Created
October 10, 2015 11:07
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SDL2 + OpenGL ES 2.0 - "Hello triangle" example that works both on X11 and Emscripten
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#include <exception> | |
#include <functional> | |
#ifdef __EMSCRIPTEN__ | |
#include <emscripten.h> | |
#include <SDL.h> | |
#include <SDL_image.h> | |
#include <SDL_ttf.h> | |
#define GL_GLEXT_PROTOTYPES 1 | |
#include <SDL_opengles2.h> | |
#else | |
#include <SDL2/SDL.h> | |
#define GL_GLEXT_PROTOTYPES 1 | |
#include <SDL2/SDL_opengles2.h> | |
#endif | |
// Shader sources | |
const GLchar* vertexSource = | |
"attribute vec4 position; \n" | |
"void main() \n" | |
"{ \n" | |
" gl_Position = vec4(position.xyz, 1.0); \n" | |
"} \n"; | |
const GLchar* fragmentSource = | |
"precision mediump float;\n" | |
"void main() \n" | |
"{ \n" | |
" gl_FragColor = vec4 (1.0, 1.0, 1.0, 1.0 );\n" | |
"} \n"; | |
std::function<void()> loop; | |
void main_loop() { loop(); } | |
int main(int argc, char** argv) | |
{ | |
// SDL_Init(SDL_INIT_VIDEO); | |
auto wnd( | |
SDL_CreateWindow("test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, | |
640, 480, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN)); | |
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2); | |
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0); | |
SDL_GL_SetSwapInterval(0); | |
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1); | |
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24); | |
auto glc = SDL_GL_CreateContext(wnd); | |
auto rdr = SDL_CreateRenderer( | |
wnd, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE); | |
// Create Vertex Array Object | |
GLuint vao; | |
glGenVertexArraysOES(1, &vao); | |
glBindVertexArrayOES(vao); | |
// Create a Vertex Buffer Object and copy the vertex data to it | |
GLuint vbo; | |
glGenBuffers(1, &vbo); | |
GLfloat vertices[] = {0.0f, 0.5f, 0.5f, -0.5f, -0.5f, -0.5f}; | |
glBindBuffer(GL_ARRAY_BUFFER, vbo); | |
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); | |
// Create and compile the vertex shader | |
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER); | |
glShaderSource(vertexShader, 1, &vertexSource, NULL); | |
glCompileShader(vertexShader); | |
// Create and compile the fragment shader | |
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); | |
glShaderSource(fragmentShader, 1, &fragmentSource, NULL); | |
glCompileShader(fragmentShader); | |
// Link the vertex and fragment shader into a shader program | |
GLuint shaderProgram = glCreateProgram(); | |
glAttachShader(shaderProgram, vertexShader); | |
glAttachShader(shaderProgram, fragmentShader); | |
// glBindFragDataLocation(shaderProgram, 0, "outColor"); | |
glLinkProgram(shaderProgram); | |
glUseProgram(shaderProgram); | |
// Specify the layout of the vertex data | |
GLint posAttrib = glGetAttribLocation(shaderProgram, "position"); | |
glEnableVertexAttribArray(posAttrib); | |
glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0); | |
loop = [&] | |
{ | |
SDL_Event e; | |
while(SDL_PollEvent(&e)) | |
{ | |
if(e.type == SDL_QUIT) std::terminate(); | |
} | |
// Clear the screen to black | |
glClearColor(0.0f, 0.0f, 0.0f, 1.0f); | |
glClear(GL_COLOR_BUFFER_BIT); | |
// Draw a triangle from the 3 vertices | |
glDrawArrays(GL_TRIANGLES, 0, 3); | |
SDL_GL_SwapWindow(wnd); | |
}; | |
#ifdef __EMSCRIPTEN__ | |
emscripten_set_main_loop(main_loop, 0, true); | |
#else | |
while(true) main_loop(); | |
#endif | |
return 0; | |
} |
Thanks for your nice example. It helped us a lot to get https://github.com/jhasse/jngl running with emscripten.
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SDL_GL_SetAttribute
calls should come beforeSDL_CreateWindow
.SDL2 documentation for
SDL_GL_SetAttribute
says:One problem I noticed is that if you call
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
beforeSDL_CreateWindow
on Android it will make you lose OpenGL ES context when your window loses focus. Then, when you get back to the app, nothing will be drawn on the screen as all opengl calls will fail because you have no valid context. (At least that was what happened on my device until I moved those calls to beforeSDL_CreateWindow
or removed the lineSDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);