Add support for instanced rendering and shader storage buffers. (flutter#95)

Author: chinmaygarde

impeller/compiler/code_gen_template.h

@@ -44,16 +44,16 @@ struct {{camel_case(shader_name)}}{{camel_case(shader_stage)}}Shader {
   }; // struct {{def.name}} (size {{def.byte_length}})
 {% endfor %}
 {% endif %}
-{% if length(uniform_buffers) > 0 %}
+{% if length(buffers) > 0 %}
 
   // ===========================================================================
-  // Stage Uniforms ============================================================
+  // Stage Uniform & Storage Buffers ===========================================
   // ===========================================================================
-{% for uniform in uniform_buffers %}
+{% for buffer in buffers %}
 
-  static constexpr auto kResource{{camel_case(uniform.name)}} = ShaderUniformSlot<{{uniform.name}}> { // {{uniform.name}}
-    "{{uniform.name}}",     // name
-    {{uniform.msl_res_0}}u,   // binding
+  static constexpr auto kResource{{camel_case(buffer.name)}} = ShaderUniformSlot<{{buffer.name}}> { // {{buffer.name}}
+    "{{buffer.name}}",     // name
+    {{buffer.msl_res_0}}u, // binding
   };
 {% endfor %}
 {% endif %}
@@ -119,6 +119,10 @@ struct {{camel_case(shader_name)}}{{camel_case(shader_stage)}}Shader {
   };
 {% endif %}
 
+  // ===========================================================================
+  // Resource Binding Utilities ================================================
+  // ===========================================================================
+
 {% for proto in bind_prototypes %}
   /// {{proto.docstring}}
   static {{proto.return_type}} Bind{{proto.name}}({% for arg in proto.args %}

impeller/compiler/reflector.cc

@@ -166,11 +166,27 @@ std::optional<nlohmann::json> Reflector::GenerateTemplateArguments() const {
 
   const auto shader_resources = compiler_->get_shader_resources();
 
-  if (auto uniform_buffers = ReflectResources(shader_resources.uniform_buffers);
-      uniform_buffers.has_value()) {
-    root["uniform_buffers"] = std::move(uniform_buffers.value());
-  } else {
-    return std::nullopt;
+  // Uniform and storage buffers.
+  {
+    auto& buffers = root["buffers"] = nlohmann::json::array_t{};
+    if (auto uniform_buffers_json =
+            ReflectResources(shader_resources.uniform_buffers);
+        uniform_buffers_json.has_value()) {
+      for (const auto& uniform_buffer : uniform_buffers_json.value()) {
+        buffers.emplace_back(std::move(uniform_buffer));
+      }
+    } else {
+      return std::nullopt;
+    }
+    if (auto storage_buffers_json =
+            ReflectResources(shader_resources.storage_buffers);
+        storage_buffers_json.has_value()) {
+      for (const auto& uniform_buffer : storage_buffers_json.value()) {
+        buffers.emplace_back(std::move(uniform_buffer));
+      }
+    } else {
+      return std::nullopt;
+    }
   }
 
   {
@@ -742,6 +758,25 @@ std::vector<Reflector::BindPrototype> Reflector::ReflectBindPrototypes(
         .argument_name = "view",
     });
   }
+  for (const auto& storage_buffer : resources.storage_buffers) {
+    auto& proto = prototypes.emplace_back(BindPrototype{});
+    proto.return_type = "bool";
+    proto.name = ConvertToCamelCase(storage_buffer.name);
+    {
+      std::stringstream stream;
+      stream << "Bind storage buffer for resource named " << storage_buffer.name
+             << ".";
+      proto.docstring = stream.str();
+    }
+    proto.args.push_back(BindPrototypeArgument{
+        .type_name = "Command&",
+        .argument_name = "command",
+    });
+    proto.args.push_back(BindPrototypeArgument{
+        .type_name = "BufferView",
+        .argument_name = "view",
+    });
+  }
   for (const auto& sampled_image : resources.sampled_images) {
     auto& proto = prototypes.emplace_back(BindPrototype{});
     proto.return_type = "bool";

impeller/fixtures/BUILD.gn

@@ -12,6 +12,8 @@ impeller_shaders("shader_fixtures") {
   shaders = [
     "box_fade.vert",
     "box_fade.frag",
+    "instanced_draw.vert",
+    "instanced_draw.frag",
     "test_texture.vert",
     "test_texture.frag",
   ]

impeller/fixtures/instanced_draw.frag

@@ -0,0 +1,11 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+in vec4 v_color;
+
+out vec4 frag_color;
+
+void main() {
+  frag_color = v_color;
+}

impeller/fixtures/instanced_draw.vert

@@ -0,0 +1,24 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+uniform FrameInfo {
+  mat4 mvp;
+} frame_info;
+
+readonly buffer InstanceInfo {
+  vec4 colors[];
+} instance_info;
+
+in vec2 vtx;
+
+out vec4 v_color;
+
+void main () {
+  gl_Position = frame_info.mvp *
+    vec4(vtx.x + 105.0 * gl_InstanceIndex,
+         vtx.y + 105.0 * gl_InstanceIndex,
+         0.0,
+         1.0);
+  v_color = instance_info.colors[gl_InstanceIndex];
+}

