Embedded Files
Image 1: No multisampling
Image 2: multisampling 4x, the triangle is a little more accurately rendered, pixels that arent fully covered are partly transparent
This tutorial shows the difference between a multisampled framebuffer and another non-multisampled.
It uses 2 separate 50 x 50 framebuffers, one of them 4x multisampled.
Each second the image will be rendered into another framebuffer to show the effect that multisampling has on the image.
Complete Source Code:
Main.cpp
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <glm/gtx/transform.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/quaternion.hpp>
#include <glm/gtx/rotate_vector.hpp>
#include <iostream>
#include <vector>
#include <ctime>
#include "Shader.h"
using namespace std;
using namespace glm;
#define SCREENWIDTH 800
#define SCREENHEIGHT 600
// main functions
void Initialize();
void Render();
void CleanUp();
void CheckForGLError();
void CheckFramebuffer(GLuint framebuffer, GLenum target);
GLFWwindow* window = nullptr;
unsigned int multisample = 4;
unsigned int framebufferwidth = 50;
unsigned int framebufferheight = 50;
GLuint framebuffers[2] = { 0 };
GLuint framebuffertextures[2] = { 0 };
GLuint program = 0;
GLuint vertexshader = 0;
GLuint fragmentshader = 0;
GLuint vertexarray = 0;
GLuint vertexbuffer = 0;
struct Vertex
{
vec3 Position;
vec4 Color;
};
int main(void)
{
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(SCREENWIDTH, SCREENHEIGHT, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
/* Initialize GLEW */
if (glewInit() != GLEW_OK)
{
glfwTerminate();
return -1;
}
Initialize();
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
Render();
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
CleanUp();
glfwTerminate();
return 0;
}
void Initialize()
{
// background color
glClearColor(0.3f, 0.5f, 0.8f, 0.0f);
glEnable(GL_MULTISAMPLE);
// create all objects
glGenFramebuffers(2, framebuffers);
glGenTextures(2, framebuffertextures);
program = glCreateProgram();
vertexshader = glCreateShader(GL_VERTEX_SHADER);
fragmentshader = glCreateShader(GL_FRAGMENT_SHADER);
glGenVertexArrays(1, &vertexarray);
glGenBuffers(1, &vertexbuffer);
// setup framebuffers
glViewport(0, 0, framebufferwidth, framebufferheight);
glBindTexture(GL_TEXTURE_2D, framebuffertextures[0]);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_RGBA8, framebufferwidth, framebufferheight);
glBindTexture(GL_TEXTURE_2D, 0);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, framebuffertextures[1]);
glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, multisample, GL_RGBA8, framebufferwidth, framebufferheight, GL_TRUE);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, 0);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffers[0]);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, framebuffertextures[0], 0);
glDrawBuffer(GL_COLOR_ATTACHMENT0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffers[1]);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, framebuffertextures[1], 0);
glDrawBuffer(GL_COLOR_ATTACHMENT0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
CheckFramebuffer(framebuffers[0], GL_FRAMEBUFFER);
CheckFramebuffer(framebuffers[1], GL_FRAMEBUFFER);
// shader source code
string vertexshader_source = {
"#version 450 core\n"
"in layout (location = 0) vec3 in_position;"
"in layout (location = 1) vec4 in_color;"
"uniform layout (location = 0) mat4 MVP = mat4(1);"
"out VS_FS_INTERFACE {"
"vec4 color;"
"} vs_out;"
"void main () {"
"gl_Position = MVP * vec4(in_position, 1);"
"vs_out.color = in_color;"
"}"
};
string fragmentshader_source = {
"#version 450 core\n"
"in VS_FS_INTERFACE {"
"vec4 color;"
"} vs_out;"
"out layout (location = 0) vec4 out_color;"
"void main () {"
"out_color = vs_out.color;"
"}"
};
// compile shaders and link program
CompileShader(vertexshader, vertexshader_source);
