// NdcScissorRect.cs
//
// NDC AABB → framebuffer-pixel scissor box, CONSERVATIVE (outer bound).
// The scissor that brackets a landscape/doorway slice is a fallback BOUND on
// the slice's view region (AD-17 in the divergence register): it must CONTAIN
// every fragment the per-fragment plane clip would keep. Under-inclusion is
// the bug class — the #130 doorway top-edge background strip was this box
// computed as Floor(origin) + Ceiling(size), whose far edge
// floor(min)+ceil(max−min) lands up to one pixel SHORT of the true max edge
// at unlucky fractional alignments, scissoring away the aperture's top/right
// pixel row for the whole slice (sky, terrain, statics, weather) while the
// seal still stamps it — a strip of clear color no later pass can fill.
//
// Correct outer bound: floor both mins, ceil both maxes, width = difference.
// A fragment at pixel (i,j) rasterizes iff its CENTER (i+0.5, j+0.5) lies in
// the region ⊆ the NDC box [X0,X1]×[Y0,Y1] (pixel units). Center-inside ⇒
// i ≥ X0−0.5 ⇒ i ≥ floor(X0) and i ≤ X1−0.5 ⇒ i < ceil(X1). So
// [floor(X0), ceil(X1)) admits every center-inside pixel, over-including by
// at most one pixel per edge — safe per AD-17's doctrine (the wall shell /
// plane clip repaints or kills the surplus).
using System;
using System.Numerics;

namespace AcDream.App.Rendering;

public static class NdcScissorRect
{
    /// <summary>Convert an NDC AABB (minX, minY, maxX, maxY in [-1,1]) to a
    /// framebuffer-pixel scissor box that CONTAINS it. Inputs are clamped to
    /// the screen so a region extending past an edge still yields a valid box.
    /// Width/height are at least 1.</summary>
    public static (int X, int Y, int Width, int Height) ToPixels(
        Vector4 ndcAabb, int fbWidth, int fbHeight)
    {
        float nx0 = Math.Clamp(ndcAabb.X, -1f, 1f);
        float ny0 = Math.Clamp(ndcAabb.Y, -1f, 1f);
        float nx1 = Math.Clamp(ndcAabb.Z, -1f, 1f);
        float ny1 = Math.Clamp(ndcAabb.W, -1f, 1f);
        int px0 = (int)MathF.Floor((nx0 * 0.5f + 0.5f) * fbWidth);
        int py0 = (int)MathF.Floor((ny0 * 0.5f + 0.5f) * fbHeight);
        int px1 = (int)MathF.Ceiling((nx1 * 0.5f + 0.5f) * fbWidth);
        int py1 = (int)MathF.Ceiling((ny1 * 0.5f + 0.5f) * fbHeight);
        return (px0, py0, Math.Max(1, px1 - px0), Math.Max(1, py1 - py0));
    }
}