fix(spectrum): FFT line width slider produces visible pixel-width line (#2705). Principle III.#2706
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#2705). Principle III. The GPU triangle-strip line in SpectrumWidget computed its perpendicular normal half-width in NDC X units only (`m_fftLineWidth / width()`). The FFT trace is predominantly horizontal between adjacent bins, so the perpendicular normal almost always points in the Y direction. The spectrum viewport is `width × specH`, so the effective Y offset in screen pixels was `m_fftLineWidth * specH / (2 * width())` — a fraction of a pixel for any wide-screen panadapter (e.g. ~0.39 px at slider max on a 1920×300 viewport). The fill gradient drew right up to the line's vertex Y, masking the missing line and making the slider appear inert across all platforms. Compute the normal in pixel space using both viewport dimensions (`wPx`, `hPx = specH`), scale by `m_fftLineWidth`, then convert back to NDC per-axis. The slider's numeric label is now a true pixel measurement, honoring the user-visible label per Principle III. Blast radius: hook reported risk_score=0.334 with 11 high-risk callers (MainWindow::buildUI, wirePanadapter, etc.) — all reach SpectrumWidget only through its public interface, which is unchanged. Edit is local vertex-math arithmetic inside one block of `renderGpuFrame`; no signature, member, or observable behavior change beyond the slider acting as labeled. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Tested and working on macOS.
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…nciple III. The earlier fix in 44163fc (PR #2706) for issue #2705 patched only the QRhi/GPU render path in renderGpuFrame(). The parallel software path in drawSpectrum() hardcoded a 1.5 px pen and ignored m_fftLineWidth, so the Display → "FFT Line:" slider was a no-op for any user whose build lacked GPU acceleration (e.g., Windows builds where the AETHER_GPU_SPECTRUM CMake block was disabled because Qt6GuiPrivate was not found at configure time — confirmed in support-bundle-20260516-005340 which contains neither the QRhi success nor failure log line). Fix in src/gui/SpectrumWidget.cpp::drawSpectrum: - Use m_fftLineWidth on a cosmetic QPen so the requested pixel width survives high-DPI scaling on Windows. - Skip the line draw entirely when m_fftLineWidth <= 0 ("Off"), mirroring the GPU path's behavior at L5065. - Apply to both the heat-map and solid-fill branches. Also call update() from setFftLineWidth() so the slider takes effect immediately even when no FFT stream is flowing (matches the pattern in setFftFillAlpha / setFftFillColor that already call markOverlayDirty()). Honors Principle III: the UI label "FFT Line:" on the Display menu is the user-facing contract; making the slider inert on one of two render paths breaks that contract. Blast radius: risk_score=0.310, 10 high-risk affected (top: MainWindow::MainWindow, MainWindow::wirePanadapter, MainWindow::buildUI). The seed change is internal to drawSpectrum's rendering branch and setFftLineWidth's repaint trigger; the high-risk callers depend on SpectrumWidget instantiation/wiring, not on the rendering details modified here, so the wide reported surface does not reflect actual behavioral reach. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Fixes #2705
What was changed
fix(spectrum): FFT line width slider produces visible pixel-width line (#2705). Principle III.
Files modified
src/gui/SpectrumWidget.cppGenerated by AetherClaude (automated agent for AetherSDR)