GPU: Make nodetree GLSL Codegen render engine agnostic

This commit removes all EEVEE specific code from the `gpu_shader_material*.glsl`
files. It defines a clear interface to evaluate the closure nodes leaving
more flexibility to the render engine.

Some of the long standing workaround are fixed:
- bump mapping support is no longer duplicating a lot of node and is instead
  compiled into a function call.
- bump rewiring to Normal socket is no longer needed as we now use a global
  `g_data.N` for that.


Closure sampling with upstread weight eval is now supported if the engine needs
it.

This also makes all the material GLSL sources use `GPUSource` for better
debugging experience. The `GPUFunction` parsing now happens in `GPUSource`
creation.

The whole `GPUCodegen` now uses the `ShaderCreateInfo` and is object type
agnostic. Is has also been rewritten in C++.

This patch changes a view behavior for EEVEE:
- Mix shader node factor imput is now clamped.
- Tangent Vector displacement behavior is now matching cycles.
- The chosen BSDF used for SSR might change.
- Hair shading may have very small changes on very large hairs when using hair
  polygon stripes.
- ShaderToRGB node will remove any SSR and SSS form a shader.
- SSS radius input now is no longer a scaling factor but defines an average
  radius. The SSS kernel "shape" (radii) are still defined by the socket default
  values.

Appart from the listed changes no other regressions are expected.

1 files changed, 825 insertions, 0 deletions

diff --git a/source/blender/gpu/intern/gpu_codegen.cc b/source/blender/gpu/intern/gpu_codegen.cc
new file mode 100644
index 00000000000..8963fa45c96
--- /dev/null
+++ b/source/blender/gpu/intern/gpu_codegen.cc
@@ -0,0 +1,825 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright 2005 Blender Foundation. */
+
+/** \file
+ * \ingroup gpu
+ *
+ * Convert material node-trees to GLSL.
+ */
+
+#include "MEM_guardedalloc.h"
+
+#include "DNA_customdata_types.h"
+#include "DNA_image_types.h"
+
+#include "BLI_blenlib.h"
+#include "BLI_dynstr.h"
+#include "BLI_ghash.h"
+#include "BLI_hash_mm2a.h"
+#include "BLI_link_utils.h"
+#include "BLI_threads.h"
+#include "BLI_utildefines.h"
+
+#include "PIL_time.h"
+
+#include "BKE_material.h"
+#include "BKE_world.h"
+
+#include "GPU_capabilities.h"
+#include "GPU_material.h"
+#include "GPU_shader.h"
+#include "GPU_uniform_buffer.h"
+#include "GPU_vertex_format.h"
+
+#include "BLI_sys_types.h" /* for intptr_t support */
+
+#include "gpu_codegen.h"
+#include "gpu_material_library.h"
+#include "gpu_node_graph.h"
+#include "gpu_shader_create_info.hh"
+#include "gpu_shader_dependency_private.h"
+
+#include <stdarg.h>
+#include <string.h>
+
+#include <sstream>
+#include <string>
+
+using namespace blender::gpu::shader;
+
+struct GPUCodegenCreateInfo : ShaderCreateInfo {
+  struct NameBuffer {
+    char attr_names[16][GPU_MAX_SAFE_ATTR_NAME + 1];
+    char var_names[16][8];
+  };
+
+  /** Optional generated interface. */
+  StageInterfaceInfo *interface_generated = nullptr;
+  /** Optional name buffer containing names referenced by StringRefNull. */
+  NameBuffer *name_buffer = nullptr;
+
+  GPUCodegenCreateInfo(const char *name) : ShaderCreateInfo(name){};
+  ~GPUCodegenCreateInfo()
+  {
+    delete interface_generated;
+    MEM_delete(name_buffer);
+  };
+};
+
+struct GPUPass {
+  struct GPUPass *next;
+
+  GPUShader *shader;
+  GPUCodegenCreateInfo *create_info = nullptr;
+  /** Orphaned GPUPasses gets freed by the garbage collector. */
+  uint refcount;
+  /** Identity hash generated from all GLSL code. */
+  uint32_t hash;
+  /** Did we already tried to compile the attached GPUShader. */
+  bool compiled;
+};
+
+/* -------------------------------------------------------------------- */
+/** \name GPUPass Cache
+ *
+ * Internal shader cache: This prevent the shader recompilation / stall when
+ * using undo/redo AND also allows for GPUPass reuse if the Shader code is the
+ * same for 2 different Materials. Unused GPUPasses are free by Garbage collection.
