gl: add PlatformOSMesa as an offscreen context

CMakeLists.txt

@@ -45,6 +45,8 @@ option(FILAMENT_ENABLE_FEATURE_LEVEL_0 "Enable Feature Level 0" ON)
 
 option(FILAMENT_ENABLE_MULTIVIEW "Enable multiview for Filament" OFF)
 
+option(FILAMENT_SUPPORTS_OSMESA "Enable OSMesa (headless GL context) for Filament" OFF)
+
 set(FILAMENT_NDK_VERSION "" CACHE STRING
     "Android NDK version or version prefix to be used when building for Android."
 )
@@ -73,6 +75,10 @@ set(FILAMENT_BACKEND_DEBUG_FLAG "" CACHE STRING
     "A debug flag meant for enabling/disabling backend debugging paths"
 )
 
+set(FILAMENT_OSMESA_PATH "" CACHE STRING
+    "Path to the OSMesa header and lib"
+)
+
 # Enable exceptions by default in spirv-cross.
 set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS OFF)
 
@@ -132,12 +138,22 @@ else()
 endif()
 
 if (LINUX)
+    if (NOT FILAMENT_OSMESA_PATH STREQUAL "")
+        if (NOT EXISTS ${FILAMENT_OSMESA_PATH}/)
+            message(FATAL_ERROR "Cannot find specified OSMesa build directory: ${FILAMENT_OSMESA_PATH}")
+        endif()
+        set(FILAMENT_SUPPORTS_OSMESA TRUE)
+    endif()
+
     if (FILAMENT_SUPPORTS_WAYLAND)
         add_definitions(-DFILAMENT_SUPPORTS_WAYLAND)
         set(FILAMENT_SUPPORTS_X11 FALSE)
     elseif (FILAMENT_SUPPORTS_EGL_ON_LINUX)
         add_definitions(-DFILAMENT_SUPPORTS_EGL_ON_LINUX)
         set(FILAMENT_SUPPORTS_X11 FALSE)
+    elseif (FILAMENT_SUPPORTS_OSMESA)
+        set(FILAMENT_SUPPORTS_X11 FALSE)
+        add_definitions(-DFILAMENT_SUPPORTS_OSMESA)
     else ()
         if (FILAMENT_SUPPORTS_XCB)
             add_definitions(-DFILAMENT_SUPPORTS_XCB)

build.sh

@@ -64,6 +64,9 @@ function print_help {
     echo "        enabling debug paths in the backend from the build script. For example, make a"
     echo "        systrace-enabled build without directly changing #defines. Remember to add -f when"
     echo "        changing this option."
+    echo "    -X osmesa_path"
+    echo "        Indicates a path to a completed OSMesa build. OSMesa is used to create an offscreen GL"
+    echo "        context for software rasterization"
     echo "    -S type"
     echo "        Enable stereoscopic rendering where type is one of [instanced|multiview]. This is only"
     echo "        meant for building the samples."
@@ -180,6 +183,8 @@ BACKEND_DEBUG_FLAG_OPTION=""
 
 STEREOSCOPIC_OPTION=""
 
+OSMESA_OPTION=""
+
 IOS_BUILD_SIMULATOR=false
 BUILD_UNIVERSAL_LIBRARIES=false
 
@@ -240,6 +245,7 @@ function build_desktop_target {
             ${ASAN_UBSAN_OPTION} \
             ${BACKEND_DEBUG_FLAG_OPTION} \
             ${STEREOSCOPIC_OPTION} \
+            ${OSMESA_OPTION} \
             ${architectures} \
             ../..
         ln -sf "out/cmake-${lc_target}/compile_commands.json" \
@@ -796,7 +802,7 @@ function check_debug_release_build {
 
 pushd "$(dirname "$0")" > /dev/null
 
-while getopts ":hacCfgijmp:q:uvslwedk:bx:S:" opt; do
+while getopts ":hacCfgijmp:q:uvslwedk:bx:S:X:" opt; do
     case ${opt} in
         h)
             print_help
@@ -950,6 +956,8 @@ while getopts ":hacCfgijmp:q:uvslwedk:bx:S:" opt; do
                     exit 1
             esac
             ;;
+        X)  OSMESA_OPTION="-DFILAMENT_OSMESA_PATH=${OPTARG}"
+            ;;
         \?)
             echo "Invalid option: -${OPTARG}" >&2
             echo ""

filament/backend/CMakeLists.txt

@@ -114,6 +114,8 @@ if (FILAMENT_SUPPORTS_OPENGL AND NOT FILAMENT_USE_EXTERNAL_GLES3)
             list(APPEND SRCS src/opengl/platforms/PlatformGLX.cpp)
         elseif (FILAMENT_SUPPORTS_EGL_ON_LINUX)
             list(APPEND SRCS src/opengl/platforms/PlatformEGLHeadless.cpp)
+        elseif (FILAMENT_SUPPORTS_OSMESA)
+            list(APPEND SRCS src/opengl/platforms/PlatformOSMesa.cpp)
         endif()
     elseif (WIN32)
         list(APPEND SRCS src/opengl/platforms/PlatformWGL.cpp)
@@ -361,6 +363,15 @@ set(LINUX_LINKER_OPTIMIZATION_FLAGS
         -Wl,--exclude-libs,bluegl
 )
 
