initial commit

14 files changed, 569 insertions, 0 deletions

diff --git a/geometry_shader/build.sh b/geometry_shader/build.sh
new file mode 100755
index 0000000..2d87dc0
--- /dev/null
+++ b/geometry_shader/build.sh
@@ -0,0 +1,5 @@
+#!/bin/sh
+. ../config
+TARGET='geometry_shader'
+set -x
+gcc -o $TARGET $CFLAGS $INCLUDE $LFLAGS $TARGET.c $LIBS && ./$TARGET
diff --git a/geometry_shader/geometry_shader b/geometry_shader/geometry_shader
new file mode 100755
index 0000000..53de7d2
--- /dev/null
+++ b/geometry_shader/geometry_shader
diff --git a/geometry_shader/geometry_shader.c b/geometry_shader/geometry_shader.c
new file mode 100644
index 0000000..af2d494
--- /dev/null
+++ b/geometry_shader/geometry_shader.c
@@ -0,0 +1,337 @@
+#include "GL/glew.h"
+#include "GLFW/glfw3.h"
+
+#include "pwyazh.h"
+
+#include "common.h"
+
+#include <unistd.h>
+
+#define WIDTH 1024
+#define HEIGHT 768
+
+static F32 dt;
+static Input input;
+
+void
+key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
+{
+    switch (action)
+    {
+        case GLFW_PRESS: {
+            switch (key)
+            {
+                case GLFW_KEY_SPACE: {
+                    input.jump.state = KeyState_PRESS;
+                } break;
+            }
+        } break;
+
+        case GLFW_RELEASE: {
+            switch (key)
+            {
+                case GLFW_KEY_SPACE: {
+                    input.jump.state = KeyState_RELEASE;
+                } break;
+            }
+        } break;
+    }
+}
+
+void
+draw_cube(U32 cube_vao, U32 texture)
+{
+    glBindVertexArray(cube_vao);
+    glBindTexture(GL_TEXTURE_2D, texture);
+    glDrawArrays(GL_TRIANGLES, 0, 36);
+    glBindTexture(GL_TEXTURE_2D, 0);
+    glBindVertexArray(0);
+}
+
+int
+main(void)
+{
+    GLFWwindow *window;
+    
+    if (glfwInit() == GLFW_FALSE)
+    {
+        fprintf(stderr, "[ERROR] Failed to initialize glfw.\n");
+        return(1);
+    }
+    
+    glfwWindowHint(GLFW_RESIZABLE, 0);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+    window = glfwCreateWindow(WIDTH, HEIGHT, "depth testing", 0, 0);
+    if (!window)
+    {
+        fprintf(stderr, "[ERROR] Failed to create window.\n");
+        glfwTerminate();
+        return(1);
+    }
+    
+    glfwMakeContextCurrent(window);
+
+    glfwSetKeyCallback(window, key_callback);
+
+    if (glewInit() != GLEW_OK)
+    {
+        fprintf(stderr, "[ERROR] Failed to initialize glew.\n");
+        glfwTerminate();
+        return(1);
+    }
+
+    glEnable(GL_DEPTH_TEST);
+    
+    U32 shader = create_shader_program_geom("shaders/base.vs",
+                                            "shaders/base.fs",
+                                            "shaders/base.gs");
+    U32 explosion_shader = create_shader_program_geom("shaders/explosion.vs",
+                                                      "shaders/explosion.fs",
+                                                      "shaders/explosion.gs");
+    U32 normals_shader = create_shader_program_geom("shaders/normals.vs",
+                                                    "shaders/normals.fs",
+                                                    "shaders/normals.gs");
+    U32 basic_shader = create_shader_program("shaders/basic.vs", "shaders/basic.fs");
+
+    U32 grid_texture = load_texture("../data/textures/grid.png");
+
+    F32 points[] = {
+        -0.5f,  0.5f, 1.0f, 0.0f, 0.0f,
+         0.5f,  0.5f, 0.0f, 1.0f, 0.0f,
+         0.5f, -0.5f, 0.0f, 0.0f, 1.0f,
+        -0.5f, -0.5f, 1.0f, 1.0f, 0.0f
+    };
+
+    GLuint points_vao, vbo;
+    glGenVertexArrays(1, &points_vao);
+    glBindVertexArray(points_vao);
+    glGenBuffers(1, &vbo);
+    glBindBuffer(GL_ARRAY_BUFFER, vbo);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);
+    glEnableVertexAttribArray(0);
+    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 5*sizeof(F32), (void *)0);
+    glEnableVertexAttribArray(1);
+    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 5*sizeof(F32), (void *)(2*sizeof(F32)));
