Add source code for the cascaded shadow mapping guest article.

src/8.guest/2021/2.csm/10.debug_quad.vs

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+#version 460 core
+layout (location = 0) in vec3 aPos;
+layout (location = 1) in vec2 aTexCoords;
+
+out vec2 TexCoords;
+
+void main()
+{
+    TexCoords = aTexCoords;
+    gl_Position = vec4(aPos, 1.0);
+}

src/8.guest/2021/2.csm/10.debug_quad_depth.fs

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+#version 460 core
+out vec4 FragColor;
+
+in vec2 TexCoords;
+
+uniform sampler2DArray depthMap;
+uniform float near_plane;
+uniform float far_plane;
+uniform int layer;
+
+// required when using a perspective projection matrix
+float LinearizeDepth(float depth)
+{
+    float z = depth * 2.0 - 1.0; // Back to NDC 
+    return (2.0 * near_plane * far_plane) / (far_plane + near_plane - z * (far_plane - near_plane));	
+}
+
+void main()
+{             
+    float depthValue = texture(depthMap, vec3(TexCoords, layer)).r;
+    // FragColor = vec4(vec3(LinearizeDepth(depthValue) / far_plane), 1.0); // perspective
+    FragColor = vec4(vec3(depthValue), 1.0); // orthographic
+}

src/8.guest/2021/2.csm/10.shadow_mapping.fs

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+#version 460 core
+out vec4 FragColor;
+
+in VS_OUT {
+    vec3 FragPos;
+    vec3 Normal;
+    vec2 TexCoords;
+} fs_in;
+
+uniform sampler2D diffuseTexture;
+uniform sampler2DArray shadowMap;
+
+uniform vec3 lightDir;
+uniform vec3 viewPos;
+uniform float farPlane;
+
+uniform mat4 view;
+
+layout (std140, binding = 0) uniform LightSpaceMatrices
+{
+    mat4 lightSpaceMatrices[16];
+};
+uniform float cascadePlaneDistances[16];
+uniform int cascadeCount;   // number of frusta - 1
+
+float ShadowCalculation(vec3 fragPosWorldSpace)
+{
+    // select cascade layer
+    vec4 fragPosViewSpace = view * vec4(fragPosWorldSpace, 1.0);
+    float depthValue = abs(fragPosViewSpace.z);
+
+    int layer = -1;
+    for (int i = 0; i < cascadeCount; ++i)
+    {
+        if (depthValue < cascadePlaneDistances[i])
+        {
+            layer = i;
+            break;
+        }
+    }
+    if (layer == -1)
+    {
+        layer = cascadeCount;
+    }
+
+    vec4 fragPosLightSpace = lightSpaceMatrices[layer] * vec4(fragPosWorldSpace, 1.0);
+    // perform perspective divide
+    vec3 projCoords = fragPosLightSpace.xyz / fragPosLightSpace.w;
+    // transform to [0,1] range
+    projCoords = projCoords * 0.5 + 0.5;
+
+    // get depth of current fragment from light's perspective
+    float currentDepth = projCoords.z;
+    if (currentDepth  > 1.0)
+    {
+        return 0.0;
+    }
+    // calculate bias (based on depth map resolution and slope)
+    vec3 normal = normalize(fs_in.Normal);
+    float bias = max(0.05 * (1.0 - dot(normal, lightDir)), 0.005);
+    if (layer == cascadeCount)
+    {
+        bias *= 1 / (farPlane * 0.5f);
+    }
+    else
+    {
+        bias *= 1 / (cascadePlaneDistances[layer] * 0.5f);
+    }
+
+    // PCF
+    float shadow = 0.0;
+    vec2 texelSize = 1.0 / vec2(textureSize(shadowMap, 0));
+    for(int x = -1; x <= 1; ++x)
+    {
+        for(int y = -1; y <= 1; ++y)
+        {
+            float pcfDepth = texture(shadowMap, vec3(projCoords.xy + vec2(x, y) * texelSize, layer)).r; 
+            shadow += (currentDepth - bias) > pcfDepth ? 1.0 : 0.0;        
+        }    
+    }
+    shadow /= 9.0;
+    
+    // keep the shadow at 0.0 when outside the far_plane region of the light's frustum.
+    if(projCoords.z > 1.0)
+    {
+        shadow = 0.0;
+    }
+        
+    return shadow;
+}
+
+void main()
+{           
+    vec3 color = texture(diffuseTexture, fs_in.TexCoords).rgb;
+    vec3 normal = normalize(fs_in.Normal);
+    vec3 lightColor = vec3(0.3);
+    // ambient
+    vec3 ambient = 0.3 * color;
+    // diffuse
+    float diff = max(dot(lightDir, normal), 0.0);
+    vec3 diffuse = diff * lightColor;
+    // specular
+    vec3 viewDir = normalize(viewPos - fs_in.FragPos);
+    vec3 reflectDir = reflect(-lightDir, normal);
+    float spec = 0.0;
+    vec3 halfwayDir = normalize(lightDir + viewDir);  
+    spec = pow(max(dot(normal, halfwayDir), 0.0), 64.0);
+    vec3 specular = spec * lightColor;    
+    // calculate shadow
+    float shadow = ShadowCalculation(fs_in.FragPos);                      
+    vec3 lighting = (ambient + (1.0 - shadow) * (diffuse + specular)) * color;    
+    
+    FragColor = vec4(lighting, 1.0);
+}

