Top 10 Tips for Using TAdvShape Effectively

Troubleshooting Common TAdvShape IssuesTAdvShape is a versatile visual component used in Delphi and Lazarus development for drawing and interacting with shapes in GUI applications. While powerful, developers can encounter several common issues when using TAdvShape: rendering glitches, performance slowdowns, incorrect hit-testing, resizing artifacts, and problems when integrating with other controls or themes. This article walks through these problems, explains their usual causes, and provides practical solutions and code examples to get your TAdvShape-based UI running smoothly.

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1. Rendering artifacts and flicker

Symptoms:

• Flickering when the form repaints or when the shape is animated.
• Partial or corrupted drawing after overlapping windows or when resizing.
• Thin lines or jagged edges on rendered shapes.

Common causes:

• Lack of double buffering.
• Incorrect use of device contexts (DCs) or painting outside the proper paint event.
• Using integer coordinates for anti-aliased drawing without proper smoothing settings.
• Conflicts with parent control background painting.

Solutions:

• Enable double buffering. In Delphi, set the form’s DoubleBuffered property to True or use a double-buffered offscreen bitmap for the shape’s drawing routine.

• Use the component’s OnPaint/OnPaintBackground events correctly; avoid painting in arbitrary events.

• Use high-quality drawing flags and antialiasing where available:

  • If using GDI+, enable SmoothingMode := smAntiAlias.
  • If using GDI, consider higher-quality pen settings and draw to an offscreen bitmap then blit.

• Ensure clipping and invalidation are minimized: call InvalidateRect for only the required region instead of forcing full repaints.

• Example pattern (pseudo-Delphi):

  procedure TMyShape.Paint; var bmp: TBitmap; begin bmp := TBitmap.Create; try bmp.SetSize(Width, Height); bmp.Canvas.Brush.Color := Parent.Color; bmp.Canvas.FillRect(Rect(0,0,Width,Height)); // draw shape on bmp.Canvas with smoothing options if available Canvas.Draw(0,0,bmp); finally bmp.Free; end; end; 

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2. Slow performance with many shapes or complex paths

Symptoms:

• UI becomes sluggish when many TAdvShape instances are visible.
• Animations or redraws cause noticeable lag.
• High CPU usage during complex path drawing.

Common causes:

• Redrawing everything on each frame instead of incremental updates.
• Complex path computations on the main thread.
• Not caching rendered results for static shapes.
• Excessive use of transparency blending which is expensive.

Solutions:

• Cache static or rarely-changing shapes in bitmaps and reuse them.
• Use region-based invalidation: only redraw areas that changed.
• Offload heavy path calculations to a background thread, then synchronize the final bitmap back to the UI thread.
• Reduce complexity of shapes where possible (simplify paths, fewer control points).
• Use hardware-accelerated drawing when available (Direct2D/DirectX), or libraries that leverage GPU.
• Example caching approach:

  
  if FCacheBitmap = nil then begin FCacheBitmap := TBitmap.Create; FCacheBitmap.SetSize(Width, Height); RenderShapeToBitmap(FCacheBitmap.Canvas); end; Canvas.Draw(0,0,FCacheBitmap); 

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3. Incorrect hit-testing or mouse interaction

Symptoms:

• Clicks register outside visible shape bounds or don’t register on transparent areas.
• Mouse events (OnMouseDown/OnClick) fire unexpectedly when shapes overlap.
• Dragging or selection behaves inconsistently.

Common causes:

• Hit-testing using bounding rectangles instead of the actual shape region.
• Transparent areas not excluded from mouse events.
• Overlapping controls with different Z-order handling.

Solutions:

• Implement precise hit-testing using point-in-polygon tests or Windows regions (HRGN).
• For polygons, use ray-casting or winding-number algorithms to test whether a point lies inside the path.
• Create and assign a region to the control using CreatePolygonRgn/CreateRectRgn and set window region where supported.
• Example point-in-polygon (even-odd rule) approach (pseudo-Delphi):

  
  function PointInPolygon(const P: TPoint; const Polygon: array of TPoint): Boolean; var i, j: Integer; c: Boolean; begin c := False; j := High(Polygon); for i := 0 to High(Polygon) do begin if ((Polygon[i].Y > P.Y) <> (Polygon[j].Y > P.Y)) and    (P.X < (Polygon[j].X - Polygon[i].X) * (P.Y - Polygon[i].Y) /          (Polygon[j].Y - Polygon[i].Y) + Polygon[i].X) then   c := not c; j := i; end; Result := c; end; 

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4. Incorrect scaling, DPI, or resizing behavior

Symptoms:

• Shapes appear blurred or misaligned when the user changes DPI or when the form is resized.
• Coordinates and stroke widths don’t scale properly on high-DPI displays.
• Anchors and alignments yield unexpected layout.

Common causes:

• Using hard-coded pixel values and not accounting for DPI scaling.
• Not handling WM_DPICHANGED or relevant VCL/LCL scaling notifications.
• Stroke widths and anti-aliasing not adjusted with scale factor.