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -482,7 +482,7 @@ static bool Bind(PassBindingsCache& pass,
                          indexType:ToMTLIndexType(command.index_type)
                        indexBuffer:mtl_index_buffer
                  indexBufferOffset:command.index_buffer.range.offset
-                     instanceCount:1u
+                     instanceCount:command.instance_count
                         baseVertex:command.base_vertex
                       baseInstance:0u];
   }

impeller/renderer/command.h

@@ -90,6 +90,7 @@ struct Command {
   /// If unset, no scissor is applied.
   ///
   std::optional<IRect> scissor;
+  size_t instance_count = 1u;
 
   bool BindVertices(const VertexBuffer& buffer);
 

impeller/renderer/host_buffer.h

@@ -49,6 +49,29 @@ class HostBuffer final : public std::enable_shared_from_this<HostBuffer>,
     );
   }
 
+  //----------------------------------------------------------------------------
+  /// @brief      Emplace storage buffer data onto the host buffer. Ensure that
+  ///             backend specific uniform alignment requirements are respected.
+  ///
+  /// @param[in]  uniform     The storage buffer to emplace onto the buffer.
+  ///
+  /// @tparam     StorageBufferType The type of the shader storage buffer.
+  ///
+  /// @return     The buffer view.
+  ///
+  template <
+      class StorageBufferType,
+      class = std::enable_if_t<std::is_standard_layout_v<StorageBufferType>>>
+  [[nodiscard]] BufferView EmplaceStorageBuffer(
+      const std::vector<StorageBufferType>& buffer) {
+    const auto alignment =
+        std::max(alignof(StorageBufferType), DefaultUniformAlignment());
+    return Emplace(buffer.data(),                              // buffer
+                   buffer.size() * sizeof(StorageBufferType),  // size
+                   alignment                                   // alignment
+    );
+  }
+
   //----------------------------------------------------------------------------
   /// @brief      Emplace non-uniform data (like contiguous vertices) onto the
   ///             host buffer.

impeller/renderer/renderer_unittests.cc

@@ -6,6 +6,8 @@
 #include "flutter/testing/testing.h"
 #include "impeller/fixtures/box_fade.frag.h"
 #include "impeller/fixtures/box_fade.vert.h"
+#include "impeller/fixtures/instanced_draw.frag.h"
+#include "impeller/fixtures/instanced_draw.vert.h"
 #include "impeller/fixtures/test_texture.frag.h"
 #include "impeller/fixtures/test_texture.vert.h"
 #include "impeller/geometry/path_builder.h"
@@ -270,5 +272,60 @@ TEST_F(RendererTest, CanRenderToTexture) {
   ASSERT_TRUE(r2t_pass->EncodeCommands(*context->GetTransientsAllocator()));
 }
 
+TEST_F(RendererTest, CanRenderInstanced) {
+  using VS = InstancedDrawVertexShader;
+  using FS = InstancedDrawFragmentShader;
+
+  VertexBufferBuilder<VS::PerVertexData> builder;
+
+  ASSERT_TRUE(
+      Tessellator{}.Tessellate(FillType::kPositive,
+                               PathBuilder{}
+                                   .AddRect(Rect::MakeXYWH(10, 10, 100, 100))
+                                   .TakePath()
+                                   .CreatePolyline(),
+                               [&builder](Point vtx) {
+                                 VS::PerVertexData data;
+                                 data.vtx = vtx;
+                                 builder.AppendVertex(data);
+                               }));
+
+  auto pipeline =
+      GetContext()
+          ->GetPipelineLibrary()
+          ->GetRenderPipeline(
+              PipelineBuilder<VS, FS>::MakeDefaultPipelineDescriptor(
+                  *GetContext())
+                  ->SetSampleCount(SampleCount::kCount4))
+          .get();
+  ASSERT_TRUE(pipeline && pipeline->IsValid());
+
+  Command cmd;
+  cmd.pipeline = pipeline;
+  cmd.label = "InstancedDraw";
+
+  static constexpr size_t kInstancesCount = 5u;
+  std::vector<VS::InstanceInfo> instances;
+  for (size_t i = 0; i < kInstancesCount; i++) {
+    VS::InstanceInfo info;
+    info.colors = Color::Random();
+    instances.emplace_back(info);
+  }
+
+  ASSERT_TRUE(OpenPlaygroundHere([&](RenderPass& pass) -> bool {
+    VS::FrameInfo frame_info;
+    frame_info.mvp = Matrix::MakeOrthographic(pass.GetRenderTargetSize());
+    VS::BindFrameInfo(cmd,
+                      pass.GetTransientsBuffer().EmplaceUniform(frame_info));
+    VS::BindInstanceInfo(
+        cmd, pass.GetTransientsBuffer().EmplaceStorageBuffer(instances));
+    cmd.BindVertices(builder.CreateVertexBuffer(pass.GetTransientsBuffer()));
+
+    cmd.instance_count = kInstancesCount;
+    pass.AddCommand(cmd);
+    return true;
+  }));
+}
+
 }  // namespace testing
 }  // namespace impeller