add higher-level app library

Fixes hexops/mach#190

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

build.zig

@@ -1,23 +1,73 @@
-const Builder = @import("std").build.Builder;
+const std = @import("std");
+const gpu = @import("gpu/build.zig");
+const gpu_dawn = @import("gpu-dawn/build.zig");
 const glfw = @import("glfw/build.zig");
 
-pub fn build(b: *Builder) void {
+pub fn build(b: *std.build.Builder) void {
     const mode = b.standardReleaseOptions();
     const target = b.standardTargetOptions(.{});
 
-    const lib = b.addStaticLibrary("engine", "src/main.zig");
-    lib.setBuildMode(mode);
-    lib.setTarget(target);
-    lib.addPackagePath("glfw", "glfw/src/main.zig");
-    glfw.link(b, lib, .{});
-    lib.install();
+    const gpu_dawn_options = gpu_dawn.Options{
+        .from_source = b.option(bool, "dawn-from-source", "Build Dawn from source") orelse false,
+    };
+    const options = Options {.gpu_dawn_options = gpu_dawn_options};
 
     const main_tests = b.addTest("src/main.zig");
     main_tests.setBuildMode(mode);
     main_tests.setTarget(target);
-    main_tests.addPackagePath("glfw", "glfw/src/main.zig");
-    glfw.link(b, main_tests, .{});
+    main_tests.addPackage(pkg);
+    main_tests.addPackage(gpu.pkg);
+    link(b, main_tests, options);
 
     const test_step = b.step("test", "Run library tests");
     test_step.dependOn(&main_tests.step);
+
+    const example = b.addExecutable("hello-triangle", "examples/main.zig");
+    example.setTarget(target);
+    example.setBuildMode(mode);
+    example.addPackage(pkg);
+    example.addPackage(gpu.pkg);
+    link(b, example, options);
+    example.install();
+
+    const example_run_cmd = example.run();
+    example_run_cmd.step.dependOn(b.getInstallStep());
+    const example_run_step = b.step("run-example", "Run the example");
+    example_run_step.dependOn(&example_run_cmd.step);
+}
+
+pub const Options = struct {
+    glfw_options: glfw.Options = .{},
+    gpu_dawn_options: gpu_dawn.Options = .{},
+};
+
+pub const pkg = .{
+    .name = "mach",
+    .path = .{ .path = thisDir() ++ "/src/main.zig" },
+    .dependencies = &.{ gpu.pkg, glfw.pkg },
+};
+
+pub fn link(b: *std.build.Builder, step: *std.build.LibExeObjStep, options: Options) void {
+    const gpu_options = gpu.Options{
+        .glfw_options = @bitCast(@import("gpu/libs/mach-glfw/build.zig").Options, options.glfw_options),
+        .gpu_dawn_options = @bitCast(@import("gpu/libs/mach-gpu-dawn/build.zig").Options, options.gpu_dawn_options),
+    };
+
+    const main_abs = std.fs.path.join(b.allocator, &.{ thisDir(), "src/main.zig" }) catch unreachable;
+    const lib = b.addStaticLibrary("mach", main_abs);
+    lib.setBuildMode(step.build_mode);
+    lib.setTarget(step.target);
+    lib.addPackage(gpu.pkg);
+    lib.addPackage(glfw.pkg);
+
+    glfw.link(b, lib, options.glfw_options);
+    gpu.link(b, lib, gpu_options);
+    lib.install();
+
+    glfw.link(b, step, options.glfw_options);
+    gpu.link(b, step, gpu_options);
+}
+
+fn thisDir() []const u8 {
+    return std.fs.path.dirname(@src().file) orelse ".";
 }