chartjs · etimberg · Feb 28, 2021 · Feb 28, 2021 · Feb 28, 2021 · Feb 28, 2021
diff --git a/docs/docs/developers/charts.md b/docs/docs/developers/charts.md
@@ -26,17 +26,21 @@ Dataset controllers must implement the following interface.
 
 ```javascript
 {
-    // Create elements for each piece of data in the dataset. Store elements in an array on the dataset as dataset.metaData
-    addElements: function() {},
-
-    // Draw the representation of the dataset
-    draw: function() {},
-
-    // Remove hover styling from the given element
-    removeHoverStyle: function(element, datasetIndex, index) {},
+    // Defaults for charts of this type
+    defaults: {
+        // If set to `false` or `null`, no dataset level element is created.
+        // If set to a string, this is the type of element to create for the dataset.
+        // For example, a line create needs to create a line element so this is the string 'line'
+        datasetElementType: string | null | false,
+
+        // If set to `false` or `null`, no elements are created for each data value.
+        // If set to a string, this is the type of element to create for each data value.
+        // For example, a line create needs to create a point element so this is the string 'point'
+        dataElementType: string | null | false,
+    }
 
-    // Add hover styling to the given element
-    setHoverStyle: function(element, datasetIndex, index) {},
+    // ID of the controller
+    id: string;
 
     // Update the elements in response to new data
     // @param mode : update mode, core calls this method using any of `'active'`, `'hide'`, `'reset'`, `'resize'`, `'show'` or `undefined`
@@ -48,15 +52,20 @@ The following methods may optionally be overridden by derived dataset controller
 
 ```javascript
 {
+    // Draw the representation of the dataset. The base implementation works in most cases, and an example of a derived version
+    // can be found in the line controller
+    draw: function() {},
+
     // Initializes the controller
     initialize: function() {},
 
     // Ensures that the dataset represented by this controller is linked to a scale. Overridden to helpers.noop in the polar area and doughnut controllers as these
     // chart types using a single scale
     linkScales: function() {},
 
