wip: Basic spinning triangle demonstration

src/CMakeLists.txt

@@ -1,6 +1,12 @@
 add_executable(Exponent
     main.cc
+    GLProgramLoader.cc
 )
 
 target_link_libraries(Exponent PUBLIC glfw glm::glm)
-target_include_directories(Exponent PUBLIC ${CMAKE_SOURCE_DIR}/include)
+target_include_directories(Exponent PUBLIC ${CMAKE_SOURCE_DIR}/include)
+
+target_compile_definitions(Exponent PRIVATE GLFW_INCLUDE_NONE)
+
+file(COPY "${CMAKE_CURRENT_SOURCE_DIR}/shaders/shader.frag" DESTINATION "${CMAKE_CURRENT_BINARY_DIR}/shaders/")
+file(COPY "${CMAKE_CURRENT_SOURCE_DIR}/shaders/shader.vert" DESTINATION "${CMAKE_CURRENT_BINARY_DIR}/shaders/")

src/GLProgramLoader.cc

@@ -0,0 +1,81 @@
+#include "GLProgramLoader.hh"
+
+#include <exception>
+#include <format>
+#include <fstream>
+#include <sstream>
+
+static GLuint compile_shader(GLenum shader_type, const std::string &path) {
+    if (shader_type != GL_VERTEX_SHADER && shader_type != GL_FRAGMENT_SHADER) {
+        throw GLProgramException(std::format("Unsupported shader type {} provided.", shader_type));
+    }
+
+    // Check that the path actually exists
+    std::ifstream shader_file_handle;
+    shader_file_handle.open(path);
+
+    if (!shader_file_handle.is_open()) {
+        throw GLProgramException(std::format("Failed to open path {}.", path));
+    }
+
+    // Read the data in.
+    std::stringstream shader_source_stream;
+    shader_source_stream << shader_file_handle.rdbuf();
+    std::string shader_source_str = shader_source_stream.str();
+    const GLchar *shader_source = shader_source_str.c_str();
+
+    GLuint shader_id = glCreateShader(shader_type);
+
+    if (shader_id == 0) {
+        throw GLProgramException(std::format("Error when creating shader type {}.", shader_type));
+    }
+
+    glShaderSource(shader_id, 1, &shader_source, NULL);
+    glCompileShader(shader_id);
+    GLint did_compile;
+    glGetShaderiv(shader_id, GL_COMPILE_STATUS, &did_compile);
+    if(!did_compile) {
+        GLint len = 0;
+
+        glGetShaderiv(shader_id, GL_INFO_LOG_LENGTH, &len);
+        std::string error_log(len, ' ');
+
+        glGetShaderInfoLog(shader_id, len, &len, error_log.data());
+
+        glDeleteShader(shader_id);
+        throw GLProgramException(std::format("Shader {} compilation failed:\n{}", path, error_log));
+    }
+
+    return shader_id;
+}
+
+GLuint compile_and_link_program(const std::vector<std::pair<GLuint, std::string>> &shaders) {
+    // Firstly, compile all the shaders and get all of their ids.
+    // I would love to use a functional map here, but C++ doesn't really do that.
+    std::vector<GLuint> shader_ids = {};
+    for(auto &s:shaders) {
+        shader_ids.push_back(compile_shader(s.first, s.second));
+    }
+
+    GLuint program_id = glCreateProgram();
+    for (auto &s:shader_ids) {
+        glAttachShader(program_id, s);
+    }
+    glLinkProgram(program_id);
+
+    GLint link_worked;
+    glGetProgramiv(program_id, GL_LINK_STATUS, &link_worked);
+    if (!link_worked) {
+        GLint len = 0;
+        glGetProgramiv(program_id, GL_INFO_LOG_LENGTH, &len);
+
+        std::string error_log(len, ' ');
+
+        glGetProgramInfoLog(program_id, len, &len, error_log.data());
+
+        glDeleteProgram(program_id);
+        throw GLProgramException(std::format("Program {} link failed:\n{}", program_id, error_log));
+    }
+
+    return program_id;
+}

src/GLProgramLoader.hh

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "glad/gl.h"
+
+#include <string>
+#include <optional>
+#include <vector>
+
+class GLProgramException : public std::exception {
+    std::string m_what;
+    public:
+        GLProgramException(const char *str):m_what(str) {
+        }
+
+        GLProgramException(const std::string &str):m_what(str) {
+        }
+
+        virtual const char* what() const throw() { 
+            return m_what.c_str();
+        }
+};
+
+
+GLuint compile_and_link_program(const std::vector<std::pair<GLuint, std::string>> &shaders);

src/main.cc

@@ -1,9 +1,20 @@
-#define GLAD_GL_IMPLEMENTATION
-#include "glad/gl.h"
-#define GLFW_INCLUDE_NONE
 #include "GLFW/glfw3.h"
 