src/8.guest/2021/2.csm/10.shadow_mapping.vs

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+#version 460 core
+layout (location = 0) in vec3 aPos;
+layout (location = 1) in vec3 aNormal;
+layout (location = 2) in vec2 aTexCoords;
+
+out vec2 TexCoords;
+
+out VS_OUT {
+    vec3 FragPos;
+    vec3 Normal;
+    vec2 TexCoords;
+} vs_out;
+
+uniform mat4 projection;
+uniform mat4 view;
+uniform mat4 model;
+
+void main()
+{
+    vs_out.FragPos = vec3(model * vec4(aPos, 1.0));
+    vs_out.Normal = transpose(inverse(mat3(model))) * aNormal;
+    vs_out.TexCoords = aTexCoords;
+    gl_Position = projection * view * model * vec4(aPos, 1.0);
+}

src/8.guest/2021/2.csm/10.shadow_mapping_depth.fs

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+#version 460 core
+
+void main()
+{             
+}

src/8.guest/2021/2.csm/10.shadow_mapping_depth.gs

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+#version 460 core
+
+layout(triangles, invocations = 5) in;
+layout(triangle_strip, max_vertices = 3) out;
+
+layout (std140, binding = 0) uniform LightSpaceMatrices
+{
+    mat4 lightSpaceMatrices[16];
+};
+
+void main()
+{          
+	for (int i = 0; i < 3; ++i)
+	{
+		gl_Position = lightSpaceMatrices[gl_InvocationID] * gl_in[i].gl_Position;
+		gl_Layer = gl_InvocationID;
+		EmitVertex();
+	}
+	EndPrimitive();
+}  

src/8.guest/2021/2.csm/10.shadow_mapping_depth.vs

@@ -0,0 +1,9 @@
+#version 460 core
+layout (location = 0) in vec3 aPos;
+
+uniform mat4 model;
+
+void main()
+{
+    gl_Position = model * vec4(aPos, 1.0);
+}

