Make code friendly to WebAssembly. (#140)

This does not add any build stuff or new sample code yet, it just does
some prep to our C++ codebase:

- Similar to Android, WebAssembly will not be using BlueGL. We were
  using a mixture of #if and #ifdef when checking for the existence of
  certain GL prototypes, but the latter is what we want in order to
  build robustly with any GL headers. (We still perform run-time checks
  for extensions, this doesn't change that.)

- Add a trivial ContextManager, does a bit more than Dummy since it
  needs to create an actual driver. This doesn't get compiled yet, it
  just adds files to the tree.

- WebAssembly does not support mmap, execinfo, or asm volatile.

filament/src/driver/CircularBuffer.cpp

@@ -16,9 +16,12 @@
 
 #include "driver/CircularBuffer.h"
 
-#if !defined(WIN32)
+#if !defined(WIN32) && !defined(__EMSCRIPTEN__)
 #    include <sys/mman.h>
 #    include <unistd.h>
+#    define HAS_MMAP 1
+#else
+#    define HAS_MMAP 0
 #endif
 
 #include <stdio.h>
@@ -27,12 +30,6 @@
 #include <utils/Log.h>
 #include <utils/Panic.h>
 
-#if defined(WIN32)
-#    define HAS_MMAP 0
-#else
-#    define HAS_MMAP 1
-#endif
-
 using namespace utils;
 
 namespace filament {

filament/src/driver/ExternalContext.cpp

@@ -44,6 +44,8 @@
     #if defined (FILAMENT_DRIVER_SUPPORTS_VULKAN)
         #include "driver/vulkan/ContextManagerVkWindows.h"
     #endif
+#elif defined(__EMSCRIPTEN__)
+    #include "driver/opengl/ContextManagerWebGL.h"
 #else
     #ifndef USE_EXTERNAL_GLES3
         #include "driver/opengl/ContextManagerDummy.h"
@@ -92,6 +94,8 @@ ExternalContext* ExternalContext::create(Backend* backend) noexcept {
         return new ContextManagerGLX();
     #elif defined(WIN32)
         return new ContextManagerWGL();
+    #elif defined(__EMSCRIPTEN__)
+        return new ContextManagerWebGL();
     #else
         return new ContextManagerDummy();
     #endif

filament/src/driver/opengl/ContextManagerWebGL.cpp

@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "driver/opengl/ContextManagerWebGL.h"
+#include "driver/opengl/OpenGLDriver.h"
+
+namespace filament {
+
+using namespace driver;
+
+std::unique_ptr<Driver> ContextManagerWebGL::createDriver(void* const sharedGLContext) noexcept {
+    return OpenGLDriver::create(this, sharedGLContext);
+}
+
+void ContextManagerWebGL::terminate() noexcept {
+}
+
+ExternalContext::SwapChain* ContextManagerWebGL::createSwapChain(
+        void* nativeWindow, uint64_t& flags) noexcept {
+    return (SwapChain*) nativeWindow;
+}
+
+void ContextManagerWebGL::destroySwapChain(ExternalContext::SwapChain* swapChain) noexcept {
+}
+
+void ContextManagerWebGL::makeCurrent(ExternalContext::SwapChain* swapChain) noexcept {
+}
+
+void ContextManagerWebGL::commit(ExternalContext::SwapChain* swapChain) noexcept {
+}
+
+ExternalContext::Fence* ContextManagerWebGL::createFence() noexcept {
+    Fence* f = new Fence();
+    return f;
+}
+
+void ContextManagerWebGL::destroyFence(Fence* fence) noexcept {
+    delete fence;
+}
+
+driver::FenceStatus ContextManagerWebGL::waitFence(Fence* fence, uint64_t timeout) noexcept {
+    return driver::FenceStatus::CONDITION_SATISFIED;
+}
+
+} // namespace filament

filament/src/driver/opengl/ContextManagerWebGL.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef TNT_FILAMENT_DRIVER_OPENGL_CONTEXT_MANAGER_WEBGL_H
+#define TNT_FILAMENT_DRIVER_OPENGL_CONTEXT_MANAGER_WEBGL_H
+
+#include <stdint.h>
+
+#include <filament/driver/DriverEnums.h>
+#include <filament/driver/ExternalContext.h>
+
+#include <EGL/egl.h>
+#include <EGL/eglext.h>
+
+namespace filament {
+
+class ContextManagerWebGL final : public driver::ContextManagerGL {
+public:
+
+    std::unique_ptr<Driver> createDriver(void* const sharedGLContext) noexcept override;
+    void terminate() noexcept override;
+
+    SwapChain* createSwapChain(void* nativewindow, uint64_t& flags) noexcept final override;
+    void destroySwapChain(SwapChain* swapChain) noexcept final override;
+    void makeCurrent(SwapChain* swapChain) noexcept final override;
+    void commit(SwapChain* swapChain) noexcept final override;
+
+    Fence* createFence() noexcept final override;
+    void destroyFence(Fence* fence) noexcept final override;
+    driver::FenceStatus waitFence(Fence* fence, uint64_t timeout) noexcept final override;
+
+    Stream* createStream(void* nativeStream) noexcept final override { return nullptr; }
+    void destroyStream(Stream* stream) noexcept final override {}
+    void attach(Stream* stream, intptr_t tname) noexcept final override {}
+    void detach(Stream* stream) noexcept final override {}
+    void updateTexImage(Stream* stream) noexcept final override {}
+
+    ExternalTexture* createExternalTextureStorage() noexcept final override { return nullptr; }
+    void reallocateExternalStorage(ExternalTexture* ets,
+            uint32_t w, uint32_t h, driver::TextureFormat format) noexcept final override { }
+    void destroyExternalTextureStorage(ExternalTexture* ets) noexcept final override { }
+
+    int getOSVersion() const noexcept final override { return 0; }
+};
+
+using ContextManager = filament::ContextManagerWebGL;
+
+} // namespace filament
+
+#endif // TNT_FILAMENT_DRIVER_OPENGL_CONTEXT_MANAGER_WEBGL_H

