bounded rotate works, ish

_examples/text_rotation/main.go

@@ -24,12 +24,12 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 				TextRotationDegrees: 45.0,
 			},
 			Ticks: []chart.Tick{
-				{0.0, "0.00"},
-				{2.0, "2.00"},
-				{4.0, "4.00"},
-				{6.0, "6.00"},
-				{8.0, "Eight"},
-				{10.0, "Ten"},
+				{Value: 0.0, Label: "0.00"},
+				{Value: 2.0, Label: "2.00"},
+				{Value: 4.0, Label: "4.00"},
+				{Value: 6.0, Label: "6.00"},
+				{Value: 8.0, Label: "Eight"},
+				{Value: 10.0, Label: "Ten"},
 			},
 		},
 		XAxis: chart.XAxis{
@@ -40,12 +40,12 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 				TextRotationDegrees: 45.0,
 			},
 			Ticks: []chart.Tick{
-				{0.0, "0.00"},
-				{2.0, "2.00"},
-				{4.0, "4.00"},
-				{6.0, "6.00"},
-				{8.0, "Eight"},
-				{10.0, "Ten"},
+				{Value: 0.0, Label: "0.00"},
+				{Value: 2.0, Label: "2.00"},
+				{Value: 4.0, Label: "4.00"},
+				{Value: 6.0, Label: "6.00"},
+				{Value: 8.0, Label: "Eight"},
+				{Value: 10.0, Label: "Ten"},
 			},
 		},
 		Series: []chart.Series{
@@ -60,15 +60,28 @@ func drawChart(res http.ResponseWriter, req *http.Request) {
 	graph.Elements = []chart.Renderable{
 		func(r chart.Renderer, cb chart.Box, defaults chart.Style) {
 
-			b := chart.Box{50, 50, 90, 110}
+			b := chart.Box{Top: 50, Left: 50, Right: 150, Bottom: 300}
+
+			cx, cy := b.Center()
+
+			chart.Draw.Box(r, chart.Box{Top: cy - 2, Left: cx - 2, Right: cx + 2, Bottom: cy + 2}, chart.Style{
+				StrokeWidth: 2,
+				StrokeColor: chart.ColorBlack,
+			})
+
 			chart.Draw.Box(r, b, chart.Style{
 				StrokeWidth: 2,
 				StrokeColor: chart.ColorBlue,
 			})
-			chart.Draw.Box(r, b.Rotate(chart.Math.DegreesToRadians(45)), chart.Style{
+			chart.Draw.Box(r, b.BoundedRotate(chart.Math.DegreesToRadians(45)), chart.Style{
 				StrokeWidth: 2,
 				StrokeColor: chart.ColorRed,
 			})
+
+			chart.Draw.BoxRotated(r, b, chart.Math.DegreesToRadians(45), chart.Style{
+				StrokeWidth: 2,
+				StrokeColor: chart.ColorOrange,
+			})
 		},
 	}
 	graph.Render(chart.PNG, res)

box.go

@@ -220,16 +220,20 @@ func (b Box) OuterConstrain(bounds, other Box) Box {
 	return newBox
 }
 
-// Rotate rotates a box's corners by a given radian rotation angle.
-func (b Box) Rotate(radians float64) Box {
+// BoundedRotate rotates a box's corners by a given radian rotation angle
+// and returns the maximum bounds or clipping rectangle.
+func (b Box) BoundedRotate(radians float64) Box {
 	cx, cy := b.Center()
 
 	ltx, lty := Math.RotateCoordinate(cx, cy, b.Left, b.Top, radians)
+	lbx, lby := Math.RotateCoordinate(cx, cy, b.Left, b.Bottom, radians)
+	rtx, rty := Math.RotateCoordinate(cx, cy, b.Right, b.Top, radians)
 	rbx, rby := Math.RotateCoordinate(cx, cy, b.Right, b.Bottom, radians)
+
 	return Box{
-		Left:   ltx,
-		Top:    lty,
-		Right:  rbx,
-		Bottom: rby,
+		Left:   Math.MinInt(ltx, lbx),
+		Top:    Math.MinInt(lty, rty),
+		Right:  Math.MaxInt(rtx, rbx),
+		Bottom: Math.MaxInt(lby, rby),
 	}
 }

box_test.go

@@ -158,7 +158,7 @@ func TestBoxCenter(t *testing.T) {
 	assert.Equal(20, cy)
 }
 
-func TestBoxRotate(t *testing.T) {
+func TestBoxBoundedRotate(t *testing.T) {
 	assert := assert.New(t)
 
 	b := Box{
@@ -167,9 +167,9 @@ func TestBoxRotate(t *testing.T) {
 		Right:  20,
 		Bottom: 10,
 	}
-	rotated := b.Rotate(Math.DegreesToRadians(45))
+	rotated := b.BoundedRotate(Math.DegreesToRadians(45))
 	assert.Equal(1, rotated.Top)
-	assert.Equal(4, rotated.Left)
-	assert.Equal(10, rotated.Right)
+	assert.Equal(5, rotated.Left)
+	assert.Equal(19, rotated.Right)
 	assert.Equal(14, rotated.Bottom)
 }

draw.go

@@ -219,6 +219,22 @@ func (d draw) Box(r Renderer, b Box, s Style) {
 	r.FillStroke()
 }
 
+func (d draw) BoxRotated(r Renderer, b Box, thetaRadians float64, s Style) {
+	s.WriteToRenderer(r)
+	cx, cy := b.Center()
+	ltx, lty := Math.RotateCoordinate(cx, cy, b.Left, b.Top, thetaRadians)
+	lbx, lby := Math.RotateCoordinate(cx, cy, b.Left, b.Bottom, thetaRadians)
+	rtx, rty := Math.RotateCoordinate(cx, cy, b.Right, b.Top, thetaRadians)
+	rbx, rby := Math.RotateCoordinate(cx, cy, b.Right, b.Bottom, thetaRadians)
+
+	r.MoveTo(ltx, lty)
+	r.LineTo(rtx, rty)
+	r.LineTo(rbx, rby)
+	r.LineTo(lbx, lby)
+	r.Close()
+	r.FillStroke()
+}
+
 // DrawText draws text with a given style.
 func (d draw) Text(r Renderer, text string, x, y int, style Style) {
 	style.GetTextOptions().WriteToRenderer(r)

math.go

@@ -225,7 +225,7 @@ func (m mathUtil) RotateCoordinate(cx, cy, x, y int, thetaRadians float64) (rx,
 	tempX, tempY := float64(x-cx), float64(y-cy)
 	rotatedX := tempX*math.Cos(thetaRadians) - tempY*math.Sin(thetaRadians)
 	rotatedY := tempX*math.Sin(thetaRadians) + tempY*math.Cos(thetaRadians)
-	rx = int(rotatedX) + cy
+	rx = int(rotatedX) + cx
 	ry = int(rotatedY) + cy
 	return
 }

raster_renderer.go

@@ -187,7 +187,7 @@ func (rr *rasterRenderer) MeasureText(body string) Box {
 		return textBox
 	}
 
-	return textBox.Rotate(*rr.rotateRadians)
+	return textBox.BoundedRotate(*rr.rotateRadians)
 }
 
 // SetTextRotation sets a text rotation.

vector_renderer.go

@@ -170,7 +170,7 @@ func (vr *vectorRenderer) MeasureText(body string) (box Box) {
 		if vr.c.textTheta == nil {
 			return
 		}
-		box = box.Rotate(*vr.c.textTheta)
+		box = box.BoundedRotate(*vr.c.textTheta)
 	}
 	return
 }