Fix viewport scaling for high DPI displays - geometry now properly fitted and centered

[Copilot]

Problem

On high DPI displays (1.5x, 2x scaling, etc.), the viewport was not correctly fitting or centering geometry. Objects would appear smaller than expected, and zoom-to-extents would fail to properly frame the content. This made the viewport difficult to use on modern high-resolution displays.

Root Cause

The viewport code was inconsistently mixing physical pixel dimensions (RenderWidth/RenderHeight) with logical dimensions (Width/Height). On high DPI displays, these differ significantly:

• Logical dimensions (Width/Height): Control size in logical pixels (e.g., 800×600)
• Physical dimensions (RenderWidth/RenderHeight): Actual framebuffer size scaled by DPI (e.g., 1600×1200 on 2×)

The orthographic projection, zoom calculations, and coordinate conversions were using physical dimensions, causing:

1. View frustum to be 2× too large in world space, making objects appear 2× smaller
2. Zoom-to-extents to divide by the wrong dimensions, resulting in incorrect zoom levels
3. Mouse coordinates to be incorrectly transformed, breaking interaction

Solution

Changed the viewport to consistently use logical dimensions throughout the rendering pipeline:

Files Modified

• VeldridDriver_Draw.cs: Orthographic projection, grid, and axes rendering now use Width/Height
• VeldridDriver_Public.cs: zoomExtents() zoom calculation now uses logical dimensions
• VeldridDriver_Conversions.cs: WorldToScreen() and ScreenToWorld() conversions use logical dimensions
• VeldridDriver_Handlers.cs: Mouse coordinates no longer scaled by LogicalPixelSize

Mathematical Example

For world space geometry with bounds 0-1000 units:

Before (2× DPI):

zoomLevel = 1000 / 1600 = 0.625  // Too zoomed out!

After (2× DPI):

zoomLevel = 1000 / 800 = 1.25    // Correct!

Key Insight

The framebuffer size should only be used when creating GPU resources (swapchain, buffers). For all viewport calculations—projection matrix, zoom levels, coordinate transformations—we must use logical dimensions to maintain consistent behavior across different DPI settings.

Testing

• ✅ All 437 existing unit tests pass
• ✅ No compilation errors or warnings introduced
• ✅ Consistent behavior validated mathematically for 1×, 1.5×, and 2× DPI

Documentation

Added comprehensive documentation:

• VIEWPORT_DPI_FIX.md: Detailed explanation of the problem, solution, and technical implementation
• DPI_SCALING_VALIDATION.md: Mathematical validation with concrete examples for different DPI scenarios

This fix ensures geometry is properly fitted and centered regardless of display DPI scaling, making the viewport usable on modern high-resolution displays.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• invalid.nonexistent.host
  • Triggering command: /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/DesignLibs_GPL/DesignLibs_GPL/artifacts/bin/UnitTests/Debug/net8.0/UnitTests.runtimeconfig.json --depsfile /home/REDACTED/work/DesignLibs_GPL/DesignLibs_GPL/artifacts/bin/UnitTests/Debug/net8.0/UnitTests.deps.json /home/REDACTED/work/DesignLibs_GPL/DesignLibs_GPL/artifacts/bin/UnitTests/Debug/net8.0/testhost.dll --port 45589 --endpoint 127.0.0.1:045589 --role client --parentprocessid 4026 --telemetryoptedin false (dns block)
  • Triggering command: /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/DesignLibs_GPL/DesignLibs_GPL/artifacts/bin/UnitTests/Debug/net8.0/UnitTests.runtimeconfig.json --depsfile /home/REDACTED/work/DesignLibs_GPL/DesignLibs_GPL/artifacts/bin/UnitTests/Debug/net8.0/UnitTests.deps.json /home/REDACTED/work/DesignLibs_GPL/DesignLibs_GPL/artifacts/bin/UnitTests/Debug/net8.0/testhost.dll --port 36073 --endpoint 127.0.0.1:036073 --role client --parentprocessid 5001 --telemetryoptedin false (dns block)
• t1.symcb.com
  • Triggering command: dotnet restore (dns block)
• t2.symcb.com
  • Triggering command: dotnet restore (dns block)
• tl.symcb.com
  • Triggering command: dotnet restore (dns block)
• tl.symcd.com
  • Triggering command: dotnet restore (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Something still isn't quite right about the viewport on scaled high DPI. The geometry is not fitted correctly and the view is not centered.

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