sdl ui backend

1 files changed, 81 insertions, 0 deletions

diff --git a/build.zig b/build.zig
index 34450fa9..ca8560fd 100644
--- a/build.zig
+++ b/build.zig
@@ -16,6 +16,12 @@ pub fn build(b: *std.Build) void {
     const static_link = b.option(bool, "static", "link all build executables and test binaries statically") orelse false;
     const exe_linkage: ?std.builtin.LinkMode = if (static_link) .static else null;
     const strip = b.option(bool, "strip", "strip debug info from the compiled pardes binary") orelse false;
+    // -Dsdl: build the SDL3 GPU UI frontend (a windowed cell-grid renderer)
+    //   instead of the default libvaxis terminal backend. The sdl/stb deps are
+    //   lazy, so a plain `zig build` never fetches or compiles them; they're only
+    //   pulled in when this flag is set. Use `zig build test-sdl -Dsdl` for the
+    //   rendered-image SDL e2e suite.
+    const sdl = b.option(bool, "sdl", "build the SDL3 GPU UI frontend instead of the terminal backend") orelse false;
 
     const exe = b.addExecutable(.{
         .name = "pardes",
@@ -93,6 +99,50 @@ pub fn build(b: *std.Build) void {
     vaxis_mod.addImport("uucode", uucode_mod);
     exe.root_module.addImport("vaxis", vaxis_mod);
 
+    // The UI backend module (`-Dui`). main.zig + image.zig import `"ui"` instead of
+    // `"vaxis"` directly; the chosen backend file re-exports the shared UI types
+    // (Key/Mouse/Window/Cell/…) and provides the renderer/loop (`Vaxis`/`Tty`/
+    // `Loop`/`init`). vaxis = transparent passthrough; sdl = SDL3 GPU frontend.
+    const ui_root = if (sdl) b.path("ui_sdl.zig") else b.path("ui_vaxis.zig");
+    const ui_mod = b.createModule(.{
+        .target = target,
+        .optimize = optimize,
+        .root_source_file = ui_root,
+    });
+    ui_mod.addImport("vaxis", vaxis_mod);
+    exe.root_module.addImport("ui", ui_mod);
+
+    // SDL3 GPU backend wiring (`-Dsdl`). The sdl package builds SDL3 from source
+    // as a static lib + emits the SDL3/ headers; we @cImport those headers in
+    // ui_sdl.zig, link the lib, and pull in stb_truetype (for the glyph atlas) and
+    // the embedded DejaVuSansMono font. All gated on the flag so a plain `zig build`
+    // (vaxis) never fetches or compiles SDL.
+    if (sdl) {
+        const sdl_dep = b.lazyDependency("sdl", .{
+            .target = target,
+            .optimize = optimize,
+        }) orelse return; // not fetched (offline?) — skip SDL wiring
+        const sdl_lib = sdl_dep.artifact("SDL3");
+        ui_mod.linkLibrary(sdl_lib);
+        ui_mod.addIncludePath(sdl_dep.path("include"));
+        ui_mod.link_libc = true;
+
+        // stb_truetype: the header (declarations, via include path) + the impl TU
+        // + a small C shim (font.c) so ui_sdl.zig doesn't feed the whole
+        // single-header lib to translate-c.
+        ui_mod.addIncludePath(b.path("vendor/stb"));
+        ui_mod.addCSourceFile(.{ .file = b.path("vendor/stb/stb_truetype_impl.c") });
+        ui_mod.addCSourceFile(.{ .file = b.path("vendor/stb/font.c") });
+
+        // GLSL -> SPIR-V at build time, embedded into ui_sdl.zig via @embedFile.
+        ui_mod.addAnonymousImport("ui.vert.spv", .{
+            .root_source_file = compileGlsl(b, "shaders/ui.vert.glsl", "vertex", "ui.vert.spv"),
+        });
+        ui_mod.addAnonymousImport("ui.frag.spv", .{
+            .root_source_file = compileGlsl(b, "shaders/ui.frag.glsl", "fragment", "ui.frag.spv"),
+        });
+    }
+
     // zstbi: C (stb_image)-backed image decoder for the image-viewer panes. We use
     // it instead of zigimg because zigimg's pure-Zig decoder crashes the Zig 0.16
     // compiler here; stb_image is plain C (extern fns), so it compiles fine, decodes
@@ -201,6 +251,28 @@ pub fn build(b: *std.Build) void {
     const test_step = b.step("test", "run deterministic tests");
     test_step.dependOn(&run_tests.step);
 
+    // `test-sdl`: e2e tests for the SDL3 GPU backend. The SDL pardes exe runs in
+    // test mode (PARDES_TEST=1): stdin drives app events through a pty, while the
+    // real GPU renderer writes the latest framebuffer capture to a temp PPM file.
+    // Requires `-Dsdl` so the SDL exe is the one under test.
+    const sdl_tests = b.addExecutable(.{
+        .name = "pardes-e2e-sdl",
+        .linkage = exe_linkage,
+        .root_module = b.createModule(.{
+            .target = target,
+            .optimize = optimize,
+            .root_source_file = b.path("tests_sdl.zig"),
+            .link_libc = true,
+        }),
+    });
+    const run_sdl_tests = b.addRunArtifact(sdl_tests);
+    run_sdl_tests.addArtifactArg(exe);
+    const sdl_test_opts = b.addOptions();
+    sdl_test_opts.addOption(bool, "trace", trace);
+    sdl_tests.root_module.addOptions("config", sdl_test_opts);
+    const test_sdl_step = b.step("test-sdl", "run SDL3 GPU e2e tests (requires -Dsdl)");
+    test_sdl_step.dependOn(&run_sdl_tests.step);
+
     // Unit tests for the pure modal-editing math (modal.zig has no vaxis/ghostty
     // deps, so `zig test` on it is fast and needs no wired-in modules).
     const unit_tests = b.addTest(.{
@@ -254,3 +326,12 @@ pub fn build(b: *std.Build) void {
     tutor_step.dependOn(&run_tutor.step);
     test_step.dependOn(&run_tutor.step);
 }
+
+// glslc <src> -fshader-stage=<stage> -o <out> -> .spv, returned as a LazyPath to
+// @embedFile. Only used by the SDL3 GPU UI backend (`-Dui=sdl`).
+fn compileGlsl(b: *std.Build, src: []const u8, stage: []const u8, out: []const u8) std.Build.LazyPath {
+    const cmd = b.addSystemCommand(&.{ "glslc", b.fmt("-fshader-stage={s}", .{stage}) });
+    cmd.addFileArg(b.path(src));
+    cmd.addArg("-o");
+    return cmd.addOutputFileArg(out);
+}