Visual expressiveness in QML isn’t about “designer tricks,” but about precise control over graphical primitives. Here it’s revealed how to manage color, images, and effects so that the interface looks modern, works faster, and doesn’t overload the system. You’ll discover why developers rely specifically on these tools.
3 color models will be covered, scalable graphics without distortion, as well as the basics of Canvas and ShaderEffect — those very mechanisms that allow achieving effects “like in native applications.”
Skipping this chapter means continuing to write interfaces “the old way,” while the market has long moved forward.
This chapter includes ready-to-use code examples.
Chapter Self-Check
Why does the BorderImage element split an image into nine parts?Answer
Correct answer: This allows creating scalable graphics without corner distortion — central parts stretch while corners remain unchanged, which is critical for elements with rounded edges.
Why is it recommended to use ready-made gradient images instead of programmatic creation on mobile devices?Answer
Correct answer: Creating gradients requires significant CPU resources, which leads to increased battery drain and reduced performance on mobile devices.
What will happen if you don’t check the status property of the Image element when loading an image from the internet?Answer
Correct answer: The user will see an empty window without any indication of the loading process, and in case of an error won’t receive notification about the problem, creating the impression of a non-working application.
How do shaders differ from regular drawing code and why are they faster?Answer
Correct answer: Shaders execute on the GPU (graphics card) rather than on the CPU, and are written in the GLSL language, which provides parallel pixel processing and multiplies the speed of graphics operations.
Why are the save() and restore() methods used for the drawing context in the Canvas element?Answer
Correct answer: Canvas has a single drawing context, and its state changes with transformations; save() preserves the current state, and restore() restores it, preventing unwanted effects from previous operations.
What is the transformOrigin property used for and what value does it have by default?Answer
Correct answer: It defines the point around which transformations (rotation, scaling) are performed; by default it’s the center of the element, but it can be changed to any other point.
Why is the smooth: true property important when transforming images?Answer
Correct answer: It enables smoothing during scaling and rotation, preventing jagged edges and pixelation, making the image visually high-quality.
How can you create a semi-transparent Rectangle element in QML?Answer
Correct answer: Set the opacity property with a value from 0 to 1, where 0 is full transparency, 1 is full opacity; for example, opacity: 0.5 will create a semi-transparent element.
What role does the onPaint property play in the Canvas element?Answer
Correct answer: It’s a handler analogous to the paintEvent() event in Qt Widgets, inside which the algorithm for drawing graphical primitives on the canvas is implemented in JavaScript.
What will happen if you try to create multiple transformations without using a list in the transform property?Answer
Correct answer: You can only specify one transformation; to apply multiple (Scale, Rotation, etc.), you must use a list in square brackets with comma-separated elements.
Why is the Image element used in ShaderEffect made invisible (visible: false)?Answer
Correct answer: It serves only as a data source for the shader (texture), and the processed ShaderEffect result is displayed; showing the original would be redundant and would create duplication.
What’s the difference between using scale/rotation properties and Scale/Rotation transformation elements?Answer
Correct answer: Properties provide simplicity for basic cases, while transformation elements give finer control (for example, specifying the origin point for each transformation separately).
What three types of gradients are available in modern QML and how do they differ?Answer
Correct answer: Linear (transition between points along a line), radial (from center to edges in a circle), and conical (around a central point); each creates its own unique visual effect.
Why is the beginPath() method used before drawing in Canvas and closePath() after?Answer
Correct answer: beginPath() starts a new graphics path, and closePath() completes it, connecting the last point with the first; this is necessary for correct formation of closed figures.
What does the “2d” argument mean in the getContext() method of the Canvas element?Answer
Correct answer: This indicates that drawing will be performed on a plane using two coordinates X and Y; the context provides a 2D API for drawing graphical primitives.
Practical Assignments
Easy Level
Image Gallery with Transformations
Create a QML application displaying three images in a row, each with a different transformation: the first — scaled down to 70%, the second — rotated 45 degrees, the third — semi-transparent (opacity 0.6). Use the Row element for placement and apply different background colors for each image.
Hints: Use the Row element for horizontal placement. Set scale, rotation, and opacity properties accordingly. For background, wrap each Image in a Rectangle with a specified color. Don’t forget smooth: true for quality display.
Medium Level
Scalable Button with Gradient
Create a custom button using BorderImage or gradient that scales correctly when resizing. Add centered text and implement a visual reaction to mouse hover (color/gradient change). The button should have rounded corners and not distort when width changes from 80 to 200 pixels.
Hints: Use BorderImage with correct border values or Rectangle with Gradient. Apply MouseArea to track hovering. For text, use Text with anchors.centerIn. Create a state property (states) for visual changes on hover. You can create a button image in a graphics editor or use a gradient.
Hard Level
Animated Canvas with Interactive Gradient
Create an application with a Canvas element drawing an animated geometric pattern (spiral, mandala, or abstract figure). Add three sliders to control pattern parameters in real-time (number of elements, rotation angle, color/gradient). Use Timer for automatic animation or make it redraw on slider changes.
Hints: In onPaint, implement a drawing algorithm in JavaScript (you can adapt the pattern example from the chapter). Use three Sliders for parameters and bind their values to Canvas properties. Call the requestPaint() method to redraw when parameters change. Experiment with createLinearGradient() or createRadialGradient() for dynamic color changes. Use loops and mathematical functions to create patterns.
💬 Join the Discussion!
Dove into the world of QML graphics? Figured out the difference between Image and BorderImage, understood why shaders work faster, and gradients can “eat” battery?
Maybe you created your own unique effect on Canvas or encountered interesting transformation features? Share your experiments, visual discoveries, or ask questions about practical application of graphical elements!
Help other readers master the art of creating beautiful interfaces in QML! 🎨✨