CompileShader(fragmentshader, fragmentshader_source);
LinkProgram(program, { vertexshader, fragmentshader });
// setup vertex array
glBindVertexArray(vertexarray);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)(0));
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)(sizeof(vec3)));
glBindBuffer(GL_ARRAY_BUFFER, 0);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glBindVertexArray(0);
// setup vertex buffer
vector<Vertex> vertices = {
{ { 0, 0, 0 },{ 1, 0, 0, 1 } },
{ { 1, 0, 0 },{ 0, 1, 0, 1 } },
{ { 0, 1, 0 },{ 0, 0, 1, 1 } },
};
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * vertices.size(), vertices.data(), GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
void Render()
{
time_t t = time(NULL);
if (t % 2)
{
// render into the off-screen multisampled framebuffer
glBindFramebuffer(GL_FRAMEBUFFER, framebuffers[1]);
// clear the off-screen framebuffer
glClear(GL_COLOR_BUFFER_BIT);
// render a triangle
glUseProgram(program);
glBindVertexArray(vertexarray);
glDrawArrays(GL_TRIANGLES, 0, 3);
glBindVertexArray(0);
glUseProgram(0);
// now blit the result of the multisampled framebuffer into the other, non-multisampled framebuffer:
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, framebuffers[0]);
glBlitFramebuffer(
0, 0, framebufferwidth, framebufferheight,
0, 0, framebufferwidth, framebufferheight,
GL_COLOR_BUFFER_BIT, GL_NEAREST);
// finally blit the non-multisampled framebuffer into the default framebuffer (screen)
glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffers[0]);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBlitFramebuffer(
0, 0, framebufferwidth, framebufferheight,
0, 0, SCREENWIDTH, SCREENHEIGHT,
GL_COLOR_BUFFER_BIT, GL_NEAREST);
}
else
{
// render into the off-screen non-multisampled framebuffer
glBindFramebuffer(GL_FRAMEBUFFER, framebuffers[0]);
// clear the off-screen framebuffer
glClear(GL_COLOR_BUFFER_BIT);
// render a triangle
glUseProgram(program);
glBindVertexArray(vertexarray);
glDrawArrays(GL_TRIANGLES, 0, 3);
glBindVertexArray(0);
glUseProgram(0);
// finally blit the non-multisampled framebuffer into the default framebuffer (screen)
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBlitFramebuffer(
0, 0, framebufferwidth, framebufferheight,
0, 0, SCREENWIDTH, SCREENHEIGHT,
GL_COLOR_BUFFER_BIT, GL_NEAREST);
}
CheckForGLError();
}
void CleanUp()
{
// destroy all objects
glDeleteFramebuffers(2, framebuffers);
glDeleteTextures(2, framebuffertextures);
glDeleteProgram(program);
glDeleteShader(vertexshader);
glDeleteShader(fragmentshader);
glDeleteVertexArrays(1, &vertexarray);
glDeleteBuffers(1, &vertexbuffer);
}
void CheckForGLError()
{
for (GLenum error; (error = glGetError()) != GL_NO_ERROR;)
{
cout << "OpenGL Error: \t";
if (error == GL_INVALID_ENUM)
cout << "GL_INVALID_ENUM";
if (error == GL_INVALID_VALUE)
cout << "GL_INVALID_VALUE";
if (error == GL_INVALID_OPERATION)
cout << "GL_INVALID_OPERATION";
if (error == GL_STACK_OVERFLOW)
cout << "GL_STACK_OVERFLOW";
if (error == GL_STACK_UNDERFLOW)
cout << "GL_STACK_UNDERFLOW";
if (error == GL_OUT_OF_MEMORY)
cout << "GL_OUT_OF_MEMORY";
if (error == GL_INVALID_FRAMEBUFFER_OPERATION)
cout << "GL_INVALID_FRAMEBUFFER_OPERATION";
if (error == GL_CONTEXT_LOST)
cout << "GL_CONTEXT_LOST";
cout << (char)7 << endl; /*play sound*/
cin.get();
}
}
void CheckFramebuffer(GLuint framebuffer, GLenum target)
{
GLenum status = glCheckNamedFramebufferStatus(framebuffer, target);
if (status != GL_FRAMEBUFFER_COMPLETE)
{
cout << "OpenGL Framebuffer Error: \t";
if (status == GL_FRAMEBUFFER_UNDEFINED)
cout << "undefined framebuffer";
if (status == GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT)
cout << "a necessary attachment is uninitialized";
if (status == GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT)
cout << "no attachments";
if (status == GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER)