+ */
+
+/* Only use one linklist that contains the GPUPasses grouped by hash. */
+static GPUPass *pass_cache = nullptr;
+static SpinLock pass_cache_spin;
+
+/* Search by hash only. Return first pass with the same hash.
+ * There is hash collision if (pass->next && pass->next->hash == hash) */
+static GPUPass *gpu_pass_cache_lookup(uint32_t hash)
+{
+  BLI_spin_lock(&pass_cache_spin);
+  /* Could be optimized with a Lookup table. */
+  for (GPUPass *pass = pass_cache; pass; pass = pass->next) {
+    if (pass->hash == hash) {
+      BLI_spin_unlock(&pass_cache_spin);
+      return pass;
+    }
+  }
+  BLI_spin_unlock(&pass_cache_spin);
+  return nullptr;
+}
+
+static void gpu_pass_cache_insert_after(GPUPass *node, GPUPass *pass)
+{
+  BLI_spin_lock(&pass_cache_spin);
+  if (node != nullptr) {
+    /* Add after the first pass having the same hash. */
+    pass->next = node->next;
+    node->next = pass;
+  }
+  else {
+    /* No other pass have same hash, just prepend to the list. */
+    BLI_LINKS_PREPEND(pass_cache, pass);
+  }
+  BLI_spin_unlock(&pass_cache_spin);
+}
+
+/* Check all possible passes with the same hash. */
+static GPUPass *gpu_pass_cache_resolve_collision(GPUPass *pass,
+                                                 GPUShaderCreateInfo *info,
+                                                 uint32_t hash)
+{
+  BLI_spin_lock(&pass_cache_spin);
+  for (; pass && (pass->hash == hash); pass = pass->next) {
+    if (*reinterpret_cast<ShaderCreateInfo *>(info) ==
+        *reinterpret_cast<ShaderCreateInfo *>(pass->create_info)) {
+      BLI_spin_unlock(&pass_cache_spin);
+      return pass;
+    }
+  }
+  BLI_spin_unlock(&pass_cache_spin);
+  return nullptr;
+}
+
+static bool gpu_pass_is_valid(GPUPass *pass)
+{
+  /* Shader is not null if compilation is successful. */
+  return (pass->compiled == false || pass->shader != nullptr);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Type > string conversion
+ * \{ */
+
+static std::ostream &operator<<(std::ostream &stream, const GPUInput *input)
+{
+  switch (input->source) {
+    case GPU_SOURCE_FUNCTION_CALL:
+    case GPU_SOURCE_OUTPUT:
+      return stream << "tmp" << input->id;
+    case GPU_SOURCE_CONSTANT:
+      return stream << "cons" << input->id;
+    case GPU_SOURCE_UNIFORM:
+      return stream << "node_tree.u" << input->id;
+    case GPU_SOURCE_ATTR:
+      return stream << "var_attrs.v" << input->attr->id;
+    case GPU_SOURCE_UNIFORM_ATTR:
+      return stream << "unf_attrs[resource_id].attr" << input->uniform_attr->id;
+    case GPU_SOURCE_STRUCT:
+      return stream << "strct" << input->id;
+    case GPU_SOURCE_TEX:
+      return stream << input->texture->sampler_name;
+    case GPU_SOURCE_TEX_TILED_MAPPING:
+      return stream << input->texture->tiled_mapping_name;
+    case GPU_SOURCE_VOLUME_GRID:
+      return stream << input->volume_grid->sampler_name;
+    case GPU_SOURCE_VOLUME_GRID_TRANSFORM:
+      return stream << input->volume_grid->transform_name;
+    default:
+      BLI_assert(0);
+      return stream;
+  }
+}
+
+static std::ostream &operator<<(std::ostream &stream, const GPUOutput *output)
+{
+  return stream << "tmp" << output->id;
+}
+
+/* Trick type to change overload and keep a somewhat nice syntax. */
+struct GPUConstant : public GPUInput {
+};
+
+/* Print data constructor (i.e: vec2(1.0f, 1.0f)). */
+static std::ostream &operator<<(std::ostream &stream, const GPUConstant *input)
+{
+  stream << input->type << "(";
+  for (int i = 0; i < input->type; i++) {
+    char formated_float[32];
+    /* Print with the maximum precision for single precision float using scientific notation.
