From 2996e8ecaf4a42d6398cf7a0445070a19851a03a Mon Sep 17 00:00:00 2001
From: Emil Kosz <ekosz@int.pl>
Date: Tue, 3 Jun 2025 22:03:11 +0200
Subject: [PATCH] Sort entities by render type, bind buffers less often

---
 game/src/entity/#entity.h# | 22 ++++++++++++++++++++++
 game/src/entity/.#entity.h |  1 +
 game/src/entity/entity.h   |  9 ++++++++-
 game/src/entity/manager.c  |  9 ++++++++-
 game/src/entity/manager.h  | 29 ++++++++++++++++++++++++++++-
 game/src/entity/meshes.c   |  6 +++++-
 game/src/entity/meshes.h   |  1 +
 7 files changed, 73 insertions(+), 4 deletions(-)
 create mode 100644 game/src/entity/#entity.h#
 create mode 120000 game/src/entity/.#entity.h

diff --git a/game/src/entity/#entity.h# b/game/src/entity/#entity.h#
new file mode 100644
index 0000000..615d1b2
--- /dev/null
+++ b/game/src/entity/#entity.h#
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdbool.h>
+
+/* There should also be an entity mesh type of QUAD1, as billboards
+   always face the camera, thus the back side need not be rendered. */
+
+typedef struct Entity
+{
+  enum { MESH_QUAD2, MESH_QUAD_X } mesh_type;
+  enum { ORIGIN_CENTER, ORIGIN_BOTTOM } origin;
+  enum { RENDER_NORMAL, RENDER_BILLBOARD_Y, RENDER_BILLBOARD } render_type;
+
+  void *userdata;
+  
+  void (*on_tick) (struct Entity *self);
+  
+  vec3 position;
+  float rotation;
+  vec3 scale;			/* Unused for now. */
+  char *texture;
+} Entity;
diff --git a/game/src/entity/.#entity.h b/game/src/entity/.#entity.h
new file mode 120000
index 0000000..9eac588
--- /dev/null
+++ b/game/src/entity/.#entity.h
@@ -0,0 +1 @@
+emssej@Komputer-Ze-Smieci.2233:1748755544
\ No newline at end of file
diff --git a/game/src/entity/entity.h b/game/src/entity/entity.h
index 615d1b2..65299eb 100644
--- a/game/src/entity/entity.h
+++ b/game/src/entity/entity.h
@@ -5,11 +5,18 @@
 /* There should also be an entity mesh type of QUAD1, as billboards
    always face the camera, thus the back side need not be rendered. */
 
+typedef enum EntityRenderType
+  {
+    RENDER_NORMAL,
+    RENDER_BILLBOARD,
+    RENDER_BILLBOARD_Y
+  } EntityRenderType;
+
 typedef struct Entity
 {
   enum { MESH_QUAD2, MESH_QUAD_X } mesh_type;
   enum { ORIGIN_CENTER, ORIGIN_BOTTOM } origin;
-  enum { RENDER_NORMAL, RENDER_BILLBOARD_Y, RENDER_BILLBOARD } render_type;
+  EntityRenderType render_type;
 
   void *userdata;
   
diff --git a/game/src/entity/manager.c b/game/src/entity/manager.c
index 451e2fc..c6b18c4 100644
--- a/game/src/entity/manager.c
+++ b/game/src/entity/manager.c
@@ -10,6 +10,8 @@ EntityMesh mesh_quad2, mesh_quad_x;
 extern GameState game_state;
 extern Resources resources;
 
+unsigned int last_type = -1;
+
 void
 EntityManager_init ()
 {
@@ -81,7 +83,6 @@ em_render_internal (gpointer data, gpointer userdata)
     case RENDER_BILLBOARD_Y:
       /* It's not quite a "real" billboard, but the effect is much
 	 better on the eye. */
-      
       vec3 delta;
       glm_vec3_sub (game_state.camera.position, entity->position, delta);
       delta[1] = 0.0;
@@ -107,7 +108,13 @@ em_render_internal (gpointer data, gpointer userdata)
 
   glActiveTexture (GL_TEXTURE0);
   glBindTexture (GL_TEXTURE_2D, R_TEXGET (entity->texture));
+
+  if (entity->mesh_type != last_type)
+    {
+      EntityMesh_bind (&to_render);
+    }
   
+  last_type = entity->mesh_type;
   EntityMesh_render (&to_render);
 }
 
diff --git a/game/src/entity/manager.h b/game/src/entity/manager.h
index 80db2f1..08f635e 100644
--- a/game/src/entity/manager.h
+++ b/game/src/entity/manager.h
@@ -9,7 +9,34 @@
 #include "../resources.h"
 #include "../state.h"
 
-#define EM_ENTADD(entity) (g_sequence_append (entity_manager, entity));
+#define EM_ENTADD(entity) (g_sequence_insert_sorted (entity_manager, entity, em_compare, NULL));
+
+static inline int
+em_compare (gconstpointer a, gconstpointer b, gpointer userdata)
+/* This function is used to sort Entities by their mesh type, so that
+   diferrent buffers aren't bound every single frame. */
+{
+  UNUSED (userdata);
+  const Entity *entity1 = a;
+  const Entity *entity2 = b;
+
+  if (entity1->mesh_type == entity2->mesh_type)
+    {
+      return 0;
+    }
+
+  if (entity1->mesh_type == MESH_QUAD_X && entity2->mesh_type == MESH_QUAD2)
+    {
+      return -1;
+    }
+
+  if (entity1->mesh_type == MESH_QUAD2 && entity2->mesh_type == MESH_QUAD_X)
+    {
+      return 1;
+    }
+
+  return (int) entity1->mesh_type - (int) entity2->mesh_type;
+}
 
 void EntityManager_init ();
 void EntityManager_tick ();
diff --git a/game/src/entity/meshes.c b/game/src/entity/meshes.c
index 7e43710..8a127a4 100644
--- a/game/src/entity/meshes.c
+++ b/game/src/entity/meshes.c
@@ -5,7 +5,7 @@
 extern GameFlags game_flags;
 
 void
-EntityMesh_render (EntityMesh *mesh)
+EntityMesh_bind (EntityMesh *mesh)
 {
   glBindBuffer (GL_ARRAY_BUFFER, mesh->pbo);
   glEnableVertexAttribArray (0);
@@ -16,7 +16,11 @@ EntityMesh_render (EntityMesh *mesh)
   glVertexAttribPointer (1, 2, GL_FLOAT, GL_FALSE, sizeof (float) * 2, 0);
   
   glBindBuffer (GL_ELEMENT_ARRAY_BUFFER, mesh->ebo);
+}
 
+void
+EntityMesh_render (EntityMesh *mesh)
+{
   if (game_flags.wireframe_enabled)
     {
       glDrawElements (GL_LINES, mesh->indices_len, GL_UNSIGNED_INT, 0);
diff --git a/game/src/entity/meshes.h b/game/src/entity/meshes.h
index 08329aa..0959c8d 100644
--- a/game/src/entity/meshes.h
+++ b/game/src/entity/meshes.h
@@ -13,6 +13,7 @@ typedef struct EntityMesh
   unsigned int ebo;
 } EntityMesh;
 
+void EntityMesh_bind (EntityMesh *mesh);
 void EntityMesh_render (EntityMesh *mesh);
 EntityMesh EntityMesh_make_quad2 ();
 EntityMesh EntityMesh_make_quad_x ();