+    glBindVertexArray(0);
+
+    F32 a = 0.5f;
+    /* NOTE(pryazha): Counter-clockwise order */
+    F32 cube_vertices[] = {
+        /* NOTE(pryazha): Back face */
+         a, -a, -a,  0.0f, 0.0f, /* bottom-left */
+        -a,  a, -a,  1.0f, 1.0f, /* top-right */
+         a,  a, -a,  0.0f, 1.0f, /* top-left */
+         a, -a, -a,  0.0f, 0.0f, /* bottom-left */
+        -a, -a, -a,  1.0f, 0.0f, /* bottom-right */
+        -a,  a, -a,  1.0f, 1.0f, /* top-right */
+
+         /* NOTE(pryazha): Front face */
+        -a, -a,  a,  0.0f, 0.0f, /* bottom-left */
+         a,  a,  a,  1.0f, 1.0f, /* top-right */
+        -a,  a,  a,  0.0f, 1.0f, /* top-left */
+        -a, -a,  a,  0.0f, 0.0f, /* bottom-left */
+         a, -a,  a,  1.0f, 0.0f, /* bottom-right */
+         a,  a,  a,  1.0f, 1.0f, /* top-right */
+         
+         /* NOTE(pryazha): Left face */
+        -a, -a, -a,  0.0f, 0.0f, /* bottom-left */
+        -a,  a,  a,  1.0f, 1.0f, /* top-right */
+        -a,  a, -a,  0.0f, 1.0f, /* top-left */
+        -a, -a, -a,  0.0f, 0.0f, /* bottom-left */
+        -a, -a,  a,  1.0f, 0.0f, /* bottom-right */
+        -a,  a,  a,  1.0f, 1.0f, /* top-right */
+
+         /* NOTE(pryazha): Right face */
+         a, -a,  a,  0.0f, 0.0f, /* bottom-left */
+         a,  a, -a,  1.0f, 1.0f, /* top-right */
+         a,  a,  a,  0.0f, 1.0f, /* top-left */
+         a, -a,  a,  0.0f, 0.0f, /* bottom-left */
+         a, -a, -a,  1.0f, 0.0f, /* bottom-right */
+         a,  a, -a,  1.0f, 1.0f, /* top-right */
+
+         /* NOTE(pryazha): Top face */
+        -a,  a,  a,  0.0f, 0.0f, /* bottom-left */
+         a,  a, -a,  1.0f, 1.0f, /* top-right */
+        -a,  a, -a,  0.0f, 1.0f, /* top-left */
+        -a,  a,  a,  0.0f, 0.0f, /* bottom-left */
+         a,  a,  a,  1.0f, 0.0f, /* bottom-right */
+         a,  a, -a,  1.0f, 1.0f, /* top-right */
+
+         /* NOTE(pryazha): Bottom face */
+        -a, -a, -a,  0.0f, 0.0f, /* bottom-left */
+         a, -a,  a,  1.0f, 1.0f, /* top-right */
+        -a, -a,  a,  0.0f, 1.0f, /* top-left */
+        -a, -a, -a,  0.0f, 0.0f, /* bottom-left */
+         a, -a, -a,  1.0f, 0.0f, /* bottom-right */
+         a, -a,  a,  1.0f, 1.0f, /* top-right */
+    };
+
+    U32 cube_vao;
+    glGenVertexArrays(1, &cube_vao);
+    glBindVertexArray(cube_vao);
+    glGenBuffers(1, &vbo);
+    glBindBuffer(GL_ARRAY_BUFFER, vbo);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(cube_vertices), cube_vertices, GL_STATIC_DRAW);
+    glEnableVertexAttribArray(0);
+    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5*sizeof(F32), (void *)0);
+    glEnableVertexAttribArray(1);
+    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5*sizeof(F32), (void *)(3*sizeof(F32)));
+    glBindVertexArray(0);
+
+    F32 vertices[] = {
+        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
+         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
+         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
+         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
+        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
+        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
+
+        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
+         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  0.0f,
+         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
+         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
+        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  1.0f,
+        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
+
+        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
+        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
+        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
+        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
+        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
+        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