+     * See https://stackoverflow.com/questions/16839658/#answer-21162120 */
+    SNPRINTF(formated_float, "%.9g", input->vec[i]);
+    stream << formated_float;
+    if (i < input->type - 1) {
+      stream << ", ";
+    }
+  }
+  stream << ")";
+  return stream;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name GLSL code generation
+ * \{ */
+
+class GPUCodegen {
+ public:
+  GPUMaterial &mat;
+  GPUNodeGraph &graph;
+  GPUCodegenOutput output = {};
+  GPUCodegenCreateInfo *create_info = nullptr;
+
+ private:
+  uint32_t hash_ = 0;
+  BLI_HashMurmur2A hm2a_;
+  ListBase ubo_inputs_ = {nullptr, nullptr};
+
+ public:
+  GPUCodegen(GPUMaterial *mat_, GPUNodeGraph *graph_) : mat(*mat_), graph(*graph_)
+  {
+    BLI_hash_mm2a_init(&hm2a_, GPU_material_uuid_get(&mat));
+    BLI_hash_mm2a_add_int(&hm2a_, GPU_material_flag(&mat));
+    create_info = new GPUCodegenCreateInfo("codegen");
+    output.create_info = reinterpret_cast<GPUShaderCreateInfo *>(
+        static_cast<ShaderCreateInfo *>(create_info));
+
+    if (GPU_material_flag_get(mat_, GPU_MATFLAG_OBJECT_INFO)) {
+      create_info->additional_info("draw_object_infos");
+    }
+  }
+
+  ~GPUCodegen()
+  {
+    MEM_SAFE_FREE(output.attr_load);
+    MEM_SAFE_FREE(output.surface);
+    MEM_SAFE_FREE(output.volume);
+    MEM_SAFE_FREE(output.thickness);
+    MEM_SAFE_FREE(output.displacement);
+    MEM_SAFE_FREE(output.material_functions);
+    delete create_info;
+    BLI_freelistN(&ubo_inputs_);
+  };
+
+  void generate_graphs();
+  void generate_uniform_buffer();
+  void generate_attribs();
+  void generate_resources();
+  void generate_library();
+
+  uint32_t hash_get() const
+  {
+    return hash_;
+  }
+
+ private:
+  void set_unique_ids();
+
+  void node_serialize(std::stringstream &eval_ss, const GPUNode *node);
+  char *graph_serialize(eGPUNodeTag tree_tag, GPUNodeLink *output_link);
+
+  static char *extract_c_str(std::stringstream &stream)
+  {
+    auto string = stream.str();
+    return BLI_strdup(string.c_str());
+  }
+};
+
+static char attr_prefix_get(CustomDataType type)
+{
+  switch (type) {
+    case CD_MTFACE:
+      return 'u';
+    case CD_TANGENT:
+      return 't';
+    case CD_MCOL:
+    case CD_MLOOPCOL:
+      return 'c';
+    case CD_PROP_COLOR:
+      return 'c';
+    case CD_AUTO_FROM_NAME:
+      return 'a';
+    case CD_HAIRLENGTH:
+      return 'l';
+    default:
+      BLI_assert_msg(0, "GPUVertAttr Prefix type not found : This should not happen!");
+      return '\0';
+  }
+}
+
+void GPUCodegen::generate_attribs()
+{
+  if (BLI_listbase_is_empty(&graph.attributes)) {
+    output.attr_load = nullptr;
+    return;
+  }
+
+  GPUCodegenCreateInfo &info = *create_info;
+
+  info.name_buffer = MEM_new<GPUCodegenCreateInfo::NameBuffer>("info.name_buffer");
+  info.interface_generated = new StageInterfaceInfo("codegen_iface", "var_attrs");
+  StageInterfaceInfo &iface = *info.interface_generated;
+  info.vertex_out(iface);
+
+  /* Input declaration, loading / assignment to interface and geometry shader passthrough. */
+  std::stringstream decl_ss, iface_ss, load_ss;
+
+  int slot = 15;
+  LISTBASE_FOREACH (GPUMaterialAttribute *, attr, &graph.attributes) {