-    // Called by the main chart controller when an update is triggered. The default implementation handles the number of data points changing and creating elements appropriately.
-    buildOrUpdateElements: function() {}
+    // Parse the data into the controller meta data. The default implementation will work for cartesian parsing, but an example of an overridden
+    // version can be found in the doughnut controller
+    parse: function(start, count) {},
 }
 ```
 
@@ -83,19 +92,21 @@ For example, to derive a new chart type that extends from a bubble chart, you wo
 import {BubbleController} from 'chart.js';
 class Custom extends BubbleController {
     draw() {
-        // Call super method first
+        // Call bubble controller method to draw all the points
         super.draw(arguments);
 
         // Now we can do some custom drawing for this dataset. Here we'll draw a red box around the first point in each dataset
-        var meta = this.getMeta();
-        var pt0 = meta.data[0];
-        var radius = pt0.radius;
+        const meta = this.getMeta();
+        const pt0 = meta.data[0];
+
+        const {x, y} = pt0.getProps(['x', 'y']);
+        const {radius} = pt0.options;
 
-        var ctx = this.chart.chart.ctx;
+        const ctx = this.chart.ctx;
         ctx.save();
         ctx.strokeStyle = 'red';
         ctx.lineWidth = 1;
-        ctx.strokeRect(pt0.x - radius, pt0.y - radius, 2 * radius, 2 * radius);
+        ctx.strokeRect(x - radius, y - radius, 2 * radius, 2 * radius);
         ctx.restore();
     }
 });

diff --git a/samples/advanced/derived-axis-type.html b/samples/advanced/derived-axis-type.html
@@ -0,0 +1,136 @@
+<!doctype html>
+<html>
+
+<head>
+	<title>Logarithmic Line Chart</title>
+	<script src="../../dist/chart.min.js"></script>
+	<script src="../utils.js"></script>
+	<style>
+	canvas {
+		-moz-user-select: none;
+		-webkit-user-select: none;
+		-ms-user-select: none;
+	}
+	</style>
+</head>
+
+<body>
+	<div style="width:75%;">
+		<canvas id="canvas"></canvas>
+	</div>
+	<script>
+	var randomScalingFactor = function() {
+		return Math.pow(2, Math.ceil(Math.random() * 10));
+	};
+
+	class Log2Axis extends Chart.Scale {
+		constructor(cfg) {
+			super(cfg);
+			this._startValue = undefined;
+			this._valueRange = 0;
+		}
+
+		parse(raw, index) {
+			const value = Chart.registry.getScale('linear').prototype.parse.apply(this, [raw, index]);
+			return isFinite(value) && value > 0 ? value : null;
+		}
+
+		determineDataLimits() {
+			const {min, max} = this.getMinMax(true);
+			this.min = isFinite(min) ? Math.max(0, min) : null;
+			this.max = isFinite(max) ? Math.max(0, max) : null;
+		}
+
+		buildTicks() {
+			const ticks = [];
+
+			let power = Math.floor(Math.log2(this.min));
+			let maxPower = Math.ceil(Math.log2(this.max));
+			while (power <= maxPower) {
+				ticks.push({value: Math.pow(2, power)});
+				power += 1;
+			}
+
+			this.min = ticks[0].value;
+			this.max = ticks[ticks.length - 1].value;
+			return ticks;
+		}
+
+		/**
+		 * @protected
+		 */
+		configure() {
+			const start = this.min;
+
+			super.configure();
+
+			this._startValue = Math.log2(start);
+			this._valueRange = Math.log2(this.max) - Math.log2(start);
+		}
+
+		getPixelForValue(value) {
+			if (value === undefined || value === 0) {
+				value = this.min;
+			}
+
+			return this.getPixelForDecimal(value === this.min ? 0 : (Math.log2(value) - this._startValue) / this._valueRange);
+		}
+
+		getValueForPixel(pixel) {
+			const decimal = this.getDecimalForPixel(pixel);
+			return Math.pow(2, this._startValue + decimal * this._valueRange);
+		}
+	}
+
+	Log2Axis.id = 'log2';
+	Log2Axis.defaults = {};
+	Chart.register(Log2Axis);
+
+	var config = {
+		type: 'line',
+		data: {
+			labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
+			datasets: [{
+				label: 'My First dataset',
+				backgroundColor: window.chartColors.red,
+				borderColor: window.chartColors.red,
+				fill: false,
+				data: [
+					randomScalingFactor(),
+					randomScalingFactor(),
+					randomScalingFactor(),
+					randomScalingFactor(),
+					randomScalingFactor(),
+					randomScalingFactor(),
+					randomScalingFactor()
+				],
+			}]
+		},
+		options: {
+			responsive: true,
+			plugins: {
+				title: {
+					display: true,
+					text: 'Derived Axis Type - Log2'
+				}
+			},
+			scales: {
+				x: {
+					display: true,
+				},
+				y: {
+					display: true,
+					type: 'log2',
+				}
+			}
+		}
+	};
+
+	window.onload = function() {
+		var ctx = document.getElementById('canvas').getContext('2d');
+		window.myLine = new Chart(ctx, config);
+	};
+	</script>
+</body>
+
+</html>
diff --git a/samples/advanced/derived-chart-type.html b/samples/advanced/derived-chart-type.html
@@ -0,0 +1,106 @@
+<!doctype html>
+<html>
+
+<head>
+	<title>Derived Chart Type</title>
+	<script src="../../dist/chart.min.js"></script>
+	<script src="../utils.js"></script>
+	<style type="text/css">
+		canvas{
+			-moz-user-select: none;
+			-webkit-user-select: none;
+			-ms-user-select: none;
+		}
+	</style>
+</head>
+
+<body>
+	<div id="container" style="width: 75%;">
+		<canvas id="canvas"></canvas>
+	</div>
+	<script>
+		class Custom extends Chart.controllers.bubble {
+			draw() {
+				// Call bubble controller method to draw all the points
+				super.draw(arguments);
+
+				// Now we can do some custom drawing for this dataset. Here we'll draw a red box around the first point in each dataset
+				var meta = this.getMeta();
+				var pt0 = meta.data[0];
+
+				const {x, y} = pt0.getProps(['x', 'y']);
+				const {radius} = pt0.options;
+
+				var ctx = this.chart.ctx;
+				ctx.save();
+				ctx.strokeStyle = 'red';
+				ctx.lineWidth = 1;
+				ctx.strokeRect(x - radius, y - radius, 2 * radius, 2 * radius);
+				ctx.restore();
+			}
+		}
+		Custom.id = 'derivedBubble';
+		Custom.defaults = Chart.controllers.bubble.defaults;
+
+		// Stores the controller so that the chart initialization routine can look it up
+		Chart.register(Custom);
+
+		var color = Chart.helpers.color;
+		var bubbleChartData = {
+			datasets: [{
+				label: 'My First dataset',
+				backgroundColor: color(window.chartColors.blue).alpha(0.5).rgbString(),
+				borderColor: window.chartColors.blue,
+				borderWidth: 1,
+				data: [{
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}, {
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}, {
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}, {
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}, {
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}, {
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}, {
+					x: randomScalingFactor(),
+					y: randomScalingFactor(),
+					r: Math.abs(randomScalingFactor()) / 5,
+				}]
+			}]
+		};
+
+		window.onload = function() {
+			var ctx = document.getElementById('canvas').getContext('2d');
+			window.myChart = new Chart(ctx, {
+				type: 'derivedBubble',
+				data: bubbleChartData,
+				options: {
+					responsive: true,
+					plugins: {
+						title: {
+							display: true,
+							text: 'Derived Chart Type'
+						},
+					}
+				}
+			});
+		};
+	</script>
+</body>
+
+</html>
diff --git a/samples/samples.js b/samples/samples.js
@@ -268,6 +268,12 @@
 		}, {
 			title: 'Programmatic Event Triggers',
 			path: 'advanced/programmatic-events.html'
+		}, {
+			title: 'Derived Chart Type',
+			path: 'advanced/derived-chart-type.html'
+		}, {
+			title: 'Derived Axis Type',
+			path: 'advanced/derived-axis-type.html'
 		}]
 	}];