Eevee: SSR: Rewrote the raytracing algorithm.

It now uses a quality slider instead of stride.
Lower quality takes larger strides between samples and use lower mips when tracing rough rays.

Now raytracing is done entierly in homogeneous coordinate space. This run much faster.
Should be fairly optimized. We are still Bandwidth bound.

Add a line-line intersection refine.
Add a ray jitter between the multiple ray per pixel to fill some undersampling in mirror reflections.

The tracing now stops if it goes behind an object. This needs some work to allow it to continue even if behind objects.

1 files changed, 33 insertions, 50 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl
index 3a8430f14e6..673440c3d54 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl
@@ -47,7 +47,7 @@ bool has_hit_backface(vec3 hit_pos, vec3 R, vec3 V)
 	return (dot(-R, hit_N) < 0.0);
 }
 
-vec4 do_planar_ssr(int index, vec3 V, vec3 N, vec3 planeNormal, vec3 viewPosition, float a2, vec3 rand)
+vec4 do_planar_ssr(int index, vec3 V, vec3 N, vec3 planeNormal, vec3 viewPosition, float a2, vec3 rand, float ray_nbr)
 {
 	float pdf;
 	vec3 R = generate_ray(V, N, a2, rand, pdf);
@@ -57,46 +57,34 @@ vec4 do_planar_ssr(int index, vec3 V, vec3 N, vec3 planeNormal, vec3 viewPositio
 
 	/* If ray is bad (i.e. going below the plane) do not trace. */
 	if (dot(R, planeNormal) > 0.0) {
-		vec3 R = generate_ray(V, N, a2, rand, pdf);
+		vec3 R = generate_ray(V, N, a2, rand * vec3(1.0, -1.0, -1.0), pdf);
 	}
 
-	float hit_dist;
+	vec3 hit_pos;
 	if (abs(dot(-R, V)) < 0.9999) {
-		hit_dist = raycast(index, viewPosition, R, rand.x);
+		/* Since viewspace hit position can land behind the camera in this case,
+		 * we save the reflected view position (visualize it as the hit position
+		 * below the reflection plane). This way it's garanted that the hit will
+		 * be in front of the camera. That let us tag the bad rays with a negative
+		 * sign in the Z component. */
+		hit_pos = raycast(index, viewPosition, R, fract(rand.x + (ray_nbr / float(rayCount))), a2);
 	}
 	else {
-		float z = get_view_z_from_depth(texelFetch(planarDepth, ivec3(project_point(PixelProjMatrix, viewPosition).xy, index), 0).r);
-		hit_dist = (z - viewPosition.z) / R.z;
-	}
-
-	/* Since viewspace hit position can land behind the camera in this case,
-	 * we save the reflected view position (visualize it as the hit position
-	 * below the reflection plane). This way it's garanted that the hit will
-	 * be in front of the camera. That let us tag the bad rays with a negative
-	 * sign in the Z component. */
-	vec3 hit_pos = viewPosition + R * abs(hit_dist);
-
-	/* Ray did not hit anything. No backface test because it's not possible
-	 * to hit a backface in this case. */
-	if (hit_dist <= 0.0) {
-		hit_pos.z *= -1.0;
+		vec2 uvs = project_point(ProjectionMatrix, viewPosition).xy * 0.5 + 0.5;
+		float raw_depth = textureLod(planarDepth, vec3(uvs, float(index)), 0.0).r;
+		hit_pos = get_view_space_from_depth(uvs, raw_depth);
+		hit_pos.z *= (raw_depth < 1.0) ? 1.0 : -1.0;
 	}
 
 	return vec4(hit_pos, pdf);
 }
 
-vec4 do_ssr(vec3 V, vec3 N, vec3 viewPosition, float a2, vec3 rand)
+vec4 do_ssr(vec3 V, vec3 N, vec3 viewPosition, float a2, vec3 rand, float ray_nbr)
 {
 	float pdf;
 	vec3 R = generate_ray(V, N, a2, rand, pdf);
 
-	float hit_dist = raycast(-1, viewPosition, R, rand.x);
-	vec3 hit_pos = viewPosition + R * abs(hit_dist);
-
-	/* Ray did not hit anything. Tag it as failled. */
-	if (has_hit_backface(hit_pos, R, V) || (hit_dist <= 0.0)) {
-		hit_pos.z *= -1.0;
-	}
+	vec3 hit_pos = raycast(-1, viewPosition, R, fract(rand.x + (ray_nbr / float(rayCount))), a2);
 
 	return vec4(hit_pos, pdf);
 }
@@ -141,7 +129,7 @@ void main()
 	vec3 rand = texelFetch(utilTex, ivec3(halfres_texel % LUT_SIZE, 2), 0).rba;
 
 	vec3 worldPosition = transform_point(ViewMatrixInverse, viewPosition);
-	vec3 wN = mat3(ViewMatrixInverse) * N;
+	vec3 wN = transform_direction(ViewMatrixInverse, N);
 
 	/* Planar Reflections */
 	for (int i = 0; i < MAX_PLANAR && i < planar_count; ++i) {
@@ -154,22 +142,22 @@ void main()
 			/* TODO optimize, use view space for all. */
 			vec3 tracePosition = line_plane_intersect(worldPosition, cameraVec, pd.pl_plane_eq);
 			tracePosition = transform_point(ViewMatrix, tracePosition);
-			vec3 planeNormal = mat3(ViewMatrix) * pd.pl_normal;
+			vec3 planeNormal = transform_direction(ViewMatrix, pd.pl_normal);
 
