add sdl3_renderer demo

This is a highly updated demo for SDL_renderer
It brings few new features specific to libSDL3
and fixes some bugs from old sdl_renderer(SDL2) demo

Author: sleeptightAnsiC

demo/sdl3_renderer/Makefile

@@ -0,0 +1,41 @@
+# this Makefile is specific to GNU Make and GCC'compatible compilers
+
+PKG_CONFIG ?= $(shell command -v pkg-config)
+ifeq (,$(PKG_CONFIG))
+    $(error missing pkg-config utility!)
+endif
+
+PKG_SDL3 ?= sdl3
+ifeq (,$(shell $(PKG_CONFIG) --path $(PKG_SDL3)))
+    $(error $(PKG_CONFIG) could not find: $(PKG_SDL3))
+endif
+
+OS ?= $(shell uname -s)
+BINEXT-Windows_NT = .exe
+BINEXT ?= $(BINEXIT-$(OS))
+
+TEMPDIR ?= ./bin
+BIN ?= $(TEMPDIR)/demo$(BINEXT)
+
+CFLAGS += -std=c89 -Wall -Wextra -Wpedantic
+CFLAGS += -O2
+#CFLAGS += -O0 -g
+#CFLAGS += -fsanitize=address
+#CFLAGS += -fsanitize=undefined
+CFLAGS += $(shell $(PKG_CONFIG) $(PKG_SDL3) --cflags)
+
+LIBS += -lm
+LIBS += $(shell $(PKG_CONFIG) $(PKG_SDL3) --libs)
+
+DEP ?= $(BIN).d
+
+SRC = main.c
+
+$(BIN):
+	mkdir -p $(dir $@)
+	$(CC) $(SRC) -o $@ -MD -MF $(DEP) $(CFLAGS) $(LIBS)
+
+$(BIN): $(SRC) ./Makefile ./nuklear_sdl3_renderer.h ./../../nuklear.h
+
+-include $(DEP)
+