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Force redraw on attribute changes

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Andrew Stephens
2022-12-18 20:58:18 -05:00
parent 898cfb2107
commit f368986c74
1 changed files with 13 additions and 6 deletions
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19
as-dithered-image.js
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@@ -16,6 +16,8 @@ class ASDitheredImage extends HTMLElement {
this.crunchFactor = this.getAutoCrunchFactor()
this.drawTimestamp = 0
this.drawRect = undefined
this.drawCrunchFactor = undefined
this.drawSrc = undefined
this.altText = ""
}
@@ -112,16 +114,21 @@ class ASDitheredImage extends HTMLElement {
}
const rect = this.canvas.getBoundingClientRect()
if ((this.drawRect != undefined) && (rect.width == this.drawRect.width) && (rect.height == this.drawRect.height)) {
return // already drawn the image at this size
// we only want to draw the image if something has actually changed (usually the size)
if ((this.drawRect != undefined) && (rect.width == this.drawRect.width) && (rect.height == this.drawRect.height) &&
((this.drawCrunchFactor != undefined) && (this.crunchFactor === this.drawCrunchFactor)) &&
((this.drawSrc != undefined && this.src === this.drawSrc))) {
return
}
this.drawRect = rect;
this.drawRect = rect
this.drawCrunchFactor = this.crunchFactor
this.drawSrc = this.src
// to get really crisp pixels on retina-type displays (window.devicePixelRatio > 1) we have to set the
// canvas backing store to the element size times the devicePixelRatio
// Then, once the image has loaded we draw it manually scaled to only part of the canvas (since the canvas is bigger than the element)
// The dithering algorythm will scale up the image to the canvas size
// The dithering algorithm will scale up the image to the canvas size
const logicalPixelSize = window.devicePixelRatio * this.crunchFactor
this.canvas.width = rect.width * window.devicePixelRatio
this.canvas.height = rect.height * window.devicePixelRatio
@@ -148,7 +155,7 @@ class ASDitheredImage extends HTMLElement {
imageData.data[i] = imageData.data[i + 1] = imageData.data[i + 2] = Math.floor(imageData.data[i] * 0.3 + imageData.data[i + 1] * 0.59 + imageData.data[i + 2] * 0.11)
}
// most implementations I see just distibute error into the existing image, wrapping around edge pixels
// most implementations I see just distribute error into the existing image, wrapping around edge pixels
// this implementation uses a sliding window of floats for more accuracy (probably not needed really)
let slidingErrorWindow = [new Float32Array(imageData.width), new Float32Array(imageData.width), new Float32Array(imageData.width)]
@@ -174,7 +181,7 @@ class ASDitheredImage extends HTMLElement {
}
// this is stupid but we have to do the pixel scaling ourselves because safari insists on interpolating putImageData
// which gives us blury pixels (and it doesn't support the createImageBitmap call with an ImageData instance which
// which gives us blurry pixels (and it doesn't support the createImageBitmap call with an ImageData instance which
// would make this easy)
for (let scaleY = 0; scaleY < scaleFactor; ++scaleY) {