Core - Keep small LEDs addressable at reduced render scales

Sample each LED from its unsnapped absolute boundary instead of the
render-grid-aligned AbsoluteRectangle, ensuring at least one pixel and
clamping to the texture. Also apply the saved render scale at startup.

src/Artemis.Core/RGB.NET/SKTexture.cs

@@ -29,19 +29,32 @@ public sealed class SKTexture : ITexture, IDisposable
         foreach (ArtemisDevice artemisDevice in devices)
         {
             foreach (ArtemisLed artemisLed in artemisDevice.Leds)
-            {
+                _ledRects[artemisLed.RgbLed] = CreateSampleRect(artemisLed.RgbLed.AbsoluteBoundary, scale, width, height);
-                _ledRects[artemisLed.RgbLed] = SKRectI.Create(
-                    (int)(artemisLed.AbsoluteRectangle.Left * RenderScale),
-                    (int)(artemisLed.AbsoluteRectangle.Top * RenderScale),
-                    (int)(artemisLed.AbsoluteRectangle.Width * RenderScale),
-                    (int)(artemisLed.AbsoluteRectangle.Height * RenderScale)
-                );
-            }
         }
     }
 
     #endregion
 
+    private static SKRectI CreateSampleRect(Rectangle boundary, float scale, int width, int height)
+    {
+        (int left, int right) = ScaleSpan(boundary.Location.X, boundary.Size.Width, scale, width);
+        (int top, int bottom) = ScaleSpan(boundary.Location.Y, boundary.Size.Height, scale, height);
+        return new SKRectI(left, top, right, bottom);
+    }
+
+    private static (int Start, int End) ScaleSpan(float location, float size, float scale, int max)
+    {
+        float start = location * scale;
+        float end = (location + size) * scale;
+        if (end <= 0 || start >= max)
+            return (0, 0);
+
+        // Always sample at least one pixel
+        int startPixel = Math.Clamp(start.RoundToInt(), 0, max - 1);
+        int endPixel = Math.Clamp(end.RoundToInt(), startPixel + 1, max);
+        return (startPixel, endPixel);
+    }
+
     internal Color GetColorAtRenderTarget(in RenderTarget renderTarget)
     {
         if (_image == null) return Color.Transparent;

src/Artemis.Core/Services/RenderService.cs

@@ -47,6 +47,7 @@ internal class RenderService : IRenderService, IRenderer, IDisposable
         _preferredGraphicsContext.SettingChanged += PreferredGraphicsContextOnSettingChanged;
 
         Utilities.ShutdownRequested += UtilitiesOnShutdownRequested;
+        ApplyRenderScaleMultiplier();
         _surfaceManager = new SurfaceManager(this, GraphicsContext, _targetFrameRateSetting.Value, (float) _renderScaleSetting.Value);
     }
 
@@ -189,9 +190,14 @@ internal class RenderService : IRenderService, IRenderer, IDisposable
         _surfaceManager.UpdateTargetFrameRate(_targetFrameRateSetting.Value);
     }
 
-    private void RenderScaleSettingOnSettingChanged(object? sender, EventArgs e)
+    private void ApplyRenderScaleMultiplier()
     {
         RenderScale.SetRenderScaleMultiplier((int) (1 / _renderScaleSetting.Value));
+    }
+
+    private void RenderScaleSettingOnSettingChanged(object? sender, EventArgs e)
+    {
+        ApplyRenderScaleMultiplier();
         _surfaceManager.UpdateRenderScale((float) _renderScaleSetting.Value);
     }