src/8.guest/2021/2.csm/shadow_mapping.cpp

@@ -0,0 +1,671 @@
+#include <glad/glad.h>
+#include <GLFW/glfw3.h>
+#include <stb_image.h>
+
+#include <glm/glm.hpp>
+#include <glm/gtc/matrix_transform.hpp>
+#include <glm/gtc/type_ptr.hpp>
+
+#include <learnopengl/filesystem.h>
+#include <learnopengl/shader.h>
+#include <learnopengl/camera.h>
+#include <learnopengl/model.h>
+
+#include <iostream>
+#include <random>
+
+void framebuffer_size_callback(GLFWwindow* window, int width, int height);
+void mouse_callback(GLFWwindow* window, double xpos, double ypos);
+void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
+void processInput(GLFWwindow *window);
+unsigned int loadTexture(const char *path);
+void renderScene(const Shader &shader);
+void renderCube();
+void renderQuad();
+std::vector<glm::mat4> getLightSpaceMatrices();
+
+// settings
+const unsigned int SCR_WIDTH = 2560;
+const unsigned int SCR_HEIGHT = 1440;
+
+// camera
+Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
+float lastX = (float)SCR_WIDTH / 2.0;
+float lastY = (float)SCR_HEIGHT / 2.0;
+bool firstMouse = true;
+float cameraNearPlane = 0.1f;
+float cameraFarPlane = 500.0f;
+
+// timing
+float deltaTime = 0.0f;
+float lastFrame = 0.0f;
+
+std::vector<float> shadowCascadeLevels{ cameraFarPlane / 50.0f, cameraFarPlane / 25.0f, cameraFarPlane / 10.0f, cameraFarPlane / 2.0f };
+int debugLayer = 0;
+
+// meshes
+unsigned int planeVAO;
+
+// lighting info
+// -------------
+const glm::vec3 lightDir = glm::normalize(glm::vec3(20.0f, 50, 20.0f));
+unsigned int lightFBO;
+unsigned int lightDepthMaps;
+constexpr unsigned int depthMapResolution = 4096;
+
+bool showQuad = false;
+
+std::random_device device;
+std::mt19937 generator = std::mt19937(device());
+
+int main()
+{
+    // glfw: initialize and configure
+    // ------------------------------
+    glfwInit();
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+
+#ifdef __APPLE__
+    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
+#endif
+
+    // glfw window creation
+    // --------------------
+    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
+    if (window == NULL)
+    {
+        std::cout << "Failed to create GLFW window" << std::endl;
+        glfwTerminate();
+        return -1;
+    }
+    glfwMakeContextCurrent(window);
+    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
+    glfwSetCursorPosCallback(window, mouse_callback);
+    glfwSetScrollCallback(window, scroll_callback);
+
+    // tell GLFW to capture our mouse
+    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
+
+    // glad: load all OpenGL function pointers
+    // ---------------------------------------
+    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
+    {
+        std::cout << "Failed to initialize GLAD" << std::endl;
+        return -1;
+    }
+
+    // configure global opengl state
+    // -----------------------------
+    glEnable(GL_DEPTH_TEST);
+
+    // build and compile shaders
+    // -------------------------
+    Shader shader("10.shadow_mapping.vs", "10.shadow_mapping.fs");
+    Shader simpleDepthShader("10.shadow_mapping_depth.vs", "10.shadow_mapping_depth.fs", "10.shadow_mapping_depth.gs");
+    Shader debugDepthQuad("10.debug_quad.vs", "10.debug_quad_depth.fs");
+
+    // set up vertex data (and buffer(s)) and configure vertex attributes
+    // ------------------------------------------------------------------
+    float planeVertices[] = {
+        // positions            // normals         // texcoords
+         25.0f, -2.0f,  25.0f,  0.0f, 1.0f, 0.0f,  25.0f,  0.0f,
+        -25.0f, -2.0f,  25.0f,  0.0f, 1.0f, 0.0f,   0.0f,  0.0f,
+        -25.0f, -2.0f, -25.0f,  0.0f, 1.0f, 0.0f,   0.0f, 25.0f,
+         25.0f, -2.0f,  25.0f,  0.0f, 1.0f, 0.0f,  25.0f,  0.0f,
+        -25.0f, -2.0f, -25.0f,  0.0f, 1.0f, 0.0f,   0.0f, 25.0f,
+         25.0f, -2.0f, -25.0f,  0.0f, 1.0f, 0.0f,  25.0f, 25.0f
+    };
+    // plane VAO
+    unsigned int planeVBO;
+    glGenVertexArrays(1, &planeVAO);
+    glGenBuffers(1, &planeVBO);
+    glBindVertexArray(planeVAO);
+    glBindBuffer(GL_ARRAY_BUFFER, planeVBO);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(planeVertices), planeVertices, GL_STATIC_DRAW);
