Transforming canvas point to canvas context point
I have a canvas built with Fabric js. I need to draw rectangles of 1x1 pixels on mouse down event at the clicked coordinate. When a click is made in the canvas the point must be converted if the canvas has been transformed before. For doing that i am using the following approach:
const point = new fabric.Point(offsetX, offsetY);
const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);
After converting the point i just add the rectangle:
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
this.add(p);
The problem is that the transformed point is not 100% accurate and the rectangle is always drawn X pixels away from the original point.
I made a snippet to explain this behaviour. The context is initially transformed with a zoom of 60:
fabric.Object.prototype.selectable = false;
const screenWidth = window.innerWidth;
const screenHeight = window.innerHeight;
canvas = new fabric.Canvas('canvas');
canvas.setWidth(screenWidth);
canvas.setHeight(screenHeight);
canvas.setZoom(60);
canvas.on('mouse:down', (opt) => {
const evt = opt.e;
canvas.selection = false;
canvas.isDragging = true;
const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);
const iM = fabric.util.invertTransform(canvas.viewportTransform);
const transformedPoint = fabric.util.transformPoint(point, iM);
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
canvas.add(p);
});
body {
margin:0;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.3/fabric.min.js"></script>
<canvas id="canvas"></canvas>What am i missing here? Thank you very much
javascript canvas fabricjs
asked Nov 24 '18 at 7:41
xepexepe
5016
add a comment |
I have a canvas built with Fabric js. I need to draw rectangles of 1x1 pixels on mouse down event at the clicked coordinate. When a click is made in the canvas the point must be converted if the canvas has been transformed before. For doing that i am using the following approach:
const point = new fabric.Point(offsetX, offsetY);
const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);
After converting the point i just add the rectangle:
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
this.add(p);
The problem is that the transformed point is not 100% accurate and the rectangle is always drawn X pixels away from the original point.
I made a snippet to explain this behaviour. The context is initially transformed with a zoom of 60:
fabric.Object.prototype.selectable = false;
const screenWidth = window.innerWidth;
const screenHeight = window.innerHeight;
canvas = new fabric.Canvas('canvas');
canvas.setWidth(screenWidth);
canvas.setHeight(screenHeight);
canvas.setZoom(60);
canvas.on('mouse:down', (opt) => {
const evt = opt.e;
canvas.selection = false;
canvas.isDragging = true;
const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);
const iM = fabric.util.invertTransform(canvas.viewportTransform);
const transformedPoint = fabric.util.transformPoint(point, iM);
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
canvas.add(p);
});
body {
margin:0;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.3/fabric.min.js"></script>
<canvas id="canvas"></canvas>What am i missing here? Thank you very much
javascript canvas fabricjs
asked Nov 24 '18 at 7:41
xepexepe
5016
add a comment |
I have a canvas built with Fabric js. I need to draw rectangles of 1x1 pixels on mouse down event at the clicked coordinate. When a click is made in the canvas the point must be converted if the canvas has been transformed before. For doing that i am using the following approach:
const point = new fabric.Point(offsetX, offsetY);
const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);
After converting the point i just add the rectangle:
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
this.add(p);
The problem is that the transformed point is not 100% accurate and the rectangle is always drawn X pixels away from the original point.
I made a snippet to explain this behaviour. The context is initially transformed with a zoom of 60:
fabric.Object.prototype.selectable = false;
const screenWidth = window.innerWidth;
const screenHeight = window.innerHeight;
canvas = new fabric.Canvas('canvas');
canvas.setWidth(screenWidth);
canvas.setHeight(screenHeight);
canvas.setZoom(60);
canvas.on('mouse:down', (opt) => {
const evt = opt.e;
canvas.selection = false;
canvas.isDragging = true;
const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);
const iM = fabric.util.invertTransform(canvas.viewportTransform);
const transformedPoint = fabric.util.transformPoint(point, iM);
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
canvas.add(p);
});
body {
margin:0;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.3/fabric.min.js"></script>
<canvas id="canvas"></canvas>What am i missing here? Thank you very much
javascript canvas fabricjs
asked Nov 24 '18 at 7:41
xepexepe
5016
I have a canvas built with Fabric js. I need to draw rectangles of 1x1 pixels on mouse down event at the clicked coordinate. When a click is made in the canvas the point must be converted if the canvas has been transformed before. For doing that i am using the following approach:
const point = new fabric.Point(offsetX, offsetY);
const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);
After converting the point i just add the rectangle:
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
this.add(p);
The problem is that the transformed point is not 100% accurate and the rectangle is always drawn X pixels away from the original point.
