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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Use Qt Quick Shapes when your content is best described as paths, fills, gradients, and strokes in the Qt Quick scene. Choose Canvas when you need imperative JavaScript drawing through a Context2D API, especially for pixel operations or image output. Neither is universally faster: Canvas updates can upload textures, while changing Shape geometry can trigger CPU-side retriangulation. Measure your actual workload on its target backend and hardware.
How Canvas and Shapes differ
These APIs solve related drawing problems with different models. Canvas is a drawing surface that you paint with JavaScript commands. Shapes describes path geometry declaratively, then renders that geometry as part of the Qt Quick scene.
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| Aspect | Canvas | Qt Quick Shapes |
|---|---|---|
| Drawing model | Imperative JavaScript commands using Context2D, commonly in response to the paint signal. |
Declarative paths, with fills and strokes configured through Shape and ShapePath. |
| Best-fitting content | Pixel-oriented drawing, referenced images, image saving, and drawing expressed as a sequence of commands. | Vector-like path geometry such as lines, curves, arcs, fills, gradients, and strokes. |
| What changes can cost | With accelerated graphics APIs, updating a Canvas image leads to a texture upload. | Changing path elements or relevant properties can require CPU-side retriangulation. |
| Module import | import QtQuick |
import QtQuick.Shapes |
When Canvas is the better fit
Qt 6.12’s Canvas QML type exposes a Context2D object and supports straight and curved lines, shapes, graphs, referenced images, text, colors, shadows, gradients, patterns, and pixel operations. It can also save output as an image or serialize it to a URL. Those capabilities make Canvas a natural choice when the drawing logic itself is a sequence of commands or when code needs Context2D-style pixel access. See the Qt 6.12 Canvas QML Type reference.
Canvas provides markDirty() and requestPaint() to schedule updates. Its documented render target is Canvas.Image, the only target Qt documents as supported by all Qt Quick backends; that target also supports background-thread rendering. The documented default render strategy is Canvas.Immediate.
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Account for redraw behavior
Qt cautions against large canvases, frequent updates, and animation when using Canvas.Image: on accelerated graphics APIs, each update leads to a texture upload. This is a workload warning, not a numeric cutoff or proof that every Canvas implementation will perform poorly. Limit the area and frequency of redraws where practical, then profile if updates are central to the experience.
Canvas is QML, not a browser canvas
Browser-oriented Canvas code does not transfer unchanged. Qt’s guidance is to replace DOM calls with QML bindings or Canvas methods, HTML event handlers with QML input items, and timer calls with Qt mechanisms such as Timer or requestAnimationFrame(). For more demanding painting, Qt suggests considering QQuickPaintedItem with C++ QPainter instead of JavaScript and Context2D.
When Qt Quick Shapes is the better fit
Shapes is suited to content that can be expressed as paths in the Qt Quick scene. Its path operations include move-to, line-to, quadratic and cubic curves, and arcs. The module also provides higher-level path elements for text and SVG-style path descriptions. An SVG-style path element is a compact way to describe a path; it does not provide full SVG support. See the Qt Quick Shapes QML Types reference.
With the default hardware-accelerated RHI backend, Shape converts paths into triangles for rendering rather than software-rasterizing the path before display. Geometry generation still takes CPU work: changes to path elements, their properties, or certain Shape properties can cause affected paths to be triangulated again. Qt says declarative Shape data can be cached, and a change to one ShapePath need only reprocess that path. A changing path may therefore still be appropriate, depending on the rest of the scene and the workload. See the Qt 6.12 Shape QML Type reference.
Keep the scene structure purposeful
Each Shape item has scene-graph costs. Qt advises using one Shape with multiple ShapePath elements rather than many separate Shape items when the content can be grouped that way. Grouping is not a reason to combine unrelated content indiscriminately, but it is worth considering when separate items add no useful structure.
Choose a renderer for curve quality needs
The general renderer flattens curves into short line segments, which can become visible at high zoom. Shape.CurveRenderer instead solves curves on the GPU and includes built-in antialiasing. Qt notes an additional performance cost on first rendering; later scaling and transforms do not add extra cost according to its 2D Graphics overview. The Shape reference identifies properties including preferredRendererType as available since Qt 6.6, so check the Qt version when using version-specific options.
Which is faster: Canvas or Shapes?
There is no universal winner or documented break-even threshold in the Qt 6.12 references. The costs differ: a Canvas update may require a texture upload, while changing Shape path data may require CPU retriangulation. The balance depends on how much is drawn, how often it changes, the number and organization of scene items, the rendering backend, and the target hardware.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsQt’s general performance guidance says, “60 FPS means that there is approximately 16 milliseconds between each frame in which processing can be done, which includes the processing required to upload the draw primitives to the graphics hardware.” That is a general frame-budget guideline, not a Canvas-versus-Shapes benchmark. See Qt Quick performance considerations.
Profile a representative interaction
- Reproduce the real drawing area, scene structure, and update pattern in the app.
- Measure on the Qt version, rendering backend, and hardware you intend to support.
- Include the costly interaction—for example, repeated Canvas repainting or animated Shape path properties—not only the initial static render.
- Compare frame behavior and responsiveness with the same visual result, then choose the API that meets the app’s needs.
Qt’s Shapes documentation specifically warns that animating relevant Shape or path properties can affect performance on less powerful systems. That caution supports measurement; it does not establish that Shapes is slower than Canvas.
A practical decision checklist
- Choose Canvas if imperative JavaScript drawing, Context2D pixel operations, image loading, image saving, or
toDataURL()is central to the feature. - Choose Shapes if paths and ShapePath properties describe the content clearly and the result belongs naturally in the Qt Quick scene.
- For frequent changes, consider the specific cost on each side: Canvas image uploads versus Shape path retriangulation. Profile rather than assuming either is cheaper.
- For many paths, consider multiple ShapePath elements in fewer Shape items, while keeping the scene organized around actual content.
- For curves viewed at high zoom, weigh the general renderer’s line-segment flattening against CurveRenderer’s first-render cost and curve quality.
This comparison follows the Qt 6.12 documentation. Canvas is in QtQuick, Shapes is in QtQuick.Shapes, and version-specific properties and performance behavior should be checked against the Qt version and rendering backend used by the project.
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