Leave brush opacities untouched when picking with the pipette

The pipette now samples only what is painted (albedo, metallic,
smoothness, emission), not how strongly - the albedo alpha,
metallic/smoothness opacity and emission alpha are preserved instead
of being forced to 1 in every pick path and in FinalizePick.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/MeshPainter.Pick.cs

@@ -7,9 +7,10 @@ public partial class MeshPainter
     //
     // A sampling MODE rather than a paint channel: while active (Shift or Ctrl held, or the HUD toggle), a
     // left-click raycasts onto ANY surface (not just the paint mesh) and reads the channel values at
-    // the hit point (albedo, metallic, smoothness, emission) into the brush properties - with every
+    // the hit point (albedo, metallic, smoothness, emission) into the brush properties. The brush
-    // opacity/alpha forced to 1 so re-painting reproduces the picked look at full strength. Occlusion is
+    // opacities/alphas (albedo alpha, metallic/smoothness opacity, emission alpha) are left UNTOUCHED,
-    // excluded: it drives painted height now, so the pipette neither samples it nor enables its toggle.
+    // so a pick changes only WHAT is painted, not how strongly. Occlusion is excluded: it drives painted
+    // height now, so the pipette neither samples it nor enables its toggle.
     //
     // On a FOREIGN object the data channels (metallic/smoothness/emission) come texel-exact
     // from the material (raw, UNLIT). Albedo follows the 'pipetteAlbedoFromScreen' toggle: OFF (default)
@@ -22,8 +23,8 @@ public partial class MeshPainter
     [Header("Brush - pipette (eyedropper)")]
     [Tooltip("Pipette mode: a click samples the channel values at the hit point on ANY surface " +
              "(albedo, metallic, smoothness, emission - NOT occlusion/height) and adopts them into the " +
-             "brush (all alphas set to 1) instead of painting. On a foreign object the data channels are " +
+             "brush (opacities/alphas left untouched) instead of painting. On a foreign object the data " +
-             "read texel-exact from the material; albedo follows 'Pipette Albedo From Screen'. Held button picks once.")]
+             "channels are read texel-exact from the material; albedo follows 'Pipette Albedo From Screen'. Held button picks once.")]
     public bool pipette = false;
 
     [Tooltip("On a foreign-object pick, where albedo comes from. OFF (default): albedo is read " +
@@ -46,8 +47,8 @@ public partial class MeshPainter
 
     /// <summary>
     /// Raycasts at a screen position against ANY collider, samples the channel values at the hit
-    /// (texel-exact where possible) and copies them into the brush, forcing the sampled opacities/alphas
+    /// (texel-exact where possible) and copies them into the brush, leaving the brush opacities/alphas
-    /// to 1 and enabling those paint channels. Occlusion/height is excluded (see FinalizePick). Reads
+    /// untouched and enabling those paint channels. Occlusion/height is excluded (see FinalizePick). Reads
     /// regardless of which channels are currently toggled.
     /// Pick paths, by what was hit:
     ///   - our paint mesh        -> texel-exact from the painted maps (full PBR);
@@ -85,16 +86,15 @@ public partial class MeshPainter
     }
 
     /// <summary>
-    /// Common tail of every successful pick: forces the sampled opacities/alphas to 1, enables the
+    /// Common tail of every successful pick: enables the sampled paint channels, leaves pipette mode
-    /// sampled paint channels, leaves pipette mode (one-shot) and notifies listeners (the in-game HUD) to
+    /// (one-shot) and notifies listeners (the in-game HUD) to re-sync their widgets. The brush
-    /// re-sync their widgets. Occlusion is deliberately EXCLUDED: that channel now drives painted height,
+    /// opacities/alphas (albedo alpha, metallic/smoothness opacity, emission alpha) are left UNTOUCHED,
-    /// not a surface property to sample, so the pipette neither reads it (see the pick paths) nor enables
+    /// so a pick changes only WHAT is painted, not how strongly. Occlusion is deliberately EXCLUDED:
-    /// its toggle - the deliberate height brush value is left untouched.
+    /// that channel now drives painted height, not a surface property to sample, so the pipette neither
+    /// reads it (see the pick paths) nor enables its toggle - the deliberate height brush value is left untouched.
     /// </summary>
     private void FinalizePick()
     {
-        metallicSmoothnessOpacity = 1f;
-
         paintAlbedo = true;
         paintMetallicSmoothness = true;
         paintOcclusion = false;
@@ -138,12 +138,13 @@ public partial class MeshPainter
         Color32 m = mso[idx];
         Color32 e = em[idx];
 