I made a snippet to explain this behaviour. The context is initially transformed with a zoom of 60:
fabric.Object.prototype.selectable = false;
const screenWidth = window.innerWidth;
const screenHeight = window.innerHeight;
canvas = new fabric.Canvas('canvas');
canvas.setWidth(screenWidth);
canvas.setHeight(screenHeight);
canvas.setZoom(60);
canvas.on('mouse:down', (opt) => {
const evt = opt.e;
canvas.selection = false;
canvas.isDragging = true;
const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);
const iM = fabric.util.invertTransform(canvas.viewportTransform);
const transformedPoint = fabric.util.transformPoint(point, iM);
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
canvas.add(p);
});
body {
margin:0;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.3/fabric.min.js"></script>
<canvas id="canvas"></canvas>What am i missing here? Thank you very much
fabric.Object.prototype.selectable = false;
const screenWidth = window.innerWidth;
const screenHeight = window.innerHeight;
canvas = new fabric.Canvas('canvas');
canvas.setWidth(screenWidth);
canvas.setHeight(screenHeight);
canvas.setZoom(60);
canvas.on('mouse:down', (opt) => {
const evt = opt.e;
canvas.selection = false;
canvas.isDragging = true;
const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);
const iM = fabric.util.invertTransform(canvas.viewportTransform);
const transformedPoint = fabric.util.transformPoint(point, iM);
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
canvas.add(p);
});
body {
margin:0;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.3/fabric.min.js"></script>
<canvas id="canvas"></canvas> fabric.Object.prototype.selectable = false;
const screenWidth = window.innerWidth;
const screenHeight = window.innerHeight;
canvas = new fabric.Canvas('canvas');
canvas.setWidth(screenWidth);
canvas.setHeight(screenHeight);
canvas.setZoom(60);
canvas.on('mouse:down', (opt) => {
const evt = opt.e;
canvas.selection = false;
canvas.isDragging = true;
const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);
const iM = fabric.util.invertTransform(canvas.viewportTransform);
const transformedPoint = fabric.util.transformPoint(point, iM);
const p = new fabric.Rect({
left: transformedPoint.x,
top: transformedPoint.y,
fill: 'red',
width: 1,
height: 1,
});
canvas.add(p);
});
body {
margin:0;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.3/fabric.min.js"></script>
<canvas id="canvas"></canvas>javascript canvas fabricjs
javascript canvas fabricjs
asked Nov 24 '18 at 7:41
xepexepe
5016
asked Nov 24 '18 at 7:41
xepexepe
5016
asked Nov 24 '18 at 7:41
xepexepe
5016
asked Nov 24 '18 at 7:41
xepexepe
5016
asked Nov 24 '18 at 7:41
xepexepe
5016
5016
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
I finally solved it. I thought the problem was transforming the point! But actually it was something as silly as that fabric was drawing an invisible border.
All I had to do was set Object.strokeWidth = 0
answered Nov 24 '18 at 14:24
xepexepe
5016
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
active
oldest
votes
active
oldest
votes
I finally solved it. I thought the problem was transforming the point! But actually it was something as silly as that fabric was drawing an invisible border.
All I had to do was set Object.strokeWidth = 0
answered Nov 24 '18 at 14:24
xepexepe
5016
add a comment |
I finally solved it. I thought the problem was transforming the point! But actually it was something as silly as that fabric was drawing an invisible border.
All I had to do was set Object.strokeWidth = 0
answered Nov 24 '18 at 14:24
xepexepe
5016
add a comment |
I finally solved it. I thought the problem was transforming the point! But actually it was something as silly as that fabric was drawing an invisible border.
All I had to do was set Object.strokeWidth = 0
answered Nov 24 '18 at 14:24
xepexepe
5016
I finally solved it. I thought the problem was transforming the point! But actually it was something as silly as that fabric was drawing an invisible border.
All I had to do was set Object.strokeWidth = 0
answered Nov 24 '18 at 14:24
xepexepe
5016
answered Nov 24 '18 at 14:24
xepexepe
5016
answered Nov 24 '18 at 14:24
xepexepe
5016
answered Nov 24 '18 at 14:24
xepexepe
5016
5016
add a comment |
add a comment |
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