Support writing again

zig/sdl/hello_sdl.zig

    defer c.TTF_CloseFont(font);
    c.SDL_Log("Using font %s", font_file.ptr);
    const msg = "howdy there, enby! 🐘                                          ";
    c.SDL_Log(msg);
    const screen = c.SDL_CreateWindow("hello fonts", c.SDL_WINDOWPOS_CENTERED, c.SDL_WINDOWPOS_CENTERED, 600, 100, c.SDL_WINDOW_BORDERLESS) orelse {
        c.SDL_Log("Unable to create window: %s", c.SDL_GetError());
        return error.SDLInitializationFailed;
    const surface = c.SDL_GetWindowSurface(screen);
    // assume monospace font
    var glyph_width: c_int = 0;
    if (c.TTF_GlyphMetrics(font, 'x', 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 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 quit = false;
    while (!quit) {
        var event: c.SDL_Event = undefined;
                        else => {},
                    }
                },
                c.SDL_TEXTINPUT => {
                    if (event.text.text.len > 0) {
                        c.SDL_Log("input: '%s' at %d", event.text.text, pos);
                        msg[pos] = event.text.text[0];
                        pos = (pos + 1) % (max_chars - 1);
                    }
                },
                else => {},
            }
        }
        const black: c.SDL_Color = c.SDL_Color{ .r = 0, .g = 0, .b = 0, .a = 255 };
        // Shaded vs Solid gives a nicer output, with solid the output
        // was squiggly and not aligned with a baseline.
        const text = c.TTF_RenderUTF8_Shaded(font, msg, white, black);
        const text = c.TTF_RenderUTF8_Shaded(font, &msg, white, black);
        _ = c.SDL_BlitSurface(text, null, surface, null);
        _ = c.SDL_UpdateWindowSurface(screen);