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

4 files changed, 59 insertions, 0 deletions

diff --git a/source/blender/gpu/GPU_material.h b/source/blender/gpu/GPU_material.h
index 3ca465fa57a..ddd8300bf0f 100644
--- a/source/blender/gpu/GPU_material.h
+++ b/source/blender/gpu/GPU_material.h
@@ -77,12 +77,20 @@ typedef enum eGPUMaterialFlag {
   GPU_MATFLAG_HOLDOUT = (1 << 6),
   GPU_MATFLAG_SHADER_TO_RGBA = (1 << 7),
   GPU_MATFLAG_AO = (1 << 8),
+  GPU_MATFLAG_CLEARCOAT = (1 << 9),
 
   GPU_MATFLAG_OBJECT_INFO = (1 << 10),
   GPU_MATFLAG_AOV = (1 << 11),
 
   GPU_MATFLAG_BARYCENTRIC = (1 << 20),
 
+  /* Optimization to only add the branches of the principled shader that are necessary. */
+  GPU_MATFLAG_PRINCIPLED_CLEARCOAT = (1 << 21),
+  GPU_MATFLAG_PRINCIPLED_METALLIC = (1 << 22),
+  GPU_MATFLAG_PRINCIPLED_DIELECTRIC = (1 << 23),
+  GPU_MATFLAG_PRINCIPLED_GLASS = (1 << 24),
+  GPU_MATFLAG_PRINCIPLED_ANY = (1 << 25),
+
   /* Tells the render engine the material was just compiled or updated. */
   GPU_MATFLAG_UPDATED = (1 << 29),
 
diff --git a/source/blender/gpu/intern/gpu_codegen.cc b/source/blender/gpu/intern/gpu_codegen.cc
index 82441c3c89c..a05bf51242f 100644
--- a/source/blender/gpu/intern/gpu_codegen.cc
+++ b/source/blender/gpu/intern/gpu_codegen.cc
@@ -351,6 +351,24 @@ void GPUCodegen::generate_resources()
 {
   GPUCodegenCreateInfo &info = *create_info;
 
+  /* Ref. T98190: Defines are optimizations for old compilers.
+   * Might become unecessary with EEVEE-Next. */
+  if (GPU_material_flag_get(&mat, GPU_MATFLAG_PRINCIPLED_CLEARCOAT)) {
+    info.define("PRINCIPLED_CLEARCOAT");
+  }
+  if (GPU_material_flag_get(&mat, GPU_MATFLAG_PRINCIPLED_METALLIC)) {
+    info.define("PRINCIPLED_METALLIC");
+  }
+  if (GPU_material_flag_get(&mat, GPU_MATFLAG_PRINCIPLED_DIELECTRIC)) {
+    info.define("PRINCIPLED_DIELECTRIC");
+  }
+  if (GPU_material_flag_get(&mat, GPU_MATFLAG_PRINCIPLED_GLASS)) {
+    info.define("PRINCIPLED_GLASS");
+  }
+  if (GPU_material_flag_get(&mat, GPU_MATFLAG_PRINCIPLED_ANY)) {
+    info.define("PRINCIPLED_ANY");
+  }
+
   std::stringstream ss;
 
   /* Textures. */
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_principled.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_principled.glsl
index 2e695fa3e14..0d8f2272c10 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_principled.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_principled.glsl
@@ -149,25 +149,37 @@ void node_bsdf_principled(vec4 base_color,
                                                        max(roughness, transmission_roughness);
   refraction_data.ior = ior;
 
+  /* Ref. T98190: Defines are optimizations for old compilers.
+   * Might become unecessary with EEVEE-Next. */
   if (do_diffuse == 0.0 && do_refraction == 0.0 && do_clearcoat != 0.0) {
+#ifdef PRINCIPLED_CLEARCOAT
     /* Metallic & Clearcoat case. */
     result = closure_eval(reflection_data, clearcoat_data);
+#endif
   }
   else if (do_diffuse == 0.0 && do_refraction == 0.0 && do_clearcoat == 0.0) {
+#ifdef PRINCIPLED_METALLIC
     /* Metallic case. */
     result = closure_eval(reflection_data);
+#endif
   }
   else if (do_diffuse != 0.0 && do_refraction == 0.0 && do_clearcoat == 0.0) {
+#ifdef PRINCIPLED_DIELECTRIC
     /* Dielectric case. */
     result = closure_eval(diffuse_data, reflection_data);
+#endif
   }
   else if (do_diffuse == 0.0 && do_refraction != 0.0 && do_clearcoat == 0.0) {
+#ifdef PRINCIPLED_GLASS
     /* Glass case. */
     result = closure_eval(reflection_data, refraction_data);
+#endif
   }
   else {
+#ifdef PRINCIPLED_ANY
     /* Un-optimized case. */
     result = closure_eval(diffuse_data, reflection_data, clearcoat_data, refraction_data);
+#endif
   }
   Closure emission_cl = closure_eval(emission_data);
   Closure transparency_cl = closure_eval(transparency_data);
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);