Match external handles to the panel gradient

src/panel_surface.cpp

@@ -353,6 +353,17 @@ struct PanelSurface::Impl {
         rounded({400, 721, 200, 6}, 3, handle, handle);
         rounded({1008, 721, 36, 6}, 3, handle, handle);
         rounded({1038, 691, 6, 36}, 3, handle, handle);
+        // Give each handle the same full mint-to-blue theme gradient as the
+        // main frame, without changing its antialiased alpha coverage.
+        for (Rect bounds : {Rect{400, 721, 200, 6}, Rect{1008, 691, 36, 36}})
+            for (int y = bounds.y; y < bounds.y + bounds.h; ++y)
+                for (int x = bounds.x; x < bounds.x + bounds.w; ++x) {
+                    auto* dst = pixels.data() + (size_t(y) * W + x) * 4;
+                    if (!dst[3]) continue;
+                    const auto color = mix(theme.frame_start, theme.frame_end,
+                                           float(x - bounds.x) / (bounds.w - 1));
+                    std::copy_n(color.begin(), 3, dst);
+                }
         dirty = false;
         return true;
     }

tests/panel_test.cpp

@@ -89,6 +89,20 @@ int main(int argc, char** argv) {
     assert(alpha(500, 690) == 0 && alpha(1030, 704) == 0);
     // Antialiased handle edges carry real alpha, not RGB hidden at alpha zero.
     assert(alpha(401, 721) > 0 && alpha(401, 721) < 255);
+    // Both external handles use the configured full frame gradient, not a
+    // fixed blue or a tint that fills in their transparent surroundings.
+    Theme gradient_theme;
+    gradient_theme.frame_start = {255, 0, 0, 255};
+    gradient_theme.frame_end = {0, 0, 255, 255};
+    PanelSurface gradient_surface(argv[1], Mount::World, gradient_theme);
+    gradient_surface.render(p);
+    const auto channel = [&](int x, int y, int c) {
+        return gradient_surface.pixels()[(y * PanelSurface::width + x) * 4 + c];
+    };
+    assert(channel(410, 723, 0) > 230 && channel(590, 723, 2) > 230);
+    assert(channel(1012, 723, 0) > 220 && channel(1040, 705, 2) > 220);
+    assert(channel(1030, 704, 3) == 0 && channel(800, 724, 3) == 0);
+    assert(channel(401, 721, 3) == alpha(401, 721));
 
     p.enabled = true;
     p.record_available = false;