+
+         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
+         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
+         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
+         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
+         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
+         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
+
+        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
+         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  1.0f,
+         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
+         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
+        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  0.0f,
+        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
+
+        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f,
+         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  1.0f,
+         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
+         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
+        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  0.0f,
+        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f
+    };
+
+    U32 normals_cube_vao;
+    glGenVertexArrays(1, &normals_cube_vao);
+    glBindVertexArray(normals_cube_vao);
+    glGenBuffers(1, &vbo);
+    glBindBuffer(GL_ARRAY_BUFFER, vbo);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
+    glEnableVertexAttribArray(0);
+    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8*sizeof(F32), (void *)0);
+    glEnableVertexAttribArray(1);
+    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8*sizeof(F32), (void *)(3*sizeof(F32)));
+    glEnableVertexAttribArray(2);
+    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8*sizeof(F32), (void *)(6*sizeof(F32)));
+    glBindVertexArray(0);
+
+    F32 target_fps = 60.0f;
+    F32 target_spf = 1.0f/target_fps;
+    
+    F32 last_time = glfwGetTime();
+    F32 time = last_time;
+
+    S32 scene = 0;
+
+    while (!glfwWindowShouldClose(window))
+    {
+        glfwPollEvents();
+
+        /* NOTE(pryazha): Update */
+        if (key_first_press(input.jump))
+        {
+            scene++;
+            scene %= 3;
+        }
+
+        input_update_last_state(&input);
+        
+        /* NOTE(pryazha): Render */
+        glClearColor(0.15f, 0.15f, 0.15f, 1.0f);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+        if (scene == 0)
+        {
+            glUseProgram(shader);
+            glBindVertexArray(points_vao);
+            glDrawArrays(GL_POINTS, 0, 4);
+            glBindVertexArray(0);
+        }
+        else if (scene == 1)
+        {
+            F32 radius = 2.0f;
+            F32 x = f32_sin(0.5*time)*radius;
+            F32 z = f32_cos(0.5*time)*radius;
+            MAT4 projection = perspective(90.0f, (F32)WIDTH/(F32)HEIGHT, 0.1f, 100.0f);
+            MAT4 view = look_at(v3f(x, 1.0f, z), v3f_zero(), v3f(0.0f, 1.0f, 0.0f));
+            MAT4 model = mat4_identity();
+            glUseProgram(explosion_shader);
+            shader_set_mat4fv(explosion_shader, "projection", projection);
+            shader_set_mat4fv(explosion_shader, "view", view);
+            shader_set_mat4fv(explosion_shader, "model", model);
+            shader_set_1f(explosion_shader, "time", time);
+            glBindVertexArray(cube_vao);
+            glBindTexture(GL_TEXTURE_2D, grid_texture);
+            glDrawArrays(GL_TRIANGLES, 0, 36);
+            glBindVertexArray(0);
+        }
+        else
+        {
+            MAT4 projection, view, model;
+            F32 radius, x, z;
+            
+            radius = 2.0f;
+            x = f32_sin(0.5*time)*radius;
+            z = f32_cos(0.5*time)*radius;
+
+            projection = perspective(90.0f, (F32)WIDTH/(F32)HEIGHT, 0.1f, 100.0f);
+            view = look_at(v3f(x, 1.0f, z), v3f_zero(), v3f(0.0f, 1.0f, 0.0f));
+            model = mat4_identity();