+if (LINUX AND FILAMENT_SUPPORTS_OSMESA)
+    set(OSMESA_COMPILE_FLAGS
+        -I${FILAMENT_OSMESA_PATH}/include/GL)
+    set(OSMESA_LINKER_FLAGS
+        -Wl,-L${FILAMENT_OSMESA_PATH}/lib/x86_64-linux-gnu/
+        -lOSMesa
+    )
+endif()
+
 if (MSVC)
     set(FILAMENT_WARNINGS /W3)
 else()
@@ -381,6 +392,7 @@ endif()
 
 target_compile_options(${TARGET} PRIVATE
         ${FILAMENT_WARNINGS}
+        ${OSMESA_COMPILE_FLAGS}
         $<$<CONFIG:Release>:${OPTIMIZATION_FLAGS}>
         $<$<AND:$<PLATFORM_ID:Darwin>,$<CONFIG:Release>>:${DARWIN_OPTIMIZATION_FLAGS}>
 )
@@ -390,6 +402,7 @@ if (FILAMENT_SUPPORTS_METAL)
 endif()
 
 target_link_libraries(${TARGET} PRIVATE
+        ${OSMESA_LINKER_FLAGS}
         $<$<AND:$<PLATFORM_ID:Linux>,$<CONFIG:Release>>:${LINUX_LINKER_OPTIMIZATION_FLAGS}>
 )
 

filament/backend/include/backend/platforms/PlatformOSMesa.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2024 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_BACKEND_OPENGL_OPENGL_PLATFORM_OSMESA_H
+#define TNT_FILAMENT_BACKEND_OPENGL_OPENGL_PLATFORM_OSMESA_H
+
+#include <stdint.h>
+
+#include "bluegl/BlueGL.h"
+
+#include "osmesa.h"
+
+#include <backend/platforms/OpenGLPlatform.h>
+#include <backend/DriverEnums.h>
+
+namespace filament::backend {
+
+/**
+ * A concrete implementation of OpenGLPlatform that uses OSMesa, which is an offscreen
+ * context that can be used in conjunction with Mesa for software rasterization.
+ * See https://docs.mesa3d.org/osmesa.html for more information.
+ */
+class PlatformOSMesa : public OpenGLPlatform {
+protected:
+    // --------------------------------------------------------------------------------------------
+    // Platform Interface
+
+    Driver* createDriver(void* sharedGLContext, const DriverConfig& driverConfig) noexcept override;
+
+    int getOSVersion() const noexcept final override { return 0; }
+
+    // --------------------------------------------------------------------------------------------
+    // OpenGLPlatform Interface
+
+    void terminate() noexcept override;
+
+    SwapChain* createSwapChain(void* nativewindow, uint64_t flags) noexcept override;
+    SwapChain* createSwapChain(uint32_t width, uint32_t height, uint64_t flags) noexcept override;
+    void destroySwapChain(SwapChain* swapChain) noexcept override;
+    bool makeCurrent(ContextType type, SwapChain* drawSwapChain,
+            SwapChain* readSwapChain) noexcept override;
+    void commit(SwapChain* swapChain) noexcept override;
+
+private:
+    OSMesaContext mContext;
+};
+
+} // namespace filament::backend
+
+#endif // TNT_FILAMENT_BACKEND_OPENGL_OPENGL_PLATFORM_OSMESA_H

filament/backend/src/PlatformFactory.cpp

@@ -41,6 +41,10 @@
         #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3)
             #include "backend/platforms/PlatformEGLHeadless.h"
         #endif
+    #elif defined(FILAMENT_SUPPORTS_OSMESA)
+        #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3)
+            #include "backend/platforms/PlatformOSMesa.h"
+        #endif
     #endif
 #elif defined(WIN32)
     #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3)
@@ -124,6 +128,8 @@ Platform* PlatformFactory::create(Backend* backend) noexcept {
                 return new PlatformGLX();
             #elif defined(FILAMENT_SUPPORTS_EGL_ON_LINUX)
                 return new PlatformEGLHeadless();
+            #elif defined(FILAMENT_SUPPORTS_OSMESA)
+                return new PlatformOSMesa();
             #else
                 return nullptr;
             #endif

