[Impeller Scene] Wire up camera (#38053)

* [Impeller Scene] Wire up camera

* Resolve view transform once

Author: bdero

impeller/scene/camera.cc

@@ -7,7 +7,7 @@
 namespace impeller {
 namespace scene {
 
-Camera Camera::MakePerspective(Scalar fov_y, Vector3 position) {
+Camera Camera::MakePerspective(Radians fov_y, Vector3 position) {
   Camera camera;
   camera.fov_y_ = fov_y;
   camera.position_ = position;
@@ -26,9 +26,8 @@ Matrix Camera::GetTransform(ISize target_size) const {
     return transform_.value();
   }
 
-  transform_ =
-      Matrix::MakePerspective(Radians(fov_y_), target_size, z_near_, z_far_) *
-      Matrix::MakeLookAt(position_, target_, up_).Invert();
+  transform_ = Matrix::MakePerspective(fov_y_, target_size, z_near_, z_far_) *
+               Matrix::MakeLookAt(position_, target_, up_);
 
   return transform_.value();
 }

impeller/scene/camera.h

@@ -13,14 +13,14 @@ namespace scene {
 
 class Camera {
  public:
-  static Camera MakePerspective(Scalar fov_y, Vector3 position);
+  static Camera MakePerspective(Radians fov_y, Vector3 position);
 
   Camera LookAt(Vector3 target, Vector3 up = Vector3(0, -1, 0)) const;
 
   Matrix GetTransform(ISize target_size) const;
 
  private:
-  Scalar fov_y_ = 60;
+  Radians fov_y_ = Degrees(60);
   Vector3 position_ = Vector3();
   Vector3 target_ = Vector3(0, 0, -1);
   Vector3 up_ = Vector3(0, -1, 0);

impeller/scene/scene.cc

@@ -26,15 +26,15 @@ bool Scene::Render(const RenderTarget& render_target,
                    const Camera& camera) const {
   // Collect the render commands from the scene.
   SceneEncoder encoder;
-  if (!root_.Render(encoder, camera)) {
+  if (!root_.Render(encoder)) {
     FML_LOG(ERROR) << "Failed to render frame.";
     return false;
   }
 
   // Encode the commands.
 
   std::shared_ptr<CommandBuffer> command_buffer =
-      encoder.BuildSceneCommandBuffer(*scene_context_, render_target);
+      encoder.BuildSceneCommandBuffer(*scene_context_, camera, render_target);
 
   // TODO(bdero): Do post processing.
 

impeller/scene/scene_encoder.cc

@@ -22,6 +22,7 @@ void SceneEncoder::Add(const SceneCommand& command) {
 }
 
 static void EncodeCommand(const SceneContext& scene_context,
+                          const Matrix& view_transform,
                           RenderPass& render_pass,
                           const SceneCommand& scene_command) {
   auto& host_buffer = render_pass.GetTransientsBuffer();
@@ -39,14 +40,15 @@ static void EncodeCommand(const SceneContext& scene_context,
   scene_command.material->BindToCommand(scene_context, host_buffer, cmd);
 
   GeometryVertexShader::VertInfo info;
-  info.mvp = scene_command.transform;
+  info.mvp = view_transform * scene_command.transform;
   GeometryVertexShader::BindVertInfo(cmd, host_buffer.EmplaceUniform(info));
 
   render_pass.AddCommand(std::move(cmd));
 }
 
 std::shared_ptr<CommandBuffer> SceneEncoder::BuildSceneCommandBuffer(
     const SceneContext& scene_context,
+    const Camera& camera,
     const RenderTarget& render_target) const {
   auto command_buffer = scene_context.GetContext()->CreateCommandBuffer();
   if (!command_buffer) {
@@ -61,7 +63,9 @@ std::shared_ptr<CommandBuffer> SceneEncoder::BuildSceneCommandBuffer(
   }
 
   for (auto& command : commands_) {
-    EncodeCommand(scene_context, *render_pass, command);
+    Matrix view_transform =
+        camera.GetTransform(render_pass->GetRenderTargetSize());
+    EncodeCommand(scene_context, view_transform, *render_pass, command);
   }
 
   if (!render_pass->EncodeCommands()) {

impeller/scene/scene_encoder.h

@@ -10,6 +10,7 @@
 
 #include "flutter/fml/macros.h"
 #include "impeller/renderer/command_buffer.h"
+#include "impeller/scene/camera.h"
 #include "impeller/scene/geometry.h"
 #include "impeller/scene/material.h"
 