+    glEnableVertexAttribArray(0);
+    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
+    glEnableVertexAttribArray(1);
+    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
+    glEnableVertexAttribArray(2);
+    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
+    glBindVertexArray(0);
+
+    // load textures
+    // -------------
+    unsigned int woodTexture = loadTexture(FileSystem::getPath("resources/textures/wood.png").c_str());
+
+    // configure light FBO
+    // -----------------------
+    glGenFramebuffers(1, &lightFBO);
+
+    glGenTextures(1, &lightDepthMaps);
+    glBindTexture(GL_TEXTURE_2D_ARRAY, lightDepthMaps);
+    glTexImage3D(
+        GL_TEXTURE_2D_ARRAY, 0, GL_DEPTH_COMPONENT32F, depthMapResolution, depthMapResolution, int(shadowCascadeLevels.size()) + 1,
+        0, GL_DEPTH_COMPONENT, GL_FLOAT, nullptr);
+
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
+
+    constexpr float bordercolor[] = { 1.0f, 1.0f, 1.0f, 1.0f };
+    glTexParameterfv(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_BORDER_COLOR, bordercolor);
+
+    glBindFramebuffer(GL_FRAMEBUFFER, lightFBO);
+    glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, lightDepthMaps, 0);
+    glDrawBuffer(GL_NONE);
+    glReadBuffer(GL_NONE);
+
+    int status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
+    if (status != GL_FRAMEBUFFER_COMPLETE)
+    {
+        std::cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!";
+        throw 0;
+    }
+
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+
+    // configure UBO
+    // --------------------
+    unsigned int matricesUBO;
+    glGenBuffers(1, &matricesUBO);
+    glBindBuffer(GL_UNIFORM_BUFFER, matricesUBO);
+    glBufferData(GL_UNIFORM_BUFFER, sizeof(glm::mat4x4) * 16, nullptr, GL_STATIC_DRAW);
+    glBindBufferBase(GL_UNIFORM_BUFFER, 0, matricesUBO);
+    glBindBuffer(GL_UNIFORM_BUFFER, 0);
+
+    // shader configuration
+    // --------------------
+    shader.use();
+    shader.setInt("diffuseTexture", 0);
+    shader.setInt("shadowMap", 1);
+    debugDepthQuad.use();
+    debugDepthQuad.setInt("depthMap", 0);
+
+    // render loop
+    // -----------
+    while (!glfwWindowShouldClose(window))
+    {
+        // per-frame time logic
+        // --------------------
+        float currentFrame = glfwGetTime();
+        deltaTime = currentFrame - lastFrame;
+        lastFrame = currentFrame;
+
+        // input
+        // -----
+        processInput(window);
+
+        // change light position over time
+        //lightPos.x = sin(glfwGetTime()) * 3.0f;
+        //lightPos.z = cos(glfwGetTime()) * 2.0f;
+        //lightPos.y = 5.0 + cos(glfwGetTime()) * 1.0f;
+
+        // render
+        // ------
+        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+        // 0. UBO setup
+        const auto lightMatrices = getLightSpaceMatrices();
+        glBindBuffer(GL_UNIFORM_BUFFER, matricesUBO);
+        for (size_t i = 0; i < lightMatrices.size(); ++i)
+        {
+            glBufferSubData(GL_UNIFORM_BUFFER, i * sizeof(glm::mat4x4), sizeof(glm::mat4x4), &lightMatrices[i]);
+        }
+        glBindBuffer(GL_UNIFORM_BUFFER, 0);
+
+        // 1. render depth of scene to texture (from light's perspective)
+        // --------------------------------------------------------------
+        //lightProjection = glm::perspective(glm::radians(45.0f), (GLfloat)SHADOW_WIDTH / (GLfloat)SHADOW_HEIGHT, near_plane, far_plane); // note that if you use a perspective projection matrix you'll have to change the light position as the current light position isn't enough to reflect the whole scene
+        // render scene from light's point of view
+        simpleDepthShader.use();
+
+        glBindFramebuffer(GL_FRAMEBUFFER, lightFBO);
+        glFramebufferTexture(GL_FRAMEBUFFER, GL_TEXTURE_2D_ARRAY, lightDepthMaps, 0);
+        glViewport(0, 0, depthMapResolution, depthMapResolution);
+        glClear(GL_DEPTH_BUFFER_BIT);
+        glCullFace(GL_FRONT);  // peter panning
+        renderScene(simpleDepthShader);
+        glCullFace(GL_BACK);
+        glBindFramebuffer(GL_FRAMEBUFFER, 0);
