notebook: add tricks for faster rendering

Win10 in particular sucks at stretching a completely white bitmap

1 files changed, 9 insertions, 0 deletions

diff --git a/alf/alfgroupbox.cpp b/alf/alfgroupbox.cpp
index 9786323..5c459dc 100644
--- a/alf/alfgroupbox.cpp
+++ b/alf/alfgroupbox.cpp
@@ -62,6 +62,15 @@ ALF_GroupBox_PaintFrameUxtheme(ALFGroupBoxPriv *priv, HWND hwnd, HDC dc, RECT *r
     RECT rc;
     GetClientRect(hwnd, &rc);
 
+    // Skip drawing the border if that is not requested, since stretching that bitmap might be expensive.
+    // Will happen when a transparent child calls DrawThemeParentBackground.
+    RECT rcTop = { 0, 0, rc.right-rc.left, priv->layout.containerMargins.top };
+    RECT rcLeft = { 0, 0, priv->layout.containerMargins.left, rc.bottom-rc.top };
+    RECT rcRight = { rc.right-rc.left-priv->layout.containerMargins.right, 0, rc.right-rc.left, rc.bottom-rc.top };
+    RECT rcBottom = { 0, rc.bottom-rc.top-priv->layout.containerMargins.bottom, rc.right-rc.left, rc.bottom-rc.top };
+    if (!RectVisible(dc, &rcTop) && !RectVisible(dc, &rcLeft) && !RectVisible(dc, &rcRight) && !RectVisible(dc, &rcBottom))
+        return;
+
     rc.top += priv->calculatedLabelSize.cy / 2;
 
     HRGN oldClipR = CreateRectRgn(0, 0, 0, 0);