Eevee: Add support for Nishita sky texture

Sun Disc is currently not supported because it'll need special handling - on the one hand, I'm not sure if Eevee would handle a 1e6 coming out of a background shader without issues, and on the other hand it won't actually cast sharp shadows anyways.
I guess we'd want to internally add a sun to the lamps if Sun Disc is enabled, but getting that right is tricky since the user could e.g. swap RGB channels in the node tree and the lamp wouldn't match that.
Anyways, that can be handled later, the sky itself is already a start.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D13522

1 files changed, 42 insertions, 2 deletions

diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_tex_sky.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_tex_sky.glsl
index b6aad5904ff..c4b47bc1756 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_tex_sky.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_tex_sky.glsl
@@ -144,7 +144,47 @@ void node_tex_sky_hosekwilkie(vec3 co,
   color = vec4(dot(xyz_to_r, xyz), dot(xyz_to_g, xyz), dot(xyz_to_b, xyz), 1);
 }
 
-void node_tex_sky_nishita(vec3 co, out vec4 color)
+void node_tex_sky_nishita(vec3 co,
+                          float sun_rotation,
+                          vec3 xyz_to_r,
+                          vec3 xyz_to_g,
+                          vec3 xyz_to_b,
+                          sampler2DArray ima,
+                          float layer,
+                          out vec4 color)
 {
-  color = vec4(1.0);
+  vec3 spherical = sky_spherical_coordinates(co);
+
+  vec3 xyz;
+  if (co.z < -0.4) {
+    /* too far below the horizon, just return black */
+    color = vec4(0, 0, 0, 1);
+  }
+  else {
+    /* evaluate longitudinal position on the map */
+    float x = (spherical.y + M_PI + sun_rotation) / M_2PI;
+    if (x > 1.0) {
+      x -= 1.0;
+    }
+
+    float fade;
+    float y;
+    if (co.z < 0.0) {
+      /* we're below the horizon, so extend the map by blending from values at the horizon
+       * to zero according to a cubic falloff */
+      fade = 1.0 + co.z * 2.5;
+      fade = fade * fade * fade;
+      y = 0.0;
+    }
+    else {
+      /* we're above the horizon, so compute the lateral position by inverting the remapped
+       * coordinates that are preserve to have more detail near the horizon. */
+      fade = 1.0;
+      y = sqrt((M_PI_2 - spherical.x) / M_PI_2);
+    }
+
+    /* look up color in the precomputed map and convert to RGB */
+    xyz = fade * texture(ima, vec3(x, y, layer)).rgb;
+    color = vec4(dot(xyz_to_r, xyz), dot(xyz_to_g, xyz), dot(xyz_to_b, xyz), 1);
+  }
 }