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emscripten_opengl_es3_sdl.cpp
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emscripten_opengl_es3_sdl.cpp
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#ifndef __EMSCRIPTEN__
#define USE_GLEW 0
#endif
#if USE_GLEW
#include "GL/glew.h"
#endif
#include <SDL/SDL.h>
#if !USE_GLEW
#include "SDL/SDL_opengl.h"
#endif
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#include <emscripten/html5.h>
#endif
#include <assert.h>
#include <iostream>
#include <string>
#include <vector>
#include <chrono>
std::string vert_shader = R"(#version 300 es
//precision mediump float;
layout (location = 0) in vec3 a_pos;
out float v_id;
void main()
{
v_id = float(gl_VertexID);
gl_Position = vec4(a_pos, 1.0);
}
)";
std::string frag_shader = R"(#version 300 es
precision mediump float;
in float v_id;
layout (location = 0) out vec4 frag_color;
uniform float u_time;
vec3 HUEtoRGB(in float H)
{
float R = abs(H * 6.0 - 3.0) - 1.0;
float G = 2.0 - abs(H * 6.0 - 2.0);
float B = 2.0 - abs(H * 6.0 - 4.0);
return clamp( vec3(R,G,B), 0.0, 1.0 );
}
void main()
{
float hue = fract(u_time * 0.3 + v_id * 0.5);
frag_color = vec4(HUEtoRGB(hue), 1.0);
}
)";
bool CompileStatus(GLuint shader)
{
GLint status = GL_TRUE;
glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
if (status == GL_FALSE)
{
GLint logLen;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLen);
std::vector<char>log( logLen );
GLsizei written;
glGetShaderInfoLog(shader, logLen, &written, log.data());
std::cout << "compile error:" << std::endl << log.data() << std::endl;
}
return status != GL_FALSE;
}
bool LinkStatus(GLuint program)
{
GLint status = GL_TRUE;
glGetProgramiv(program, GL_LINK_STATUS, &status);
if (status == GL_FALSE)
{
GLint logLen;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLen);
std::vector<char>log(logLen);
GLsizei written;
glGetProgramInfoLog( program, logLen, &written, log.data() );
std::cout << "link error:" << std::endl << log.data() << std::endl;
}
return status != GL_FALSE;
}
GLuint shader_program_object = 0;
GLuint triangle_vbo, triangle_vao;
GLint time_uniform_location;
std::chrono::high_resolution_clock::time_point start_time;
void gl_init()
{
auto vert_sh_obj = glCreateShader(GL_VERTEX_SHADER);
const char *vert_shader_ptr = vert_shader.c_str();
glShaderSource(vert_sh_obj, 1, &vert_shader_ptr, nullptr);
glCompileShader(vert_sh_obj);
CompileStatus(vert_sh_obj);
auto frag_sh_obj = glCreateShader(GL_FRAGMENT_SHADER);
const char *frag_shader_ptr = frag_shader.c_str();
glShaderSource(frag_sh_obj, 1, &frag_shader_ptr, nullptr);
glCompileShader(frag_sh_obj);
CompileStatus(frag_sh_obj);
shader_program_object = glCreateProgram();
glAttachShader(shader_program_object, vert_sh_obj);
glAttachShader(shader_program_object, frag_sh_obj);
glLinkProgram(shader_program_object);
LinkStatus(shader_program_object);
glDeleteShader(vert_sh_obj);
glDeleteShader(frag_sh_obj);
time_uniform_location = glGetUniformLocation(shader_program_object, "u_time");
std::cout << "`u_time` uniform location: " << time_uniform_location << std::endl;
static const std::vector<float> varray{ -0.866f, -0.75f, 0.0f, 0.866f, -0.75f, 0.0f, 0.0f, 0.75f, 0.0f };
glGenBuffers(1, &triangle_vbo);
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo);
glBufferData(GL_ARRAY_BUFFER, varray.size()*sizeof(*varray.data()), varray.data(), GL_STATIC_DRAW );
glGenVertexArrays(1, &triangle_vao);
glBindVertexArray(triangle_vao);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
start_time = std::chrono::high_resolution_clock::now();
}
bool sdl_events()
{
bool end = false;
SDL_Event sdl_event;
while (SDL_PollEvent(&sdl_event))
{
switch (sdl_event.type)
{
case SDL_QUIT:
end = false;
break;
case SDL_KEYDOWN:
end = sdl_event.key.keysym.sym == SDLK_ESCAPE;
break;
}
}
return end;
}
void gl_draw()
{
std::chrono::high_resolution_clock::time_point current_time = std::chrono::high_resolution_clock::now();
auto delta_time = current_time - start_time;
double time_s = (double)std::chrono::duration_cast<std::chrono::milliseconds>(delta_time).count() / 1000;
sdl_events();
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shader_program_object);
glUniform1f(time_uniform_location, static_cast<float>(time_s));
glBindVertexArray(triangle_vao);
glDrawArrays(GL_TRIANGLES, 0, 3);
}
EM_BOOL gl_animation_frame(double time, void* userData)
{
gl_draw();
return EM_TRUE;
}
int main(int argc, char *argv[])
{
std::cout << "SDL, OpenGL ES 3.0" << std::endl;
std::cout << "initialize view ..." << std::endl;
if (SDL_Init(SDL_INIT_VIDEO) != 0)
{
std::cout << "Unable to initialize SDL: " << SDL_GetError() << std::endl;
return 1;
}
int width = 800;
int height = 450;
#ifdef __EMSCRIPTEN__
SDL_Surface *screen = SDL_SetVideoMode( width, height, 16, SDL_OPENGL );
if ( !screen )
{
std::cout << "Unable to set video mode: " << SDL_GetError() << std::endl;
return 1;
}
#else
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_Window *window = SDL_CreateWindow("OpenGL Window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, SDL_WINDOW_OPENGL);
if (!window)
{
std::cout << "Couldn't create window: " << SDL_GetError() << std::endl;
return 0;
}
SDL_GLContext context = SDL_GL_CreateContext(window);
if (!context)
{
std::cout << "Couldn't create context: " << SDL_GetError() << std::endl;
return 0;
}
#endif
std::cout << "initialize OpenGL/WebGL ..." << std::endl;
gl_init();
std::cout << "run application ..." << std::endl;
#ifdef __EMSCRIPTEN__
//emscripten_request_animation_frame_loop(gl_animation_frame, 0);
emscripten_set_main_loop(gl_draw, 0, false);
#else
while (!sdl_events())
{
gl_draw();
SDL_GL_SwapBuffers();
}
std::cout << "quit..." << std::endl;
SDL_Quit();
#endif
return 0;
}