+
+    /* NOTE: Replicate changes to mesh_render_data_create() in draw_cache_impl_mesh.c */
+    if (attr->type == CD_ORCO) {
+      /* OPTI: orco is computed from local positions, but only if no modifier is present. */
+      STRNCPY(info.name_buffer->attr_names[slot], "orco");
+    }
+    else {
+      char *name = info.name_buffer->attr_names[slot];
+      name[0] = attr_prefix_get(static_cast<CustomDataType>(attr->type));
+      name[1] = '\0';
+      if (attr->name[0] != '\0') {
+        /* XXX FIXME: see notes in mesh_render_data_create() */
+        GPU_vertformat_safe_attr_name(attr->name, &name[1], GPU_MAX_SAFE_ATTR_NAME);
+      }
+    }
+    SNPRINTF(info.name_buffer->var_names[slot], "v%d", attr->id);
+
+    blender::StringRefNull attr_name = info.name_buffer->attr_names[slot];
+    blender::StringRefNull var_name = info.name_buffer->var_names[slot];
+
+    eGPUType input_type, iface_type;
+
+    load_ss << "var_attrs." << var_name;
+    switch (attr->type) {
+      case CD_ORCO:
+        /* Need vec4 to detect usage of default attribute. */
+        input_type = GPU_VEC4;
+        iface_type = GPU_VEC3;
+        load_ss << " = attr_load_orco(" << attr_name << ");\n";
+        break;
+      case CD_HAIRLENGTH:
+        iface_type = input_type = GPU_FLOAT;
+        load_ss << " = attr_load_" << input_type << "(" << attr_name << ");\n";
+        break;
+      case CD_TANGENT:
+        iface_type = input_type = GPU_VEC4;
+        load_ss << " = attr_load_tangent(" << attr_name << ");\n";
+        break;
+      case CD_MTFACE:
+        iface_type = input_type = GPU_VEC3;
+        load_ss << " = attr_load_uv(" << attr_name << ");\n";
+        break;
+      case CD_MCOL:
+        iface_type = input_type = GPU_VEC4;
+        load_ss << " = attr_load_color(" << attr_name << ");\n";
+        break;
+      default:
+        iface_type = input_type = GPU_VEC4;
+        load_ss << " = attr_load_" << input_type << "(" << attr_name << ");\n";
+        break;
+    }
+
+    info.vertex_in(slot--, to_type(input_type), attr_name);
+    iface.smooth(to_type(iface_type), var_name);
+  }
+
+  output.attr_load = extract_c_str(load_ss);
+}
+
+void GPUCodegen::generate_resources()
+{
+  GPUCodegenCreateInfo &info = *create_info;
+
+  std::stringstream ss;
+
+  /* Textures. */
+  LISTBASE_FOREACH (GPUMaterialTexture *, tex, &graph.textures) {
+    if (tex->colorband) {
+      info.sampler(0, ImageType::FLOAT_1D_ARRAY, tex->sampler_name, Frequency::BATCH);
+    }
+    else if (tex->tiled_mapping_name[0] != '\0') {
+      info.sampler(0, ImageType::FLOAT_2D_ARRAY, tex->sampler_name, Frequency::BATCH);
+      info.sampler(0, ImageType::FLOAT_1D_ARRAY, tex->tiled_mapping_name, Frequency::BATCH);
+    }
+    else {
+      info.sampler(0, ImageType::FLOAT_2D, tex->sampler_name, Frequency::BATCH);
+    }
+  }
+  /* Volume Grids. */
+  LISTBASE_FOREACH (GPUMaterialVolumeGrid *, grid, &graph.volume_grids) {
+    info.sampler(0, ImageType::FLOAT_3D, grid->sampler_name, Frequency::BATCH);
+    /* TODO(@fclem): Global uniform. To put in an UBO. */
+    info.push_constant(Type::MAT4, grid->transform_name);
