repaint_damage.hpp

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#pragma once
 
#include <pulp/view/geometry.hpp>
 
// FU-2 / WI-17 — the partial-repaint damage model.
//
// `compute_effective_damage` is the pure, side-effect-free heart of partial
// repaint: given the requested dirty rect (in ROOT logical coordinates, exactly
// what `View::request_repaint(Rect)` produces) it returns either a bounded clip
// rect that is PIXEL-IDENTICAL to a full repaint, or a "repaint everything"
// escalation when any view in the tree would sample pixels the clip cannot
// preserve.
//
// It has no GPU, canvas, or platform dependency and is unit-tested directly
// (test/test_partial_repaint_equivalence.cpp). Three hosts consume it, all
// gated behind PULP_PARTIAL_REPAINT=1: the macOS GPU WINDOW host, and the
// Windows and Linux PLUG-IN hosts via `compute_frame_clip()` in
// plugin_frame_renderer.hpp.
//
// One thing that decision does NOT do, and callers must: this function works in
// ROOT logical coordinates, because that is the space damage is produced in. A
// host that paints through a design-viewport letterbox installs its clip in
// SURFACE space, BEFORE that transform is applied — so the returned rect has to
// be mapped through the same translate+scale and re-snapped to whole surface
// pixels before use. `compute_frame_clip()` does that; a host that skips it
// clips the wrong region rather than failing visibly.
 
namespace pulp::view {
 
class View;

struct DamageDecision {
    bool full = true;
    Rect bounds{};
};

DamageDecision compute_effective_damage(const View& root,
                                        const Rect& requested_root_rect,
                                        float device_scale = 1.0f);
 
}  // namespace pulp::view