From a44e38afa38ca98a7b7b6e9317967fbef7a3642c Mon Sep 17 00:00:00 2001
From: karl <karl.bittner@hexaquo.at>
Date: Sun, 9 May 2021 19:47:44 +0200
Subject: [PATCH] Add basic collision detection for particle origin placement

---
 include/Gedeng/Camera.h     |  5 +++++
 include/Gedeng/Input.h      | 17 ++++++++++++++++-
 include/Gedeng/Ray.h        | 36 ++++++++++++++++++++++++++++++++++++
 test/particle-demo/main.cpp |  8 ++++++--
 4 files changed, 63 insertions(+), 3 deletions(-)
 create mode 100644 include/Gedeng/Ray.h

diff --git a/include/Gedeng/Camera.h b/include/Gedeng/Camera.h
index 2e27e34..e4355a7 100644
--- a/include/Gedeng/Camera.h
+++ b/include/Gedeng/Camera.h
@@ -7,6 +7,7 @@
 #include <glm/gtx/dual_quaternion.hpp>
 
 #include "Gedeng/Logger.h"
+#include "Gedeng/Ray.h"
 #include "Input.h"
 #include "Spatial.h"
 
@@ -28,6 +29,10 @@ class Camera : public Spatial {
         return glm::inverse(get_matrix());
     }
 
+    Ray get_view_ray() const {
+        return Ray(get_translation(), forward());
+    }
+
   private:
     glm::mat4 projection;
 };
diff --git a/include/Gedeng/Input.h b/include/Gedeng/Input.h
index f990441..6237087 100644
--- a/include/Gedeng/Input.h
+++ b/include/Gedeng/Input.h
@@ -18,6 +18,7 @@ class Input {
     static void initialize(GLFWwindow *window) {
         glfwSetKeyCallback(window, key_callback);
         glfwSetCursorPosCallback(window, mouse_callback);
+        glfwSetMouseButtonCallback(window, mouse_button_callback);
 
         glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
         is_mouse_active = true;
@@ -28,7 +29,7 @@ class Input {
     static void key_callback(GLFWwindow *window, int key, int scancode, int action, int mods) {
         if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, GLFW_TRUE);
 
-        Input::set_key_down(key, action == GLFW_RELEASE ? false : true);
+        set_key_down(key, action == GLFW_RELEASE ? false : true);
     }
 
     static void mouse_callback(GLFWwindow *window, double xpos, double ypos) {
@@ -36,6 +37,10 @@ class Input {
         mouse_position.y = ypos;
     }
 
+    static void mouse_button_callback(GLFWwindow *window, int button, int action, int mods) {
+        set_mouse_down(button, action == GLFW_RELEASE ? false : true);
+    }
+
     static void poll_input() {
         glfwPollEvents();
     }
@@ -48,12 +53,22 @@ class Input {
         return keys_down[key];
     }
 
+    static void set_mouse_down(int button, bool down) {
+        mouse_down[button] = down;
+    }
+
+    static bool is_mouse_down(int button) {
+        return mouse_down[button];
+    }
+
     static glm::vec2 get_mouse_position() {
         return is_mouse_active ? mouse_position : glm::vec2(0.0, 0.0);
     }
 
   private:
     inline static std::map<int, bool> keys_down;
+    inline static std::map<int, bool> mouse_down;
+
     inline static glm::vec2 mouse_position;
     inline static bool is_mouse_active;
 };
diff --git a/include/Gedeng/Ray.h b/include/Gedeng/Ray.h
new file mode 100644
index 0000000..36f5e24
--- /dev/null
+++ b/include/Gedeng/Ray.h
@@ -0,0 +1,36 @@
+#include <glm/geometric.hpp>
+#include <glm/glm.hpp>
+
+namespace Gedeng {
+
+class CollisionResult {
+  public:
+    explicit CollisionResult(bool is_colliding, glm::vec3 collision_position = glm::vec3(0, 0, 0))
+        : is_colliding(is_colliding), collision_position(collision_position) {
+    }
+
+    bool is_colliding;
+    glm::vec3 collision_position;
+};
+
+class Ray {
+  public:
+    glm::vec3 origin;
+    glm::vec3 direction;
+
+    Ray(glm::vec3 origin, glm::vec3 direction) : origin(origin), direction(direction) {
+    }
+
+    CollisionResult get_plane_collision(glm::vec3 normal = glm::vec3(0, 1, 0)) {
+        float denom = glm::dot(normal, direction);
+
+        if (glm::abs(denom) > 0.0001f) {
+            float t = glm::dot(-origin, normal) / denom;
+
+            if (t >= 0) return CollisionResult(true, origin + t * direction);
+        }
+        return CollisionResult(false);
+    }
+};
+
+} // namespace Gedeng
\ No newline at end of file
diff --git a/test/particle-demo/main.cpp b/test/particle-demo/main.cpp
index 4732ee3..d656333 100644
--- a/test/particle-demo/main.cpp
+++ b/test/particle-demo/main.cpp
@@ -3,6 +3,7 @@
 #include "Gedeng/QuadMesh.h"
 #include "Gedeng/TextLabel.h"
 #include "Gedeng/Vector3.h"
+#include <GLFW/glfw3.h>
 #define GEDENG_MAIN
 #include <Gedeng.h>
 
@@ -19,8 +20,8 @@ class ParticleApp : public Gedeng::Application {
           normal("Resources/Textures/PavingStones/PavingStones070_2K_Normal.jpg", Gedeng::Texture::Settings()),
           quad_mesh(Gedeng::QuadMesh(10.0)) {
         particles.set_position(glm::vec3(0.0f, 0.0f, -5.0f));
-        particles.set_velocity(glm::vec3(-1, 0, -1), glm::vec3(1, 5, 1));
-        particles.set_gravity(glm::vec3(0, -2, 0));
+        particles.set_velocity(glm::vec3(-2, 4, -2), glm::vec3(2, 6, 2));
+        particles.set_gravity(glm::vec3(0, -4, 0));
         particles.set_color(glm::vec3(0.0f, 0.5f, 1.0f));
         particles.set_lifetime(1.0f, 1.5f);
         particles.set_size(0.1);
@@ -37,6 +38,9 @@ class ParticleApp : public Gedeng::Application {
     void fixed_update(double delta) override {
         // camera.rotate(delta * 180, glm::vec3(0.0, 1.0, 0.0));
         camera.update(delta);
+
+        if (Gedeng::Input::is_mouse_down(GLFW_MOUSE_BUTTON_LEFT))
+            particles.set_position(camera.get_view_ray().get_plane_collision().collision_position);
     }
 
     void dynamic_update(double delta) override {