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WGSL · 22 Stage Constraints on Texture Functions
Series contents · Technology map
Stage: Numeric Verification and Kernel Design · Editable example · Storage ID: wgsl-step-22
Goals and learning outcomes
- Choose texture functions appropriate to the stage.
- Distinguish texel and normalized coordinates.
Prerequisites
Continue using the output and records from Unit 21. Before experimenting with Stage Constraints on Texture Functions, preserve the previous inputs and reference outputs.
Key concepts and explanations
Implicit Derivatives
textureSample is a sampling path that uses implicit derivatives. In compute, choose an appropriate function such as textureLoad or textureSampleLevel with an explicit level.
Coordinate Units
textureLoad accesses integer texel coordinates, while filtered sampling uses normalized coordinates. The same numbers do not represent the same position.
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. This document-guided exercise requires your own implementation in a separate localhost or HTTPS project. Check the secure context, navigator.gpu, and adapter request result, and provide an unsupported-environment message. Retain device.lost handling and resource cleanup.
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 texture-kernel.wgsl, obtain the input dimensions using textureDimensions.
- Use textureLoad to read a hand-built 4×4 texture and copy it to a storage output.
- Compare corner and center values with a separate fragment path or an explicit-level sampling path.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| Access method | Integer texel load | Normalized coordinates and linear sampling | Colors are expected to blend at interpolated positions, while texel load reads stored values. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- The 16 texel load results match the original.
- Compute code does not depend on implicit-derivative sampling.
Self-check
- Why is a 0.5 offset needed when converting texel centers to UVs?
- How does fixing the mipmap level affect minification quality?
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Runs actual WebGPU/WGSL. Requires HTTPS/localhost and a supported adapter; unsupported environments display a reason, and CPU results are not presented as GPU results.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: Ping-pong and Data Races · Next: Storage Texture Output