Prepare for possible commands

zig/sdl/hello_sdl.zig

    // assume monospace font
    var glyph_width: c_int = 0;
    if (c.TTF_GlyphMetrics(font, 'x', null, null, null, null, &glyph_width) != 0) {
    if (c.TTF_GlyphMetrics(font, 'g', null, null, null, null, &glyph_width) != 0) {
        c.SDL_Log("Unable to measure glyph: %s", c.TTF_GetError());
        return error.TTFInitializationFailed;
    }
    std.debug.assert(glyph_width < 1000);
    var glyph_height = c.TTF_FontLineSkip(font);
    var msg = "howdy there, enby! 🐘                                          ".*;
    var pos: usize = 0;
    var max_chars = std.math.min(@divTrunc(@intCast(usize, surface.*.w), @intCast(usize, glyph_width)), msg.len);
    var result: ?[*:0]u8 = null;
    result = "";
    const keyboardState = c.SDL_GetKeyboardState(null);
    var quit = false;
    while (!quit) {
        var event: c.SDL_Event = undefined;
                            pos = if (pos == 0) max_chars - 1 else (pos - 1) % (max_chars - 1);
                            msg[pos] = '_';
                        },
                        c.SDLK_RETURN => {
                            result = runCommand(&msg);
                        },
                        else => {},
                    }
                    // ctrl + key combinations
                    if (keyboardState[c.SDL_SCANCODE_LCTRL] != 0) {
                        switch (event.key.keysym.sym) {
                            c.SDLK_a => {
                                pos = 0;
                                msg[pos] = '_';
                            },
                            c.SDLK_k => {
                                var i: usize = 0;
                                while (i < max_chars) : (i += 1) {
                                    msg[i] = ' ';
                                }
                                msg[max_chars] = 0;
                            },
                            else => {},
                        }
                    }
                },
                c.SDL_TEXTINPUT => {
                    if (event.text.text.len > 0) {
        const text = c.TTF_RenderUTF8_Shaded(font, &msg, white, black);
        _ = c.SDL_BlitSurface(text, null, surface, null);
        const result_text = c.TTF_RenderUTF8_Shaded(font, result, white, black);
        _ = c.SDL_BlitSurface(result_text, null, surface, &c.SDL_Rect{ .x = 0, .y = glyph_height, .w = surface.*.w, .h = surface.*.h - glyph_height });
        _ = c.SDL_UpdateWindowSurface(screen);
        c.SDL_Delay(16);
    }
}
fn runCommand(cmd: ?[*:0]u8) ?[*:0]u8 {
    c.SDL_Log("cmd is '%s'", cmd);
    return "unknown command";
}