@@ -34,6 +35,7 @@ class SceneEncoder {
 
   std::shared_ptr<CommandBuffer> BuildSceneCommandBuffer(
       const SceneContext& scene_context,
+      const Camera& camera,
       const RenderTarget& render_target) const;
 
   std::vector<SceneCommand> commands_;

impeller/scene/scene_entity.cc

@@ -56,17 +56,17 @@ bool SceneEntity::Add(const std::shared_ptr<SceneEntity>& child) {
   return true;
 }
 
-bool SceneEntity::Render(SceneEncoder& encoder, const Camera& camera) const {
-  OnRender(encoder, camera);
+bool SceneEntity::Render(SceneEncoder& encoder) const {
+  OnRender(encoder);
   for (auto& child : children_) {
-    if (!child->Render(encoder, camera)) {
+    if (!child->Render(encoder)) {
       return false;
     }
   }
   return true;
 }
 
-bool SceneEntity::OnRender(SceneEncoder& encoder, const Camera& camera) const {
+bool SceneEntity::OnRender(SceneEncoder& encoder) const {
   return true;
 }
 

impeller/scene/scene_entity.h

@@ -34,13 +34,13 @@ class SceneEntity {
 
   bool Add(const std::shared_ptr<SceneEntity>& child);
 
-  bool Render(SceneEncoder& encoder, const Camera& camera) const;
+  bool Render(SceneEncoder& encoder) const;
 
  protected:
   Matrix local_transform_;
 
  private:
-  virtual bool OnRender(SceneEncoder& encoder, const Camera& camera) const;
+  virtual bool OnRender(SceneEncoder& encoder) const;
 
   SceneEntity* parent_ = nullptr;
   std::vector<std::shared_ptr<SceneEntity>> children_;

impeller/scene/scene_unittests.cc

@@ -37,20 +37,21 @@ TEST_P(SceneTest, CuboidUnlit) {
       material->SetColor(Color::Red());
       mesh->SetMaterial(std::move(material));
 
-      Vector3 size(1, 2, 3);
+      Vector3 size(1, 1, 0);
       mesh->SetGeometry(Geometry::MakeCuboid(size));
 
-      mesh->SetLocalTransform(Matrix::MakeTranslation(size / 2));
+      mesh->SetLocalTransform(Matrix::MakeTranslation(-size / 2));
 
       scene.Add(mesh);
     }
 
+    // Face towards the +Z direction (+X right, +Y up).
     auto camera = Camera::MakePerspective(
-                      /* fov */ kPiOver4,
-                      /* position */ {50, -30, 50})
+                      /* fov */ Radians(kPiOver4),
+                      /* position */ {2, 2, -5})
                       .LookAt(
                           /* target */ Vector3(),
-                          /* up */ {0, -1, 0});
+                          /* up */ {0, 1, 0});
 
     scene.Render(render_target, camera);
     return true;

impeller/scene/static_mesh_entity.cc

@@ -24,8 +24,7 @@ void StaticMeshEntity::SetMaterial(std::shared_ptr<Material> material) {
 }
 
 // |SceneEntity|
-bool StaticMeshEntity::OnRender(SceneEncoder& encoder,
-                                const Camera& camera) const {
+bool StaticMeshEntity::OnRender(SceneEncoder& encoder) const {
   SceneCommand command = {
       .label = "Static Mesh",
       .transform = GetGlobalTransform(),

impeller/scene/static_mesh_entity.h

@@ -25,7 +25,7 @@ class StaticMeshEntity final : public SceneEntity {
 
  private:
   // |SceneEntity|
-  bool OnRender(SceneEncoder& encoder, const Camera& camera) const override;
+  bool OnRender(SceneEncoder& encoder) const override;
 
   std::shared_ptr<Material> material_;
   std::shared_ptr<Geometry> geometry_;