertyIDs._BumpMap)) {
                _decalMPB.SetTexture(DecalPropertyIDs._BumpMap, targetMaterial.GetTexture(DecalPropertyIDs._BumpMap));

                var normalScale = targetMaterial.GetTextureScale(DecalPropertyIDs._BumpMap);
                var normalOffset = targetMaterial.GetTextureOffset(DecalPropertyIDs._BumpMap);

                _decalMPB.SetVector(DecalPropertyIDs._BumpMap_ST, new Vector4(normalScale.x, normalScale.y, normalOffset.x, normalOffset.y));
            }
            else {
                _decalMPB.SetTexture(DecalPropertyIDs._BumpMap, DecalConfig.BlankNormal);
            }
        }

        public bool Render(Material decalMaterial, MaterialPropertyBlock partMPB, Camera camera) {
            if (_projectionEnabled) {
                _decalMPB.SetFloat(PropertyIDs._RimFalloff, partMPB.GetFloat(PropertyIDs._RimFalloff));
                _decalMPB.SetColor(PropertyIDs._RimColor, partMPB.GetColor(PropertyIDs._RimColor));

                Graphics.DrawMesh(_targetMesh, target.localToWorldMatrix, decalMaterial, 0, camera, 0, _decalMPB, ShadowCastingMode.Off, true);

                return true;
            }

            return false;
        }
    }
}