Add the vkQuake2 Vulkan renderer ported to YQ2.

This was first developed in a feature branch in the main yquake2 repo.
It was merged into master in early 2021, but the experiences of the
following month showed that it is not ready for prime time. There're
glitches with 3rd party assets, restarts are still shaky, etc. Having
the code in a separate repo allows us to:

  * Release Vulkan independent if YQ2.
  * Give commit access to contributors interested in Vulkan.

This code is the same as in yquake/yquake2 ecdf912713eef55d6c5d5a772259b44e3fc232c4.

Makefile

@@ -0,0 +1,362 @@
+# ----------------------------------------------------- #
+# Makefile for the Vulkan renderer lib for Quake II     #
+#                                                       #
+# Just type "make" to compile the                       #
+#  - Vulkan renderer lib (ref_vk.so / rev_vk.dll)       #
+#                                                       #
+# Dependencies:                                         #
+# - SDL2                                                #
+# - Vulkan headers                                      #
+#                                                       #
+# Platforms:                                            #
+# - FreeBSD                                             #
+# - Linux                                               #
+# - Mac OS X                                            #
+# - OpenBSD                                             #
+# - Windows                                             #
+# ----------------------------------------------------- #
+
+# Detect the OS
+ifdef SystemRoot
+YQ2_OSTYPE ?= Windows
+else
+YQ2_OSTYPE ?= $(shell uname -s)
+endif
+
+# Special case for MinGW
+ifneq (,$(findstring MINGW,$(YQ2_OSTYPE)))
+YQ2_OSTYPE := Windows
+endif
+
+# Detect the architecture
+ifeq ($(YQ2_OSTYPE), Windows)
+ifdef MINGW_CHOST
+ifeq ($(MINGW_CHOST), x86_64-w64-mingw32)
+YQ2_ARCH ?= x86_64
+else # i686-w64-mingw32
+YQ2_ARCH ?= i386
+endif
+else # windows, but MINGW_CHOST not defined
+ifdef PROCESSOR_ARCHITEW6432
+# 64 bit Windows
+YQ2_ARCH ?= $(PROCESSOR_ARCHITEW6432)
+else
+# 32 bit Windows
+YQ2_ARCH ?= $(PROCESSOR_ARCHITECTURE)
+endif
+endif # windows but MINGW_CHOST not defined
+else
+# Normalize some abiguous YQ2_ARCH strings
+YQ2_ARCH ?= $(shell uname -m | sed -e 's/i.86/i386/' -e 's/amd64/x86_64/' -e 's/^arm.*/arm/')
+endif
+
+# On Windows / MinGW $(CC) is undefined by default.
+ifeq ($(YQ2_OSTYPE),Windows)
+CC ?= gcc
+endif
+
+# Detect the compiler
+ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
+COMPILER := clang
+COMPILERVER := $(shell $(CC)  -dumpversion | sed -e 's/\.\([0-9][0-9]\)/\1/g' -e 's/\.\([0-9]\)/0\1/g' -e 's/^[0-9]\{3,4\}$$/&00/')
+else ifeq ($(shell $(CC) -v 2>&1 | grep -c -E "(gcc version|gcc-Version)"), 1)
+COMPILER := gcc
+COMPILERVER := $(shell $(CC)  -dumpversion | sed -e 's/\.\([0-9][0-9]\)/\1/g' -e 's/\.\([0-9]\)/0\1/g' -e 's/^[0-9]\{3,4\}$$/&00/')
+else
+COMPILER := unknown
+endif
+
+# ASAN includes DEBUG
+ifdef ASAN
+DEBUG=1
+endif
+
+# UBSAN includes DEBUG
+ifdef UBSAN
+DEBUG=1
+endif
+
+# ----------
+
+# Base CFLAGS. These may be overridden by the environment.
+# Highest supported optimizations are -O2, higher levels
+# will likely break this crappy code.
+ifdef DEBUG
+CFLAGS ?= -O0 -g -Wall -pipe
+ifdef ASAN