filament/backend/src/opengl/platforms/PlatformOSMesa.cpp

@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2024 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 <backend/platforms/PlatformOSMesa.h>
+
+#include <utils/Log.h>
+#include <utils/Panic.h>
+
+#include <memory>
+
+namespace filament::backend {
+
+using namespace backend;
+
+namespace {
+
+using BackingType = GLfloat;
+#define BACKING_GL_TYPE GL_FLOAT
+
+struct OSMesaSwapchain {
+    OSMesaSwapchain(uint32_t width, uint32_t height)
+        : width(width),
+          height(height),
+          buffer(new uint8_t[width * height * 4 * sizeof(BackingType)]) {}
+
+    uint32_t width = 0;
+    uint32_t height = 0;
+    std::unique_ptr<uint8_t[]> buffer;
+};
+
+} // anonymous namespace
+
+Driver* PlatformOSMesa::createDriver(void* const sharedGLContext,
+        const DriverConfig& driverConfig) noexcept {
+    FILAMENT_CHECK_PRECONDITION(sharedGLContext == nullptr)
+            << "shared GL context is not supported with PlatformOSMesa";
+    mContext = OSMesaCreateContext(GL_RGBA, NULL);
+
+    // We need to do a no-op makecurrent here so that the context will be in a correct state before
+    // any GL calls.
+    auto chain = createSwapChain(1, 1, 0);
+    makeCurrent(ContextType::UNPROTECTED, chain, nullptr);
+    destroySwapChain(chain);
+
+    int result = bluegl::bind();
+    FILAMENT_CHECK_POSTCONDITION(!result) << "Unable to load OpenGL entry points.";
+
+    return OpenGLPlatform::createDefaultDriver(this, sharedGLContext, driverConfig);
+}
+
+void PlatformOSMesa::terminate() noexcept {
+    OSMesaDestroyContext(mContext);
+    bluegl::unbind();
+}
+
+Platform::SwapChain* PlatformOSMesa::createSwapChain(void* nativeWindow, uint64_t flags) noexcept {
+    FILAMENT_CHECK_POSTCONDITION(false) << "Cannot create non-headless swapchain";
+    return (SwapChain*) nativeWindow;
+}
+
+Platform::SwapChain* PlatformOSMesa::createSwapChain(uint32_t width, uint32_t height,
+        uint64_t flags) noexcept {
+    OSMesaSwapchain* swapchain = new OSMesaSwapchain(width, height);
+    return (SwapChain*) swapchain;
+}
+
+void PlatformOSMesa::destroySwapChain(Platform::SwapChain* swapChain) noexcept {
+    OSMesaSwapchain* impl = (OSMesaSwapchain*) swapChain;
+    delete impl;
+}
+
+bool PlatformOSMesa::makeCurrent(ContextType type, SwapChain* drawSwapChain,
+        SwapChain* readSwapChain) noexcept {
+    OSMesaSwapchain* impl = (OSMesaSwapchain*) drawSwapChain;
+
+    auto result = OSMesaMakeCurrent(mContext, (BackingType*) impl->buffer.get(), BACKING_GL_TYPE,
+            impl->width, impl->height);
+    FILAMENT_CHECK_POSTCONDITION(result) << "OSMesaMakeCurrent failed!";
+
+    return true;
+}
+
+void PlatformOSMesa::commit(Platform::SwapChain* swapChain) noexcept {
+    // No-op since we are not scanning out to a display.
+}
+
+} // namespace filament::backend

third_party/libsdl2/include/SDL_config.h

@@ -46,6 +46,10 @@
 #include "SDL_config_linux_wayland.h"
 #elif defined(FILAMENT_SUPPORTS_X11)
 #include "SDL_config_linux_x11.h"
+#elif defined(FILAMENT_SUPPORTS_OSMESA)
+// We still want the same defines and libs as x11 but we won't actually
+// open any windows.
+#include "SDL_config_linux_x11.h"
 #endif
 #else
 /* This is a minimal configuration just to get SDL running on new platforms */

third_party/libsdl2/tnt/CMakeLists.txt

@@ -103,7 +103,7 @@ if (LINUX)
     if (FILAMENT_SUPPORTS_WAYLAND)
         file(GLOB SRCS_LINUX_WAYLAND ${SRC_DIR}/video/wayland/*.c)
         list(APPEND SRCS ${SRCS_LINUX_WAYLAND})
-    elseif(FILAMENT_SUPPORTS_X11)
+    elseif(FILAMENT_SUPPORTS_X11 OR FILAMENT_SUPPORTS_OSMESA)
         file(GLOB SRCS_LINUX_X11 ${SRC_DIR}/video/x11/*.c)
         list(APPEND SRCS ${SRCS_LINUX_X11})
     endif()