voxel-game/src/asset_pipeline.zig

const std = @import("std");

const main = @import("main.zig");
const zstbi = @import("zstbi");

pub const Texture = struct {
    width: u32,
    height: u32,
    depth: u32,
    data: []u8,

    pub fn deinit(self: *Texture, allocator: std.mem.Allocator) void {
        allocator.free(self.data);
        self.* = undefined;
    }
};

pub const AssetMap = std.hash_map.StringHashMapUnmanaged;

pub fn visitTextures(allocator: std.mem.Allocator) AssetMap(Texture) {
    zstbi.init(allocator);
    defer zstbi.deinit();

    const cwd = std.fs.cwd();
    const sub_path = "assets/textures";

    var ret: AssetMap(Texture) = .empty;

    var textures_dir = cwd.openDir(sub_path, .{ .iterate = true }) catch |err| {
        std.log.err("Could not open \"{s}\" directory: {s}", .{ sub_path, @errorName(err) });
        return ret;
    };
    defer textures_dir.close();

    var it = textures_dir.iterate();
    while (it.next() catch |err| blk: {
        std.log.err("Directory iteration interrupted due to an error: {s}", .{@errorName(err)});
        break :blk null;
    }) |entry| {
        if (entry.kind != .file) {
            std.log.warn("Skipping \"{s}\", which is not a file.", .{entry.name});
            continue;
        }

        var texture = visitTexture(allocator, textures_dir, entry.name) catch {
            continue;
        };

        const name = allocator.dupe(u8, std.fs.path.stem(entry.name)) catch {
            std.log.err("Ran out of memory while trying to allocate asset name", .{});
            texture.deinit(allocator);
            continue;
        };

        ret.putNoClobber(allocator, name, texture) catch {
            std.log.err("Ran out of memory while trying to save asset to map", .{});
            texture.deinit(allocator);
            allocator.free(name);
            continue;
        };
    }

    return ret;
}

pub fn visitTexture(allocator: std.mem.Allocator, dir: std.fs.Dir, filename: []const u8) !Texture {
    std.log.info("Processing \"{s}\"...", .{filename});

    const file = dir.openFile(filename, .{}) catch |err| {
        std.log.err("Could not open \"{s}\" file: {s}", .{ filename, @errorName(err) });
        return err;
    };
    defer file.close();

    const file_buf = file.readToEndAlloc(allocator, std.math.maxInt(usize)) catch |err| {
        std.log.err("Could not read \"{s}\" file contents due to an error: {s}", .{ filename, @errorName(err) });
        return err;
    };
    defer allocator.free(file_buf);

    var img = zstbi.Image.loadFromMemory(file_buf, 4) catch |err| {
        std.log.err("Error reading \"{s}\" as an image file: {s}", .{ filename, @errorName(err) });
        return err;
    };
    defer img.deinit();

    std.log.debug("size: {}×{} | components: {}", .{ img.width, img.height, img.num_components });

    const grid_w = 4;
    const grid_h = 4;
    const tile_count = grid_w * grid_h;

    const tile_w = std.math.divExact(u32, img.width, grid_w) catch |err| {
        std.log.err("Cannot divide image width ({}) by {}: {s}", .{ img.width, grid_w, @errorName(err) });
        return err;
    };
    const tile_h = std.math.divExact(u32, img.height, grid_h) catch |err| {
        std.log.err("Cannot divide image height ({}) by {}: {s}", .{ img.height, grid_h, @errorName(err) });
        return err;
    };

    std.log.debug("tile size: {}×{}", .{ tile_w, tile_h });

    const data = allocator.alloc(u8, 4 * tile_w * tile_h * tile_count) catch |err| {
        std.log.err("Ran out of memory while trying to allocate output buffer", .{});
        return err;
    };
    errdefer allocator.free(data);

    rearrange(grid_w, grid_h, tile_w, tile_h, img.data, data);

    return .{
        .width = tile_w,
        .height = tile_h,
        .depth = tile_count,
        .data = data,
    };
}

fn rearrange(grid_w: u32, grid_h: u32, tile_w: u32, tile_h: u32, inbuf: []const u8, outbuf: []u8) void {
    std.log.debug("rearrange: {}×{} grid of {}×{} tiles", .{ grid_w, grid_h, tile_w, tile_h });

    const row_size = 4 * tile_w;
    const row_stride = row_size * grid_w;
    const tile_stride = row_stride * tile_h;

    std.debug.assert(inbuf.len == tile_stride * grid_h);
    std.debug.assert(outbuf.len == tile_stride * grid_h);

    var outptr: usize = 0;

    var tile_y: u32 = 0;
    while (tile_y < grid_h) : (tile_y += 1) {
        const tile_byte_offset = tile_y * tile_stride;

        var tile_x: u32 = 0;
        while (tile_x < grid_w) : (tile_x += 1) {
            const column_byte_offset = tile_x * row_size;

            var row: u32 = 0;
            while (row < tile_h) : (row += 1) {
                const row_byte_offset = row * row_stride + tile_byte_offset;
                const byte_offset = row_byte_offset + column_byte_offset;

                @memcpy(
                    outbuf[outptr .. outptr + row_size],
                    inbuf[byte_offset .. byte_offset + row_size],
                );

                outptr += row_size;
            }
        }
    }
}

pub fn deinitTextures(allocator: std.mem.Allocator, map: *AssetMap(Texture)) void {
    var it = map.iterator();
    while (it.next()) |entry| {
        allocator.free(entry.key_ptr.*);
        entry.value_ptr.deinit(allocator);
    }
    map.deinit(allocator);
}