[wayne@pyra]~/test/sdl2_example $ cat gles2_test.cpp
#include <SDL.h>
#ifdef USE_OPENGLES
#include <SDL_opengles2.h>
#else
#define GL_GLEXT_PROTOTYPES
#include <SDL_opengl.h>
#include <SDL_opengl_glext.h>
#endif
#include <stdio.h> // for printf
SDL_Window *sdl_window;
SDL_GLContext sdl_gl_context;
void initSDL() {
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
fprintf(stderr, "Couldn't init SDL2: %s\n", SDL_GetError());
exit(1);
}
#ifdef USE_OPENGLES
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
SDL_GL_CONTEXT_PROFILE_ES);
#endif
int video_width = 800;
int video_height = 480;
int window_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_FULLSCREEN;
sdl_window = SDL_CreateWindow("Test",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
video_width, video_height, window_flags);
if (!sdl_window) {
fprintf(stderr, "Failed to create OpenGL window: %s\n", SDL_GetError());
exit(1);
}
sdl_gl_context = SDL_GL_CreateContext(sdl_window);
if (!sdl_gl_context) {
fprintf(stderr, "Failed to create OpenGL context: %s\n", SDL_GetError());
exit(2);
}
}
void quitSDL() {
SDL_GL_DeleteContext(sdl_gl_context);
SDL_DestroyWindow(sdl_window);
SDL_Quit();
}
int main(int argc, char *argv[]) {
initSDL();
// create shader
const char *shader_vert_src =
"uniform float u_time;\n"
"attribute vec2 va_position;\n"
"varying vec3 v_color;\n"
"void main() {\n"
" v_color = vec3(1.0 - 0.5*(va_position.x+va_position.y),va_position);\n"
" float c = cos(u_time), s = sin(u_time);"
" vec2 t = mat2(c, s, -s, c)*(va_position-vec2(0.33));\n"
" gl_Position = vec4(t.x*3.0/5.0, t.y, 0.0, 1.0);\n"
"}\n";
const char *shader_frag_src =
"#ifdef GL_ES\n"
"precision mediump float;\n"
"#endif\n"
"varying vec3 v_color;\n"
"void main() {\n"
" gl_FragColor = vec4(v_color, 1.0);\n"
"}\n";
GLint is_compiled;
GLuint program, shader_vert, shader_frag;
program = glCreateProgram();
shader_vert = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(shader_vert, 1, &shader_vert_src, NULL);
glCompileShader(shader_vert);
glGetShaderiv(shader_vert, GL_COMPILE_STATUS, &is_compiled);
printf("vert shader compiled %d\n", is_compiled);
glAttachShader(program, shader_vert);
shader_frag = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(shader_frag, 1, &shader_frag_src, NULL);
glCompileShader(shader_frag);
glGetShaderiv(shader_frag, GL_COMPILE_STATUS, &is_compiled);
printf("frag shader compiled %d\n", is_compiled);
glAttachShader(program, shader_frag);
glLinkProgram(program);
glUseProgram(program);
GLuint u_time_loc = glGetUniformLocation(program, "u_time");
float u_time = 0.0f;
// create vbo
GLuint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
float vertex_data[] = {0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f};
glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_data), vertex_data, GL_STATIC_DRAW);
// setup vertex attribs
GLuint va_position = 0;
glEnableVertexAttribArray(va_position);
glVertexAttribPointer(va_position, 2, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0);
glClearColor(0.4, 0.6, 0.8, 1.0);
bool running = true;
do {
SDL_Event event;
while (SDL_PollEvent(&event)) {
running = !(event.type == SDL_QUIT
|| (event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_ESCAPE));
}
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUniform1f(u_time_loc, u_time += 1.0f/60.0f);
glDrawArrays(GL_TRIANGLES, 0, 3);
SDL_GL_SwapWindow(sdl_window);
} while (running);
glUseProgram(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glDeleteProgram(program);
glDeleteBuffers(1, &vbo);
quitSDL();
return 0;
}
