Improve drawing with digital zone highligts, futher colour tweaks, & thicker lines in GL.

It's also now no longer possible to trigger NW & SE angles when digital is set to 4 direction.

CMakeLists.txt

@@ -2,19 +2,25 @@ cmake_minimum_required(VERSION 3.8 FATAL_ERROR)
 project(padlab C)
 set(TARGET padlab)
 
+option(USE_OPENGL "Use legacy OpenGL for drawing" ON)
+
 set(CMAKE_C_STANDARD 99)
 
 find_package(SDL2 REQUIRED)
-find_package(OpenGL)
+if (USE_OPENGL)
+	find_package(OpenGL REQUIRED)
+endif()
 
 set(SOURCES
 	maths.h
-	draw.h  $<IF:$<BOOL:${OPENGL_FOUND}>,draw_opengl.c,draw.c>
+	draw.h  $<IF:$<BOOL:${USE_OPENGL}>,draw_opengl.c,draw.c>
 	stick.c stick.h
 	analogue.c)
 
 add_executable(${TARGET} ${SOURCES})
 target_link_libraries(${TARGET}
-	SDL2::SDL2 $<$<BOOL:${OPENGL_FOUND}>:OpenGL::GL> m)
+	SDL2::SDL2 $<$<BOOL:${USE_OPENGL}>:OpenGL::GL> m)
 target_compile_options(${TARGET} PRIVATE
 	-Wall -Wextra -pedantic -Wno-unused-parameter)
+target_compile_definitions(${TARGET} PRIVATE
+	$<$<BOOL:${USE_OPENGL}>:USE_OPENGL>)