Fix note list rendering at fractional display scaling

[Shriram-Vasudevan]

Summary

• set Qt high-DPI scale factor rounding to pass through before creating the application
• create note-list delegate paint buffers with the owning widget/window device-pixel ratio
• use logical buffer geometry while painting cropped row backgrounds/labels, so Windows fractional scaling does not mix physical pixmap pixels with logical item rects

Fixes #164.

Verification

• git diff --check
• c++ -std=c++17 -fsyntax-only -include arm_acle.h ... src/notelistdelegate.cpp src/notelistdelegateeditor.cpp against locally installed Qt 6.9.2 headers
• syntax-only check for QGuiApplication::setHighDpiScaleFactorRoundingPolicy(...) against Qt 6.9.2 headers

I could not run the full CMake build locally because cmake is not installed in this environment, and clang-format is also unavailable locally.

[zjeffer]

@nuttyartist Do we have an AI-policy? Personally I'm not a big fan of these fully AI-generated PRs, I mean the OP didn't even bother to let the AI install cmake:

I could not run the full CMake build locally because cmake is not installed in this environment, and clang-format is also unavailable locally.

I recently added one in a personal repo if you want an example: https://github.com/zjeffer/split-monitor-workspaces/blob/main/CONTRIBUTING.md

[Shriram-Vasudevan]

I installed the missing local build tooling and pushed follow-up commit 404e7cf with the clang-format adjustments found by the repo format gate.

Verification now run locally:

• /opt/homebrew/opt/llvm/bin/clang-format -style=file --dry-run --Werror --color=false src/main.cpp src/notelistdelegate.cpp src/notelistdelegateeditor.cpp src/utils.h -> passed
• find src/ -iregex '.*\.\(cpp\|h\|mm\)$' -print0 | xargs -n 1 -0 /opt/homebrew/opt/llvm/bin/clang-format -style=file --dry-run --Werror --color=false -> passed
• cmake . --warn-uninitialized --warn-unused-vars -G Ninja -B build -DCMAKE_BUILD_TYPE=debug -DCMAKE_PREFIX_PATH="$(brew --prefix qt@6)" -DPRO_VERSION=OFF -> passed with Qt 6.9.2
• cmake --build build -> passed
• ctest --test-dir build --output-on-failure -> no tests registered
• git diff --check -> passed

The build produced only existing/project-wide Qt deprecation and macOS deployment-target linker warnings, not errors in the touched note-list files.

[nuttyartist]

Thanks for the fix. I left a few inline suggestions for the remaining DPR source-rect issue. The helper approach looks good; the main thing is making the later drawPixmap source rectangles use the same coordinate space as the DPR pixmaps.

[nuttyartist]

This helper will also need QRect for converting logical source rects to pixmap/device-pixel source rects.

Suggested change

	#include <QPixmap>
	#include <QPixmap>
	#include <QRect>

[nuttyartist]

Could we pair the DPR pixmap allocator with a small source-rect conversion helper? Painting into the pixmap stays in logical coordinates, but QPainter::drawPixmap(..., sourceRect) reads sourceRect in pixmap/device pixels.

Suggested change

	inline QPixmap makeDevicePixelRatioPixmap(const QSize &logicalSize, const QWidget *widget)
	{
	const qreal scale = devicePixelRatioForWidget(widget);
	QPixmap pixmap(logicalSize * scale);
	pixmap.setDevicePixelRatio(scale);
	return pixmap;
	}
	inline QPixmap makeDevicePixelRatioPixmap(const QSize &logicalSize, const QWidget *widget)
	{
	const qreal scale = devicePixelRatioForWidget(widget);
	QPixmap pixmap(logicalSize * scale);
	pixmap.setDevicePixelRatio(scale);
	return pixmap;
	}
	inline QRect devicePixelRatioPixmapSourceRect(const QRect &logicalRect, const QPixmap &pixmap)
	{
	const qreal scale = pixmap.devicePixelRatio();
	const QRectF scaledRect(logicalRect.x() * scale, logicalRect.y() * scale, logicalRect.width() * scale, logicalRect.height() * scale);
	return scaledRect.toAlignedRect();
	}

[nuttyartist]

Once this buffer is DPR-aware, the drawPixmap(..., buffer, QRect{...}) calls lower in paintBackground() still need to convert their source rects before drawing. One compact way is to add this near the draw section and route those calls through it:

auto drawBuffer = [&buffer, painter](const QRect &targetRect, const QRect &sourceRect) {
    painter->drawPixmap(targetRect, buffer, utils::devicePixelRatioPixmapSourceRect(sourceRect, buffer));
};

Then replace each painter->drawPixmap(..., buffer, QRect{...}) in this function with drawBuffer(..., QRect{...}). The same pattern applies to the animated label buffer in paintLabels().

[nuttyartist]

Same coordinate-space issue here: the buffer is now DPR-aware, but the later source rect passed to drawPixmap() is still logical. The final draw should convert that source rect first, for example:

auto rowHeight = rect().height();
const QRect sourceRect{ 0, bufferSize.height() - rowHeight, rect().width(), rowHeight };
painter->drawPixmap(rect(), buffer, utils::devicePixelRatioPixmapSourceRect(sourceRect, buffer));

[nuttyartist]

@zjeffer Not really yet, and I agree, we should have. Yours seems reasonable enough, I'll add them to the repo.

@Shriram-Vasudevan Thanks for your PR.
I've added some comments using GPT 5.5, please look at them.
Can you please share before and after screenshots after you make changes?