int main() {
/**
* 1. Initialize GLFW, setup required options, create a window
* 2. Set key callback functions
* 3. Initialize GLEW
* 4. Set a viewport
* 5. Set up shaders
* 6. Create vertices and indices
* 7. Create VAO, VBO, EBO, and setup the bindings
* 8. Set vertex attribute pointers
* 9. Unbind VAO
* 10. Create texture1, set parameters, load image, free resources
* 11. So does texture2
* 12. Game Loop:
* 12.1. Poll events
* 12.2. Clear color buffer
* 12.3. Active GL_TEXTURE0, bind texture1, correspond uniform variables
* 12.4. So does texture2
* 12.5. Use the shader program
* 12.6. Bind VAO
* 12.7. Do the drawing
* 12.8. Unbind VAO
* 12.9. Swap buffers
* 13. Recycle resources (VAO, VBO, EBO)
* 14. Terminate glfw
*/
//******************************************************************************************************************
// 1.1. Init GLFW
glfwInit();
// 1.2. Set all the required options for GLFW
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
// 1.3. Create a GLFW window object that we can use for GLFW's functions
GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);
if (window == nullptr) {
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
// 1.4. Make window our current window
glfwMakeContextCurrent(window);
//******************************************************************************************************************
// 2. Set the required callback functions
glfwSetKeyCallback(window, key_callback);
//******************************************************************************************************************
// 3.1. Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions
glewExperimental = GL_TRUE;
// 3.2. Initialize GLEW to setup the OpenGL Function pointers
if (glewInit() != GLEW_OK) {
std::cout << "Failed to initialize GLEW" << std::endl;
return -1;
}
//******************************************************************************************************************
// 4. Define the viewport dimensions
glViewport(0, 0, WIDTH, HEIGHT);
//******************************************************************************************************************
// 5. Link shaders
Shader aShader("vs.vert", "fs.frag");
//******************************************************************************************************************
// 6.1. Create vertices
// Note: Texture could be distorted
GLfloat vertices[] = {
// position color texture coordinate
0.8f, 0.8f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, // upper right corner
0.8f, -0.8f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, // lower right corner
-0.8f, -0.8f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // lower left corner
-0.8f, 0.8f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f // upper left corner
};
// 6.2. Create indices
GLuint indices[] = {
0, 1, 3,
1, 2, 3
};
//******************************************************************************************************************
// 7.1.1. Create a vertex array object and bind it
GLuint VAO;
glGenVertexArrays(1, &VAO);
// 7.1.2. Make VAO the "active" vertex array
// i.e: opengl->vertex_array = VAO
glBindVertexArray(VAO);
// 7.2.1. Create a vertex buffer object
GLuint VBO;
glGenBuffers(1, &VBO);
// 7.2.2. Make VBO the "active" array buffer
// i.e: opengl->array_buffer = VBO
glBindBuffer(GL_ARRAY_BUFFER, VBO);
// 7.2.3. Copy vertices into it
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
// 7.3.1. Create an element buffer object and copy indices into it
GLuint EBO;
glGenBuffers(1, &EBO);
// 7.3.2. Make EBO the "active" element array buffer
// i.e: opengl->element_array_buffer = EBO
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
// 7.3.3. Copy indices into it
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
//******************************************************************************************************************
// 8. Set the vertex attributes pointers
// Attribute position
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);
// Attribute color
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(1);
// Attribute textureCoordinate
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
glEnableVertexAttribArray(2);
//******************************************************************************************************************
// 9. Unbind VAO
// glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); // TODO: Not OK, why?
// glBindBuffer(GL_ARRAY_BUFFER, 0); // TODO: OK, why?
glBindVertexArray(0);
//******************************************************************************************************************
// 10.1. Create texture1
GLuint texture1;
glGenTextures(1, &texture1);
// 10.2. Bind texture1 to GL_TEXTURE_2D
// i.e: opengl->GL_TEXTURE_2D = texture1
glBindTexture(GL_TEXTURE_2D, texture1);
// 10.3. Set texture1 wrapping parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
// 10.4. Set texture1 filtering parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); // minify
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // magnify
// 10.5. Load image
int imageWidth, imageHeight;
unsigned char* image = SOIL_load_image("doge.jpg", &imageWidth, &imageHeight, 0, SOIL_LOAD_RGB);
// 10.6. Generate texture and mipmap
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, imageWidth, imageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
glGenerateMipmap(GL_TEXTURE_2D);
// 10.7. Free image and GL_TEXTURE_2D
SOIL_free_image_data(image);
glBindTexture(GL_TEXTURE_2D, 0);
//******************************************************************************************************************
// 11.1. Create texture2
GLuint texture2;
glGenTextures(1, &texture2);
// 11.2. Bind texture2 to GL_TEXTURE_2D
// i.e: opengl->GL_TEXTURE_2D = texture1
glBindTexture(GL_TEXTURE_2D, texture2);
// 11.3. Set texture2 wrapping parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
// 11.4. Set texture2 filtering parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// 11.5. Load image
image = SOIL_load_image("longcat.jpg", &imageWidth, &imageHeight, 0, SOIL_LOAD_RGB);
// 11.6. Generate texture and mipmap
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, imageWidth, imageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
glGenerateMipmap(GL_TEXTURE_2D);
// 11.7. Free image and GL_TEXTURE_2D
SOIL_free_image_data(image);
glBindTexture(GL_TEXTURE_2D, 0);
//******************************************************************************************************************
// 12. Game loop
while (glfwWindowShouldClose(window) == false) {
// 12.1. Check if any events have been activated (key pressed, mouse moved etc.) and call corresponding response functions
glfwPollEvents();
// 12.2. Clear the color buffer
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// 12.3.1. Active 1st texture unit Bind texture 1
glActiveTexture(GL_TEXTURE0);
// 12.3.2. Bind texture 1
glBindTexture(GL_TEXTURE_2D, texture1);
// 12.3.3. Corresponds variable uniformTexture1 in the shader
glUniform1i(glGetUniformLocation(aShader.getProgram(), "uniformTexture1"), 0);
// 12.4. So does texture 2
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, texture2);
glUniform1i(glGetUniformLocation(aShader.getProgram(), "uniformTexture2"), 1);
// 12.5. Use the shader program
aShader.use();
// 12.6. Bind VAO
glBindVertexArray(VAO);
// 12.7. Do actual drawing
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0); // draw a rectangle with glDrawElements
// 12.8. Unbind VAO
glBindVertexArray(0);
// 12.9. Swap the screen buffers
glfwSwapBuffers(window);
}
//******************************************************************************************************************
// 13. De-allocate resources
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
//******************************************************************************************************************
// 14. Terminate GLFW, clearing any resources allocated by GLFW.
glfwTerminate();
return 0;
}
void makeShader(GLuint aShaderType, const GLchar* fileName, GLuint& aProgram)
{
Shader aShader(aShaderType, fileName);
glAttachShader(aProgram, aShader.getShader());
}
