EEVEE: Implement the missing Sky texture

I'm not sure if the Sky was deliberately left out or was just waiting for a
better moment, but so many I was disappointed that Sky in EEVEE is
completely white.

There are already 2 implementations (osl and gpu) so this is the third one.
Looking at other cases it seems that we are not supposed to share sources
between cycles and the rest? So the new util_sky_model files are just
copies of what is already in cycles, except that the data file uses the RGB
variant of the Hosek/Wilkie model, because we output RGB anyway (but can be
easily changed to XYZ if desired - the results are nearly identical).
I am not sure if it is okay to pass 3*9 float values as 3 mat4 uniforms (I
wanted to use mat3 but it does not work).
Also, should I cache the sky model data between renders if the parameters
do not change?

Reviewed By: fclem, brecht

Differential Revision: https://developer.blender.org/D7108

1 files changed, 151 insertions, 5 deletions

diff --git a/source/blender/nodes/shader/nodes/node_shader_tex_sky.c b/source/blender/nodes/shader/nodes/node_shader_tex_sky.c
index 0daa948c139..70f3f80eb4b 100644
--- a/source/blender/nodes/shader/nodes/node_shader_tex_sky.c
+++ b/source/blender/nodes/shader/nodes/node_shader_tex_sky.c
@@ -18,6 +18,7 @@
  */
 
 #include "../node_shader_util.h"
+#include "sky_model.h"
 
 /* **************** OUTPUT ******************** */
 
@@ -53,19 +54,164 @@ static void node_shader_init_tex_sky(bNodeTree *UNUSED(ntree), bNode *node)
   node->storage = tex;
 }
 
+typedef struct SkyModelPreetham {
+  float config_Y[5], config_x[5], config_y[5]; /* named after xyY color space */
+  float radiance[3];
+} SkyModelPreetham;
+
+typedef struct XYZ_to_RGB /* transposed imbuf_xyz_to_rgb, passed as 3x vec3 */
+{
+  float r[3], g[3], b[3];
+} XYZ_to_RGB;
+
+static float sky_perez_function(float *lam, float theta, float gamma)
+{
+  float ctheta = cosf(theta);
+  float cgamma = cosf(gamma);
+
+  return (1.0 + lam[0] * expf(lam[1] / ctheta)) *
+         (1.0 + lam[2] * expf(lam[3] * gamma) + lam[4] * cgamma * cgamma);
+}
+
+static void sky_precompute_old(SkyModelPreetham *sunsky, float sun_angles[], float turbidity)
+{
+  float theta = sun_angles[0];
+  float theta2 = theta * theta;
+  float theta3 = theta2 * theta;
+  float T = turbidity;
+  float T2 = T * T;
+  float chi = (4.0f / 9.0f - T / 120.0f) * (M_PI - 2.0f * theta);
+
+  sunsky->radiance[0] = (4.0453f * T - 4.9710f) * tanf(chi) - 0.2155f * T + 2.4192f;
+  sunsky->radiance[0] *= 0.06f;
+
+  sunsky->radiance[1] = (0.00166f * theta3 - 0.00375f * theta2 + 0.00209f * theta) * T2 +
+                        (-0.02903f * theta3 + 0.06377f * theta2 - 0.03202f * theta + 0.00394f) *
+                            T +
+                        (0.11693f * theta3 - 0.21196f * theta2 + 0.06052f * theta + 0.25886f);
+
+  sunsky->radiance[2] = (0.00275f * theta3 - 0.00610f * theta2 + 0.00317f * theta) * T2 +
+                        (-0.04214f * theta3 + 0.08970f * theta2 - 0.04153f * theta + 0.00516f) *
+                            T +
+                        (0.15346f * theta3 - 0.26756f * theta2 + 0.06670f * theta + 0.26688f);
+
+  sunsky->config_Y[0] = (0.1787f * T - 1.4630f);
+  sunsky->config_Y[1] = (-0.3554f * T + 0.4275f);
+  sunsky->config_Y[2] = (-0.0227f * T + 5.3251f);
+  sunsky->config_Y[3] = (0.1206f * T - 2.5771f);
+  sunsky->config_Y[4] = (-0.0670f * T + 0.3703f);
+
+  sunsky->config_x[0] = (-0.0193f * T - 0.2592f);
+  sunsky->config_x[1] = (-0.0665f * T + 0.0008f);
+  sunsky->config_x[2] = (-0.0004f * T + 0.2125f);
+  sunsky->config_x[3] = (-0.0641f * T - 0.8989f);
+  sunsky->config_x[4] = (-0.0033f * T + 0.0452f);
+
+  sunsky->config_y[0] = (-0.0167f * T - 0.2608f);
+  sunsky->config_y[1] = (-0.0950f * T + 0.0092f);
+  sunsky->config_y[2] = (-0.0079f * T + 0.2102f);
+  sunsky->config_y[3] = (-0.0441f * T - 1.6537f);
+  sunsky->config_y[4] = (-0.0109f * T + 0.0529f);
+
+  sunsky->radiance[0] /= sky_perez_function(sunsky->config_Y, 0, theta);
+  sunsky->radiance[1] /= sky_perez_function(sunsky->config_x, 0, theta);
+  sunsky->radiance[2] /= sky_perez_function(sunsky->config_y, 0, theta);
+}
+
+static void get_XYZ_to_RGB_for_gpu(XYZ_to_RGB *data)
+{
+  const float *xyz_to_rgb = IMB_colormangement_get_xyz_to_rgb();
+  data->r[0] = xyz_to_rgb[0];
+  data->r[1] = xyz_to_rgb[3];
+  data->r[2] = xyz_to_rgb[6];
+  data->g[0] = xyz_to_rgb[1];
+  data->g[1] = xyz_to_rgb[4];
+  data->g[2] = xyz_to_rgb[7];
+  data->b[0] = xyz_to_rgb[2];
+  data->b[1] = xyz_to_rgb[5];
+  data->b[2] = xyz_to_rgb[8];
+}
+
 static int node_shader_gpu_tex_sky(GPUMaterial *mat,
                                    bNode *node,
                                    bNodeExecData *UNUSED(execdata),
                                    GPUNodeStack *in,
                                    GPUNodeStack *out)
 {
-  if (!in[0].link) {
-    in[0].link = GPU_attribute(mat, CD_ORCO, "");
-  }
-
+  node_shader_gpu_default_tex_coord(mat, node, &in[0].link);
   node_shader_gpu_tex_mapping(mat, node, in, out);
+  NodeTexSky *tex = (NodeTexSky *)node->storage;
+  float sun_angles[2]; /* [0]=theta=zenith angle  [1]=phi=azimuth */
+  sun_angles[0] = acosf(tex->sun_direction[2]);
+  sun_angles[1] = atan2f(tex->sun_direction[0], tex->sun_direction[1]);
 