+
+        // reset viewport
+        glViewport(0, 0, SCR_WIDTH, SCR_HEIGHT);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+        // 2. render scene as normal using the generated depth/shadow map  
+        // --------------------------------------------------------------
+        glViewport(0, 0, SCR_WIDTH, SCR_HEIGHT);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+        shader.use();
+        const glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, cameraNearPlane, cameraFarPlane);
+        const glm::mat4 view = camera.GetViewMatrix();
+        shader.setMat4("projection", projection);
+        shader.setMat4("view", view);
+        // set light uniforms
+        shader.setVec3("viewPos", camera.Position);
+        shader.setVec3("lightDir", lightDir);
+        shader.setFloat("farPlane", cameraFarPlane);
+        shader.setInt("cascadeCount", shadowCascadeLevels.size());
+        for (size_t i = 0; i < shadowCascadeLevels.size(); ++i)
+        {
+            shader.setFloat("cascadePlaneDistances[" + std::to_string(i) + "]", shadowCascadeLevels[i]);
+        }
+        glActiveTexture(GL_TEXTURE0);
+        glBindTexture(GL_TEXTURE_2D, woodTexture);
+        glActiveTexture(GL_TEXTURE1);
+        glBindTexture(GL_TEXTURE_2D_ARRAY, lightDepthMaps);
+        renderScene(shader);
+
+        // render Depth map to quad for visual debugging
+        // ---------------------------------------------
+        debugDepthQuad.use();
+        debugDepthQuad.setInt("layer", debugLayer);
+        glActiveTexture(GL_TEXTURE0);
+        glBindTexture(GL_TEXTURE_2D_ARRAY, lightDepthMaps);
+        if (showQuad)
+        {
+            renderQuad();
+        }
+        std::cout << glm::length(camera.Position) << "\n";
+
+        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
+        // -------------------------------------------------------------------------------
+        glfwSwapBuffers(window);
+        glfwPollEvents();
+    }
+
+    // optional: de-allocate all resources once they've outlived their purpose:
+    // ------------------------------------------------------------------------
+    glDeleteVertexArrays(1, &planeVAO);
+    glDeleteBuffers(1, &planeVBO);
+
+    glfwTerminate();
+    return 0;
+}
+
+// renders the 3D scene
+// --------------------
+void renderScene(const Shader &shader)
+{
+    // floor
+    glm::mat4 model = glm::mat4(1.0f);
+    shader.setMat4("model", model);
+    glBindVertexArray(planeVAO);
+    glDrawArrays(GL_TRIANGLES, 0, 6);
+
+    static std::vector<glm::mat4> modelMatrices;
+    if (modelMatrices.size() == 0)
+    {
+        for (int i = 0; i < 10; ++i)
+        {
+            static std::uniform_real_distribution<float> offsetDistribution = std::uniform_real_distribution<float>(-10, 10);
+            static std::uniform_real_distribution<float> scaleDistribution = std::uniform_real_distribution<float>(1.0, 2.0);
+            static std::uniform_real_distribution<float> rotationDistribution = std::uniform_real_distribution<float>(0, 180);
+
+            auto model = glm::mat4(1.0f);
+            model = glm::translate(model, glm::vec3(offsetDistribution(generator), offsetDistribution(generator) + 10.0f, offsetDistribution(generator)));
+            model = glm::rotate(model, glm::radians(rotationDistribution(generator)), glm::normalize(glm::vec3(1.0, 0.0, 1.0)));
+            model = glm::scale(model, glm::vec3(scaleDistribution(generator)));
+            modelMatrices.push_back(model);
+        }
+    }
+
+    for (const auto& model : modelMatrices)
+    {
+        shader.setMat4("model", model);
+        renderCube();
+    }
+
+
+    // cubes
+    //model = glm::mat4(1.0f);
+    //model = glm::translate(model, glm::vec3(-5.0f, -3.0f, 0.0));
+    //model = glm::scale(model, glm::vec3(2));
+    //shader.setMat4("model", model);
+    //renderCube();
+    //model = glm::mat4(1.0f);
+    //model = glm::translate(model, glm::vec3(2.0f, 3.0f, 1.0));
+    //model = glm::scale(model, glm::vec3(2));
+    //shader.setMat4("model", model);
+    //renderCube();
+    //model = glm::mat4(1.0f);
+    //model = glm::translate(model, glm::vec3(-1.0f, 3.0f, 2.0));