+
+            glUseProgram(basic_shader);
+            shader_set_mat4fv(basic_shader, "projection", projection);
+            shader_set_mat4fv(basic_shader, "view", view);
+            shader_set_mat4fv(basic_shader, "model", model);
+            draw_cube(normals_cube_vao, grid_texture);
+
+            glUseProgram(normals_shader);
+            shader_set_mat4fv(normals_shader, "projection", projection);
+            shader_set_mat4fv(normals_shader, "view", view);
+            shader_set_mat4fv(normals_shader, "model", model);
+            draw_cube(normals_cube_vao, grid_texture);
+        }
+
+        glfwSwapBuffers(window);
+
+        F32 elapsed = glfwGetTime()-last_time;
+        if (elapsed < target_spf)
+        {
+            U32 sleep_time = (U32)(target_spf-elapsed);
+            if (sleep_time > 0)
+                sleep(sleep_time);
+        }
+        F32 current_time = glfwGetTime();
+        dt = current_time-last_time;
+        time += dt;
+        last_time = current_time;
+    }
+
+    glDeleteBuffers(1, &vbo);
+    glDeleteVertexArrays(1, &points_vao);
+
+    glfwTerminate();
+    return(0);
+}
diff --git a/geometry_shader/shaders/base.fs b/geometry_shader/shaders/base.fs
new file mode 100644
index 0000000..283d885
--- /dev/null
+++ b/geometry_shader/shaders/base.fs
@@ -0,0 +1,11 @@
+#version 330 core
+
+in vec3 fcolor;
+
+out vec4 frag_color;
+
+void
+main(void)
+{
+    frag_color = vec4(fcolor, 1.0f);
+}
diff --git a/geometry_shader/shaders/base.gs b/geometry_shader/shaders/base.gs
new file mode 100644
index 0000000..6b140c5
--- /dev/null
+++ b/geometry_shader/shaders/base.gs
@@ -0,0 +1,27 @@
+#version 330 core
+layout(points) in;
+layout(triangle_strip, max_vertices = 5) out;
+
+in VS_OUT {
+    vec3 color;
+} gs_in[];
+
+out vec3 fcolor;
+
+void
+main(void)
+{
+    fcolor = gs_in[0].color;
+    gl_Position = gl_in[0].gl_Position+vec4(-0.2, -0.2, 0.0, 0.0);
+    EmitVertex();
+    gl_Position = gl_in[0].gl_Position+vec4(0.2, -0.2, 0.0, 0.0);
+    EmitVertex();
+    gl_Position = gl_in[0].gl_Position+vec4(-0.2, 0.2, 0.0, 0.0);
+    EmitVertex();
+    gl_Position = gl_in[0].gl_Position+vec4(0.2, 0.2, 0.0, 0.0);
+    EmitVertex();
+    fcolor = vec3(1.0, 1.0, 1.0);
+    gl_Position = gl_in[0].gl_Position+vec4(0.0, 0.4, 0.0, 0.0);
+    EmitVertex();
+    EndPrimitive();
+}
diff --git a/geometry_shader/shaders/base.vs b/geometry_shader/shaders/base.vs
new file mode 100644
index 0000000..2924e6c
--- /dev/null
+++ b/geometry_shader/shaders/base.vs
@@ -0,0 +1,14 @@
+#version 330 core
+layout(location = 0) in vec2 apos;
+layout(location = 1) in vec3 acolor;
+
+out VS_OUT {
+    vec3 color;
+} vs_out;
+
+void
+main(void)
+{
+    vs_out.color = acolor;
+    gl_Position = vec4(apos, 0.0f, 1.0f);
+}
diff --git a/geometry_shader/shaders/basic.fs b/geometry_shader/shaders/basic.fs
new file mode 100644
index 0000000..bdd4b9a
--- /dev/null
+++ b/geometry_shader/shaders/basic.fs
@@ -0,0 +1,13 @@
+#version 330 core
+
+in vec2 tex_coords;
+
+out vec4 frag_color;
+
+uniform sampler2D texture1;
+
+void
+main(void)
+{
+    frag_color = texture(texture1, tex_coords);
+}
diff --git a/geometry_shader/shaders/basic.vs b/geometry_shader/shaders/basic.vs
new file mode 100644
index 0000000..9a630b6
--- /dev/null
+++ b/geometry_shader/shaders/basic.vs
@@ -0,0 +1,16 @@
+#version 330 core
+layout(location = 0) in vec3 apos;
+layout(location = 2) in vec2 atex_coords;
+
+out vec2 tex_coords;
+
+uniform mat4 model;
+uniform mat4 view;
+uniform mat4 projection;
+
+void
+main(void)
+{
+    gl_Position = projection*view*model*vec4(apos, 1.0f);
+    tex_coords = atex_coords;
+}
diff --git a/geometry_shader/shaders/explosion.fs b/geometry_shader/shaders/explosion.fs
new file mode 100644
index 0000000..70e7151
--- /dev/null
+++ b/geometry_shader/shaders/explosion.fs
@@ -0,0 +1,13 @@
+#version 330 core
+
+in vec2 ftex_coords;
+
+out vec4 frag_color;
+
+uniform sampler2D texture0;
+
+void
+main(void)
+{
