Eevee: Fix SSR in orthographic view.

The problem was that orthographic views can have hit position that are negative. Thus we cannot encode the hit in the sign of the Z component.

The workaround is to store the hit position in screenspace. But since we are using floating point render target, we are loosing quite a bit of precision.
TODO: use RGBA16 instead of RGBA16F. But that means encoding the pdf value somehow.

source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl

@@ -252,12 +252,13 @@ vec4 get_ssr_sample(
         inout float weight_acc)
 {
 	vec4 hit_co_pdf = texelFetch(hitBuffer, target_texel, 0).rgba;
-	bool has_hit = (hit_co_pdf.z < 0.0);
+	bool has_hit = (hit_co_pdf.z > 0.0);
 	bool is_planar = (hit_co_pdf.w < 0.0);
-	hit_co_pdf.z = -abs(hit_co_pdf.z);
+	hit_co_pdf.z = abs(hit_co_pdf.z);
 	hit_co_pdf.w = abs(hit_co_pdf.w);
 
 	/* Hit position in world space. */
+	hit_co_pdf.xyz = get_view_space_from_depth(hit_co_pdf.xy, hit_co_pdf.z);
 	vec3 hit_pos = transform_point(ViewMatrixInverse, hit_co_pdf.xyz);
 
 	vec2 ref_uvs;

source/blender/draw/engines/eevee/shaders/raytrace_lib.glsl

@@ -211,11 +211,10 @@ vec3 raycast(int index, vec3 ray_origin, vec3 ray_dir, float thickness, float ra
 	ray_time = max(0.001, min(ray_time, max_time - 1.5));
 
 	vec4 ss_ray = ss_start + ss_step * ray_time;
-	vec3 hit_pos = get_view_space_from_depth(ss_ray.xy, ss_ray.z);
 
 	/* Tag Z if ray failed. */
-	hit_pos.z *= (hit) ? 1.0 : -1.0;
-	return hit_pos;
+	ss_ray.z *= (hit) ? 1.0 : -1.0;
+	return ss_ray.xyz;
 }
 
 float screen_border_mask(vec2 hit_co)

source/blender/draw/engines/eevee/shaders/ssr_lib.glsl

@@ -36,6 +36,7 @@ vec4 screen_space_refraction(vec3 viewPosition, vec3 N, vec3 V, float ior, float
 	vec3 hit_pos = raycast(-1, viewPosition, R, ssrThickness, jitter, roughnessSquared);
 
 	if ((hit_pos.z < 0.0) && (F_eta(ior, dot(H, V)) < 1.0)) {
+		hit_pos = get_view_space_from_depth(hit_pos.xy, hit_pos.z);
 		float hit_dist = distance(hit_pos, viewPosition);
 
 		float cone_cos = cone_cosine(roughnessSquared);