+  }
+
+  if (!BLI_listbase_is_empty(&ubo_inputs_)) {
+    /* NOTE: generate_uniform_buffer() should have sorted the inputs before this. */
+    ss << "struct NodeTree {\n";
+    LISTBASE_FOREACH (LinkData *, link, &ubo_inputs_) {
+      GPUInput *input = (GPUInput *)(link->data);
+      ss << input->type << " u" << input->id << ";\n";
+    }
+    ss << "};\n\n";
+
+    info.uniform_buf(0, "NodeTree", GPU_UBO_BLOCK_NAME, Frequency::BATCH);
+  }
+
+  if (!BLI_listbase_is_empty(&graph.uniform_attrs.list)) {
+    ss << "struct UniformAttrs {\n";
+    LISTBASE_FOREACH (GPUUniformAttr *, attr, &graph.uniform_attrs.list) {
+      ss << "vec4 attr" << attr->id << ";\n";
+    }
+    ss << "};\n\n";
+
+    /* TODO(fclem): Use the macro for length. Currently not working for EEVEE. */
+    /* DRW_RESOURCE_CHUNK_LEN = 512 */
+    info.uniform_buf(0, "UniformAttrs", GPU_ATTRIBUTE_UBO_BLOCK_NAME "[512]", Frequency::BATCH);
+  }
+
+  info.typedef_source_generated = ss.str();
+}
+
+void GPUCodegen::generate_library()
+{
+  GPUCodegenCreateInfo &info = *create_info;
+
+  void *value;
+  GSetIterState pop_state = {};
+  while (BLI_gset_pop(graph.used_libraries, &pop_state, &value)) {
+    auto deps = gpu_shader_dependency_get_resolved_source((const char *)value);
+    info.dependencies_generated.extend_non_duplicates(deps);
+  }
+}
+
+void GPUCodegen::node_serialize(std::stringstream &eval_ss, const GPUNode *node)
+{
+  /* Declare constants. */
+  LISTBASE_FOREACH (GPUInput *, input, &node->inputs) {
+    switch (input->source) {
+      case GPU_SOURCE_FUNCTION_CALL:
+        eval_ss << input->type << " " << input << "; " << input->function_call << input << ");\n";
+        break;
+      case GPU_SOURCE_STRUCT:
+        eval_ss << input->type << " " << input << " = CLOSURE_DEFAULT;\n";
+        break;
+      case GPU_SOURCE_CONSTANT:
+        eval_ss << input->type << " " << input << " = " << (GPUConstant *)input << ";\n";
+        break;
+      default:
+        break;
+    }
+  }
+  /* Declare temporary variables for node output storage. */
+  LISTBASE_FOREACH (GPUOutput *, output, &node->outputs) {
+    eval_ss << output->type << " " << output << ";\n";
+  }
+
+  /* Function call. */
+  eval_ss << node->name << "(";
+  /* Input arguments. */
+  LISTBASE_FOREACH (GPUInput *, input, &node->inputs) {
+    switch (input->source) {
+      case GPU_SOURCE_OUTPUT:
+      case GPU_SOURCE_ATTR: {
+        /* These inputs can have non matching types. Do conversion. */
+        eGPUType to = input->type;
+        eGPUType from = (input->source == GPU_SOURCE_ATTR) ? input->attr->gputype :
+                                                             input->link->output->type;
+        if (from != to) {
+          /* Use defines declared inside codegen_lib (i.e: vec4_from_float). */
+          eval_ss << to << "_from_" << from << "(";
+        }
+
+        if (input->source == GPU_SOURCE_ATTR) {
+          eval_ss << input;
+        }
+        else {
+          eval_ss << input->link->output;
+        }
+
+        if (from != to) {
+          eval_ss << ")";
+        }
+        break;
+      }
+      default:
+        eval_ss << input;
