Mastering the Control Paint Event

Drawing & Painting in Wisej.NETModule 2The samples are ready before the course is: the module outline is on learnwisej.com, and the lessons, the knowledge checks and the hands-on labs follow when it launches — free, with an AI tutor in every lesson.

See the outline

The inline paint handler from Module 1 is retired in favour of a reusable TelemetryGauge control: ring, threshold zones, needle, numeric value and caption, with all of its coordinate maths in a pure GaugeGeometry helper. The three remaining Module 1 surfaces - Label + ProgressBar, a Wisej.Web.Canvas and an off-screen Bitmap in a PictureBox - stay on the operations page under the gauges, so the same reading can still be compared across surfaces. Surface 2, the inline Paint handler, is now the TelemetryGauge control itself.

This folder is the complete application at this point in the course, with its own solution and port.

The source of this sample

iceteagroup/LearnWisej-SamplesDrawing and Painting Course/Module 2

Browse this folder on GitHub

Or clone it: git clone https://github.com/iceteagroup/LearnWisej-Samples.git — then open VisualOperationsStudio.slnx in Visual Studio and press F5.

Run it

cd "Drawing and Painting Course/Module 2/VisualOperationsStudio"
dotnet run -f net10.0 --urls http://localhost:6002

Open http://localhost:6002. In Visual Studio, open VisualOperationsStudio.slnx and press F5.

What to try

Action	Expected result
Press Take reading	The spindle gauge moves; the other two setters compare and return early, so the status line reports Repaints this request: 1.
Press it until the scripted 132 % arrives	The value is clamped to 100 %, the status line names both numbers, and the gauge turns red because 100 ≥ CriticalThreshold.
Watch the panel on the right	The same three numbers as text. Each gauge also publishes its reading through AccessibleDescription.
Narrow the browser until a gauge is under 60 px wide	GaugeGeometry.Measure returns an empty layout and nothing is drawn — no exception, no half-drawn ring.
Resize the browser	All three repaint, because every coordinate a painted control uses comes from its own size.
In VisualOperationsPage.ConfigureGauge, set gauge.Maximum below gauge.Minimum	The range degrades to an empty grey track instead of throwing.

Notes for anyone extending the gauge

• A custom painted control must subscribe to Paint. Overriding OnPaint alone is not enough in Wisej.NET 4.1 — the event is never raised — and a bare Wisej.Web.Control never paints at all, which is why TelemetryGauge derives from Panel.
• It must also Invalidate() on Resize, or a docked control that receives its size after construction never produces a first picture.
• Managed.System.Drawing has no Graphics.Save/Restore; BeginContainer/EndContainer is the pair, and Pen has EndCap but no StartCap.