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fix: color-op alpha (0x202/0x203/0x232) is TINT STRENGTH, not object opacity

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Root cause (evidence: gfx-log) of the opening-CG grey background: a CG drawn with
(alpha=0, color=white) means 'no tint' = fully opaque, but slice-A conflated the
color alpha with object opacity -> the CG rendered transparent. RenderObject now
carries TintStrength separately from Alpha (opacity); resolution keeps textured
objects opaque. Tests updated to the evidence-based semantics.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
gamer147
2026-07-08 23:41:03 -04:00
parent 620ffb4fb7
commit c0b6199dbc
3 changed files with 36 additions and 21 deletions
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19
engine/Age.Engine/Model/GfxState.cs
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@@ -14,9 +14,13 @@ public readonly record struct AnimState(bool Enabled, bool Normalized, long TX,
/// (= the engine's z-order) each frame. Built by <see cref="GfxState.SnapshotVisibleObjects"/>; the surface
/// resId/colorkey are resolved from the object's live source slot at snapshot time (see docs/engine-re.md,
/// "The full gfx render model").</summary>
/// <summary><paramref name="Alpha"/> is the object's OPACITY (0-255). <paramref name="TintStrength"/> is how
/// strongly <paramref name="Tint"/> (RGB) is blended into the texel (0=keep texel, 255=full tint) — this is the
/// op 0x202/0x203/0x232 "alpha" byte, which is a tint strength, NOT opacity (conflating them made opaque CGs
/// vanish — the grey-background bug).</summary>
public readonly record struct RenderObject(long Handle, long SurfaceResId, long ColorKey,
int SrcX, int SrcY, int W, int H, int DstX, int DstY,
AnimState Anim, int Alpha, long Tint, BlendKind Blend);
AnimState Anim, int Alpha, long Tint, int TintStrength, BlendKind Blend);
/// <summary>Host-agnostic model of the AGE native gfx command-buffer (reversed in
/// docs/engine-re.md, gfx op-contract table). One registry maps an object handle to a GfxObject — the
@@ -236,20 +240,21 @@ public sealed class GfxState
if (!o.Visible) continue;
var (resId, ck) = _surfaces.TryGetValue(o.SourceSlot, out var s) ? s : (0L, 0L);
// ---- color: slice-A static base, then op-0x232 ping-pong toward the target ----
int alpha = 255; long tint = 0xFFFFFF; var blend = BlendKind.Opaque;
// ---- color: object stays OPAQUE; the op-0x202/0x203 alpha is a TINT STRENGTH (0=keep texel,
// 255=full tint), NOT opacity. 0x232 ping-pongs the strength (+tint) toward the target (glow). ----
int alpha = 255; long tint = 0xFFFFFF; int strength = 0; var blend = BlendKind.Opaque;
if (o.HasColor)
{
var (a, r, g, b) = BlendMath.UnpackArgb(o.Color);
alpha = a; tint = ((long)r << 16) | ((long)g << 8) | (long)b; blend = BlendKind.Alpha;
strength = a; tint = ((long)r << 16) | ((long)g << 8) | (long)b; blend = BlendKind.Alpha;
}
if (o.ColorAnim)
{
if (o.ColorStart < 0) o.ColorStart = nowMs;
double t = PingPongWeight(nowMs, o.ColorStart, o.ColorPeriod);
var (ta, tr, tg, tb) = BlendMath.UnpackArgb(o.ColorTarget);
var (ba, br, bg, bb) = (alpha, (int)((tint >> 16) & 0xff), (int)((tint >> 8) & 0xff), (int)(tint & 0xff));
alpha = (int)(ba + (ta - ba) * t);
var (br, bg, bb) = ((int)((tint >> 16) & 0xff), (int)((tint >> 8) & 0xff), (int)(tint & 0xff));
strength = (int)(strength + (ta - strength) * t);
tint = ((long)(br + (tr - br) * t) << 16) | ((long)(bg + (tg - bg) * t) << 8) | (long)(bb + (tb - bb) * t);
blend = BlendKind.Alpha;
}
@@ -278,7 +283,7 @@ public sealed class GfxState
new AnimState(o.AnimEnabled, o.AnimNormalized,
o.AnimTarget.X, o.AnimTarget.Y, o.AnimTarget.Z,
o.AnimDurationTicks, o.AnimGeneration),
alpha, tint, blend));
alpha, tint, strength, blend));
}
return list;
}