+        break;
+    }
+    eval_ss << ", ";
+  }
+  /* Output arguments. */
+  LISTBASE_FOREACH (GPUOutput *, output, &node->outputs) {
+    eval_ss << output;
+    if (output->next) {
+      eval_ss << ", ";
+    }
+  }
+  eval_ss << ");\n\n";
+}
+
+char *GPUCodegen::graph_serialize(eGPUNodeTag tree_tag, GPUNodeLink *output_link)
+{
+  if (output_link == nullptr) {
+    return nullptr;
+  }
+
+  std::stringstream eval_ss;
+  /* NOTE: The node order is already top to bottom (or left to right in node editor)
+   * because of the evaluation order inside ntreeExecGPUNodes(). */
+  LISTBASE_FOREACH (GPUNode *, node, &graph.nodes) {
+    if ((node->tag & tree_tag) == 0) {
+      continue;
+    }
+    node_serialize(eval_ss, node);
+  }
+  eval_ss << "return " << output_link->output << ";\n";
+
+  char *eval_c_str = extract_c_str(eval_ss);
+  BLI_hash_mm2a_add(&hm2a_, (uchar *)eval_c_str, eval_ss.str().size());
+  return eval_c_str;
+}
+
+void GPUCodegen::generate_uniform_buffer()
+{
+  /* Extract uniform inputs. */
+  LISTBASE_FOREACH (GPUNode *, node, &graph.nodes) {
+    LISTBASE_FOREACH (GPUInput *, input, &node->inputs) {
+      if (input->source == GPU_SOURCE_UNIFORM && !input->link) {
+        /* We handle the UBO uniforms separately. */
+        BLI_addtail(&ubo_inputs_, BLI_genericNodeN(input));
+      }
+    }
+  }
+  if (!BLI_listbase_is_empty(&ubo_inputs_)) {
+    /* This sorts the inputs based on size. */
+    GPU_material_uniform_buffer_create(&mat, &ubo_inputs_);
+  }
+}
+
+/* Sets id for unique names for all inputs, resources and temp variables. */
+void GPUCodegen::set_unique_ids()
+{
+  int id = 1;
+  LISTBASE_FOREACH (GPUNode *, node, &graph.nodes) {
+    LISTBASE_FOREACH (GPUInput *, input, &node->inputs) {
+      input->id = id++;
+    }
+    LISTBASE_FOREACH (GPUOutput *, output, &node->outputs) {
+      output->id = id++;
+    }
+  }
+}
+
+void GPUCodegen::generate_graphs()
+{
+  set_unique_ids();
+
+  output.surface = graph_serialize(GPU_NODE_TAG_SURFACE | GPU_NODE_TAG_AOV, graph.outlink_surface);
+  output.volume = graph_serialize(GPU_NODE_TAG_VOLUME, graph.outlink_volume);
+  output.displacement = graph_serialize(GPU_NODE_TAG_DISPLACEMENT, graph.outlink_displacement);
+  output.thickness = graph_serialize(GPU_NODE_TAG_THICKNESS, graph.outlink_thickness);
+
+  if (!BLI_listbase_is_empty(&graph.material_functions)) {
+    std::stringstream eval_ss;
+    eval_ss << "\n/* Generated Functions */\n\n";
+    LISTBASE_FOREACH (GPUNodeGraphFunctionLink *, func_link, &graph.material_functions) {
+      char *fn = graph_serialize(GPU_NODE_TAG_FUNCTION, func_link->outlink);
+      eval_ss << "float " << func_link->name << "() {\n" << fn << "}\n\n";
+      MEM_SAFE_FREE(fn);
+    }
+    output.material_functions = extract_c_str(eval_ss);
+  }
+
+  LISTBASE_FOREACH (GPUMaterialAttribute *, attr, &graph.attributes) {
+    BLI_hash_mm2a_add(&hm2a_, (uchar *)attr->name, strlen(attr->name));
+  }
+
+  hash_ = BLI_hash_mm2a_end(&hm2a_);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name GPUPass
+ * \{ */
+
+GPUPass *GPU_generate_pass(GPUMaterial *material,
+                           GPUNodeGraph *graph,
