Simple triangle in OpenGL
main.cpp
#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>
#include <SDL3/SDL_opengles2.h>
#include <iostream>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#include <emscripten/html5.h>
#endif // __EMSCRIPTEN__
struct AppContext
{
SDL_Window *window;
SDL_GLContext glcontext;
SDL_bool app_quit = SDL_FALSE;
};
const char *vertexShaderSource =
"attribute vec2 aPosition;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPosition, 0.0, 1.0);\n"
"}\n";
const char *fragmentShaderSource =
"void main()\n"
"{\n"
" gl_FragColor = vec4(0.2, 0.7, 0.3, 1.0);\n"
"}\n";
// Helper function for creating shaders
GLuint createShader(const char *shaderSource, int shaderType)
{
GLuint shader = glCreateShader(shaderType);
glShaderSource(shader, 1, &shaderSource, NULL);
glCompileShader(shader);
GLint status;
glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
if (status == GL_FALSE)
{
GLint maxLength = 0;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &maxLength);
std::vector<GLchar> errorLog(maxLength);
glGetShaderInfoLog(shader, maxLength, &maxLength, &errorLog[0]);
glDeleteShader(shader); // Don't leak the shader
std::cout << &(errorLog[0]) << std::endl;
std::cout << shaderSource << std::endl;
}
return shader;
}
// Helper function for creating a shader program
GLuint createShaderProgram()
{
GLuint program = glCreateProgram();
GLuint vShader = createShader(vertexShaderSource, GL_VERTEX_SHADER);
GLuint fShader = createShader(fragmentShaderSource, GL_FRAGMENT_SHADER);
glAttachShader(program, vShader);
glAttachShader(program, fShader);
glLinkProgram(program);
glUseProgram(program);
return program;
}
// Load a triangle to the video card
void initVertexBuffers(GLuint program)
{
float vertPositions[] = {
-0.5f, -0.5f,
0.5f, -0.5f,
0.f, 0.5f
};
GLuint vertPosBuffer;
glGenBuffers(1, &vertPosBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertPosBuffer);
int amount = sizeof(vertPositions) / sizeof(vertPositions[0]);
glBufferData(GL_ARRAY_BUFFER, amount * sizeof(GLfloat),
vertPositions, GL_STATIC_DRAW);
GLint aPositionLocation = glGetAttribLocation(program, "aPosition");
glVertexAttribPointer(aPositionLocation, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(aPositionLocation);
}
int SDL_Fail()
{
SDL_LogError(SDL_LOG_CATEGORY_CUSTOM, "Error %s", SDL_GetError());
return -1;
}
int SDL_AppInit(void **appstate, int argc, char *argv[])
{
// init the library, here we make a window so we only need the Video capabilities.
if (SDL_Init(SDL_INIT_VIDEO))
{
return SDL_Fail();
}
// create a window
SDL_Window *window = SDL_CreateWindow("Window", 352, 430,
SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
if (!window)
{
return SDL_Fail();
}
SDL_GLContext glcontext = SDL_GL_CreateContext(window);
if (!glcontext)
{
return SDL_Fail();
}
// Create a shader program and load a triangle to the video card
GLuint program = createShaderProgram();
initVertexBuffers(program);
// print some information about the window
SDL_ShowWindow(window);
{
int width, height, bbwidth, bbheight;
SDL_GetWindowSize(window, &width, &height);
SDL_GetWindowSizeInPixels(window, &bbwidth, &bbheight);
SDL_Log("Window size: %ix%i", width, height);
SDL_Log("Backbuffer size: %ix%i", bbwidth, bbheight);
if (width != bbwidth)
{
SDL_Log("This is a highdpi environment.");
}
}
// set up the application data
*appstate = new AppContext {
window,
glcontext,
};
SDL_Log("Application started successfully!");
return 0;
}
int SDL_AppEvent(void *appstate, const SDL_Event *event)
{
auto *app = (AppContext *)appstate;
switch (event->type)
{
case SDL_EVENT_QUIT:
{
app->app_quit = SDL_TRUE;
break;
}
default:
{
break;
}
}
return 0;
}
int SDL_AppIterate(void *appstate)
{
auto *app = (AppContext *)appstate;
glClearColor(0.188f, 0.22f, 0.255f, 1.f);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
SDL_GL_SwapWindow(app->window);
return app->app_quit;
}
void SDL_AppQuit(void *appstate)
{
auto *app = (AppContext *)appstate;
if (app)
{
SDL_GL_DeleteContext(app->glcontext);
SDL_DestroyWindow(app->window);
delete app;
}
SDL_Quit();
SDL_Log("Application quit successfully!");
}