Standardizing on precision

Author: brett-estabrook

Sources/Microcharts.Forms/ChartView.cs

@@ -92,8 +92,8 @@ private void OnPaintCanvas(object sender, SKPaintSurfaceEventArgs e)
         }
 
 
-        double zoomCurScale = 1;
-        double zoomStartScale = 1;
+        float zoomCurScale = 1;
+        float zoomStartScale = 1;
 
         SKPoint zoomStartOrigin = new SKPoint(0, 0);
         SKPoint zoomStartOffset = new SKPoint(0, 0);
@@ -115,45 +115,43 @@ void OnPinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
 
             if (e.Status == GestureStatus.Running)
             {
+                float eScale = (float)e.Scale;
+                SKPoint eScaleOrigin = new SKPoint((float)e.ScaleOrigin.X, (float)e.ScaleOrigin.Y);
+                SKPoint canvasSize = new SKPoint(CanvasSize.Width, CanvasSize.Height);
+
                 // e.Scale is the delta to be applied for the current frame
                 // Calculate the scale factor to be applied.
-                zoomCurScale += (e.Scale - 1) * zoomStartScale;
+                zoomCurScale += (eScale - 1) * zoomStartScale;
                 zoomCurScale = Math.Max(1, zoomCurScale);
                 zoomCurScale = Math.Min(5, zoomCurScale);
 
-
-                SKPoint zoomPanDelta = new SKPoint((float)((e.ScaleOrigin.X - zoomStartOrigin.X) * CanvasSize.Width), (float)((e.ScaleOrigin.Y - zoomStartOrigin.Y) * CanvasSize.Height));
+                SKPoint zoomPanDelta = new SKPoint((eScaleOrigin.X - zoomStartOrigin.X) * CanvasSize.Width, (eScaleOrigin.Y - zoomStartOrigin.Y) * CanvasSize.Height);
 
                 // The ScaleOrigin is in relative coordinates to the wrapped user interface element,
                 // so get the X pixel coordinate.
-                double renderedX = X + zoomStartOffset.X;
-                double deltaX = renderedX / CanvasSize.Width;
-                double deltaWidth = CanvasSize.Width / (CanvasSize.Width * zoomStartScale);
-                double originX = (e.ScaleOrigin.X - deltaX) * deltaWidth;
+                float renderedX = (float)X + zoomStartOffset.X;
+                float deltaX = renderedX / CanvasSize.Width;
+                float deltaWidth = CanvasSize.Width / (CanvasSize.Width * zoomStartScale);
+                float originX = (eScaleOrigin.X - deltaX) * deltaWidth;
 
                 //Console.WriteLine("ScaleOrigin: {0}, {1}", e.ScaleOrigin.X, e.ScaleOrigin.Y);
 
                 // The ScaleOrigin is in relative coordinates to the wrapped user interface element,
                 // so get the Y pixel coordinate.
-                double renderedY = Y + zoomStartOffset.Y;
-                double deltaY = renderedY / CanvasSize.Height;
-                double deltaHeight = CanvasSize.Height / (CanvasSize.Height * zoomStartScale);
-                double originY = (e.ScaleOrigin.Y - deltaY) * deltaHeight;
+                float renderedY = (float)Y + zoomStartOffset.Y;
+                float deltaY = renderedY / CanvasSize.Height;
+                float deltaHeight = CanvasSize.Height / (CanvasSize.Height * zoomStartScale);
+                float originY = (eScaleOrigin.Y - deltaY) * deltaHeight;
 
                 // Calculate the transformed element pixel coordinates.
-                double targetX = zoomStartOffset.X - (originX * CanvasSize.Width) * (zoomCurScale - zoomStartScale);
-                double targetY = zoomStartOffset.Y - (originY * CanvasSize.Height) * (zoomCurScale - zoomStartScale);
-
-                // Apply translation based on the change in origin.
-                zoomTranslation.X = (float)targetX;
-                zoomTranslation.Y = (float)targetY;
-
+                zoomTranslation.X = zoomStartOffset.X - (originX * CanvasSize.Width) * (zoomCurScale - zoomStartScale);
+                zoomTranslation.Y = zoomStartOffset.Y - (originY * CanvasSize.Height) * (zoomCurScale - zoomStartScale);
 
+                // Calculate final translation with pan, and clamp the whole thing
                 SKPoint final = zoomTranslation + zoomPanDelta;
-                final.X = Math.Min(Math.Max(final.X, -CanvasSize.Width * (float)(zoomCurScale - 1)), 0);
-                final.Y = Math.Min(Math.Max(final.Y, -CanvasSize.Height * (float)(zoomCurScale - 1)), 0);
+                final.X = Math.Min(Math.Max(final.X, -CanvasSize.Width * (zoomCurScale - 1)), 0);
+                final.Y = Math.Min(Math.Max(final.Y, -CanvasSize.Height * (zoomCurScale - 1)), 0);
 
-
                 axisChart.XForm.Scale = (float)zoomCurScale;
                 axisChart.XForm.Offset = final;
                 InvalidateSurface();