+                           GPUCodegenCallbackFn finalize_source_cb,
+                           void *thunk)
+{
+  /* Prune the unused nodes and extract attributes before compiling so the
+   * generated VBOs are ready to accept the future shader. */
+  gpu_node_graph_prune_unused(graph);
+  gpu_node_graph_finalize_uniform_attrs(graph);
+
+  GPUCodegen codegen(material, graph);
+  codegen.generate_graphs();
+  codegen.generate_uniform_buffer();
+
+  /* Cache lookup: Reuse shaders already compiled. */
+  GPUPass *pass_hash = gpu_pass_cache_lookup(codegen.hash_get());
+
+  /* FIXME(fclem): This is broken. Since we only check for the hash and not the full source
+   * there is no way to have a collision currently. Some advocated to only use a bigger hash. */
+  if (pass_hash && (pass_hash->next == nullptr || pass_hash->next->hash != codegen.hash_get())) {
+    if (!gpu_pass_is_valid(pass_hash)) {
+      /* Shader has already been created but failed to compile. */
+      return nullptr;
+    }
+    /* No collision, just return the pass. */
+    pass_hash->refcount += 1;
+    return pass_hash;
+  }
+
+  /* Either the shader is not compiled or there is a hash collision...
+   * continue generating the shader strings. */
+  codegen.generate_attribs();
+  codegen.generate_resources();
+  codegen.generate_library();
+
+  /* Make engine add its own code and implement the generated functions. */
+  finalize_source_cb(thunk, material, &codegen.output);
+
+  GPUPass *pass = nullptr;
+  if (pass_hash) {
+    /* Cache lookup: Reuse shaders already compiled. */
+    pass = gpu_pass_cache_resolve_collision(
+        pass_hash, codegen.output.create_info, codegen.hash_get());
+  }
+
+  if (pass) {
+    /* Cache hit. Reuse the same GPUPass and GPUShader. */
+    if (!gpu_pass_is_valid(pass)) {
+      /* Shader has already been created but failed to compile. */
+      return nullptr;
+    }
+    pass->refcount += 1;
+  }
+  else {
+    /* We still create a pass even if shader compilation
+     * fails to avoid trying to compile again and again. */
+    pass = (GPUPass *)MEM_callocN(sizeof(GPUPass), "GPUPass");
+    pass->shader = nullptr;
+    pass->refcount = 1;
+    pass->create_info = codegen.create_info;
+    pass->hash = codegen.hash_get();
+    pass->compiled = false;
+
+    codegen.create_info = nullptr;
+
+    gpu_pass_cache_insert_after(pass_hash, pass);
+  }
+  return pass;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Compilation
+ * \{ */
+
+static int count_active_texture_sampler(GPUPass *pass, GPUShader *shader)
+{
+  int num_samplers = 0;
+
+  for (const ShaderCreateInfo::Resource &res : pass->create_info->pass_resources_) {
+    if (res.bind_type == ShaderCreateInfo::Resource::BindType::SAMPLER) {
+      if (GPU_shader_get_uniform(shader, res.sampler.name.c_str()) != -1) {
+        num_samplers += 1;
+      }
+    }
+  }
+
+  return num_samplers;
+}
+
+static bool gpu_pass_shader_validate(GPUPass *pass, GPUShader *shader)
+{
+  if (shader == nullptr) {
+    return false;
+  }
+
+  /* NOTE: The only drawback of this method is that it will count a sampler