+    //model = glm::rotate(model, glm::radians(60.0f), glm::normalize(glm::vec3(1.0, 0.0, 1.0)));
+    //model = glm::scale(model, glm::vec3(2));
+    //shader.setMat4("model", model);
+    //renderCube();
+}
+
+
+// renderCube() renders a 1x1 3D cube in NDC.
+// -------------------------------------------------
+unsigned int cubeVAO = 0;
+unsigned int cubeVBO = 0;
+void renderCube()
+{
+    // initialize (if necessary)
+    if (cubeVAO == 0)
+    {
+        float vertices[] = {
+            // back face
+            -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
+             1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
+             1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 0.0f, // bottom-right         
+             1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
+            -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
+            -1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 1.0f, // top-left
+            // front face
+            -1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
+             1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 0.0f, // bottom-right
+             1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
+             1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
+            -1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 1.0f, // top-left
+            -1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
+            // left face
+            -1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
+            -1.0f,  1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-left
+            -1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
+            -1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
+            -1.0f, -1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-right
+            -1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
+            // right face
+             1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
+             1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
+             1.0f,  1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-right         
+             1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
+             1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
+             1.0f, -1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-left     
+            // bottom face
+            -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
+             1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 1.0f, // top-left
+             1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
+             1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
+            -1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 0.0f, // bottom-right
+            -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
+            // top face
+            -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
+             1.0f,  1.0f , 1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
+             1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 1.0f, // top-right     
+             1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
+            -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
+            -1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 0.0f  // bottom-left        
+        };
+        glGenVertexArrays(1, &cubeVAO);
+        glGenBuffers(1, &cubeVBO);
+        // fill buffer
+        glBindBuffer(GL_ARRAY_BUFFER, cubeVBO);
+        glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
+        // link vertex attributes
+        glBindVertexArray(cubeVAO);
+        glEnableVertexAttribArray(0);
+        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
+        glEnableVertexAttribArray(1);
+        glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
+        glEnableVertexAttribArray(2);
+        glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
+        glBindBuffer(GL_ARRAY_BUFFER, 0);
+        glBindVertexArray(0);
+    }
+    // render Cube
+    glBindVertexArray(cubeVAO);
+    glDrawArrays(GL_TRIANGLES, 0, 36);
