This program is supposed to create a new window, color it blue as the background color, then draw a triangle to the screen and fill it in with orange:
#include <stdio.h>
#include <string>
#include <iostream>
#include <SDL.h>
#include "SDL_CheckError.h"
#include <OpenGL/gl3.h>
#include <OpenGL/gl3ext.h>
const char *vertexShaderSource =
"layout(location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
"gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
const char *fragmentShaderSource =
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"FragColor = vec4(1.0, 0.5, 0.2, 1.0);\n"
"}\n\0";
int main() {
// Initialize SDL
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s", SDL_GetError());
return 3;
}
// Setup the window
SDL_Window *window;
SDL_Renderer *renderer;
// Window mode MUST include SDL_WINDOW_OPENGL for use with OpenGL.
SDL_CreateWindowAndRenderer(720, 480, SDL_WINDOW_OPENGL, &window, &renderer);
SDL_GL_LoadLibrary(NULL);
// Create an OpenGL context associated with the window.
SDL_GLContext glcontext = SDL_GL_CreateContext(window);
SDL_CheckError(__LINE__);
// This makes our buffer swap syncronized with the monitor's vertical refresh
SDL_GL_SetSwapInterval(1);
// Set up window
glViewport(0, 0, 720, 480);
// build and compile our shader program
// ------------------------------------
// vertex shader
int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
// check for shader compile errors
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// fragment shader
int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// check for shader compile errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// link shaders
int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
// set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
float vertices[] = {
0.5f, 0.5f, 0.0f, // top right
0.5f, -0.5f, 0.0f, // bottom right
-0.5f, -0.5f, 0.0f, // bottom left
-0.5f, 0.5f, 0.0f // top left
};
unsigned int indices[] = { // note that we start from 0!
0, 1, 3, // first Triangle
1, 2, 3 // second Triangle
};
unsigned int VBO, VAO, EBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
// bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
glBindBuffer(GL_ARRAY_BUFFER, 0);
// remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
//glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
glBindVertexArray(0);
// Render loop
SDL_Event event;
while (1) {
// Checking for quit events.
SDL_PollEvent(&event);
if (event.type == SDL_QUIT) {
break;
}
// render
// ------
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// draw our first triangle
glUseProgram(shaderProgram);
glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
//glDrawArrays(GL_TRIANGLES, 0, 6);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
// glBindVertexArray(0); // no need to unbind it every time
SDL_GL_SwapWindow(window);
}
// De-allocate resources
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
// Once finished with OpenGL functions, the SDL_GLContext can be deleted.
SDL_GL_DeleteContext(glcontext);
SDL_Quit();
return 0;
}
It compiles correctly and the background is colored blue, just like I want. However, the triangle is not displayed, and I get these errors:
ERROR::SHADER::VERTEX::COMPILATION_FAILED
ERROR: 0:1: 'layout' : syntax error: syntax error
ERROR::SHADER::FRAGMENT::COMPILATION_FAILED
ERROR: 0:1: Invalid storage qualifiers 'out' in global variable context
ERROR: 0:4: Use of undeclared identifier 'FragColor'
ERROR::SHADER::PROGRAM::LINKING_FAILED
ERROR: One or more attached shaders not successfully compiled
What is going on? I can't seem to figure it out. If it is pertinent, I use Xcode, run Mac OSX 10.13.2, and I am using SDL version 2.0
Gotta request a versioned Core context on OSX (they only provide Core contexts for anything after GL 2.1) when you create your window:
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE );
SDL_Window* window = SDL_CreateWindow
(
"SDL",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
720, 480,
SDL_WINDOW_OPENGL
);
SDL_GLContext glcontext = SDL_GL_CreateContext(window);
If SDL_CreateWindow() and SDL_GL_CreateContext() succeed you should be able to use #version 330 in your shaders.