DOCS/client_api_examples: add SDL OpenGL example

DOCS/client_api_examples/README.md

@@ -24,6 +24,11 @@ qml_direct
 Alternative example, which typically avoids a FBO indirection. Might be
 slightly faster, but is less flexible and harder to use.
 
+sdl
+---
+
+Show how to embed the mpv OpenGL renderer in SDL.
+
 simple
 ------
 

DOCS/client_api_examples/sdl/main.c

@@ -0,0 +1,137 @@
+// Build with: gcc -o main main.c `pkg-config --libs --cflags mpv sdl2`
+
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <SDL.h>
+
+#include <mpv/client.h>
+#include <mpv/opengl_cb.h>
+
+static Uint32 wakeup_on_mpv_redraw, wakeup_on_mpv_events;
+
+static void die(const char *msg)
+{
+    fprintf(stderr, "%s\n", msg);
+    exit(1);
+}
+
+static void *get_proc_address_mpv(void *fn_ctx, const char *name)
+{
+    return SDL_GL_GetProcAddress(name);
+}
+
+static void on_mpv_events(void *ctx)
+{
+    SDL_Event event = {.type = wakeup_on_mpv_events};
+    SDL_PushEvent(&event);
+}
+
+static void on_mpv_redraw(void *ctx)
+{
+    SDL_Event event = {.type = wakeup_on_mpv_redraw};
+    SDL_PushEvent(&event);
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc != 2)
+        die("pass a single media file as argument");
+
+    mpv_handle *mpv = mpv_create();
+    if (!mpv)
+        die("context init failed");
+
+    // Done setting up options.
+    if (mpv_initialize(mpv) < 0)
+        die("mpv init failed");
+
+    if (SDL_Init(SDL_INIT_VIDEO) < 0)
+        die("SDL init failed");
+
+    SDL_Window *window =
+        SDL_CreateWindow("hi", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+                         1000, 500, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
+    if (!window)
+        die("failed to create SDL window");
+
+    mpv_opengl_cb_context *mpv_gl = mpv_get_sub_api(mpv, MPV_SUB_API_OPENGL_CB);
+    if (!mpv_gl)
+        die("failed to create mpv GL API handle");
+
+    SDL_GLContext glcontext = SDL_GL_CreateContext(window);
+    if (!glcontext)
+        die("failed to create SDL GL context");
+
+    if (mpv_opengl_cb_init_gl(mpv_gl, NULL, get_proc_address_mpv, NULL) < 0)
+        die("failed to initialize mpv GL context");
+
+    // Actually using the opengl_cb state has to be explicitly requested.
+    // Otherwise, mpv will create a separate platform window.
+    if (mpv_set_option_string(mpv, "vo", "opengl-cb") < 0)
+        die("failed to set VO");
+
+    // Play this file. Note that this asynchronously starts playback.
+    const char *cmd[] = {"loadfile", argv[1], NULL};
+    mpv_command(mpv, cmd);
+
+    // We use events for thread-safe notification of the SDL main loop.
+    wakeup_on_mpv_redraw = SDL_RegisterEvents(1);
+    wakeup_on_mpv_events = SDL_RegisterEvents(1);
+    if (wakeup_on_mpv_redraw == (Uint32)-1 || wakeup_on_mpv_events == (Uint32)-1)
+        die("could not register events");
+
+    // When normal mpv events are available.
+    mpv_set_wakeup_callback(mpv, on_mpv_events, NULL);
+
+    // When a new frame should be drawn with mpv_opengl_cb_draw().
+    // (Separate from the normal event handling mechanism for the sake of
+    //  users which run OpenGL on a different thread.)
+    mpv_opengl_cb_set_update_callback(mpv_gl, on_mpv_redraw, NULL);
+
+    while (1) {
+        SDL_Event event;
+        if (SDL_WaitEvent(&event) != 1)
+            die("event loop error");
+        int redraw = 0;
+        switch (event.type) {
+        case SDL_QUIT:
+            goto done;
+        case SDL_WINDOWEVENT:
+            if (event.window.event == SDL_WINDOWEVENT_EXPOSED)
+                redraw = 1;
+            break;
+        case SDL_KEYDOWN:
+            if (event.key.keysym.sym == SDLK_SPACE)
+                mpv_command_string(mpv, "cycle pause");
+            break;
+        default:
+            // Happens when a new video frame should be rendered, or if the
+            // current frame has to be redrawn e.g. due to OSD changes.
+            if (event.type == wakeup_on_mpv_redraw)
+                redraw = 1;
+            // Happens when at least 1 new event is in the mpv event queue.
+            if (event.type == wakeup_on_mpv_events) {
+                // Handle all remaining mpv events.
+                while (1) {
+                    mpv_event *mp_event = mpv_wait_event(mpv, 0);
+                    if (mp_event->event_id == MPV_EVENT_NONE)
+                        break;
+                    printf("event: %s\n", mpv_event_name(mp_event->event_id));
+                }
+            }
+        }
+        if (redraw) {
+            int w, h;
+            SDL_GetWindowSize(window, &w, &h);
+            mpv_opengl_cb_draw(mpv_gl, 0, w, -h);
+            SDL_GL_SwapWindow(window);
+        }
+    }
+done:
+
+    mpv_opengl_cb_uninit_gl(mpv_gl);
+    mpv_terminate_destroy(mpv);
+    return 0;
+}