+    glBindVertexArray(0);
+}
+
+// renderQuad() renders a 1x1 XY quad in NDC
+// -----------------------------------------
+unsigned int quadVAO = 0;
+unsigned int quadVBO;
+void renderQuad()
+{
+    if (quadVAO == 0)
+    {
+        float quadVertices[] = {
+            // positions        // texture Coords
+            -1.0f,  1.0f, 0.0f, 0.0f, 1.0f,
+            -1.0f, -1.0f, 0.0f, 0.0f, 0.0f,
+             1.0f,  1.0f, 0.0f, 1.0f, 1.0f,
+             1.0f, -1.0f, 0.0f, 1.0f, 0.0f,
+        };
+        // setup plane VAO
+        glGenVertexArrays(1, &quadVAO);
+        glGenBuffers(1, &quadVBO);
+        glBindVertexArray(quadVAO);
+        glBindBuffer(GL_ARRAY_BUFFER, quadVBO);
+        glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), &quadVertices, GL_STATIC_DRAW);
+        glEnableVertexAttribArray(0);
+        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
+        glEnableVertexAttribArray(1);
+        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
+    }
+    glBindVertexArray(quadVAO);
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+    glBindVertexArray(0);
+}
+
+// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
+// ---------------------------------------------------------------------------------------------------------
+void processInput(GLFWwindow *window)
+{
+    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
+        glfwSetWindowShouldClose(window, true);
+
+    camera.MovementSpeed = glfwGetKey(window, GLFW_KEY_LEFT_SHIFT) == GLFW_PRESS ? 2.5 * 10 : 2.5;
+
+    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
+        camera.ProcessKeyboard(FORWARD, deltaTime);
+    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
+        camera.ProcessKeyboard(BACKWARD, deltaTime);
+    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
+        camera.ProcessKeyboard(LEFT, deltaTime);
+    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
+        camera.ProcessKeyboard(RIGHT, deltaTime);
+
+    static int fPress = GLFW_RELEASE;
+    if (glfwGetKey(window, GLFW_KEY_F) == GLFW_RELEASE && fPress == GLFW_PRESS)
+    {
+        showQuad = !showQuad;
+    }
+    fPress = glfwGetKey(window, GLFW_KEY_F);
+
+    static int plusPress = GLFW_RELEASE;
+    if (glfwGetKey(window, GLFW_KEY_KP_ADD) == GLFW_RELEASE && plusPress == GLFW_PRESS)
+    {
+        debugLayer++;
+        if (debugLayer > shadowCascadeLevels.size())
+        {
+            debugLayer = 0;
+        }
+    }
+    plusPress = glfwGetKey(window, GLFW_KEY_KP_ADD);
+}
+
+// glfw: whenever the window size changed (by OS or user resize) this callback function executes
+// ---------------------------------------------------------------------------------------------
+void framebuffer_size_callback(GLFWwindow* window, int width, int height)
+{
+    // make sure the viewport matches the new window dimensions; note that width and 
+    // height will be significantly larger than specified on retina displays.
+    glViewport(0, 0, width, height);
+}
+
+// glfw: whenever the mouse moves, this callback is called
+// -------------------------------------------------------
+void mouse_callback(GLFWwindow* window, double xpos, double ypos)
+{
+    if (firstMouse)
+    {
+        lastX = xpos;
+        lastY = ypos;
+        firstMouse = false;
+    }
+
+    float xoffset = xpos - lastX;
+    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top
+
+    lastX = xpos;
+    lastY = ypos;
+
+    camera.ProcessMouseMovement(xoffset, yoffset);
+}
+
+// glfw: whenever the mouse scroll wheel scrolls, this callback is called
+// ----------------------------------------------------------------------
+void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
+{
+    camera.ProcessMouseScroll(yoffset);
+}
+
+// utility function for loading a 2D texture from file
+// ---------------------------------------------------
+unsigned int loadTexture(char const * path)
+{
+    unsigned int textureID;
+    glGenTextures(1, &textureID);
+
+    int width, height, nrComponents;
+    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
+    if (data)
+    {
+        GLenum format;
+        if (nrComponents == 1)
