Feature/524 point cloud with multiple cameras

[RedImp1470]

Closes #524

Summary

• added "Camera" property to PointCloudComponent (see PointCloudCompnent doesn't render correctly when using multiple cameras #524)
• added "Clear Pass": the SceneRenderers clear for all active cameras and render for all active cameras separately
• removed GL.Clear calls from RCI SetRenderTarget methods for clarity

Render using multiple viewports / cameras, with or without render texture should now function correctly.

[RedImp1470]

Test Code: Simple Examle

using Fusee.Base.Core;
using Fusee.Engine.Common;
using Fusee.Engine.Core;
using Fusee.Engine.Core.Scene;
using Fusee.Engine.Gui;
using Fusee.Math.Core;
using System;
using System.Threading.Tasks;
using static Fusee.Engine.Core.Input;
using static Fusee.Engine.Core.Time;

namespace Fusee.Examples.Simple.Core
{
    [FuseeApplication(Name = "FUSEE Simple Example", Description = "A very simple example.")]
    public class Simple : RenderCanvas
    {
        // angle variables
        private static float _angleHorz, _angleVert, _angleVelHorz, _angleVelVert;

        private const float RotationSpeed = 7;
        private const float Damping = 0.8f;

        private SceneContainer _rocketScene;
        private SceneRendererDeferred _sceneRenderer;

        private const float ZNear = 1f;
        private const float ZFar = 1000;
        private readonly float _fovy = M.PiOver4;

        private SceneRendererForward _guiRenderer;
        private SceneContainer _gui;
        private SceneInteractionHandler _sih;

        private Transform _camPivotTransform;

        private bool _keys;

        private WritableTexture rt1 = WritableTexture.CreateAlbedoTex(1920, 1080, new Base.Common.ImagePixelFormat(Base.Common.ColorFormat.RGBA));
        private WritableTexture rt2 = WritableTexture.CreateAlbedoTex(1920, 1080, new Base.Common.ImagePixelFormat(Base.Common.ColorFormat.RGBA));

        private async Task Load()
        {
            Console.WriteLine("Loading scene ...");

            _gui = await FuseeGuiHelper.CreateDefaultGuiAsync(this, CanvasRenderMode.Screen, "FUSEE Simple Example");

            // Create the interaction handler
            _sih = new SceneInteractionHandler(_gui);

            // Load the rocket model
            _rocketScene = await AssetStorage.GetAsync<SceneContainer>("RocketFus.fus");
            _camPivotTransform = new Transform();
            var camNode = new SceneNode()
            {
                Name = "CamPivoteNode",
                Children = new ChildList()
                {
                    new SceneNode()
                    {
                        Name = "MainCam",
                        Components = new System.Collections.Generic.List<SceneComponent>()
                        {
                            new Transform() { Translation = new float3(0, 2, -10) },
                            new Camera(ProjectionMethod.Perspective, ZNear, ZFar, _fovy) 
                            { 
                                BackgroundColor = float4.One,
                                Viewport = new float4(50, 0, 50, 100),
                                RenderTexture = rt1
                            },
                            new Camera(ProjectionMethod.Perspective, ZNear, ZFar, _fovy)
                            {
                                BackgroundColor = float4.One,
                                Viewport = new float4(0, 0, 50, 100),
                                //RenderTexture = rt2
                            }
                        }
                    }
                },
                Components = new System.Collections.Generic.List<SceneComponent>()
                {
                    _camPivotTransform
                }
            };
            _rocketScene.Children.Add(camNode);

            // Wrap a SceneRenderer around the model.
            _sceneRenderer = new SceneRendererDeferred(_rocketScene);
            _guiRenderer = new SceneRendererForward(_gui);
        }

        public override async Task InitAsync()
        {
            await Load();
            await base.InitAsync();
        }

        // Init is called on startup.
        public override void Init()
        {

        }

        public override void Update()
        {
            _camPivotTransform.RotationQuaternion = QuaternionF.FromEuler(_angleVert, _angleHorz, 0);

            // Mouse and keyboard movement
            if (Keyboard.LeftRightAxis != 0 || Keyboard.UpDownAxis != 0)
            {
                _keys = true;
            }

            if (Mouse.LeftButton)
            {
                _keys = false;
                _angleVelHorz = RotationSpeed * Mouse.XVel * DeltaTimeUpdate * 0.0005f;
                _angleVelVert = RotationSpeed * Mouse.YVel * DeltaTimeUpdate * 0.0005f;
            }
            else if (Touch != null && Touch.GetTouchActive(TouchPoints.Touchpoint_0))
            {
                _keys = false;
                var touchVel = Touch.GetVelocity(TouchPoints.Touchpoint_0);
                _angleVelHorz = RotationSpeed * touchVel.x * DeltaTimeUpdate * 0.0005f;
                _angleVelVert = RotationSpeed * touchVel.y * DeltaTimeUpdate * 0.0005f;
            }
            else
            {
                if (_keys)
                {
                    _angleVelHorz = RotationSpeed * Keyboard.LeftRightAxis * DeltaTimeUpdate;
                    _angleVelVert = RotationSpeed * Keyboard.UpDownAxis * DeltaTimeUpdate;
                }
                else
                {
                    var curDamp = (float)System.Math.Exp(-Damping * DeltaTimeUpdate);
                    _angleVelHorz *= curDamp;
                    _angleVelVert *= curDamp;
                }
            }

            _angleHorz += _angleVelHorz;
            _angleVert += _angleVelVert;
        }

        // RenderAFrame is called once a frame
        public override void RenderAFrame()
        {
            _sceneRenderer.Render(RC);
            _guiRenderer.Render(RC);

            //Constantly check for interactive objects.
            if (!Mouse.Desc.Contains("Android"))
                _sih.CheckForInteractiveObjects(RC, Mouse.Position, Width, Height);
            if (Touch != null && Touch.GetTouchActive(TouchPoints.Touchpoint_0) && !Touch.TwoPoint)
            {
                _sih.CheckForInteractiveObjects(RC, Touch.GetPosition(TouchPoints.Touchpoint_0), Width, Height);
            }

            // Swap buffers: Show the contents of the backbuffer (containing the currently rendered frame) on the front buffer.
            Present();
        }
    }
}