-  return GPU_stack_link(mat, node, "node_tex_sky", in, out);
+  if (tex->sky_model == 0) {
+    /* Preetham */
+    SkyModelPreetham sunsky;
+    sky_precompute_old(&sunsky, sun_angles, tex->turbidity);
+    XYZ_to_RGB xyz_to_rgb;
+    get_XYZ_to_RGB_for_gpu(&xyz_to_rgb);
+    return GPU_stack_link(mat,
+                          node,
+                          "node_tex_sky_preetham",
+                          in,
+                          out,
+                          /* Pass config_Y/x/y as 3x(vec4+float) */
+                          GPU_uniform(&sunsky.config_Y[0]),
+                          GPU_uniform(&sunsky.config_Y[4]),
+                          GPU_uniform(&sunsky.config_x[0]),
+                          GPU_uniform(&sunsky.config_x[4]),
+                          GPU_uniform(&sunsky.config_y[0]),
+                          GPU_uniform(&sunsky.config_y[4]),
+                          GPU_uniform(sun_angles),
+                          GPU_uniform(sunsky.radiance),
+                          GPU_uniform(xyz_to_rgb.r),
+                          GPU_uniform(xyz_to_rgb.g),
+                          GPU_uniform(xyz_to_rgb.b));
+  }
+  else if (tex->sky_model == 1) {
+    /* Hosek / Wilkie */
+    sun_angles[0] = fmin(M_PI_2, sun_angles[0]); /* clamp to horizon */
+    SKY_ArHosekSkyModelState *sky_state = SKY_arhosek_xyz_skymodelstate_alloc_init(
+        tex->turbidity, tex->ground_albedo, fmax(0.0, M_PI_2 - sun_angles[0]));
+    /* Pass sky_state->configs[3][9] as 3*(vec4+vec4)+vec3 */
+    float config_x07[8], config_y07[8], config_z07[8], config_xyz8[3];
+    for (int i = 0; i < 8; ++i) {
+      config_x07[i] = (float)sky_state->configs[0][i];
+      config_y07[i] = (float)sky_state->configs[1][i];
+      config_z07[i] = (float)sky_state->configs[2][i];
+    }
+    for (int i = 0; i < 3; ++i) {
+      config_xyz8[i] = (float)sky_state->configs[i][8];
+    }
+    float radiance[3];
+    for (int i = 0; i < 3; i++) {
+      radiance[i] = sky_state->radiances[i] * (2 * M_PI / 683);
+    }
+    SKY_arhosekskymodelstate_free(sky_state);
+    XYZ_to_RGB xyz_to_rgb;
+    get_XYZ_to_RGB_for_gpu(&xyz_to_rgb);
+    return GPU_stack_link(mat,
+                          node,
+                          "node_tex_sky_hosekwilkie",
+                          in,
+                          out,
+                          GPU_uniform(&config_x07[0]),
+                          GPU_uniform(&config_x07[4]),
+                          GPU_uniform(&config_y07[0]),
+                          GPU_uniform(&config_y07[4]),
+                          GPU_uniform(&config_z07[0]),
+                          GPU_uniform(&config_z07[4]),
+                          GPU_uniform(config_xyz8),
+                          GPU_uniform(sun_angles),
+                          GPU_uniform(radiance),
+                          GPU_uniform(xyz_to_rgb.r),
+                          GPU_uniform(xyz_to_rgb.g),
+                          GPU_uniform(xyz_to_rgb.b));
+  }
+  else {
+    return GPU_stack_link(mat, node, "node_tex_sky_nishita", in, out);
+  }
 }
 
 /* node type definition */