Solutions:

• Use device-independent units where possible or multiply sizes by the current DPI scaling factor.
• Handle DPI change messages (WM_DPICHANGED) and re-render any cached bitmaps at the new scale.
• For vector shapes, recompute paths with scaled coordinates (use a transformation matrix).
• Use VCL/LCL built-in scaling helpers (e.g., ScaleFactor or PixelsPerInch) to adapt sizes.
• Example scaling:

  
  Scale := CurrentDPI / 96; // 96 is standard DPI ScaledStroke := Round(BaseStroke * Scale); 

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5. Integration issues with themes and styles

Symptoms:

• TAdvShape visuals clash with application themes (flat vs. classic), or colors don’t match VCL styles.
• Transparent shapes pick up incorrect background when using themed parents or custom styles.
• Shapes don’t repaint correctly when the global style changes.

Common causes:

• Assuming parent background is a plain color instead of themed drawing.
• Not responding to style change events.
• Incorrect use of alpha blending with themed backgrounds.

Solutions:

• Query and use parent’s background painting routine or grab the parent’s background into an offscreen bitmap before drawing transparent shapes.
• Listen for style/theme change notifications and invalidate/re-render caches when they occur.
• When composing with alpha blending, pre-multiply alpha and blend against the parent background for correct results.
• Use VCL style services (StyleServices.DrawElement, etc.) to draw consistent backgrounds before overlaying shapes.

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6. Memory leaks and resource management

Symptoms:

• Application memory grows over time when shapes are created/destroyed frequently.
• GDI handle exhaustion leading to drawing failures or exceptions.
• Bitmaps or regions are not freed properly.

Common causes:

• Not freeing temporary bitmaps, regions, pens, or brushes.
• Holding references to bitmaps longer than needed.
• Recreating resources on every paint without releasing old ones.

Solutions:

• Follow RAII-style resource management: create resources in initialization or when needed and free them in the destructor or when no longer required.
• Use try…finally blocks around temporary resource creation.
• Monitor GDI handle usage (Windows Task Manager Columns) and fix leaks by ensuring DeleteObject/Free are called.
• Example:

  
  bmp := TBitmap.Create; try // use bmp finally bmp.Free; end; 

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7. Unexpected behavior when layering or using transparency

Symptoms:

• Semi-transparent areas render darker or lighter than expected.
• Overlapping semi-transparent shapes produce incorrect composite results.
• Transparent hit-test issues.

Common causes:

• Incorrect alpha premultiplication.
• Drawing order assumptions violating correct blending.
• Using per-pixel alpha without proper memory format (e.g., premultiplied BGRA).

Solutions:

• Use premultiplied alpha format for offscreen bitmaps when blending multiple layers.
• Draw from back to front and composite correctly.
• When using Windows layered windows or SetLayeredWindowAttributes, ensure the pixel format matches expectations (ARGB premultiplied).
• Test on different backends (GDI vs. GDI+) to see differences.

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8. Compilation or compatibility issues between Delphi/Lazarus versions

Symptoms:

• Unit or symbol not found errors when compiling.
• Runtime exceptions due to changes in RTL/VCL/LCL between versions.
• Component behaves differently across platforms (Windows vs. Linux).

Common causes:

• API/namespace changes between framework versions.
• Deprecated methods or conditional defines missing for cross-platform code.
• Compiler/linker differences affecting resource inclusion.

Solutions:

• Check the component’s documentation for supported Delphi/Lazarus versions.
• Use conditional compilation to handle differences:

  
  {$IFDEF FPC} // Lazarus-specific code {$ELSE} // Delphi-specific code {$ENDIF} 

• Test on target platforms and use virtualization/CI to catch regressions early.
• Update third-party component packages to the latest compatible releases.

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9. Debugging tips and tools

• Use logging around paint and mouse events to trace unexpected calls.
• Break into the paint routine and step through drawing to see where artifacts originate.
• Monitor GDI handles and memory usage to detect leaks.
• Test with simplified shapes to isolate whether complex geometry or integration is the problem.
• Use external tools: Process Explorer, Spy++ (Windows) to watch messages and window regions; graphics profilers if using GPU-accelerated drawing.

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10. Quick checklist for resolving a problem

1. Reproduce the issue consistently in a minimal test project.
2. Disable optimizations (caching, double buffering) to find the root cause.
3. Check DPI and scaling behavior on different displays.
4. Verify hit-testing logic uses actual shape regions, not bounding boxes.
5. Ensure resources (bitmaps, regions) are created/freed correctly.
6. Confirm drawing uses correct alpha premultiplication and blending order.
7. Test against different backends (GDI vs GDI+) and frameworks (Delphi vs Lazarus).

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If you give me a specific symptom, code sample, or Delphi/Lazarus version, I can provide targeted fixes and a short example project to reproduce and solve the issue.