Currently im trying to make a canvas zoom and also draw again the whole canvas
var painter = document.getElementById('painter');
var cp = painter.getContext('2d');
var scale = 1;
var originx = 0;
var savedData = [];
var originy = 0;
var zoom = 0;
$('#painter').on('mousewheel', function(event) {
var imgData = cp.getImageData(0, 0, painter.width, painter.height);
savedData.push(imgData);
var mousex = event.clientX - painter.offsetLeft;
var mousey = event.clientY - painter.offsetTop;
var wheel = event.deltaY;//n or -n
var zoom = 1 + wheel/2;
cp.translate(
originx,
originy
);
cp.scale(zoom,zoom);
cp.translate(
-( mousex / scale + originx - mousex / ( scale * zoom ) ),
-( mousey / scale + originy - mousey / ( scale * zoom ) )
);
if (savedData.length > 0) {
var imgData = savedData.pop();
cp.putImageData(imgData, 0, 0);
}
originx = ( mousex / scale + originx - mousex / ( scale * zoom ) );
originy = ( mousey / scale + originy - mousey / ( scale * zoom ) );
scale *= zoom;
});
Thing is it does not work. Canvas is never updated... the variables seems to be fine and since I need to draw again the whole canvas Im saving all the data into an array
getImageData & context.putImageData
are very expensive operations.
Instead, you could store your original content in a second in-memory-only canvas created with
var secondCanvas = document.createElement('canvas')
var secondContext = secondCanvas.getContext('2d');
secondCanvas.width=mainCanvas.width;
secondCanvas.height=mainCanvas.height;
secondContext.drawImage(mainCanvas,0,0);
Then use that second canvas as an image source for your scaled drawing on the main canvas:
mainContext.drawImage(secondCanvas,x,y);
Once you have your content cached to a second canvas, you can use this Stackoverflow answer to zoom with the mousewheel:
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