LunaLightXMG/RenderHandler.cs

using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace LunaLightXMG
{
    public class RenderHandler
    {
        // fields 
        private GraphicsDevice graphicsDevice;
        private SpriteBatch spriteBatch;
        private RenderTarget2D renderTarget;
        private Rectangle renderDestination;

        private int retroWidth;
        private int retroHeight;
        private float zoomLevel = 1.0f;
        private float zoomTarget = 1.0f;
        private readonly float zoomMin = 0.75f;
        private readonly float zoomNorm = 1.0f;
        private readonly float zoomMax = 1.25f;
        private readonly float zoomSpeed = 0.1f;
        public float ZoomLevel {get => zoomLevel;}
        
        // constructor
        public RenderHandler(GraphicsDevice graphicsDevice, SpriteBatch spriteBatch, int retroWidth, int retroHeight)
        {
            this.graphicsDevice = graphicsDevice;
            this.spriteBatch = spriteBatch;
            this.retroWidth = retroWidth;
            this.retroHeight = retroHeight;
            
            renderTarget = new RenderTarget2D(graphicsDevice, retroWidth, retroHeight);

            CalculateRenderDestination();
        }
        
        public void ZoomIn()
        {
            zoomTarget = zoomMin;
        }
        
        public void ZoomNormalize()
        {
            zoomTarget = zoomNorm;
        }

        public void ZoomOut()
        {
            zoomTarget = zoomMax;
        }

        public void UpdateZoom()
        {
            zoomLevel = MathHelper.Lerp(zoomLevel, zoomTarget, zoomSpeed);
            zoomLevel = MathHelper.Clamp(zoomLevel, zoomMin, zoomMax);
            CalculateRenderDestination();
        }

        public void CalculateRenderDestination()
        {
            Point screenSize = graphicsDevice.Viewport.Bounds.Size;
            // Calculate the integer scale factor
            int scaleX = screenSize.X / (int)(retroWidth * zoomLevel);
            int scaleY = screenSize.Y / (int)(retroHeight * zoomLevel);

            // Set renderDestination 
            renderDestination.Width = retroWidth * scaleX;
            renderDestination.Height = retroHeight * scaleY;
            renderDestination.X = (screenSize.X - renderDestination.Width) / 2;
            renderDestination.Y = (screenSize.Y - renderDestination.Height) / 2;
        }
    
        public void BeginRenderTarget(Matrix cameraMatrix)
        {
            graphicsDevice.SetRenderTarget(renderTarget);
            graphicsDevice.Clear(Color.Black);

            spriteBatch.Begin(transformMatrix: cameraMatrix, samplerState: SamplerState.PointClamp);
        }
        
        public void EndRenderTarget()
        {
            spriteBatch.End();
            graphicsDevice.SetRenderTarget(null);
        }

        public void DrawRenderTarget()
        {
            spriteBatch.Begin(samplerState: SamplerState.PointClamp);
            spriteBatch.Draw(renderTarget, renderDestination, Color.White);
            spriteBatch.End();
        }

    }
}