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OffscreenCanvas · 07 Basic Rendering Validation
Series contents · Technology map
Stage: Control and the First Render · Editable example · Storage ID: offscreen-canvas-step-07
Goals and learning outcomes
- Learning outcome: explain the role of Equivalence. Input cases: The same seed and 10 particles.
- Deliverable: Coordinate arrays and a record of the still image. Explain the rationale for handling Validation scope, linking it to the code.
Prerequisites
Prepare the experiment results for Delta and Long gaps from Unit 6, “Frame Timing”.
Key concepts and explanations
Equivalence
Compare the same initial state to isolate differences in execution context. Fix the seed for random initial values.
Validation scope
Pixel comparisons are affected by environmental differences. Also validate state such as coordinates and colors.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. The existing offscreen-canvas-01·02·03 are starting examples for supported browsers. Implement the new units in main-thread and Worker files in a separate local HTTP project. Check API and context support, and provide a main-thread fallback on a new Canvas if transfer fails. Preserve CSP and isolation, and record performance measurements yourself.
The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.
Practice tasks
- In src/day-7.js in a separate practice project, share the seed and draw function to render a static scene in both modes. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: The same seed and 10 particles. Baseline: 7. Run under the baseline conditions, then record observations and errors in notes/day-7.md.
- Variable: seed; changed value: 11. Run again through the same input path. Deliverable to save: Coordinate arrays and a record of the still image. Hypothesis to check: Matching seeds produce matching layouts, while different seeds produce different layouts. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| seed | 7 | 11 | Matching seeds produce matching layouts, while different seeds produce different layouts. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Required deliverable: Coordinate arrays and a record of the still image. Results are available for both the baseline and changed conditions, allowing comparison of 2 conditions; input values and the execution environment are recorded together.
- The explanation of differences between the two conditions connects both concepts: Equivalence and Validation scope. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Equivalence affect in this exercise? Input cases: The same seed and 10 particles.
- Variable: seed. Hypothesis to check: Matching seeds produce matching layouts, while different seeds produce different layouts. Did the actual results agree with the hypothesis? Explain the evidence in terms of Validation scope.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
An interactive Basic Rendering Validation experiment with cleanup of the resources it uses.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.