FluidSim/Scenarios/Scenario.cs

using System;
using SFML.Graphics;
using SFML.System;
using FluidSim.Components;

namespace FluidSim.Tests
{
    public abstract class Scenario
    {
        /// <summary>Initialize the scenario with a given audio sample rate.</summary>
        public abstract void Initialize(int sampleRate);

        /// <summary>Advance one simulation step and return an audio sample.</summary>
        public abstract float Process();

        /// <summary>Draw the current simulation state onto the given SFML render target.</summary>
        public abstract void Draw(RenderWindow target);

        // ---------- Shared drawing helpers ----------

        protected const double AmbientPressure = 101325.0;
        protected const double AmbientTemperature = 300.0;   // K

        /// <summary>Map temperature [0 K … 2000 K] to a color: blue (0 K) → green (300 K) → red (2000 K).</summary>
        protected Color TemperatureColor(double temperature)
        {
            // Clamp to the range we want to display
            double t = Math.Clamp(temperature, 0.0, 2000.0);

            byte r, g, b;
            if (t < AmbientTemperature)
            {
                // Blue → Green
                double factor = t / AmbientTemperature;   // 0 at 0 K, 1 at 300 K
                r = 0;
                g = (byte)(255 * factor);
                b = (byte)(255 * (1.0 - factor));
            }
            else
            {
                // Green → Red
                double factor = (t - AmbientTemperature) / (2000.0 - AmbientTemperature); // 0 at 300 K, 1 at 2000 K
                r = (byte)(255 * factor);
                g = (byte)(255 * (1.0 - factor));
                b = 0;
            }
            return new Color(r, g, b);
        }

        /// <summary>
        /// Draws the pipe as a smooth triangle‑strip whose radius varies with cell pressure (for visibility),
        /// but colored by temperature.
        /// </summary>
        protected void DrawPipe(RenderWindow target, Pipe1D pipe, float pipeCenterY, float pipeStartX, float pipeEndX)
        {
            int n = pipe.CellCount;
            if (n < 2) return;

            float pipeLengthPx = pipeEndX - pipeStartX;
            float dx = pipeLengthPx / (n - 1);   // spacing between cell centres

            float baseRadius = 25f;
            float rangeFactor = 2f;
            float scaleFactor = 2f;

            // ----- smoothstep helper -----
            static float SmoothStep(float edge0, float edge1, float x)
            {
                float t = Math.Clamp((x - edge0) / (edge1 - edge0), 0f, 1f);
                return t * t * (3f - 2f * t);
            }

            // ----- Pre‑compute cell positions, radii, and temperatures -----
            var centers = new float[n];
            var radii = new float[n];
            var temperatures = new double[n];
            double R_gas = 287.0;

            for (int i = 0; i < n; i++)
            {
                double p = pipe.GetCellPressure(i);
                double rho = pipe.GetCellDensity(i);
                double T = p / Math.Max(rho * R_gas, 1e-12);   // ideal gas
                temperatures[i] = T;

                float deviation = (float)Math.Tanh((p - AmbientPressure) / AmbientPressure / rangeFactor);
                radii[i] = baseRadius * (1f + deviation * scaleFactor);
                if (radii[i] < 2f) radii[i] = 2f;
                centers[i] = pipeStartX + i * dx;
            }

            // ----- Build triangle‑strip vertices -----
            int segmentsPerCell = 8;
            int totalPoints = n + (n - 1) * segmentsPerCell;
            Vertex[] stripVertices = new Vertex[totalPoints * 2];
            int idx = 0;

            for (int i = 0; i < n; i++)
            {
                float x = centers[i];
                float r = radii[i];
                Color col = TemperatureColor(temperatures[i]);

                stripVertices[idx++] = new Vertex(new Vector2f(x, pipeCenterY - r), col);
                stripVertices[idx++] = new Vertex(new Vector2f(x, pipeCenterY + r), col);

                if (i < n - 1)
                {
                    for (int s = 1; s <= segmentsPerCell; s++)
                    {
                        float t = s / (float)segmentsPerCell;
                        float st = SmoothStep(0f, 1f, t);
                        float xi = centers[i] + (centers[i + 1] - centers[i]) * t;
                        float ri = radii[i] + (radii[i + 1] - radii[i]) * st;
                        double Ti = temperatures[i] + (temperatures[i + 1] - temperatures[i]) * st; // linear interpolation
                        Color coli = TemperatureColor(Ti);

                        stripVertices[idx++] = new Vertex(new Vector2f(xi, pipeCenterY - ri), coli);
                        stripVertices[idx++] = new Vertex(new Vector2f(xi, pipeCenterY + ri), coli);
                    }
                }
            }

            var pipeMesh = new VertexArray(PrimitiveType.TriangleStrip, (uint)stripVertices.Length);
            for (int i = 0; i < stripVertices.Length; i++)
                pipeMesh[(uint)i] = stripVertices[i];
            target.Draw(pipeMesh);
        }
    }
}