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Better thumbnail image scaling

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fkaelberer 2015-01-02 15:40:30 +01:00
parent 50fe7c8d0a
commit 32c32c18e3
1 changed files with 18 additions and 16 deletions
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34
web/thumbnail_view.js
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@ -218,34 +218,36 @@ var ThumbnailView = function thumbnailView(container, id, defaultViewport,
}
this.renderingState = RenderingStates.FINISHED;
var ctx = this.getPageDrawContext();
var canvas = ctx.canvas;
var reducedImage = img;
var reducedWidth = img.width;
var reducedHeight = img.height;
// drawImage does an awful job of rescaling the image, doing it gradually
var MAX_SCALE_FACTOR = 2.0;
if (Math.max(img.width / ctx.canvas.width,
img.height / ctx.canvas.height) > MAX_SCALE_FACTOR) {
reducedWidth >>= 1;
reducedHeight >>= 1;
reducedImage = getTempCanvas(reducedWidth, reducedHeight);
if (img.width <= 2 * canvas.width) {
ctx.drawImage(img, 0, 0, img.width, img.height,
0, 0, canvas.width, canvas.height);
} else {
// drawImage does an awful job of rescaling the image, doing it gradually
var MAX_NUM_SCALING_STEPS = 3;
var reducedWidth = canvas.width << MAX_NUM_SCALING_STEPS;
var reducedHeight = canvas.height << MAX_NUM_SCALING_STEPS;
var reducedImage = getTempCanvas(reducedWidth, reducedHeight);
var reducedImageCtx = reducedImage.getContext('2d');
while (reducedWidth > img.width || reducedHeight > img.height) {
reducedWidth >>= 1;
reducedHeight >>= 1;
}
reducedImageCtx.drawImage(img, 0, 0, img.width, img.height,
0, 0, reducedWidth, reducedHeight);
while (Math.max(reducedWidth / ctx.canvas.width,
reducedHeight / ctx.canvas.height) > MAX_SCALE_FACTOR) {
while (reducedWidth > 2 * canvas.width) {
reducedImageCtx.drawImage(reducedImage,
0, 0, reducedWidth, reducedHeight,
0, 0, reducedWidth >> 1, reducedHeight >> 1);
reducedWidth >>= 1;
reducedHeight >>= 1;
}
ctx.drawImage(reducedImage, 0, 0, reducedWidth, reducedHeight,
0, 0, canvas.width, canvas.height);
}
ctx.drawImage(reducedImage, 0, 0, reducedWidth, reducedHeight,
0, 0, ctx.canvas.width, ctx.canvas.height);
this.hasImage = true;
};
};