ADD: Clipmap shadow better quality

shaders/deferred_lighting.frag

@@ -10,6 +10,16 @@ layout(set=1, binding=1) uniform sampler2D normalTex;
 layout(set=1, binding=2) uniform sampler2D albedoTex;
 layout(set=2, binding=0) uniform sampler2D shadowTex[4];
 
+// Tunables for shadow quality and blending
+// Border smoothing width in light-space NDC (0..1). Larger = wider cross-fade.
+const float SHADOW_BORDER_SMOOTH_NDC = 0.08;
+// Base PCF radius in texels for cascade 0; higher cascades scale this up slightly.
+const float SHADOW_PCF_BASE_RADIUS = 1.35;
+// Additional per-cascade radius scale for coarser cascades (0..1 factor added across levels)
+const float SHADOW_PCF_CASCADE_GAIN = 2.0; // extra radius at far end
+// Receiver normal-based offset to reduce acne (in world units)
+const float SHADOW_NORMAL_OFFSET = 0.0025;
+
 const float PI = 3.14159265359;
 
 float hash12(vec2 p)
@@ -29,24 +39,54 @@ vec2(0.0281, -0.2468), vec2(-0.2104, 0.0573),
 vec2(0.1197, 0.0779), vec2(-0.0905, -0.1203)
 );
 
-// Clipmap selection: choose the smallest level whose light-space XY NDC contains the point.
-uint selectCascadeIndex(vec3 worldPos)
+// Compute primary cascade and an optional neighbor for cross-fade near borders
+struct CascadeMix { uint i0; uint i1; float w1; };
+
+CascadeMix computeCascadeMix(vec3 worldPos)
 {
+    uint primary = 3u;
+    vec3 ndcP = vec3(0);
     for (uint i = 0u; i < 4u; ++i)
     {
         vec4 lclip = sceneData.lightViewProjCascades[i] * vec4(worldPos, 1.0);
         vec3 ndc = lclip.xyz / max(lclip.w, 1e-6);
         if (abs(ndc.x) <= 1.0 && abs(ndc.y) <= 1.0 && ndc.z >= 0.0 && ndc.z <= 1.0)
         {
-            return i;
+            primary = i;
+            ndcP = ndc;
+            break;
         }
     }
-    return 3u;
+
+    CascadeMix cm; cm.i0 = primary; cm.i1 = primary; cm.w1 = 0.0;
+
+    if (primary < 3u)
+    {
+        float edge = max(abs(ndcP.x), abs(ndcP.y)); // 0..1, 1 at border
+        // start blending when we are within S of the border
+        float t = clamp((edge - (1.0 - SHADOW_BORDER_SMOOTH_NDC)) / max(SHADOW_BORDER_SMOOTH_NDC, 1e-4), 0.0, 1.0);
+        float w = smoothstep(0.0, 1.0, t);
+
+        if (w > 0.0)
+        {
+            // Only blend if neighbor actually covers the point
+            uint neighbor = primary + 1u;
+            vec4 lclipN = sceneData.lightViewProjCascades[neighbor] * vec4(worldPos, 1.0);
+            vec3 ndcN = lclipN.xyz / max(lclipN.w, 1e-6);
+            bool insideN = (abs(ndcN.x) <= 1.0 && abs(ndcN.y) <= 1.0 && ndcN.z >= 0.0 && ndcN.z <= 1.0);
+            if (insideN)
+            {
+                cm.i1 = neighbor;
+                cm.w1 = w;
+            }
+        }
+    }
+
+    return cm;
 }
 
-float calcShadowVisibility(vec3 worldPos, vec3 N, vec3 L)
+float sampleCascadeShadow(uint ci, vec3 worldPos, vec3 N, vec3 L)
 {
-    uint ci = selectCascadeIndex(worldPos);
     mat4 lightMat = sceneData.lightViewProjCascades[ci];
 
     vec4 lclip = lightMat * vec4(worldPos, 1.0);
@@ -69,9 +109,8 @@ float calcShadowVisibility(vec3 worldPos, vec3 N, vec3 L)
     ivec2 dim       = textureSize(shadowTex[ci], 0);
     vec2  texelSize = 1.0 / vec2(dim);
 
-    float baseRadius = 1.25;
-
-    float radius     = mix(baseRadius, baseRadius * 3.0, float(ci) / 3.0);
+    float baseRadius = SHADOW_PCF_BASE_RADIUS;
+    float radius     = mix(baseRadius, baseRadius + SHADOW_PCF_CASCADE_GAIN, float(ci) / 3.0);
 
     float ang = hash12(suv * 4096.0) * 6.2831853;
     vec2  r   = vec2(cos(ang), sin(ang));
@@ -100,6 +139,19 @@ float calcShadowVisibility(vec3 worldPos, vec3 N, vec3 L)
     return visibility;
 }
 
+float calcShadowVisibility(vec3 worldPos, vec3 N, vec3 L)
+{
+    vec3 wp = worldPos + N * SHADOW_NORMAL_OFFSET * (0.5 + 0.5 * (1.0 - max(dot(N, L), 0.0)));
+
+    CascadeMix cm = computeCascadeMix(wp);
+    float v0 = sampleCascadeShadow(cm.i0, wp, N, L);
+    if (cm.w1 <= 0.0)
+        return v0;
+
+    float v1 = sampleCascadeShadow(cm.i1, wp, N, L);
+    return mix(v0, v1, clamp(cm.w1, 0.0, 1.0));
+}
+
 vec3 fresnelSchlick(float cosTheta, vec3 F0)
 {
     return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);