Fix T98190: EEVEE: Very slow rendering on Intel HD Graphics 4400

This particular GPU driver does not constant fold all the way in order
to discard the unused branches.

To workaround that, we introduce a series of material flag that generates
defines that only keep used branches.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D15852

1 files changed, 21 insertions, 0 deletions

diff --git a/source/blender/nodes/shader/nodes/node_shader_bsdf_principled.cc b/source/blender/nodes/shader/nodes/node_shader_bsdf_principled.cc
index a63c7aede04..2f75b7b533f 100644
--- a/source/blender/nodes/shader/nodes/node_shader_bsdf_principled.cc
+++ b/source/blender/nodes/shader/nodes/node_shader_bsdf_principled.cc
@@ -167,6 +167,27 @@ static int node_shader_gpu_bsdf_principled(GPUMaterial *mat,
   if (use_transparency) {
     flag |= GPU_MATFLAG_TRANSPARENT;
   }
+  if (use_clear) {
+    flag |= GPU_MATFLAG_CLEARCOAT;
+  }
+
+  /* Ref. T98190: Defines are optimizations for old compilers.
+   * Might become unecessary with EEVEE-Next. */
+  if (use_diffuse == false && use_refract == false && use_clear == true) {
+    flag |= GPU_MATFLAG_PRINCIPLED_CLEARCOAT;
+  }
+  else if (use_diffuse == false && use_refract == false && use_clear == false) {
+    flag |= GPU_MATFLAG_PRINCIPLED_METALLIC;
+  }
+  else if (use_diffuse == true && use_refract == false && use_clear == false) {
+    flag |= GPU_MATFLAG_PRINCIPLED_DIELECTRIC;
+  }
+  else if (use_diffuse == false && use_refract == true && use_clear == false) {
+    flag |= GPU_MATFLAG_PRINCIPLED_GLASS;
+  }
+  else {
+    flag |= GPU_MATFLAG_PRINCIPLED_ANY;
+  }
 
   if (use_subsurf) {
     bNodeSocket *socket = (bNodeSocket *)BLI_findlink(&node->original->inputs, 2);