✨ Add downscale option

src/index.js

@@ -14,29 +14,32 @@ export const MAX_CANVAS_SIZE = 10000;
  *   the dimensions of the canvas.
  * @prop {AttachCanvasUpdate=} onResize - A callback function which will be called whenever the
  *   dimensions of the canvas change.
+ * @prop {number=} downscale - An integer to downscale the canvas by,
+ *   can be used to render the canvas at a lower resolution.
  **/
 
 /**
+ * A function to call to unbind the event listeners attached to a canvas through `attachCanvas`.
  * @callback AttachCanvasUnbind
  * @returns {void}
  **/
 
 /**
- * @typedef {object} AttachCanvas
- * @prop {AttachCanvasUnbind} unbind - Call this function to remove the event listeners attached
- *   to the canvas
- **/
-
-/**
+ * Makes the given canvas pixel-perfect, by dynamically resizing it
+ * in order to have the canvas pixel resolution be always equal to the device resolution.
+ *
+ * Returns a function to "unbind" the bound listeners.
+ *
  * @param {HTMLCanvasElement} canvas
  * @param {AttachCanvasOptions} options
- * @returns {HTMLCanvasElement & AttachCanvas}
+ * @returns {AttachCanvasUnbind}
  **/
 export function attachCanvas(canvas, options = {}) {
     const EPSILON = 0.001;
     canvas.style.imageRendering = "pixelated";
     const container = options.container ?? canvas.parentNode;
     const onResize = options.onResize ?? (() => {});
+    const downscale = options.downscale ?? 1;
 
     let old_width = null;
     let old_height = null;
@@ -50,8 +53,8 @@ export function attachCanvas(canvas, options = {}) {
         };
 
         // Compute native dimensions of canvas
-        width = width * dpr;
-        height = height * dpr;
+        width = width * dpr / downscale;
+        height = height * dpr / downscale;
         if (isInteger(width, EPSILON) && isInteger(height, EPSILON)) {
             width = Math.round(width);
             height = Math.round(height);
@@ -82,8 +85,8 @@ export function attachCanvas(canvas, options = {}) {
         canvas.height = height;
 
         // Set style width to guarantee perfect scaling
-        canvas.style.width = `${width / dpr}px`;
-        canvas.style.height = `${height / dpr}px`;
+        canvas.style.width = `${width / dpr * downscale}px`;
+        canvas.style.height = `${height / dpr * downscale}px`;
 
         onResize(canvas, width, height);
     }
@@ -106,7 +109,7 @@ export function attachCanvas(canvas, options = {}) {
         resize(window.devicePixelRatio ?? 1);
     }, 0);
 
-    canvas.unbind = function unbind() {
+    return function unbind() {
         if (resize_observer) {
             resize_observer.disconnect();
             // Drop resize_observer
@@ -119,8 +122,6 @@ export function attachCanvas(canvas, options = {}) {
             unbind_dpr = null;
         }
     };
-
-    return canvas;
 }
 
 export function listenPixelRatio(element, callback, fire_first = false) {

src/solid/PixelPerfectCanvas.tsx

@@ -1,5 +1,5 @@
 import { JSX, Component, createEffect, onCleanup } from "solid-js";
-import { attachCanvas } from '../index';
+import { attachCanvas, AttachCanvasOptions } from '../index';
 import styles from './PixelPerfectCanvas.module.css';
 
 export type PixelPerfectCanvasProps = {
@@ -28,7 +28,7 @@ export type PixelPerfectCanvasProps = {
      * Callback called after the event listeners for dimension and DPR changes are detached.
      **/
     onDetach?: (canvas: HTMLCanvasElement) => void,
-}
+} & Omit<AttachCanvasOptions, 'onResize' | 'container'>
 
 /**
  * A canvas that is wrapped in a container (which will be styled with `style` or `class`),
@@ -43,20 +43,19 @@ export const PixelPerfectCanvas: Component<PixelPerfectCanvasProps> = (props) =>
     let canvasRef: HTMLCanvasElement;
     let containerRef: HTMLDivElement;
 
-    createEffect<ReturnType<typeof attachCanvas>>((old) => {
-        const result = attachCanvas(canvasRef, {
+    createEffect(() => {
+        const unbind = attachCanvas(canvasRef, {
             container: containerRef,
             onResize: props.onResize,
+            downscale: props.downscale
         });
 
-        props.onAttach?.(result);
+        props.onAttach?.(canvasRef);
 
         onCleanup(() => {
-            result.unbind();
-            props.onDetach?.(result);
+            unbind();
+            props.onDetach?.(canvasRef);
         });
-
-        return result;
     });
 
     return (<div

test/solid/App.tsx

@@ -38,6 +38,7 @@ const App: Component = () => {
             }}
             onResize={update}
             onAttach={setCanvasRef}
+            downscale={8}
         />
         <input
             type="checkbox"

vite.config.ts

@@ -21,6 +21,10 @@ export default defineConfig({
             }
         },
         rollupOptions: {
+            output: {
+                sourcemap: true,
+                format: 'iife',
+            },
             external: ["solid-js"],
             plugins: []
         }