Render the Screen from a Buffer

Now we replace the direct output example with a small buffer-based layout. This is the point where the library starts to feel more like a terminal UI toolkit than a simple print helper.

Instead of writing text directly to the terminal, the application now prepares the entire screen in memory and renders it in a single update.

Replace signal-board/src/main.cpp

Replace the contents of the file with the following version:

<project>/signal-board/src/main.cpp

#include <erbsland/cterm/all.hpp>

using namespace erbsland::cterm;

auto main() -> int {
    auto terminal = Terminal{Size{80, 25}};
    terminal.initializeScreen();

    auto buffer = Buffer{terminal.size()};
    buffer.fill(Char{" ", Color{fg::Default, bg::Black}});

    const auto rect = Rectangle{0, 0, buffer.size().width(), 6};
    buffer.drawFilledFrame(
        rect,
        FrameStyle::LightWithRoundedCorners,
        Char{" ", bg::Blue});
    buffer.drawText(
        "Signal Board",
        Rectangle{2, 1, rect.width() - 4, 1},
        Alignment::Center,
        Color{fg::BrightWhite, bg::Blue});
    buffer.drawText(
        "The whole screen is prepared in memory and rendered in one pass.",
        Rectangle{2, 3, rect.width() - 4, 2},
        Alignment::CenterLeft,
        Color{fg::BrightWhite, bg::Blue});

    auto settings = UpdateSettings{};
    settings.setMinimumSize(Size{40, 8});
    settings.setSwitchToAlternateBuffer(false);
    terminal.updateScreen(buffer, settings);
    terminal.flush();
    terminal.restoreScreen();
    return 0;
}

What Changed

This version introduces several important concepts:

• Buffer stores a complete screen-sized grid of colored terminal cells.

• fill() clears the buffer and defines the background color.

• Inherited keeps the color from below, while Default explicitly resets to the terminal default.

• drawFilledFrame() draws both the frame and its interior in a single call.

• drawText() places text inside rectangles without manually managing the cursor.

• UpdateSettings allows you to define constraints such as the minimum supported terminal size.

• setSwitchToAlternateBuffer(false) keeps this short example on the main screen instead of using the alternate full-screen buffer.

• Terminal starts in OutputMode::FullControl, which enables screen refresh, cursor control, and buffer-based rendering. Use OutputMode::Text only for plain-text output without terminal control features.

Because the entire scene is prepared in memory, the application can update the terminal in a single operation. This approach scales much better once the layout contains multiple panels, text blocks, or animated elements.

By default, Terminal::size() already returns the safe drawable size for screen updates. If you need to use the full detected terminal size, disable the compatibility margin with setSafeMarginEnabled(false).

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