Viewport

Viewports are extensions of windows that allow restricting rendering to a specific area of the screen.

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Overview

Viewports are represented by the Window::Viewport structure. They allow delimiting the rendering zone to a defined portion of a window.

By default, every object is rendered within the global viewport of the window, whose origin is the top-left corner:

(0, 0)  _ _ _ _ _ _ _ _ _ _ _ _ _ (x)
       |
       |
       |
       |
       |
       |
       |
      (y)

Viewports allow restricting this area to a defined portion:

(0, 0)  _ _ _ _ _ _ _ _ _ _ _ _ _ (x)
       |
       |
       |     (0, 0) _ _ _ _ (x')
       |           |
       |           |
       |          (y')
       |
      (y)

Their constructor is as follows:

Viewport(void);
Viewport(const Area& zone);
Viewport(const Area& zone, Camera& camera);

• zone — rendering area of the viewport
• camera — camera attached to the viewport

In this section, only the constructor taking an Area parameter will be covered. Camera usage will be addressed in the tilemap section.

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Usage

Viewports are created and managed through the following Window methods:

void addViewport(std::string_view tag, Viewport vp) noexcept; // register a named viewport
void removeViewport(std::string_view tag)           noexcept; // delete a named viewport
void useViewport(std::string_view tag)              noexcept; // activate a viewport for subsequent draws
void resetViewport(void)                            noexcept; // restore the default full-window viewport

• tag — unique identifier of the viewport

For example:

rmk::Window win;
rmk::Rectangle rect(0, 200); // position (0, 0) — size 200x200
rmk::Window::Viewport vp(rmk::Area(500, 100, 100, 100));

win.addViewport("view", vp);

win.fill(rect, rmk::color::red);
win.fill(rect, rmk::color::cyan, "view");

The useViewport method sets a default active viewport, used when no identifier is passed to the window's rendering methods. resetViewport deactivates it and restores the global viewport.

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