From 418b344dbea181e9416c0c1644388586ca7c939f Mon Sep 17 00:00:00 2001
From: karl <karl.bittner@hexaquo.at>
Date: Mon, 11 Jan 2021 12:35:52 +0100
Subject: [PATCH] Add simple line drawing component + renderer

---
 ECS/Components/Lines.h     | 38 ++++++++++++++++++++++++++++++++++++++
 ECS/Systems/RenderSystem.h | 14 +++++++++++++-
 Shaders/line-fragment.fs   |  7 +++++++
 Shaders/line-vertex.vs     | 11 +++++++++++
 main.cpp                   |  7 ++++++-
 5 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 ECS/Components/Lines.h
 create mode 100644 Shaders/line-fragment.fs
 create mode 100644 Shaders/line-vertex.vs

diff --git a/ECS/Components/Lines.h b/ECS/Components/Lines.h
new file mode 100644
index 0000000..77a83d6
--- /dev/null
+++ b/ECS/Components/Lines.h
@@ -0,0 +1,38 @@
+#ifndef ECSGAME_LINES_H
+#define ECSGAME_LINES_H
+
+#include <GLFW/glfw3.h>
+#include <glad/glad.h>
+#include <glm/fwd.hpp>
+#include <vector>
+
+struct Lines {
+    explicit Lines() {
+        GLfloat lineSeg[] = {
+            0.0f, 0.0f, 0.0f, // first vertex
+            2.0f, 2.0f, 2.0f  // second vertex
+        };
+
+        glGenVertexArrays(1, &lineVAO);
+        glGenBuffers(1, &lineVBO);
+        glBindVertexArray(lineVAO);
+        glBindBuffer(GL_ARRAY_BUFFER, lineVBO);
+        glBufferData(GL_ARRAY_BUFFER, sizeof(lineSeg), &lineSeg, GL_STATIC_DRAW);
+        glEnableVertexAttribArray(0);
+        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (void *)0);
+    }
+
+    void render() const {
+        // glEnable(GL_LINE_SMOOTH);
+        // glHint(GL_LINE_SMOOTH_HINT, GL_NICEST);
+        glBindVertexArray(lineVAO);
+        glLineWidth(3.3f);
+        glDrawArrays(GL_LINES, 0, 2);
+        glLineWidth(1.0f);
+    }
+
+  private:
+    GLuint lineVAO, lineVBO;
+};
+
+#endif // ECSGAME_LINES_H
diff --git a/ECS/Systems/RenderSystem.h b/ECS/Systems/RenderSystem.h
index 10f3bc6..f8762fe 100644
--- a/ECS/Systems/RenderSystem.h
+++ b/ECS/Systems/RenderSystem.h
@@ -10,6 +10,7 @@
 #include "../Components/Camera.h"
 #include "../Components/DirectionalLight.h"
 #include "../Components/LODObjMesh.h"
+#include "../Components/Lines.h"
 #include "../Components/Mesh.h"
 #include "../Components/ObjMesh.h"
 #include "../Components/Texture.h"
@@ -226,7 +227,8 @@ class RenderSystem : public EntitySystem, public EventSubscriber<InputEvent> {
         glBindFramebuffer(GL_FRAMEBUFFER, 0);
     }
 
-    void render(World *pWorld, Shader normalShader, Shader shadowShader, Shader debugShader) {
+    void render(World *pWorld, Shader normalShader, Shader shadowShader, Shader debugShader,
+                Shader lineShader) {
         pWorld->each<Camera, Transform>([&](Entity *ent, ComponentHandle<Camera> camera,
                                             ComponentHandle<Transform> cameraTransform) {
             // Get render objects
@@ -306,6 +308,16 @@ class RenderSystem : public EntitySystem, public EventSubscriber<InputEvent> {
             glActiveTexture(GL_TEXTURE0);
             glBindTexture(GL_TEXTURE_2D, depthMap);
             // renderQuad();
+
+            // Draw lines
+            lineShader.use();
+            lineShader.setMat4("projection", camera->projection);
+            lineShader.setMat4("view", glm::inverse(view));
+            lineShader.setMat4("model",
+                               glm::mat4(1.0f)); // TODO: integrate cameraTransform->get_origin()
+
+            pWorld->each<Lines>(
+                [&](Entity *ent, ComponentHandle<Lines> lines) { lines->render(); });
         });
     }
 
diff --git a/Shaders/line-fragment.fs b/Shaders/line-fragment.fs
new file mode 100644
index 0000000..2ab0581
--- /dev/null
+++ b/Shaders/line-fragment.fs
@@ -0,0 +1,7 @@
+#version 330 core
+out vec4 FragColor;
+
+void main()
+{
+    FragColor = vec4(1.0); // white
+}
diff --git a/Shaders/line-vertex.vs b/Shaders/line-vertex.vs
new file mode 100644
index 0000000..70a22c7
--- /dev/null
+++ b/Shaders/line-vertex.vs
@@ -0,0 +1,11 @@
+#version 330 core
+layout (location = 0) in vec3 aPos;
+
+uniform mat4 model;
+uniform mat4 view;
+uniform mat4 projection;
+
+void main()
+{
+    gl_Position = projection * view * model * vec4(aPos, 1.0);
+}
diff --git a/main.cpp b/main.cpp
index 17d161d..f15bfa1 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3,6 +3,7 @@
 #include <iostream>
 
 #include "ECS/Components/DirectionalLight.h"
+#include "ECS/Components/Lines.h"
 #include "ECS/Components/ObjMesh.h"
 #include "ECS/Components/PathMove.h"
 #include "ECS/Components/SineAnimation.h"
@@ -196,12 +197,16 @@ int main(int argc, char **argv) {
     Entity *sun = world->create();
     sun->assign<DirectionalLight>(glm::normalize(glm::vec3(1.0, 1.0, 1.0)));
 
+    Entity *kdtree_vis = world->create();
+    kdtree_vis->assign<Lines>();
+
     // We're done loading geometry -> build the collision structure
     collision_system->build();
 
     Shader defaultShader("Shaders/default-vertex.vs", "Shaders/default-fragment.fs");
     Shader shadowShader("Shaders/shadow-vertex.vs", "Shaders/shadow-fragment.fs");
     Shader debugShader("Shaders/debug-vertex.vs", "Shaders/debug-fragment.fs");
+    Shader lineShader("Shaders/line-vertex.vs", "Shaders/line-fragment.fs");
 
     double timeInLastFrame = glfwGetTime();
     double elapsed_time = 0.0;
@@ -214,7 +219,7 @@ int main(int argc, char **argv) {
         elapsed_time += delta;
 
         world->tick(delta);
-        renderSystem->render(world, defaultShader, shadowShader, debugShader);
+        renderSystem->render(world, defaultShader, shadowShader, debugShader, lineShader);
 
         ring->get<Transform>()->rotate(delta * 100.0, glm::vec3(0.0, 1.0, 0.0));
         sun->get<DirectionalLight>()->direction = glm::normalize(glm::vec3(