Fix premultiplied-alpha double-multiply crushing filter passband shading (#3294). Principle VIII.#3297
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…ing (#3294). Principle VIII. The GPU overlay compositor (m_ovPipeline) samples premultiplied QImages (Format_RGBA8888_Premultiplied) and overlay.frag emits the texel as-is, but the pipeline blend used srcColor = SrcAlpha — multiplying the already- premultiplied texel by alpha a second time (color × alpha squared). This crushed the passband fill (alpha 35/255: intended 13.7% -> actual 1.9%) below the visible floor while the brighter filter edge lines (alpha 130/255: 51% -> 26%) survived — an exact match for the reported symptom (fill gone, edges still toggle). Correct premultiplied compositing uses srcColor = One. Scope: applied to m_ovPipeline only. The FFT fill/line pipelines (m_fftFillPipeline / m_fftLinePipeline) keep SrcAlpha because they source from non-premultiplied baked vertex colors. The opaque bg quad (alpha=255) is unaffected since SrcAlpha == One at full alpha. Evidence-driven diagnosis: the fill-vs-edge survival ratio matches an alpha-squared double-multiply numerically; shading draw code is byte-for-byte unchanged since v26.5.3, and the symptom is GPU-path-only (software QPainter SourceOver does correct premultiplied math). Blast radius: local edit — single blend-factor enum inside the private initOverlayPipeline() helper (one call site). No public signature, member layout, or cross-TU symbol change; flagged high-betweenness callers (MainWindow construct/wire paths) do not depend on internal GPU blend setup. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Color change goes against previous comment about vertex fills. Holding until I can test. |
jensenpat
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Shader fix for passband contrast.
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…ing (aethersdr#3294). Principle VIII. (aethersdr#3297) ## Summary Fixes aethersdr#3294 ### What was changed Fix premultiplied-alpha double-multiply crushing filter passband shading (aethersdr#3294). Principle VIII. ### Files modified - `src/gui/SpectrumWidget.cpp` ``` src/gui/SpectrumWidget.cpp | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) ``` --- Generated by AetherClaude (automated agent for AetherSDR) --- <sub>🤖 aethersdr-agent · cost: $5.5714 · model: claude-opus-4-8</sub> Co-authored-by: aethersdr-agent[bot] <273844287+aethersdr-agent[bot]@users.noreply.github.com> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
Fixes #3294
What was changed
Fix premultiplied-alpha double-multiply crushing filter passband shading (#3294). Principle VIII.
Files modified
src/gui/SpectrumWidget.cppGenerated by AetherClaude (automated agent for AetherSDR)
🤖 aethersdr-agent · cost: $5.5714 · model: claude-opus-4-8