sx/library/modules/ui/pipeline.sx

#import "modules/std.sx";
#import "modules/std/mem.sx";
#import "modules/ui/glyph_cache.sx"; // `font: GlyphCache` — name it, import it (non-transitive).
#import "modules/ffi/opengl.sx";
#import "modules/gpu/api.sx";
#import "modules/ui/types.sx";
#import "modules/ui/render.sx";
#import "modules/ui/events.sx";
#import "modules/ui/font.sx";
#import "modules/ui/view.sx";
#import "modules/ui/renderer.sx";

UIPipeline :: struct {
    renderer: UIRenderer;
    render_tree: RenderTree;
    font: GlyphCache;
    screen_width: f32;
    screen_height: f32;
    root: ViewChild;
    has_root: bool;

    // Frame arena infrastructure. Both arenas are embedded value-typed
    // fields — Arena.init returns the state by value, so UIPipeline
    // holds the storage directly. Internal code grabs `*Arena` via
    // `@self.arena_a` when it needs to call methods through the
    // protocol; consumers in `tick_with_body` cast to Allocator at the
    // `push Context` site.
    arena_a: Arena;
    arena_b: Arena;
    frame_index: i64;
    body: Closure() -> View;
    has_body: bool;
    parent_allocator: Allocator;

    // GPU protocol backend. When set, the pipeline propagates this to its
    // renderer + font, and skips the per-frame GL state setup in
    // commit_gpu (Metal bakes blend mode into the pipeline state).
    gpu: ?GPU = null;

    // Set the GPU dispatch BEFORE calling init() / init_font() so the
    // shaders + atlas land on the right backend.
    set_gpu :: (self: *UIPipeline, gpu: GPU) {
        self.gpu = xx gpu;
        self.renderer.gpu = xx gpu;
        self.font.gpu = xx gpu;
    }

    init :: (self: *UIPipeline, width: f32, height: f32) {
        self.render_tree = RenderTree.init();
        self.renderer.init();
        self.screen_width = width;
        self.screen_height = height;
        self.has_root = false;
        self.has_body = false;
        self.frame_index = 0;
    }

    init_font :: (self: *UIPipeline, path: [:0]u8, size: f32, dpi_scale: f32) {
        self.font.init(path, size);
        self.font.set_dpi_scale(dpi_scale);
        self.renderer.dpi_scale = dpi_scale;
        set_global_font(@self.font);
    }

    set_root :: (self: *UIPipeline, view: View) {
        self.root = .{ view = view };
        self.has_root = true;
    }

    set_body :: (self: *UIPipeline, body_fn: Closure() -> View) {
        self.body = body_fn;
        self.has_body = true;
        self.parent_allocator = context.allocator;
        // Initialize both arenas (256KB initial, grows automatically)
        self.arena_a = Arena.init(self.parent_allocator, 262144);
        self.arena_b = Arena.init(self.parent_allocator, 262144);
        self.frame_index = 0;
    }

    resize :: (self: *UIPipeline, width: f32, height: f32) {
        self.screen_width = width;
        self.screen_height = height;
    }

    // Re-layout and re-render the existing view tree at current screen size.
    // Does NOT rebuild from body — safe to call from C callbacks (no arena/context needed).
    tick_relayout :: (self: *UIPipeline) {
        if self.has_root == false { return; }

        proposal := ProposedSize.fixed(self.screen_width, self.screen_height);
        self.root.view.size_that_fits(proposal);
        self.root.computed_frame = Frame.{
            origin = Point.zero(),
            size = Size.{ width = self.screen_width, height = self.screen_height }
        };
        self.root.view.layout(self.root.computed_frame);

        self.render_tree.clear();
        ctx := RenderContext.init(@self.render_tree);
        self.root.view.render(@ctx, self.root.computed_frame);

        self.commit_gpu();
    }

    // Process a single event through the view tree
    dispatch_event :: (self: *UIPipeline, event: *Event) -> bool {
        if self.has_root == false { return false; }
        self.root.view.handle_event(event, self.root.computed_frame)
    }

    // Run one frame: layout → render → commit
    tick :: (self: *UIPipeline) {
        if self.has_body {
            self.tick_with_body();
            return;
        }
        if self.has_root == false { return; }

        proposal := ProposedSize.fixed(self.screen_width, self.screen_height);

        // Layout
        self.root.view.size_that_fits(proposal);
        self.root.computed_frame = Frame.{
            origin = Point.zero(),
            size = Size.{ width = self.screen_width, height = self.screen_height }
        };
        self.root.view.layout(self.root.computed_frame);

        // Render to tree
        self.render_tree.clear();
        ctx := RenderContext.init(@self.render_tree);
        self.root.view.render(@ctx, self.root.computed_frame);

        // Commit to GPU
        self.commit_gpu();
    }

    tick_with_body :: (self: *UIPipeline) {
        build_arena : *Arena = if (self.frame_index & 1) == 0 then @self.arena_a else @self.arena_b;
        build_arena.reset();

        // Reset render_tree nodes (backing is stale after arena reset)
        self.render_tree.nodes.items = null;
        self.render_tree.nodes.len = 0;
        self.render_tree.nodes.cap = 0;

        push Context.{ allocator = xx build_arena, data = context.data } {
            // Workaround: self.body() crashes through struct field (issue-0010)
            body_fn := self.body;
            root_view := body_fn();
            self.root = .{ view = root_view };
            self.has_root = true;

            proposal := ProposedSize.fixed(self.screen_width, self.screen_height);
            self.root.view.size_that_fits(proposal);
            self.root.computed_frame = Frame.{
                origin = Point.zero(),
                size = Size.{ width = self.screen_width, height = self.screen_height }
            };
            self.root.view.layout(self.root.computed_frame);

            self.render_tree.clear();
            ctx := RenderContext.init(@self.render_tree);
            self.root.view.render(@ctx, self.root.computed_frame);

            self.commit_gpu();
        }

        self.frame_index += 1;
    }

    commit_gpu :: (self: *UIPipeline) {
        if self.gpu == null {
            glEnable(GL_BLEND);
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            glDisable(GL_DEPTH_TEST);
        }

        self.renderer.begin(self.screen_width, self.screen_height, self.font.texture_id);
        self.renderer.process(@self.render_tree);
        // Push any glyphs rasterized during process() to the GPU atlas BEFORE
        // the final draw is recorded. On Metal we deferred per-render_text
        // uploads so this is the single point where the atlas reaches the
        // GPU. On the GL path it's a no-op (uploads already happened inline).
        self.font.upload_atlas_to_gpu();
        self.renderer.flush();

        if self.gpu == null {
            glDisable(GL_BLEND);
        }
    }
}