feat(render): implement Campaign AR and terrain fidelity

src/AcDream.App/Rendering/Shaders/atmospheric_sun_rays.frag

@@ -0,0 +1,58 @@
+#version 430 core
+
+layout(location = 0) in vec2 vUv;
+layout(location = 0) out vec4 oColor;
+
+#include "atmospheric_common.glsl"
+
+float lowFusedMaskTexel(ivec2 coordinate, vec2 maskSize)
+{
+    ivec2 maximum = ivec2(maskSize) - ivec2(1);
+    ivec2 clampedCoordinate = clamp(coordinate, ivec2(0), maximum);
+    vec2 depthUv = (vec2(clampedCoordinate) + vec2(0.5)) / maskSize;
+    float depth = ACDREAM_SAMPLE_2D(uTextureIndexA, depthUv).r;
+    float unobstructedSky = smoothstep(0.9975, 0.99995, depth);
+    float enabled = uAtmosphereSunScreen.z * uAtmosphereWeather.w;
+    // Match the removed RGBA8_UNORM mask attachment before filtering it.
+    return round(clamp(unobstructedSky * enabled, 0.0, 1.0) * 255.0) / 255.0;
+}
+
+float sampleLowFusedMask(vec2 uv)
+{
+    vec2 maskSize = uPackParams1.yz;
+    vec2 texel = uv * maskSize - vec2(0.5);
+    ivec2 lower = ivec2(floor(texel));
+    vec2 fraction = fract(texel);
+    float topLeft = lowFusedMaskTexel(lower, maskSize);
+    float topRight = lowFusedMaskTexel(lower + ivec2(1, 0), maskSize);
+    float bottomLeft = lowFusedMaskTexel(lower + ivec2(0, 1), maskSize);
+    float bottomRight = lowFusedMaskTexel(lower + ivec2(1, 1), maskSize);
+    return mix(
+        mix(topLeft, topRight, fraction.x),
+        mix(bottomLeft, bottomRight, fraction.x),
+        fraction.y);
+}
+
+void main()
+{
+    const int SampleCount = 48;
+    float decay = uPackParams0.x;
+    float weight = uPackParams0.y;
+    float density = uPackParams0.z;
+    vec2 delta = (vUv - uAtmosphereSunScreen.xy) * (density / float(SampleCount));
+    vec2 sampleUv = vUv;
+    float illumination = 1.0;
+    float sum = 0.0;
+    for (int i = 0; i < SampleCount; ++i) {
+        sampleUv -= delta;
+        if (any(lessThan(sampleUv, vec2(0.0))) || any(greaterThan(sampleUv, vec2(1.0))))
+            break;
+        float mask = uPackParams1.x > 0.5
+            ? sampleLowFusedMask(sampleUv)
+            : ACDREAM_SAMPLE_2D(uTextureIndexA, sampleUv).r;
+        sum += mask * illumination;
+        illumination *= decay;
+    }
+    vec3 rays = uAtmosphereSunColor.rgb * (sum * weight / float(SampleCount));
+    oColor = vec4(rays, 1.0);
+}