maui-graphics-drawing
Guidance for custom drawing with Microsoft.Maui.Graphics, GraphicsView, canvas drawing operations, shapes, paths, text rendering, image drawing, shadows, clipping, and canvas state management. USE FOR: "custom drawing", "GraphicsView", "canvas drawing", "draw shapes", "draw path", "draw text", "I...
Full skill instructions
| Issue | Fix |
|---|---|
| Nothing draws on screen | Ensure Drawable is set on GraphicsView and the control has non-zero HeightRequest/WidthRequest |
| State bleeds between shapes | Wrap isolated sections in SaveState() / RestoreState() pairs |
| Shadows stick to later draws | Call canvas.SetShadow(SizeF.Zero, 0, null) after drawing the shadowed element |
| Clipping never resets | Clipping is cumulative per frame — use SaveState/RestoreState around clip regions |
| UI freezes during drawing | Never do I/O, network, or heavy computation inside Draw() — it runs on the UI thread |
⚠️ Unpaired SaveState/RestoreState causes state leaks across draw calls.
// ✅ Correct — isolated state
canvas.SaveState();
canvas.StrokeColor = Colors.Red;
canvas.StrokeSize = 6;
canvas.DrawRectangle(10, 10, 80, 80);
canvas.RestoreState();
// Stroke reverts to previous values
// ❌ Wrong — state leaks to everything drawn after
canvas.StrokeColor = Colors.Red;
canvas.StrokeSize = 6;
canvas.DrawRectangle(10, 10, 80, 80);
// Every subsequent shape is now red with size 6
Saves/restores: stroke, fill, font, shadow, clip, and transforms. Nest calls for layered isolation.
// ✅ Correct — queue a redraw
graphicsView.Invalidate();
// ❌ Wrong — never call Draw() directly
myDrawable.Draw(canvas, rect);
Invalidate() queues a redraw; the framework calls IDrawable.Draw on the next frame.Invalidate() in a tight loop — batch state changes, then invalidate once.Draw() fast — pre-compute paths and data outside the draw method; Draw() is called on every frame.PathF objects — create them once, store as fields, draw repeatedly.MeasureFirstItem-style thinking — if drawing many identical items, calculate dimensions once.new PathF() inside Draw() when the path doesn't change.// ✅ Pre-computed path (field)
private readonly PathF _starPath = BuildStarPath();
public void Draw(ICanvas canvas, RectF dirtyRect)
{
canvas.FillPath(_starPath);
}
// ❌ Allocating every frame
public void Draw(ICanvas canvas, RectF dirtyRect)
{
var path = new PathF();
// ...build path every frame...
canvas.FillPath(path);
}
Shadows apply to all subsequent draws until explicitly removed. Clips accumulate and can only be undone with RestoreState():
// ✅ Shadow: remove after use
canvas.SetShadow(new SizeF(5, 5), 4, Colors.Gray);
canvas.FillRectangle(20, 20, 100, 60);
canvas.SetShadow(SizeF.Zero, 0, null); // ← must remove
// ✅ Clip: isolate with SaveState/RestoreState
canvas.SaveState();
canvas.ClipRectangle(20, 20, 100, 100);
canvas.FillRectangle(0, 0, 200, 200); // clipped
canvas.RestoreState(); // clip removed
// ❌ Clip persists — everything after is also clipped
canvas.ClipRectangle(20, 20, 100, 100);
canvas.FillEllipse(150, 150, 50, 50); // unintentionally clipped!
// ✅ Properties then draw
canvas.StrokeColor = Colors.Blue;
canvas.DrawRectangle(10, 10, 100, 50);
// ❌ Setting after draw has no effect on previous shape
canvas.DrawRectangle(10, 10, 100, 50);
canvas.StrokeColor = Colors.Blue;
| Need | Approach |
|---|---|
| Simple shapes / static graphics | Single IDrawable, draw in Draw() |
| Animated graphics | Update state externally, call Invalidate() from timer/animation |
| Complex layered scene | Multiple SaveState/RestoreState blocks, or separate drawables |
| Hit testing on drawn elements | Track shape bounds manually — GraphicsView has no built-in hit test on drawn content |
| Platform-specific rendering | Use handlers/platform code; Microsoft.Maui.Graphics is cross-platform only |
GraphicsView has Drawable set and non-zero sizeDraw() is fast — no I/O, no heavy allocationsSaveState() has a matching RestoreState()SetShadow(SizeF.Zero, 0, null) after useSaveState/RestoreState blocksInvalidate() used instead of calling Draw() directly
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