Support rotation for pointStyle image (chartjs#6287)

Author: nagix

src/helpers/helpers.canvas.js

@@ -70,7 +70,11 @@ var exports = {
 		if (style && typeof style === 'object') {
 			type = style.toString();
 			if (type === '[object HTMLImageElement]' || type === '[object HTMLCanvasElement]') {
-				ctx.drawImage(style, x - style.width / 2, y - style.height / 2, style.width, style.height);
+				ctx.save();
+				ctx.translate(x, y);
+				ctx.rotate(rad);
+				ctx.drawImage(style, -style.width / 2, -style.height / 2, style.width, style.height);
+				ctx.restore();
 				return;
 			}
 		}

test/fixtures/element.point/point-style-image.js

@@ -0,0 +1,58 @@
+var imageCanvas = document.createElement('canvas');
+var imageContext = imageCanvas.getContext('2d');
+
+imageCanvas.width = 40;
+imageCanvas.height = 40;
+
+imageContext.fillStyle = '#f00';
+imageContext.beginPath();
+imageContext.moveTo(20, 0);
+imageContext.lineTo(10, 40);
+imageContext.lineTo(20, 30);
+imageContext.closePath();
+imageContext.fill();
+
+imageContext.fillStyle = '#a00';
+imageContext.beginPath();
+imageContext.moveTo(20, 0);
+imageContext.lineTo(30, 40);
+imageContext.lineTo(20, 30);
+imageContext.closePath();
+imageContext.fill();
+
+module.exports = {
+	config: {
+		type: 'line',
+		data: {
+			labels: [0, 1, 2, 3, 4, 5, 6, 7],
+			datasets: [{
+				data: [0, 0, 0, 0, 0, 0, 0, 0],
+				showLine: false
+			}]
+		},
+		options: {
+			responsive: false,
+			legend: false,
+			title: false,
+			elements: {
+				point: {
+					pointStyle: imageCanvas,
+					rotation: [0, 45, 90, 135, 180, 225, 270, 315]
+				}
+			},
+			layout: {
+				padding: 20
+			},
+			scales: {
+				xAxes: [{display: false}],
+				yAxes: [{display: false}]
+			}
+		}
+	},
+	options: {
+		canvas: {
+			height: 256,
+			width: 512
+		}
+	}
+};