[Feature]: Shadow Rendering Issue in Fabric.js 6.3.0 for Transparent Circle, Rect

[yashChapaniOB]

CheckList

• I agree to follow this project's Code of Conduct
• I have read and followed the Contributing Guide
• I have searched and referenced existing issues, feature requests and discussions
• I am filing a FEATURE request.

Description

In Fabric.js version 6.3.0, when applying a shadow to a transparent circle,Rect the shadow appears inside the circle,rect as well, instead of being limited to the outer area of the circle,Rect. The desired behavior is for the shadow to be rendered outside the circle's or Rect's boundary, without affecting the inner transparent area.

Current Behavior

Currently, when a shadow is applied to a Rect or Circle, the shadow is visible within the object's boundary, which includes the transparent areas. This behavior deviates from the expected result, where the shadow should be projected outside the shape's edge, leaving the inner transparent regions unaffected.

Current State

var option = {};
option['objectCaching'] = true;
option['isLocked'] = false;
option['element_type'] = "basicShape";

let ctx = this.canvas.getContext('2d');

const shadow = new Shadow({
affectStroke: false
blur:0
color:"#000000ff",
includeDefaultValues:true,
nonScaling:false,
offsetX:50,
offsetY:50,
});

var rect = new Rect({
angle: 0,
fill: #FFDE59
borderColor: '#0069FF',
borderScaleFactor: 1.5,
centeredScaling: false,
centeredRotation: true,
cornerSize: 15,
cornerColor: '#0069FF',
cornerStyle: 'circle',
shadow: shadow,
lockScalingFlip: true,
isLocked: false,
visible: true,
stroke: "#ffffffff"
selectionDashArray: [],
clipPath: undefined,
excludeFromExport: false,
strokeWidth: 0,
transparentCorners: false,
rx: 0,
ry:0,
_controlsVisibility: {
tl: true,
tr: true,
br: true,
bl: true,
ml: true,
mt: true,
mr: true,
mb: true,
mtr: true
},
type: 'rect',
element_type: 'basicShape',
...option
});

this.canvas.add(rect);
this.canvas.renderAll();

Expected Behavior

The shadow should be rendered outside the Rect or Circle boundaries, not within the shape's transparent inner area.

Additional Context

No response

[asturur]

that is not how shadow for the canvas works sadly and there isn't a performing fix that makes sense.
You would have to draw the shapes twice, one normally and one with global composite operation set to copy.

That would also delete anything that is under the shape with the shape itself.

[Clemweb]

@yashChapaniOB can you tell me how you do in v6 the rounded rectangle for middles handlers ?

[asturur]

You have to write your own control render function. Please look at the standard control.render function and write your own with a rounded rect.

[Clemweb]

@asturur don't find control.render, can you give a sample or the file for search in ?
Thanks

[asturur]

https://github.com/fabricjs/fabric.js/blob/master/src/controls/Control.ts#L348

[Clemweb]

@asturur ok I write this :

`Control.prototype.render = function(ctx, left, top, styleOverride, fabricObject)
{
const size = 10; // Taille du handler
const radius = 5; // Rayon des coins du rectangle
ctx.save();
ctx.translate(left, top);
ctx.fillStyle = styleOverride.cornerColor || fabricObject.cornerColor;

    ctx.beginPath();
    ctx.moveTo(-size + radius, -size);
    ctx.lineTo(size - radius, -size);
    ctx.quadraticCurveTo(size, -size, size, -size + radius);
    ctx.lineTo(size, size - radius);
    ctx.quadraticCurveTo(size, size, size - radius, size);
    ctx.lineTo(-size + radius, size);
    ctx.quadraticCurveTo(-size, size, -size, size - radius);
    ctx.lineTo(-size, -size + radius);
    ctx.quadraticCurveTo(-size, -size, -size + radius, -size);
    ctx.closePath();

    ctx.fill();

    // Dessiner la bordure
    ctx.lineWidth = 1; // Épaisseur de la bordure
    ctx.strokeStyle = '#000000'; // Couleur de la bordure
    ctx.stroke();

    ctx.restore();
};`

It's working, but how to know if it draw the top left corner ? or middle right ?

[asturur]

Please read this carefully
https://fabricjs.github.io/docs/configuring-controls/
and decide which approach is best for you to configure your controls first.

Then create a render function for each type of rendering you need, then assign it to the correct control.
You can create a new control class and instantiate it in the createControls function for your object type or assign it to the existing control instances every time the objects are created.