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Manual Render Control

Overview​

SciChart.JS provides fine-grained control over the rendering loop through the wasmContext object. This is useful for performance optimization, synchronizing multiple charts, or integrating with external animation systems.

API Reference​

wasmContext.TSRRequestDraw()​

Triggers an immediate draw of all charts associated with this wasmContext. Use this when you need to force a render right away, bypassing the normal frame scheduling.

wasmContext.TSRSetDrawRequestsEnabled(enabled: boolean)​

Controls the automatic engine draw loop:

  • true - Enables the engine's automatic rendering loop (default behavior)
  • false - Disables automatic rendering; you must manually call TSRRequestDraw() to update charts

This is called internally during chart creation with the opposite of the disableEngineLoop option. For example, if you create a chart with disableEngineLoop: true, the engine calls TSRSetDrawRequestsEnabled(false).

wasmContext.TSRRequestCanvasDraw(canvasId: string)​

Marks a specific canvas for redraw on the next frame. This is called internally by invalidateElement(). The actual draw occurs:

  • On the next call to TSRRequestDraw(), or
  • On the next animation frame if the engine loop is enabled

Scope of Effect​

All three methods affect all charts sharing the same wasmContext. When you have multiple charts using a shared WebAssembly context, these calls control rendering for the entire group.

Architecture Diagram​

Important Considerations​

Canvas Resize Behavior​

The canvas is cleared and requires a full redraw whenever it is resized. This has important implications:

Key Point: If your CSS does not specify an absolute size for the chart container div, the browser will likely trigger a resize event immediately after your initialization code yields control. This means:

  1. Any manual draw you perform during initialization may be immediately invalidated
  2. The chart will appear blank until the next render cycle

For immediate rendering after init:

// Option 1: Use absolute sizing in CSS
// .chart-container { width: 800px; height: 600px; }

// Option 2: Wait for resize to settle
const { sciChartSurface, wasmContext } = await SciChartSurface.create(divId);
// Use requestAnimationFrame to ensure layout is complete
requestAnimationFrame(() => {
    wasmContext.TSRRequestDraw();
});

For manual render control:

const { sciChartSurface, wasmContext } = await SciChartSurface.create(divId, {
    disableEngineLoop: true  // Calls TSRSetDrawRequestsEnabled(false)
});

// ... modify chart data/properties ...

// Manually trigger render when ready
wasmContext.TSRRequestDraw();

For batched updates:

// Disable automatic rendering temporarily
wasmContext.TSRSetDrawRequestsEnabled(false);

// Perform multiple updates without intermediate renders
series1.appendRange(xValues1, yValues1);
series2.appendRange(xValues2, yValues2);
axis.visibleRange = new NumberRange(0, 100);

// Single render after all updates
wasmContext.TSRRequestDraw();

// Re-enable automatic rendering
wasmContext.TSRSetDrawRequestsEnabled(true);