+   * used in the fragment shader and only declared (but not used) in the vertex
+   * shader as used by both. But this corner case is not happening for now. */
+  int active_samplers_len = count_active_texture_sampler(pass, shader);
+
+  /* Validate against opengl limit. */
+  if ((active_samplers_len > GPU_max_textures_frag()) ||
+      (active_samplers_len > GPU_max_textures_vert())) {
+    return false;
+  }
+
+  if (pass->create_info->geometry_source_.is_empty() == false) {
+    if (active_samplers_len > GPU_max_textures_geom()) {
+      return false;
+    }
+  }
+
+  return (active_samplers_len * 3 <= GPU_max_textures());
+}
+
+bool GPU_pass_compile(GPUPass *pass, const char *shname)
+{
+  bool success = true;
+  if (!pass->compiled) {
+    GPUShaderCreateInfo *info = reinterpret_cast<GPUShaderCreateInfo *>(
+        static_cast<ShaderCreateInfo *>(pass->create_info));
+
+    pass->create_info->name_ = shname;
+
+    GPUShader *shader = GPU_shader_create_from_info(info);
+
+    /* NOTE: Some drivers / gpu allows more active samplers than the opengl limit.
+     * We need to make sure to count active samplers to avoid undefined behavior. */
+    if (!gpu_pass_shader_validate(pass, shader)) {
+      success = false;
+      if (shader != nullptr) {
+        fprintf(stderr, "GPUShader: error: too many samplers in shader.\n");
+        GPU_shader_free(shader);
+        shader = nullptr;
+      }
+    }
+    pass->shader = shader;
+    pass->compiled = true;
+  }
+  return success;
+}
+
+GPUShader *GPU_pass_shader_get(GPUPass *pass)
+{
+  return pass->shader;
+}
+
+void GPU_pass_release(GPUPass *pass)
+{
+  BLI_assert(pass->refcount > 0);
+  pass->refcount--;
+}
+
+static void gpu_pass_free(GPUPass *pass)
+{
+  BLI_assert(pass->refcount == 0);
+  if (pass->shader) {
+    GPU_shader_free(pass->shader);
+  }
+  delete pass->create_info;
+  MEM_freeN(pass);
+}
+
+void GPU_pass_cache_garbage_collect(void)
+{
+  static int lasttime = 0;
+  const int shadercollectrate = 60; /* hardcoded for now. */
+  int ctime = (int)PIL_check_seconds_timer();
+
+  if (ctime < shadercollectrate + lasttime) {
+    return;
+  }
+
+  lasttime = ctime;
+
+  BLI_spin_lock(&pass_cache_spin);
+  GPUPass *next, **prev_pass = &pass_cache;
+  for (GPUPass *pass = pass_cache; pass; pass = next) {
+    next = pass->next;
+    if (pass->refcount == 0) {
+      /* Remove from list */
+      *prev_pass = next;
+      gpu_pass_free(pass);
+    }
+    else {
+      prev_pass = &pass->next;
+    }
+  }
+  BLI_spin_unlock(&pass_cache_spin);
+}
+
+void GPU_pass_cache_init(void)
+{
+  BLI_spin_init(&pass_cache_spin);
+}
+
+void GPU_pass_cache_free(void)
+{
+  BLI_spin_lock(&pass_cache_spin);
+  while (pass_cache) {
+    GPUPass *next = pass_cache->next;
+    gpu_pass_free(pass_cache);
+    pass_cache = next;
+  }
+  BLI_spin_unlock(&pass_cache_spin);
+
+  BLI_spin_end(&pass_cache_spin);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Module
+ * \{ */
+
+void gpu_codegen_init(void)
+{
+}
+
+void gpu_codegen_exit(void)
+{
+  // BKE_world_defaults_free_gpu();
+  BKE_material_defaults_free_gpu();
+  GPU_shader_free_builtin_shaders();
+}
+
+/** \} */
\ No newline at end of file