-//http://seshbot.com/blog/2015/05/05/an-introduction-to-opengl-getting-started/
+#include "GLProgramLoader.hh"
+
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+
+// This has to come last.
+#define GLAD_GL_IMPLEMENTATION
+#include <glad/gl.h>
+
+static void dbg_log(const char* str) {
+    std::cout << str << std::endl;
+}
 
 static void key_callback(GLFWwindow *w, int key, int scancode, int action, int mods) {
     if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) {
@@ -11,14 +22,74 @@ static void key_callback(GLFWwindow *w, int key, int scancode, int action, int m
     }
 }
 
+#define VERTEX_SHADER_LOCATION "shaders/shader.vert"
+#define FRAGMENT_SHADER_LOCATION "shaders/shader.frag"
+
+GLuint g_program_id = 0;
+
+static GLuint time_unif;
+
+static void init_shaders() {
+    dbg_log("Initialising shaders");
+
+    const std::vector<std::pair<GLuint, std::string>> shaders = {
+        {GL_VERTEX_SHADER, VERTEX_SHADER_LOCATION},
+        {GL_FRAGMENT_SHADER, FRAGMENT_SHADER_LOCATION},
+    };
+
+    try {
+        g_program_id = compile_and_link_program(shaders);
+    } catch (GLProgramException e) {
+        std::cerr << e.what() << std::endl;
+    } catch (...) {
+        std::cerr << "Unexpected exception while compiling shaders." << std::endl;
+    }
+
+    glUseProgram(g_program_id);
+
+    glGetUniformLocation(g_program_id, "time");
+}
+
+static const GLfloat verts[6] = {
+    0.0f, 0.0f, 0.0f, 0.5f, 0.5f, 0.0f
+};
+
+static GLuint vertex_buf;
+static GLuint array_buf;
+static const GLuint vertex_data_position = 0;
+
+// Do the work of initialising opengl so we can draw stuff
+static void init_opengl() {
+    dbg_log("Initialising opengl");
+    // Configure the context's capabilities
+    glClearColor(0.0, 0.0, 0.0, 1.0);
+
+    glGenVertexArrays(1, &array_buf);
+    glBindVertexArray(array_buf);
+
+    glGenBuffers(1, &vertex_buf);
+    glBindBuffer(GL_ARRAY_BUFFER, vertex_buf);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(verts), verts, GL_STATIC_DRAW);
+
+
+    init_shaders();
+
+    glVertexAttribPointer(vertex_data_position, 2, GL_FLOAT, GL_FALSE, 0, NULL);
+    glEnableVertexAttribArray(vertex_data_position);
+
+}
+
 int main() {
+    dbg_log("Initialising glfw");
     // Initialise GLFW
     if (!glfwInit()) {
         exit(EXIT_FAILURE);
     }
 
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
-    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+
     // Create our context
     GLFWwindow *w = glfwCreateWindow(640, 480, "Test", NULL, NULL);
     if (!w) {
@@ -32,13 +103,7 @@ int main() {
     // Set up the key handler
     glfwSetKeyCallback(w, key_callback);
 
-    // Configure the context's capabilities
-    glClearColor(1.0, 0.0, 0.0, 1.0);
-    glEnable(GL_DEPTH_TEST);
-    glEnable(GL_BLEND); // Maybe this allows transparency?
-    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
-
-    // TODO: Actually make some opengl shit happen
+    init_opengl();
     
     // Main Loop
     while(!glfwWindowShouldClose(w)) {
@@ -50,6 +115,14 @@ int main() {
         glClear(GL_COLOR_BUFFER_BIT);
         */
 
+       float time = glfwGetTime();
+
+        glClear(GL_COLOR_BUFFER_BIT);
+
+        glUniform1f(time_unif, time);
+        glBindVertexArray(array_buf);
+        glDrawArrays(GL_TRIANGLES, 0, 3);
+
         // TODO Draw primitives
 
         glfwSwapBuffers(w);

src/shaders/shader.frag

@@ -0,0 +1,8 @@
+#version 430 core
+
+out vec4 f_color;
+
+// All fragments are the same colour for now.
+void main() {
+    f_color = vec4(1.0, 1.0, 1.0, 1.0);
+}

src/shaders/shader.vert

@@ -0,0 +1,17 @@
+#version 430 core
+
+layout (location = 0) in vec4 v_position;
+
+uniform float time;
+
+// Simple passthrough shader for now.
+void main() {
+    vec2 new_xy = v_position.xy * mat2x2(
+        cos(time), -sin(time),
+        sin(time), cos(time)
+    );
+    
+    vec4 new_position = vec4(new_xy.x, new_xy.y, 0.0, 1.0);
+
+    gl_Position = new_position;
+}