[OpenGL] 기초 4. 삼각형에 vertex shader / fragment shader 적용

실행 화면

 

소스코드

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <stdlib.h>
#include <stdio.h>
#include <fstream>
#include <string>

GLuint VBO, VAO, shader;

std::string ReadFile(const char* filePath)
{
	std::string content;
	std::ifstream fileStream(filePath, std::ios::in);

	while (!fileStream.is_open())
	{
		printf("Failed to read %s file! The file doesn't exist.\n", filePath);
		return "";
	}

	std::string line = "";
	while (!fileStream.eof())
	{
		std::getline(fileStream, line);
		content.append(line + "\n");
	}

	fileStream.close();
	return content;
}

GLuint AddShader(const char* shaderCode, GLenum shaderType)
{
	GLuint new_shader = glCreateShader(shaderType);

	const GLchar* code[1];
	code[0] = shaderCode;

	glShaderSource(new_shader, 1, code, NULL);

	GLint result = 0;
	GLchar err_log[1024] = { 0 };

	glCompileShader(new_shader);
	glGetShaderiv(new_shader, GL_COMPILE_STATUS, &result);
	if (!result)
	{
		glGetShaderInfoLog(new_shader, sizeof(err_log), NULL, err_log);
		printf("Error compiling the %d shader: '%s'\n", shaderType, err_log);
		return 0;
	}
	return new_shader;
}

void CompileShader(const char* vsCode, const char* fsCode)
{
	GLuint vs, fs;

	shader = glCreateProgram();

	if (!shader)
	{
		printf("Error: Cannot create shader program.");
		return;
	}

	vs = AddShader(vsCode, GL_VERTEX_SHADER);
	fs = AddShader(fsCode, GL_FRAGMENT_SHADER);
	glAttachShader(shader, vs);  // Attach shaders to the program for linking process.
	glAttachShader(shader, fs);

	GLint result = 0;
	GLchar err_log[1024] = { 0 };

	glLinkProgram(shader);  // Create executables from shader codes to run on corresponding processors.
	glGetProgramiv(shader, GL_LINK_STATUS, &result);
	if (!result)
	{
		glGetProgramInfoLog(shader, sizeof(err_log), NULL, err_log);
		printf("Error linking program: '%s'\n", err_log);
		return;
	}
}

void CreateShaderProgramFromFiles(const char* vsPath, const char* fsPath)
{
	std::string vsFile = ReadFile(vsPath);
	std::string fsFile = ReadFile(fsPath);
	const char* vsCode = vsFile.c_str();
	const char* fsCode = fsFile.c_str();

	CompileShader(vsCode, fsCode);
}

void CreateTriangle()
{
	GLfloat vertices[] = {
		-1.0f, -1.0f, 0.0f,
		1.0f, -1.0f, 0.0f,
		0.0f, 1.0f, 0.0f
	};

	glGenVertexArrays(1, &VAO);
	glBindVertexArray(VAO);

	glGenBuffers(1, &VBO);
	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(0);

	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glBindVertexArray(0);
}

int main(void)
{
	if (!glfwInit())
		exit(EXIT_FAILURE);

	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 5);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

	GLFWwindow* window = glfwCreateWindow(1080, 720, "title", NULL, NULL);
	if (!window)
	{
		glfwTerminate();
		exit(EXIT_FAILURE);
	}

	glfwMakeContextCurrent(window);

	int framebuf_width, framebuf_height;
	glfwGetFramebufferSize(window, &framebuf_width, &framebuf_height);
	glViewport(0, 0, framebuf_width, framebuf_height);

	if (glewInit() != GLEW_OK)
	{
		glfwTerminate();
		exit(EXIT_FAILURE);
	}

	CreateTriangle();
	CreateShaderProgramFromFiles("Shaders/shader.vert", "Shaders/shader.frag");

	while (!glfwWindowShouldClose(window))
	{
		glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		glUseProgram(shader);

		glBindVertexArray(VAO);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glBindVertexArray(0);

		glUseProgram(0);

		glfwSwapBuffers(window);
		glfwPollEvents();
	}

	glfwTerminate();

	return 0;
}

 

Vertex shader

#version 460

layout (location = 0) in vec3 pos;

void main()
{
	gl_Position = vec4(pos, 1.0);
}

#version GLSL버전

0번째 vetex attribute를 가져와 vec3 pos 변수에 넣음

gl_position은 미리 정의된 vertex shader의 출력값으로 clip-space에서의 vertex 좌표

 

Fragment shader

#version 460

out vec4 color;

void main()
{
    color = vec4(0.0, 1.0, 0.0, 1.0);
}

#version GLSL버전

출력 변수로 vec4 color 선언, 내장 변수가 아니므로 변수명은 마음대로

 

관습적으로 vetex shader의 파일명은 xxxx.vert로 fragment shader의 파일명은 xxxx.frag로 함