Add zig buildfile for examples. (#2051)

* Add zig buildfile for examples.

- `zig build` to compile all examples
- `zig build [module]` to compile all examples for a module (e.g. `zig build core`)
- `zig build [example]` to compile _and run_ a particular example (e.g. `zig build core_basic_window`)

You can use `-Dtarget=` to compile for a non-native platform, such as
`zig build -Dtarget=x86_64-windows-gnu` to compile from Linux to
Windows.

* Skip pthread example on Windows.

* Select appropriate lib file based on target.

examples/README.md

@@ -1,3 +1,21 @@
+## Building the Examples
+
+The examples assume you have already built the `raylib` library in `../src`.
+
+### With GNU make
+
+- `make` builds all examples
+- `make [module]` builds all examples for a particular module (e.g `make core`)
+
+### With Zig
+
+The [Zig](https://ziglang.org/) toolchain can compile `C` and `C++` in addition to `Zig`.
+You may find it easier to use than other toolchains, especially when it comes to cross-compiling.
+
+- `zig build` to compile all examples
+- `zig build [module]` to compile all examples for a module (e.g. `zig build core`)
+- `zig build [example]` to compile _and run_ a particular example (e.g. `zig build core_basic_window`)
+
 ## EXAMPLES LIST
 
 ### category: core

examples/build.zig

@@ -0,0 +1,86 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+fn add_module(comptime module: []const u8, b: *std.build.Builder, target: std.zig.CrossTarget) !*std.build.Step {
+    // Standard release options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
+    const mode = b.standardReleaseOptions();
+
+    const all = b.step(module, "All " ++ module ++ " examples");
+    const dir = try std.fs.cwd().openDir(
+        module,
+        .{ .iterate = true },
+    );
+    var iter = dir.iterate();
+    while (try iter.next()) |entry| {
+        if (entry.kind != .File) continue;
+        const extension_idx = std.mem.lastIndexOf(u8, entry.name, ".c") orelse continue;
+        const name = entry.name[0..extension_idx];
+        const path = try std.fs.path.join(b.allocator, &.{ module, entry.name });
+
+        // zig's mingw headers do not include pthread.h
+        if (std.mem.eql(u8, "core_loading_thread", name) and target.getOsTag() == .windows) continue;
+
+        const exe = b.addExecutable(name, path);
+        exe.setTarget(target);
+        exe.setBuildMode(mode);
+        exe.linkLibC();
+        exe.addObjectFile(switch (target.getOsTag()) {
+            .windows => "../src/raylib.lib",
+            .linux => "../src/libraylib.a",
+            else => @panic("Unsupported OS"),
+        });
+
+        exe.addIncludeDir("../src");
+        exe.addIncludeDir("../src/external");
+        exe.addIncludeDir("../src/external/glfw/include");
+
+        switch (exe.target.toTarget().os.tag) {
+            .windows => {
+                exe.linkSystemLibrary("winmm");
+                exe.linkSystemLibrary("gdi32");
+                exe.linkSystemLibrary("opengl32");
+                exe.addIncludeDir("external/glfw/deps/mingw");
+            },
+            .linux => {
+                exe.linkSystemLibrary("GL");
+                exe.linkSystemLibrary("rt");
+                exe.linkSystemLibrary("dl");
+                exe.linkSystemLibrary("m");
+                exe.linkSystemLibrary("X11");
+            },
+            else => {
+                @panic("Unsupported OS");
+            },
+        }
+
+        exe.setOutputDir(module);
+
+        var run = exe.run();
+        run.step.dependOn(&b.addInstallArtifact(exe).step);
+        run.cwd = module;
+        b.step(name, name).dependOn(&run.step);
+        all.dependOn(&exe.step);
+    }
+    return all;
+}
+
+pub fn build(b: *std.build.Builder) !void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    const all = b.getInstallStep();
+
+    all.dependOn(try add_module("audio", b, target));
+    all.dependOn(try add_module("core", b, target));
+    all.dependOn(try add_module("models", b, target));
+    all.dependOn(try add_module("others", b, target));
+    all.dependOn(try add_module("physics", b, target));
+    all.dependOn(try add_module("shaders", b, target));
+    all.dependOn(try add_module("shapes", b, target));
+    all.dependOn(try add_module("text", b, target));
+    all.dependOn(try add_module("textures", b, target));
+}