-        // sRGB bytes map straight back into the gamma-space brush colours (round-trips exactly).
+        // sRGB bytes map straight back into the gamma-space brush colours (round-trips exactly). The
+        // alpha (paint opacity) is deliberately preserved, not overwritten - a pick changes only the colour.
         // Occlusion (m.g) is NOT picked: it now drives painted height, kept as the deliberate brush value.
-        brushColor = new Color(a.r / 255f, a.g / 255f, a.b / 255f, 1f);
+        brushColor = new Color(a.r / 255f, a.g / 255f, a.b / 255f, brushColor.a);
         metallic = m.r / 255f;
         smoothness = m.a / 255f;
-        emissionColor = new Color(e.r / 255f, e.g / 255f, e.b / 255f, 1f);
+        emissionColor = new Color(e.r / 255f, e.g / 255f, e.b / 255f, emissionColor.a);
         return true;
     }
 
@@ -163,7 +164,7 @@ public partial class MeshPainter
             // Keep the material's texel-exact PBR; optionally replace albedo with the lit on-screen
             // colour. No camera (headless) -> keep the material's raw albedo rather than failing.
             if (pipetteAlbedoFromScreen && TrySampleScreenColor(screenPos, out Color lit))
-                brushColor = new Color(Mathf.Clamp01(lit.r), Mathf.Clamp01(lit.g), Mathf.Clamp01(lit.b), 1f);
+                brushColor = new Color(Mathf.Clamp01(lit.r), Mathf.Clamp01(lit.g), Mathf.Clamp01(lit.b), brushColor.a);
             return true;
         }
 
@@ -224,7 +225,7 @@ public partial class MeshPainter
         Color albedo = baseCol;
         if (hasUv && baseTex)
             albedo = SampleTexel(baseTex, ApplyST(mat, "_BaseMap", "_MainTex", uv), true) * baseCol;
-        brushColor = new Color(Mathf.Clamp01(albedo.r), Mathf.Clamp01(albedo.g), Mathf.Clamp01(albedo.b), 1f);
+        brushColor = new Color(Mathf.Clamp01(albedo.r), Mathf.Clamp01(albedo.g), Mathf.Clamp01(albedo.b), brushColor.a);
 
         // --- Metallic / Smoothness: MetallicGloss map (linear) ---
         // URP/Lit: metallic = map.r ; smoothness = map.a * _Smoothness (or _Metallic/_Glossiness scalars).
@@ -248,7 +249,7 @@ public partial class MeshPainter
         Color emCol = emColor;
         if (hasUv && emTex)
             emCol = SampleTexel(emTex, ApplyST(mat, "_EmissionMap", null, uv), true) * emColor;
-        emissionColor = new Color(Mathf.Clamp01(emCol.r), Mathf.Clamp01(emCol.g), Mathf.Clamp01(emCol.b), 1f);
+        emissionColor = new Color(Mathf.Clamp01(emCol.r), Mathf.Clamp01(emCol.g), Mathf.Clamp01(emCol.b), emissionColor.a);
 
         return true;
     }
@@ -327,10 +328,10 @@ public partial class MeshPainter
         if (weightSum <= 1e-4f) return false;
         float inv = 1f / weightSum; // alphamap weights normally sum to 1, but guard anyway
 
-        brushColor = new Color(Mathf.Clamp01(albedo.r * inv), Mathf.Clamp01(albedo.g * inv), Mathf.Clamp01(albedo.b * inv), 1f);
+        brushColor = new Color(Mathf.Clamp01(albedo.r * inv), Mathf.Clamp01(albedo.g * inv), Mathf.Clamp01(albedo.b * inv), brushColor.a);
         metallic = Mathf.Clamp01(metallicVal * inv);
         smoothness = Mathf.Clamp01(smoothVal * inv);
-        emissionColor = new Color(0f, 0f, 0f, 1f); // occlusion left untouched (now painted height)
+        emissionColor = new Color(0f, 0f, 0f, emissionColor.a); // occlusion left untouched (now painted height)
         return true;
     }
 
@@ -364,10 +365,10 @@ public partial class MeshPainter
     {
         if (!TrySampleScreenColor(screenPos, out Color c)) return false;
 
-        brushColor = new Color(Mathf.Clamp01(c.r), Mathf.Clamp01(c.g), Mathf.Clamp01(c.b), 1f);
+        brushColor = new Color(Mathf.Clamp01(c.r), Mathf.Clamp01(c.g), Mathf.Clamp01(c.b), brushColor.a);
         metallic = 0f;
         smoothness = 0f;
-        emissionColor = new Color(0f, 0f, 0f, 1f); // occlusion left untouched (now painted height)
+        emissionColor = new Color(0f, 0f, 0f, emissionColor.a); // occlusion left untouched (now painted height)
         return true;
     }