+    frag_color = texture(texture0, ftex_coords);
+}
diff --git a/geometry_shader/shaders/explosion.gs b/geometry_shader/shaders/explosion.gs
new file mode 100644
index 0000000..1883ad2
--- /dev/null
+++ b/geometry_shader/shaders/explosion.gs
@@ -0,0 +1,44 @@
+#version 330 core
+layout(triangles) in;
+layout(triangle_strip, max_vertices = 3) out;
+
+in VS_OUT {
+    vec2 gtex_coords;
+} gs_in[];
+
+out vec2 ftex_coords;
+
+uniform float time;
+
+vec3
+get_normal(void)
+{
+    vec3 a = vec3(gl_in[0].gl_Position)-vec3(gl_in[1].gl_Position);
+    vec3 b = vec3(gl_in[2].gl_Position)-vec3(gl_in[1].gl_Position);
+    return(normalize(cross(a, b)));
+}
+
+vec4
+explode(vec4 position, vec3 normal)
+{
+    float magnitude = 0.2f;
+    vec3 direction = normal*magnitude*((sin(time)+1.0f)/2.0f);
+    vec4 result = position+vec4(direction, 0.0f);
+    return(result);
+}
+
+void
+main(void)
+{
+    vec3 normal = get_normal();
+    gl_Position = explode(gl_in[0].gl_Position, normal);
+    ftex_coords = gs_in[0].gtex_coords;
+    EmitVertex();
+    gl_Position = explode(gl_in[1].gl_Position, normal);
+    ftex_coords = gs_in[1].gtex_coords;
+    EmitVertex();
+    gl_Position = explode(gl_in[2].gl_Position, normal);
+    ftex_coords = gs_in[2].gtex_coords;
+    EmitVertex();
+    EndPrimitive();
+}
diff --git a/geometry_shader/shaders/explosion.vs b/geometry_shader/shaders/explosion.vs
new file mode 100644
index 0000000..5925b8f
--- /dev/null
+++ b/geometry_shader/shaders/explosion.vs
@@ -0,0 +1,18 @@
+#version 330 core
+layout(location = 0) in vec3 apos;
+layout(location = 1) in vec2 atex_coords;
+
+out VS_OUT {
+    vec2 gtex_coords;
+} vs_out;
+
+uniform mat4 projection;
+uniform mat4 view;
+uniform mat4 model;
+
+void
+main(void)
+{
+    vs_out.gtex_coords = atex_coords;
+    gl_Position = projection*view*model*vec4(apos, 1.0f);
+}
diff --git a/geometry_shader/shaders/normals.fs b/geometry_shader/shaders/normals.fs
new file mode 100644
index 0000000..fbbafbf
--- /dev/null
+++ b/geometry_shader/shaders/normals.fs
@@ -0,0 +1,9 @@
+#version 330 core
+
+out vec4 frag_color;
+
+void
+main(void)
+{
+    frag_color = vec4(1.0, 0.0, 0.0, 1.0);
+}
diff --git a/geometry_shader/shaders/normals.gs b/geometry_shader/shaders/normals.gs
new file mode 100644
index 0000000..3720a5f
--- /dev/null
+++ b/geometry_shader/shaders/normals.gs
@@ -0,0 +1,44 @@
+#version 330 core
+layout(triangles) in;
+layout(line_strip, max_vertices = 6) out;
+
+in VS_OUT {
+    vec3 normal;
+} gs_in[];
+
+uniform mat4 projection;
+
+const float MAGNITUDE = 0.4;
+
+void
+generate_line(int index)
+{
+    gl_Position = projection*gl_in[index].gl_Position;
+    EmitVertex();
+    gl_Position = projection*(gl_in[index].gl_Position+
+                              vec4(gs_in[index].normal, 0.0)*MAGNITUDE);
+    EmitVertex();
+    EndPrimitive();
+}
+
+void
+main(void)
+{
+    /*
+    vec4 center = (gl_in[0].gl_Position+
+                   gl_in[1].gl_Position+
+                   gl_in[2].gl_Position)/3.0;
+    vec4 end = center+vec4(((gs_in[0].normal+
+                             gs_in[1].normal+
+                             gs_in[2].normal)/3.0),
+                           0.0)*MAGNITUDE;
+    gl_Position = projection*center;
+    EmitVertex();
+    gl_Position = projection*end;
+    EmitVertex();
+    EndPrimitive();
+    */
+    generate_line(0);
+    generate_line(1);
+    generate_line(2);
+}
diff --git a/geometry_shader/shaders/normals.vs b/geometry_shader/shaders/normals.vs
new file mode 100644
index 0000000..3b728e5
--- /dev/null
+++ b/geometry_shader/shaders/normals.vs
@@ -0,0 +1,18 @@
+#version 330 core
+layout(location = 0) in vec3 apos;
+layout(location = 1) in vec3 anormal;
+
+out VS_OUT {
+    vec3 normal;
+} vs_out;
+
+uniform mat4 view;
+uniform mat4 model;
+
+void
+main(void)
+{
+    mat3 normal_matrix = mat3(transpose(inverse(view*model)));
+    vs_out.normal = normalize(normal_matrix*anormal);
+    gl_Position = view*model*vec4(apos, 1.0);
+}