+            format = GL_RED;
+        else if (nrComponents == 3)
+            format = GL_RGB;
+        else if (nrComponents == 4)
+            format = GL_RGBA;
+
+        glBindTexture(GL_TEXTURE_2D, textureID);
+        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
+        glGenerateMipmap(GL_TEXTURE_2D);
+
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, format == GL_RGBA ? GL_CLAMP_TO_EDGE : GL_REPEAT); // for this tutorial: use GL_CLAMP_TO_EDGE to prevent semi-transparent borders. Due to interpolation it takes texels from next repeat 
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, format == GL_RGBA ? GL_CLAMP_TO_EDGE : GL_REPEAT);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+
+        stbi_image_free(data);
+    }
+    else
+    {
+        std::cout << "Texture failed to load at path: " << path << std::endl;
+        stbi_image_free(data);
+    }
+
+    return textureID;
+}
+
+
+std::vector<glm::vec4> getFrustumCornersWorldSpace(const glm::mat4& proj, const glm::mat4& view)
+{
+    const auto inv = glm::inverse(proj * view);
+
+    std::vector<glm::vec4> frustumCorners;
+    for (unsigned int x = 0; x < 2; ++x)
+    {
+        for (unsigned int y = 0; y < 2; ++y)
+        {
+            for (unsigned int z = 0; z < 2; ++z)
+            {
+                const glm::vec4 pt = inv * glm::vec4(2.0f * x - 1.0f, 2.0f * y - 1.0f, 2.0f * z - 1.0f, 1.0f);
+                frustumCorners.push_back(pt / pt.w);
+            }
+        }
+    }
+
+    return frustumCorners;
+}
+
+glm::mat4 getLightSpaceMatrix(const float nearPlane, const float farPlane)
+{
+    const auto proj = glm::perspective(
+        glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, nearPlane,
+        farPlane);
+    const auto corners = getFrustumCornersWorldSpace(proj, camera.GetViewMatrix());
+
+    glm::vec3 center = glm::vec3(0, 0, 0);
+    for (const auto& v : corners)
+    {
+        center += glm::vec3(v);
+    }
+    center /= corners.size();
+
+    const auto lightView = glm::lookAt(center + lightDir, center, glm::vec3(0.0f, 1.0f, 0.0f));
+
+    float minX = std::numeric_limits<float>::max();
+    float maxX = std::numeric_limits<float>::min();
+    float minY = std::numeric_limits<float>::max();
+    float maxY = std::numeric_limits<float>::min();
+    float minZ = std::numeric_limits<float>::max();
+    float maxZ = std::numeric_limits<float>::min();
+    for (const auto& v : corners)
+    {
+        const auto trf = lightView * v;
+        minX = std::min(minX, trf.x);
+        maxX = std::max(maxX, trf.x);
+        minY = std::min(minY, trf.y);
+        maxY = std::max(maxY, trf.y);
+        minZ = std::min(minZ, trf.z);
+        maxZ = std::max(maxZ, trf.z);
+    }
+
+    // Tune this parameter according to the scene
+    constexpr float zMult = 10.0f;
+    if (minZ < 0)
+    {
+        minZ *= zMult;
+    }
+    else
+    {
+        minZ /= zMult;
+    }
+    if (maxZ < 0)
+    {
+        maxZ /= zMult;
+    }
+    else
+    {
+        maxZ *= zMult;
+    }
+
+    const glm::mat4 lpMatrix = glm::ortho(-1.0f, 1.0f, -1.0f, 1.0f, minZ, maxZ);
+
+    const float scaleX = 2.0f / (maxX - minX);
+    const float scaleY = 2.0f / (maxY - minY);
+    const float offsetX = -0.5f * (minX + maxX) * scaleX;
+    const float offsetY = -0.5f * (minY + maxY) * scaleY;
+
+    glm::mat4 cropMatrix(1.0f);
+    cropMatrix[0][0] = scaleX;
+    cropMatrix[1][1] = scaleY;
+    cropMatrix[3][0] = offsetX;
+    cropMatrix[3][1] = offsetY;
+
+    return cropMatrix * lpMatrix * lightView;
+}
+
+std::vector<glm::mat4> getLightSpaceMatrices()
+{
+    std::vector<glm::mat4> ret;
+    for (size_t i = 0; i < shadowCascadeLevels.size() + 1; ++i)
+    {
+        if (i == 0)
+        {
+            ret.push_back(getLightSpaceMatrix(cameraNearPlane, shadowCascadeLevels[i]));
+        }
+        else if (i < shadowCascadeLevels.size())
+        {
+            ret.push_back(getLightSpaceMatrix(shadowCascadeLevels[i - 1], shadowCascadeLevels[i]));
+        }
+        else
+        {
+            ret.push_back(getLightSpaceMatrix(shadowCascadeLevels[i - 1], cameraFarPlane));
+        }
+    }
+    return ret;
+}