+CFLAGS += -fsanitize=address
+endif
+ifdef UBSAN
+CFLAGS += -fsanitize=undefined
+endif
+else
+CFLAGS ?= -O2 -Wall -pipe -fomit-frame-pointer
+endif
+
+# Always needed are:
+#  -fno-strict-aliasing since the source doesn't comply
+#   with strict aliasing rules and it's next to impossible
+#   to get it there...
+#  -fwrapv for defined integer wrapping. MSVC6 did this
+#   and the game code requires it.
+#  -fvisibility=hidden to keep symbols hidden. This is
+#   mostly best practice and not really necessary.
+override CFLAGS += -std=gnu99 -fno-strict-aliasing -fwrapv -fvisibility=hidden
+
+# -MMD to generate header dependencies. Unsupported by
+#  the Clang shipped with OS X.
+ifneq ($(YQ2_OSTYPE), Darwin)
+override CFLAGS += -MMD
+endif
+
+# OS X architecture.
+ifeq ($(YQ2_OSTYPE), Darwin)
+override CFLAGS += -arch $(YQ2_ARCH)
+endif
+
+# ----------
+
+# Switch of some annoying warnings.
+ifeq ($(COMPILER), clang)
+	# -Wno-missing-braces because otherwise clang complains
+	#  about totally valid 'vec3_t bla = {0}' constructs.
+	CFLAGS += -Wno-missing-braces
+else ifeq ($(COMPILER), gcc)
+	# GCC 8.0 or higher.
+	ifeq ($(shell test $(COMPILERVER) -ge 80000; echo $$?),0)
+	    # -Wno-format-truncation and -Wno-format-overflow
+		# because GCC spams about 50 false positives.
+    	CFLAGS += -Wno-format-truncation -Wno-format-overflow
+	endif
+endif
+
+# ----------
+
+# Defines the operating system and architecture
+override CFLAGS += -DYQ2OSTYPE=\"$(YQ2_OSTYPE)\" -DYQ2ARCH=\"$(YQ2_ARCH)\"
+
+# ----------
+
+# For reproduceable builds, look here for details:
+# https://reproducible-builds.org/specs/source-date-epoch/
+ifdef SOURCE_DATE_EPOCH
+CFLAGS += -DBUILD_DATE=\"$(shell date --utc --date="@${SOURCE_DATE_EPOCH}" +"%b %_d %Y" | sed -e 's/ /\\ /g')\"
+endif
+
+# ----------
+
+# Using the default x87 float math on 32bit x86 causes rounding trouble
+# -ffloat-store could work around that, but the better solution is to
+# just enforce SSE - every x86 CPU since Pentium3 supports that
+# and this should even improve the performance on old CPUs
+ifeq ($(YQ2_ARCH), i386)
+override CFLAGS += -msse -mfpmath=sse
+endif
+
+# Force SSE math on x86_64. All sane compilers should do this
+# anyway, just to protect us from broken Linux distros.
+ifeq ($(YQ2_ARCH), x86_64)
+override CFLAGS += -mfpmath=sse
+endif
+
+# ----------
+
+# Extra CFLAGS for SDL.
+SDLCFLAGS := $(shell sdl2-config --cflags)
+
+# ----------
+
+# Base include path.
+ifeq ($(YQ2_OSTYPE),Linux)
+INCLUDE ?= -I/usr/include
+else ifeq ($(YQ2_OSTYPE),FreeBSD)
+INCLUDE ?= -I/usr/local/include
+else ifeq ($(YQ2_OSTYPE),NetBSD)
+INCLUDE ?= -I/usr/X11R7/include -I/usr/pkg/include
+else ifeq ($(YQ2_OSTYPE),OpenBSD)
+INCLUDE ?= -I/usr/local/include
+else ifeq ($(YQ2_OSTYPE),Windows)
+INCLUDE ?= -I/usr/include
+endif
+
+# ----------
+
+# Base LDFLAGS. This is just the library path.
+ifeq ($(YQ2_OSTYPE),Linux)
+LDFLAGS ?= -L/usr/lib
+else ifeq ($(YQ2_OSTYPE),FreeBSD)
+LDFLAGS ?= -L/usr/local/lib
+else ifeq ($(YQ2_OSTYPE),NetBSD)
+LDFLAGS ?= -L/usr/X11R7/lib -Wl,-R/usr/X11R7/lib -L/usr/pkg/lib -Wl,-R/usr/pkg/lib
+else ifeq ($(YQ2_OSTYPE),OpenBSD)
+LDFLAGS ?= -L/usr/local/lib
+else ifeq ($(YQ2_OSTYPE),Windows)
+LDFLAGS ?= -L/usr/lib
+endif
+
+# Link address sanitizer if requested.
+ifdef ASAN
+LDFLAGS += -fsanitize=address
+endif