 			/* TODO : Raytrace together if textureGather is supported. */
-			hitData0 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand);
-			if (rayCount > 1) hitData1 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand.xyz * vec3(1.0, -1.0, -1.0));
-			if (rayCount > 2) hitData2 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand.xzy * vec3(1.0,  1.0, -1.0));
-			if (rayCount > 3) hitData3 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand.xzy * vec3(1.0, -1.0,  1.0));
+			hitData0 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand, 0.0);
+			if (rayCount > 1) hitData1 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand.xyz * vec3(1.0, -1.0, -1.0), 1.0);
+			if (rayCount > 2) hitData2 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand.xzy * vec3(1.0,  1.0, -1.0), 2.0);
+			if (rayCount > 3) hitData3 = do_planar_ssr(i, V, N, planeNormal, tracePosition, a2, rand.xzy * vec3(1.0, -1.0,  1.0), 3.0);
 			return;
 		}
 	}
 
 	/* TODO : Raytrace together if textureGather is supported. */
-	hitData0 = do_ssr(V, N, viewPosition, a2, rand);
-	if (rayCount > 1) hitData1 = do_ssr(V, N, viewPosition, a2, rand.xyz * vec3(1.0, -1.0, -1.0));
-	if (rayCount > 2) hitData2 = do_ssr(V, N, viewPosition, a2, rand.xzy * vec3(1.0,  1.0, -1.0));
-	if (rayCount > 3) hitData3 = do_ssr(V, N, viewPosition, a2, rand.xzy * vec3(1.0, -1.0,  1.0));
+	hitData0 = do_ssr(V, N, viewPosition, a2, rand, 0.0);
+	if (rayCount > 1) hitData1 = do_ssr(V, N, viewPosition, a2, rand.xyz * vec3(1.0, -1.0, -1.0), 1.0);
+	if (rayCount > 2) hitData2 = do_ssr(V, N, viewPosition, a2, rand.xzy * vec3(1.0,  1.0, -1.0), 2.0);
+	if (rayCount > 3) hitData3 = do_ssr(V, N, viewPosition, a2, rand.xzy * vec3(1.0, -1.0,  1.0), 3.0);
 }
 
 #else /* STEP_RESOLVE */
@@ -258,12 +246,6 @@ float screen_border_mask(vec2 hit_co)
 	return screenfade;
 }
 
-float view_facing_mask(vec3 V, vec3 R)
-{
-	/* Fade on viewing angle (strange deformations happens at R == V) */
-	return smoothstep(0.95, 0.80, dot(V, R));
-}
-
 vec2 get_reprojected_reflection(vec3 hit, vec3 pos, vec3 N)
 {
 	/* TODO real reprojection with motion vectors, etc... */
@@ -306,13 +288,13 @@ vec4 get_ssr_sample(
 		/* Find hit position in previous frame. */
 		ref_uvs = get_reprojected_reflection(hit_pos, worldPosition, N);
 		L = normalize(hit_pos - worldPosition);
-		mask *= view_facing_mask(V, N);
-		mask *= screen_border_mask(source_uvs);
+		vec2 uvs = gl_FragCoord.xy / vec2(textureSize(depthBuffer, 0));
+		mask *= screen_border_mask(uvs);
 
 		/* Compute cone footprint Using UV distance because we are using screen space filtering. */
 		cone_footprint = 1.5 * cone_tan * distance(ref_uvs, source_uvs);
 	}
-	mask *= screen_border_mask(ref_uvs);
+	mask = min(mask, screen_border_mask(ref_uvs));
 	mask *= float(has_hit);
 
 	/* Estimate a cone footprint to sample a corresponding mipmap level. */
@@ -320,7 +302,7 @@ vec4 get_ssr_sample(
 
 	/* Slide 54 */
 	float bsdf = bsdf_ggx(N, L, V, roughnessSquared);
-	float weight = step(0.001, hit_co_pdf.w) * bsdf / hit_co_pdf.w;
+	float weight = bsdf / max(1e-8, hit_co_pdf.w);
 	weight_acc += weight;
 
 	vec3 sample;
@@ -340,7 +322,7 @@ vec4 get_ssr_sample(
 	return vec4(sample, mask) * weight;
 }
 
-#define NUM_NEIGHBORS 9
+#define NUM_NEIGHBORS 4
 
 void main()
 {
@@ -364,7 +346,8 @@ void main()
 	vec3 viewPosition = get_view_space_from_depth(uvs, depth); /* Needed for viewCameraVec */
 	vec3 worldPosition = transform_point(ViewMatrixInverse, viewPosition);
 	vec3 V = cameraVec;
-	vec3 N = mat3(ViewMatrixInverse) * normal_decode(texelFetch(normalBuffer, fullres_texel, 0).rg, viewCameraVec);
+	vec3 vN = normal_decode(texelFetch(normalBuffer, fullres_texel, 0).rg, viewCameraVec);
+	vec3 N = transform_direction(ViewMatrixInverse, vN);
 	vec4 speccol_roughness = texelFetch(specroughBuffer, fullres_texel, 0).rgba;
 
 	/* Early out */
@@ -441,7 +424,7 @@ void main()
 	if (weight_acc > 0.0) {
 		ssr_accum /= weight_acc;
 		/* fade between 0.5 and 1.0 roughness */
-		ssr_accum.a *= saturate(2.0 - roughness * 2.0);
+		//ssr_accum.a *= saturate(2.0 - roughness * 2.0);
 		accumulate_light(ssr_accum.rgb, ssr_accum.a, spec_accum);
 	}