ngui: add a way to limit LVGL logging verbosity

the commit adds a build option lvgl_loglevel and sets a default similar
to that of std.log.default_level so the two are aligned more or less.

README.md

@@ -26,6 +26,12 @@ compiling is expected to be as easy as
 the output is placed in `./zig-out/bin` directory. for example, to run the gui,
 simply execute `./zig-out/bin/ngui`.
 
+the build script has a few project-specific options. list them all with
+a `zig build --help` command. for instance, to reduce LVGL logging verbosity in
+debug build mode, one can set this extra build flag:
+
+    zig build ngui -Dlvgl_loglevel=warn
+
 run all tests with
 
     zig build test

build.zig

@@ -4,12 +4,15 @@ const nifbuild = @import("lib/nif/build.zig");
 pub fn build(b: *std.build.Builder) void {
     const target = b.standardTargetOptions(.{});
     const mode = b.standardReleaseOptions();
+
     const strip = b.option(bool, "strip", "strip output binary; default: false") orelse false;
     const drv = b.option(DriverTarget, "driver", "display and input drivers combo; default: sdl2") orelse .sdl2;
     const disp_horiz = b.option(u32, "horiz", "display horizontal pixels count; default: 800") orelse 800;
     const disp_vert = b.option(u32, "vert", "display vertical pixels count; default: 480") orelse 480;
-    const bopts = b.addOptions();
+    const lvgl_loglevel = b.option(LVGLLogLevel, "lvgl_loglevel", "LVGL lib logging level") orelse LVGLLogLevel.default(mode);
-    bopts.addOption(DriverTarget, "driver", drv);
+
+    const buildopts = b.addOptions();
+    buildopts.addOption(DriverTarget, "driver", drv);
 
     // gui build
     const ngui = b.addExecutable("ngui", "src/ngui.zig");
@@ -18,7 +21,7 @@ pub fn build(b: *std.build.Builder) void {
     ngui.pie = true;
     ngui.strip = strip;
 
-    ngui.addPackage(bopts.getPackage("build_options"));
+    ngui.addPackage(buildopts.getPackage("build_options"));
     ngui.addIncludePath("lib");
     ngui.addIncludePath("src/ui/c");
     ngui.linkLibC();
@@ -53,6 +56,7 @@ pub fn build(b: *std.build.Builder) void {
     ngui.defineCMacroRaw(b.fmt("NM_DISP_HOR={}", .{disp_horiz}));
     ngui.defineCMacroRaw(b.fmt("NM_DISP_VER={}", .{disp_vert}));
     ngui.defineCMacro("LV_CONF_INCLUDE_SIMPLE", null);
+    ngui.defineCMacro("LV_LOG_LEVEL", lvgl_loglevel.text());
     ngui.defineCMacro("LV_TICK_CUSTOM", "1");
     ngui.defineCMacro("LV_TICK_CUSTOM_INCLUDE", "\"lv_custom_tick.h\"");
     ngui.defineCMacro("LV_TICK_CUSTOM_SYS_TIME_EXPR", "(nm_get_curr_tick())");
@@ -83,7 +87,7 @@ pub fn build(b: *std.build.Builder) void {
     nd.pie = true;
     nd.strip = strip;
 
-    nd.addPackage(bopts.getPackage("build_options"));
+    nd.addPackage(buildopts.getPackage("build_options"));
     nifbuild.addPkg(b, nd, "lib/nif");
     const niflib = nifbuild.library(b, "lib/nif");
     niflib.setTarget(target);
@@ -277,3 +281,36 @@ const lvgl_generic_src: []const []const u8 = &.{
     "lib/lvgl/src/widgets/lv_table.c",
     "lib/lvgl/src/widgets/lv_textarea.c",
 };
+
+/// LVGL log levels based on LV_LOG_LEVEL_xxx.
+/// note that the messages are printed from a zig fn callback, always with .info std.log.Level.
+const LVGLLogLevel = enum {
+    trace,
+    info,
+    warn,
+    err,
+    user,
+    none,
+
+    /// returns default mode based on the compiler optimization flags.
+    /// similar to std.log.default_level.
+    fn default(mode: std.builtin.Mode) @This() {
+        return switch (mode) {
+            .Debug => .info,
+            .ReleaseSafe => .warn,
+            .ReleaseFast, .ReleaseSmall => .err,
+        };
+    }
+
+    /// returns a C #define value for LVGL config.
+    fn text(self: @This()) []const u8 {
+        return switch (self) {
+            .trace => "LV_LOG_LEVEL_TRACE",
+            .info => "LV_LOG_LEVEL_INFO",
+            .warn => "LV_LOG_LEVEL_WARN",
+            .err => "LV_LOG_LEVEL_ERROR",
+            .user => "LV_LOG_LEVEL_USER",
+            .none => "LV_LOG_LEVEL_NONE",
+        };
+    }
+};

src/ui/c/lv_conf.h

@@ -190,7 +190,8 @@
     *LV_LOG_LEVEL_ERROR       Only critical issue, when the system may fail
     *LV_LOG_LEVEL_USER        Only logs added by the user
     *LV_LOG_LEVEL_NONE        Do not log anything*/
-    #define LV_LOG_LEVEL LV_LOG_LEVEL_INFO
+    /* defined in build.zig */
+    /*#define LV_LOG_LEVEL LV_LOG_LEVEL_WARN*/
 
     /*1: Print the log with 'printf';
     *0: User need to register a callback with `lv_log_register_print_cb()`*/

src/ui/lvgl.zig

@@ -29,11 +29,12 @@ fn lvglInit() void {
     lv_init();
 }
 
+/// logs messages from LVGL logging facilities; always with the same std.log level .info.
 export fn nm_lvgl_log(msg: [*:0]const u8) void {
     const s = std.mem.span(msg);
     // info level log messages are by default printed only in Debug
     // and ReleaseSafe build modes.
-    logger.debug("{s}", .{std.mem.trimRight(u8, s, "\n")});
+    logger.info("{s}", .{std.mem.trimRight(u8, s, "\n")});
 }
 
 /// the busy-wait loop cycle wrapper for LVGL.