+
+# Link undefined behavior sanitizer if requested.
+ifdef UBSAN
+LDFLAGS += -fsanitize=undefined
+endif
+
+# Required libraries.
+ifeq ($(YQ2_OSTYPE),Linux)
+override LDFLAGS += -lm -ldl -rdynamic
+else ifeq ($(YQ2_OSTYPE),FreeBSD)
+override LDFLAGS += -lm
+else ifeq ($(YQ2_OSTYPE),NetBSD)
+override LDFLAGS += -lm
+else ifeq ($(YQ2_OSTYPE),OpenBSD)
+override LDFLAGS += -lm
+else ifeq ($(YQ2_OSTYPE),Windows)
+override LDFLAGS += -lws2_32 -lwinmm -static-libgcc
+else ifeq ($(YQ2_OSTYPE), Darwin)
+override LDFLAGS += -arch $(YQ2_ARCH)
+else ifeq ($(YQ2_OSTYPE), Haiku)
+override LDFLAGS += -lm
+endif
+
+ifneq ($(YQ2_OSTYPE), Darwin)
+ifneq ($(YQ2_OSTYPE), OpenBSD)
+# For some reason the OSX & OpenBSD
+# linker doesn't support this...
+override LDFLAGS += -Wl,--no-undefined
+endif
+endif
+
+# It's a shared library.
+override LDFLAGS += -shared
+
+# ----------
+
+# Extra LDFLAGS for SDL
+ifeq ($(YQ2_OSTYPE), Darwin)
+SDLLDFLAGS := -lSDL2
+else # not Darwin
+SDLLDFLAGS := $(shell sdl2-config --libs)
+endif # Darwin
+
+# The renderer libs don't need libSDL2main, libmingw32 or -mwindows.
+ifeq ($(YQ2_OSTYPE), Windows)
+DLL_SDLLDFLAGS = $(subst -mwindows,,$(subst -lmingw32,,$(subst -lSDL2main,,$(SDLLDFLAGS))))
+endif
+
+# ----------
+# When make is invoked by "make VERBOSE=1" print
+# the compiler and linker commands.
+
+ifdef VERBOSE
+Q :=
+else
+Q := @
+endif
+
+# ----------
+
+# Phony targets
+.PHONY : all clean xatrix
+
+# ----------
+
+# Builds everything
+all: ref_vk
+
+# ----------
+
+# Cleanup
+clean:
+	@echo "===> CLEAN"
+	${Q}rm -Rf build release
+
+# ----------
+
+ifeq ($(YQ2_OSTYPE), Windows)
+ref_vk:
+	@echo "===> Building ref_vk.dll"
+	${Q}mkdir -p release
+	$(MAKE) release/ref_vk.dll
+else
+ref_vk:
+	@echo "===> Building ref_vk.so"
+	${Q}mkdir -p release
+	$(MAKE) release/ref_vk.so
+
+release/ref_vk.so : CFLAGS += -fPIC
+endif
+
+build/%.o: %.c
+	@echo "===> CC $<"
+	${Q}mkdir -p $(@D)
+	${Q}$(CC) -c $(CFLAGS) $(SDLCFLAGS) $(INCLUDE) -o $@ $<
+
+# ----------
+
+REFVK_OBJS_ := \
+	src/vk/vk_buffer.o \
+	src/vk/vk_cmd.o \
+	src/vk/vk_common.o \
+	src/vk/vk_device.o \
+	src/vk/vk_draw.o \
+	src/vk/vk_image.o \
+	src/vk/vk_light.o \
+	src/vk/vk_mesh.o \
+	src/vk/vk_model.o \
+	src/vk/vk_pipeline.o \
+	src/vk/vk_rmain.o \
+	src/vk/vk_rmisc.o \
+	src/vk/vk_rsurf.o \
+	src/vk/vk_shaders.o \
+	src/vk/vk_swapchain.o \
+	src/vk/vk_validation.o \
+	src/vk/vk_warp.o \
+	src/vk/vk_util.o \
+	src/vk/volk/volk.o \
+	src/files/pcx.o \
+	src/files/stb.o \
+	src/files/wal.o \
+	src/files/pvs.o \
+	src/common/shared.o \
+	src/common/md4.o
+
+ifeq ($(YQ2_OSTYPE), Windows)
+REFVK_OBJS_ += \
+	src/backends/hunk_windows.o
+else # not Windows
+REFVK_OBJS_ += \
+	src/backends/hunk_unix.o
+endif
+
+# ----------
+
+# Rewrite pathes to our object directory
+REFVK_OBJS = $(patsubst %,build/%,$(REFVK_OBJS_))
+
+# ----------
+
+# Generate header dependencies
+REFVK_DEPS= $(REFVK_OBJS:.o=.d)
+
+# ----------
+
+# Suck header dependencies in
+-include $(REFVK_DEPS)
+
+# ----------
+
+# release/ref_vk.so
+ifeq ($(YQ2_OSTYPE), Windows)
+release/ref_vk.dll : $(REFVK_OBJS)
+	@echo "===> LD $@"
+	${Q}$(CC) $(REFVK_OBJS) $(LDFLAGS) $(DLL_SDLLDFLAGS) -o $@
+else
+release/ref_vk.so : $(REFVK_OBJS)
+	@echo "===> LD $@"
+	${Q}$(CC) $(REFVK_OBJS) $(LDFLAGS) $(SDLLDFLAGS) -o $@
+endif
+
+# ----------