#include <functional>
#include <SDL.h> #include <emscripten.h>
#define GL_GLEXT_PROTOTYPES 1 #include <SDL_opengles2.h>
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[0] = gl_FragCoord.x/640.0; \n" " gl_FragColor[1] = gl_FragCoord.y/480.0; \n" " gl_FragColor[2] = 0.5; \n" "} \n";
bool background_is_black = true;
extern "C" void EMSCRIPTEN_KEEPALIVE toggle_background_color() { background_is_black = !background_is_black; }
std::function<void()> loop; void main_loop() { loop(); }
int main() {
SDL_Window *window; SDL_Renderer *renderer; SDL_CreateWindowAndRenderer(640, 480, 0, &window, &renderer);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2); SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0); SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1); SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
float vertices[] = {0.0f, 0.5f, 0.5f, -0.5f, -0.5f, -0.5f};
unsigned int vbo, vao; glGenBuffers(1, &vbo); glGenVertexArraysOES(1, &vao);
glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vertexShader, 1, &vertexSource, nullptr); glCompileShader(vertexShader);
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fragmentShader, 1, &fragmentSource, nullptr); glCompileShader(fragmentShader);
unsigned int shaderProgram = glCreateProgram(); glAttachShader(shaderProgram, vertexShader); glAttachShader(shaderProgram, fragmentShader); glLinkProgram(shaderProgram); glUseProgram(shaderProgram);
unsigned int posAttrib = glGetAttribLocation(shaderProgram, "position");
glBindVertexArrayOES(vao);
glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0); glEnableVertexAttribArray(posAttrib);
loop = [&] { const uint32_t milliseconds_since_start = SDL_GetTicks(); const uint32_t milliseconds_per_loop = 3000; vertices[0] = (milliseconds_since_start % milliseconds_per_loop) / float(milliseconds_per_loop) - 0.5f; glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
if (background_is_black) glClearColor(0.0f, 0.0f, 0.0f, 1.0f); else glClearColor(0.9f, 0.9f, 0.9f, 1.0f); glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
SDL_GL_SwapWindow(window); };
emscripten_set_main_loop(main_loop, 0, true);
return EXIT_SUCCESS; }
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