From 59b7c407550d63e997ed1e7bed286be5c332c285 Mon Sep 17 00:00:00 2001
From: hachem <im@hachem.wtf>
Date: Mon, 24 Aug 2026 03:57:40 +0200
Subject: [feat]: work on render path exporting

---
 assets/shaders/geodesic.slang | 64 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 7 deletions(-)

(limited to 'assets')

diff --git a/assets/shaders/geodesic.slang b/assets/shaders/geodesic.slang
index 7acbd78..eee62da 100644
--- a/assets/shaders/geodesic.slang
+++ b/assets/shaders/geodesic.slang
@@ -19,8 +19,19 @@ struct Camera
     float  tanHalfFov;
     float  aspect;
     bool   moving;
-    int    _pad4;
+    int    outputChannel;   // 0 = colour; 1 = redshift g; 2 = emission T; 3 = impact parameter
+    int    rawOutput;       // 0 = display (false-colour / tone-mapped); 1 = raw float value
 };
+
+// A jet-ish false-colour ramp (blue -> cyan -> green -> yellow -> red) for the
+// observable export channels. t is expected in [0, 1].
+float3 Falsecolor(float t)
+{
+    t = clamp(t, 0.0, 1.0);
+    return clamp(float3(1.5 - abs(4.0 * t - 3.0),
+                        1.5 - abs(4.0 * t - 2.0),
+                        1.5 - abs(4.0 * t - 1.0)), 0.0, 1.0);
+}
 ConstantBuffer<Camera> cam;
 
 struct Disk
@@ -148,8 +159,9 @@ float3 Blackbody(float T)
 //   g = sqrt(1 - 3M/r) / (1 - beta . nhat)      (verified: g -> sqrt(1/2) at ISCO)
 // Brightness follows relativistic beaming (I_obs = g^4 I_emit); colour follows
 // the redshifted blackbody at T_obs = g * T_emit.
-float3 DiskEmission(float3 P, float3 rayDir)
+float3 DiskEmission(float3 P, float3 rayDir, out float outG, out float outTemit)
 {
+    outG = 0.0; outTemit = 0.0;
     float rc   = length(float2(P.x, P.z));   // cylindrical radius (disk axis = +Y)
     float rin  = max(disk.disk_r1, R_ISCO);
     float rout = disk.disk_r2;
@@ -172,6 +184,7 @@ float3 DiskEmission(float3 P, float3 rayDir)
     float3 nhat   = -normalize(rayDir);                  // photon direction toward the observer
 
     float g = sqrt(max(1.0 - 1.5 * SagA_rs / rc, 0.0)) / max(1.0 - dot(beta, nhat), 1e-3);
+    outG = g; outTemit = Temit;   // surfaced for the observable export channels
 
     float  Tobs   = g * Temit;
     float3 colour = Blackbody(Tobs);
@@ -317,8 +330,9 @@ float3 ACESFilm(float3 x)
 
 // Trace one primary ray for the given image UV and return its linear,
 // pre-tone-map radiance. Called once per sub-sample by fragmentMain.
-float3 TracePixel(float2 texCoord)
+float3 TracePixel(float2 texCoord, out float outG, out float outTemit, out bool outHitDisk)
 {
+    outG = 0.0; outTemit = 0.0; outHitDisk = false;
     float u = (2.0 * texCoord.x - 1.0) * cam.aspect * cam.tanHalfFov;
     float v = (1.0 - 2.0 * texCoord.y) * cam.tanHalfFov;
     float3 dir = normalize(u * cam.camRight - v * cam.camUp + cam.camForward);
@@ -367,8 +381,9 @@ float3 TracePixel(float2 texCoord)
                 float rc = length(float2(hitP.x, hitP.z));
                 if (rc >= max(disk.disk_r1, R_ISCO) && rc <= disk.disk_r2)
                 {
-                    diskColor = DiskEmission(hitP, newPos - prevPos);
-                    hitDisk   = true;
+                    diskColor  = DiskEmission(hitP, newPos - prevPos, outG, outTemit);
+                    hitDisk    = true;
+                    outHitDisk = true;
                     break;
                 }
             }
@@ -422,8 +437,43 @@ float4 fragmentMain(VSOutput input) : SV_Target
     // on BOTH axes, far better on the near-horizontal lensed edges than an
     // ordered grid). Radiance is averaged before tone-mapping; ddx/ddy give the
     // resolution-correct per-pixel UV footprint.
+    // Observable export channels: the chosen scalar quantity, either as a raw
+    // float (rawOutput: value in RGB, validity mask in A) or false-coloured.
+    // Channel 0 is the normal colour image.
+    if (cam.outputChannel != 0)
+    {
+        float g, Temit; bool hitDisk;
+        TracePixel(input.texCoord, g, Temit, hitDisk);
+
+        float value; float valid = 1.0;
+        if (cam.outputChannel == 3)   // impact parameter: a per-ray geometric quantity (r_s)
+        {
+            float uu = (2.0 * input.texCoord.x - 1.0) * cam.aspect * cam.tanHalfFov;
+            float vv = (1.0 - 2.0 * input.texCoord.y) * cam.tanHalfFov;
+            float3 dir = normalize(uu * cam.camRight - vv * cam.camUp + cam.camForward);
+            value = length(cross(cam.camPos, dir)) / SagA_rs;
+        }
+        else                          // g / T are disk-only
+        {
+            valid = hitDisk ? 1.0 : 0.0;
+            value = (cam.outputChannel == 1) ? g : Temit;
+        }
+
+        if (cam.rawOutput != 0)
+            return float4(value, value, value, valid);   // raw: physical value + validity
+
+        if (valid < 0.5) return float4(0.0, 0.0, 0.0, 1.0);
+        float norm = (cam.outputChannel == 1) ? value / 1.5
+                   : (cam.outputChannel == 2) ? value / 15000.0
+                   : value / 30.0;
+        return float4(Falsecolor(norm), 1.0);
+    }
+
+    float _g, _t; bool _hd;
+    if (cam.rawOutput != 0)   // raw colour: linear pre-tone-map radiance (HDR)
+        return float4(TracePixel(input.texCoord, _g, _t, _hd), 1.0);
     if (cam.moving)
-        return float4(ACESFilm(TracePixel(input.texCoord)), 1.0);
+        return float4(ACESFilm(TracePixel(input.texCoord, _g, _t, _hd)), 1.0);
 
     float2 dUV = float2(ddx(input.texCoord.x), ddy(input.texCoord.y));
     float2 offs[4] = {
@@ -432,7 +482,7 @@ float4 fragmentMain(VSOutput input) : SV_Target
     };
     float3 sum = float3(0.0);
     for (int i = 0; i < 4; ++i)
-        sum += TracePixel(input.texCoord + offs[i] * dUV);
+        sum += TracePixel(input.texCoord + offs[i] * dUV, _g, _t, _hd);
 
     return float4(ACESFilm(sum * 0.25), 1.0);
 }
-- 
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