gl4es: Delay feature detection until a context exists

gl4es feature detection does not work reliably with EGL.

If a context already exists, gl4es can instead reliably detect
the underlying GLES features from the context itself.

This requires gl4es to be configured with:

    -DNOEGL=ON -DNO_LOADER=ON -DNO_INIT_CONSTRUCTOR=ON

This also requires gl4es to have this fix: https://github.com/ptitSeb/gl4es/pull/271

CMakeLists.txt

@@ -16,6 +16,11 @@ endif()
 # Detect OS
 include(cmake/OSIdentity.cmake)
 
+option(OPENMW_GL4ES_MANUAL_INIT "Manually initialize gl4es. This is more reliable on platforms without a windowing system. Requires gl4es to be configured with -DNOEGL=ON -DNO_LOADER=ON -DNO_INIT_CONSTRUCTOR=ON." OFF)
+if(OPENMW_GL4ES_MANUAL_INIT)
+    add_definitions(-DOPENMW_GL4ES_MANUAL_INIT)
+endif()
+
 # Apps and tools
 option(BUILD_OPENMW             "Build OpenMW" ON)
 option(BUILD_LAUNCHER           "Build Launcher" ON)

components/CMakeLists.txt

@@ -140,7 +140,7 @@ add_component_dir (fontloader
     )
 
 add_component_dir (sdlutil
-    sdlgraphicswindow imagetosurface sdlinputwrapper sdlvideowrapper events sdlcursormanager
+    gl4es_init sdlgraphicswindow imagetosurface sdlinputwrapper sdlvideowrapper events sdlcursormanager
     )
 
 add_component_dir (version

components/sdlutil/gl4es_init.cpp

@@ -0,0 +1,36 @@
+// EGL does not work reliably for feature detection.
+// Instead, we initialize gl4es manually.
+#ifdef OPENMW_GL4ES_MANUAL_INIT
+#include "gl4es_init.h"
+
+// For glHint
+#include <GL/gl.h>
+
+extern "C" {
+
+#include <gl4es/gl4esinit.h>
+#include <gl4es/gl4eshint.h>
+
+static SDL_Window *gWindow;
+
+void openmw_gl4es_GetMainFBSize(int *width, int *height)
+{
+    SDL_GetWindowSize(gWindow, width, height);
+}
+
+void openmw_gl4es_init(SDL_Window *window)
+{
+    gWindow = window;
+    set_getprocaddress(SDL_GL_GetProcAddress);
+    set_getmainfbsize(openmw_gl4es_GetMainFBSize);
+    initialize_gl4es();
+
+    // merge glBegin/glEnd in beams and console
+    glHint(GL_BEGINEND_HINT_GL4ES, 1);
+    // dxt unpacked to 16-bit looks ugly
+    glHint(GL_AVOID16BITS_HINT_GL4ES, 1);
+}
+
+}  // extern "C"
+
+#endif  // OPENMW_GL4ES_MANUAL_INIT

components/sdlutil/gl4es_init.h

@@ -0,0 +1,13 @@
+#ifndef OPENMW_COMPONENTS_SDLUTIL_GL4ES_INIT_H
+#define OPENMW_COMPONENTS_SDLUTIL_GL4ES_INIT_H
+#ifdef OPENMW_GL4ES_MANUAL_INIT
+#include <SDL_video.h>
+
+// Must be called once SDL video mode has been set,
+// which creates a context.
+//
+// GL4ES can then query the context for features and extensions.
+extern "C" void openmw_gl4es_init(SDL_Window *window);
+
+#endif  // OPENMW_GL4ES_MANUAL_INIT
+#endif  // OPENMW_COMPONENTS_SDLUTIL_GL4ES_INIT_H

components/sdlutil/sdlgraphicswindow.cpp

@@ -2,6 +2,10 @@
 
 #include <SDL_video.h>
 
+#ifdef OPENMW_GL4ES_MANUAL_INIT
+#include "gl4es_init.h"
+#endif
+
 namespace SDLUtil
 {
 
@@ -91,7 +95,7 @@ void GraphicsWindowSDL2::init()
     SDL_Window *oldWin = SDL_GL_GetCurrentWindow();
     SDL_GLContext oldCtx = SDL_GL_GetCurrentContext();
    
-#if defined(ANDROID)
+#if defined(ANDROID) || defined(OPENMW_GL4ES_MANUAL_INIT)
     int major = 1;
     int minor = 1;
     char *ver = getenv("OPENMW_GLES_VERSION");
@@ -116,6 +120,10 @@ void GraphicsWindowSDL2::init()
         return;
     }
 
+#ifdef OPENMW_GL4ES_MANUAL_INIT
+    openmw_gl4es_init(mWindow);
+#endif
+
     setSwapInterval(_traits->vsync);
 
     // Update traits with what we've actually been given