cout << "incomplete draw buffer";
if (status == GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER)
cout << "incomplete read buffer";
if (status == GL_FRAMEBUFFER_UNSUPPORTED)
cout << "combination of attachments is not supported";
if (status == GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE)
cout << "number if samples for all attachments does not match";
cout << (char)7 << endl; /*play sound*/
cin.get();
}
}
Shader.h
#pragma once
#include <string>
#include <list>
// shader functions
std::string LoadTextFile(const std::string& filepath);
std::string ShaderTypeName(unsigned int shader);
bool CompileShader(unsigned int shader, const std::string& sourcecode);
std::string ShaderInfoLog(unsigned int shader);
bool LinkProgram(unsigned int program, const std::list<unsigned int>& shaderlist);
std::string ProgramInfoLog(unsigned int program);
Shader.cpp
#include "Shader.h"
#include <iostream>
#include <fstream>
#include <GL/glew.h>
std::string LoadTextFile(const std::string & filepath)
{
std::string result(""), line;
std::fstream f(filepath, std::ios::in);
while (f.good())
{
std::getline(f, line);
result += line + '\n';
}
return result;
}
std::string ShaderTypeName(unsigned int shader)
{
if (glIsShader(shader))
{
int type;
glGetShaderiv(shader, GL_SHADER_TYPE, &type);
if (type == GL_VERTEX_SHADER)
return "Vertex Shader";
if (type == GL_TESS_CONTROL_SHADER)
return "Tessellation Control Shader";
if (type == GL_TESS_EVALUATION_SHADER)
return "Tessellation Evaluation Shader";
if (type == GL_GEOMETRY_SHADER)
return "Geometry Shader";
if (type == GL_FRAGMENT_SHADER)
return "Fragment Shader";
if (type == GL_COMPUTE_SHADER)
return "Compute Shader";
}
return "invalid shader";
}
bool CompileShader(unsigned int shader, const std::string& sourcecode)
{
if (!glIsShader(shader))
{
std::cout << "ERROR: shader compilation failed, no valid shader specified" << std::endl;
return false;
}
if (sourcecode.empty())
{
std::cout << "ERROR: shader compilation failed, no source code specified (" << ShaderTypeName(shader) << ")" << std::endl;
return false;
}
// array of source code components
const char* sourcearray[] = { sourcecode.c_str() };
// set source code
glShaderSource(shader, 1, sourcearray, NULL);
// compile shaders
glCompileShader(shader);
// check compile status
int status;
glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
// successfully compiled shader
if (status == GL_TRUE)
return true;
// show compile errors
std::cout << "ERROR: shader compilation failed (" << ShaderTypeName(shader) << ")" << std::endl << ShaderInfoLog(shader) << std::endl;
return false;
}
std::string ShaderInfoLog(unsigned int shader)
{
if (glIsShader(shader))
{
int logsize;
char infolog[1024] = { 0 };
glGetShaderInfoLog(shader, 1024, &logsize, infolog);
return std::string(infolog);
}
return "invalid shader";
}
bool LinkProgram(unsigned int program, const std::list<unsigned int>& shaderlist)
{
if (!glIsProgram(program))
{
std::cout << "ERROR: shader linking failed, no valid program specified" << std::endl;
return false;
}
// attach all shaders to the program
for (auto& shader : shaderlist)
{
if (glIsShader(shader))
glAttachShader(program, shader);
}
// link program
glLinkProgram(program);
// detach all shaders again
for (auto& shader : shaderlist)
{
if (glIsShader(shader))
glDetachShader(program, shader);
}
int status;
glGetProgramiv(program, GL_LINK_STATUS, &status);
// successfully linked program
if (status == GL_TRUE)
return true;
// show link errors
std::cout << "ERROR: shader linking failed" << std::endl << ProgramInfoLog(program) << std::endl;
return false;
}
std::string ProgramInfoLog(unsigned int program)
{
if (glIsProgram(program))
{
int logsize;
char infolog[1024] = { 0 };
glGetProgramInfoLog(program, 1024, &logsize, infolog);
return std::string(infolog);
}
return "invalid program";
}
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