filament/src/driver/opengl/OpenGLDriver.cpp

@@ -2368,7 +2368,7 @@ GLuint OpenGLDriver::getSamplerSlow(driver::SamplerParams params) const noexcept
 }
 
 void OpenGLDriver::insertEventMarker(char const* string, size_t len) {
-#if GL_EXT_debug_marker
+#ifdef GL_EXT_debug_marker
     if (ext.EXT_debug_marker) {
         glInsertEventMarkerEXT(GLsizei(len ? len : strlen(string)), string);
     }
@@ -2376,7 +2376,7 @@ void OpenGLDriver::insertEventMarker(char const* string, size_t len) {
 }
 
 void OpenGLDriver::pushGroupMarker(char const* string,  size_t len) {
-#if GL_EXT_debug_marker
+#ifdef GL_EXT_debug_marker
     if (ext.EXT_debug_marker) {
         glPushGroupMarkerEXT(GLsizei(len ? len : strlen(string)), string);
     }
@@ -2384,7 +2384,7 @@ void OpenGLDriver::pushGroupMarker(char const* string,  size_t len) {
 }
 
 void OpenGLDriver::popGroupMarker(int) {
-#if GL_EXT_debug_marker
+#ifdef GL_EXT_debug_marker
     if (ext.EXT_debug_marker) {
         glPopGroupMarkerEXT();
     }

filament/src/driver/opengl/gl_headers.h

@@ -31,7 +31,7 @@
 #ifdef GL_OES_EGL_image
         extern PFNGLEGLIMAGETARGETTEXTURE2DOESPROC glEGLImageTargetTexture2DOES;
 #endif
-#if GL_EXT_debug_marker
+#ifdef GL_EXT_debug_marker
         extern PFNGLINSERTEVENTMARKEREXTPROC glInsertEventMarkerEXT;
         extern PFNGLPUSHGROUPMARKEREXTPROC glPushGroupMarkerEXT;
         extern PFNGLPOPGROUPMARKEREXTPROC glPopGroupMarkerEXT;

libs/utils/include/utils/compiler.h

@@ -110,7 +110,11 @@
 #define UTILS_RESTRICT __restrict__
 
 // TODO: set the proper alignment for the target
+#ifndef __EMSCRIPTEN__
 #define UTILS_ALIGN_LOOP {__asm__ __volatile__(".align 4");}
+#else
+#define UTILS_ALIGN_LOOP
+#endif
 
 #if __has_feature(cxx_thread_local)
 #   ifdef ANDROID

libs/utils/src/CallStack.cpp

@@ -22,9 +22,12 @@
 #include <algorithm>
 #include <memory>
 
-// FIXME: Android doesn't have execinfo.h (but has unwind.h)
-#if !defined(ANDROID) && !defined(WIN32)
+// FIXME: Some platforms do not have execinfo.h (but have unwind.h)
+#if !defined(ANDROID) && !defined(WIN32) && !defined(__EMSCRIPTEN__)
 #include <execinfo.h>
+#define HAS_EXECINFO 1
+#else
+#define HAS_EXECINFO 0
 #endif
 
 #if !defined(WIN32)
@@ -76,7 +79,7 @@ void CallStack::update_gcc(size_t ignore) noexcept {
     ssize_t size = 0;
 
     void *array[NUM_FRAMES];
-#if !defined(ANDROID) && !defined(WIN32)
+#if HAS_EXECINFO
     size = ::backtrace(array, NUM_FRAMES);
     size -= ignore;
 #endif
@@ -115,7 +118,7 @@ utils::CString CallStack::demangleTypeName(const char* mangled) {
 // ------------------------------------------------------------------------------------------------
 
 io::ostream& operator<<(io::ostream& stream, const CallStack& callstack) {
-#if !defined(ANDROID) && !defined(WIN32)
+#if HAS_EXECINFO
     size_t size = callstack.getFrameCount();
     for (size_t i = 0; i < size; i++) {
         intptr_t pc = callstack[i];