Canvas drawing

stephane78 0

Hi, I try to draw in a Canvas but it doesn't draw anything :

Canvas {
            id: mycanvas
            x:0
            y:40
            width:  mainwindows.width
            height: mainwindows.height-40
            ListModel {
                id: listerect
            }
            ListModel {
                id: listeind
            }
onPaint: {
                        var context = mycanvas.getContext("2d");
			//init L,H                
                        
                        context.clearRect(0, 0, mycanvas.width, mycanvas.height);


                        context.fillStyle = Qt.rgba(0, 255, 0, 0)
                        context.font = "bold 8px sans-serif";
                
                            for(var i=0; i < listerect.count; i++){
                                var ptrect = listerect.get(i)
                                context.rect(ptrect["x"],ptrect["y"],L/2,H/2)
                                var ind=listeind.get(i)
                                context.text(ind,ptrect["x"]+L/2,ptrect["y"]+H/2)
                             }

I have some listerect.append({"x": i, "y": j)}) in a loop in another function
has someone a tip ? I call mycanvas.requestPaint() in a further function (when I click on a button)

SergeiLitovko

Hi, you need to use mycanvas.requestPaint() on some events, for example onWidthChanged: mycanvas.requestPaint()

stephane78 0

Hi @SergeiLitovko yes but now,I use it (mycanvas.requestPaint())at the end of a function that defines and put the point in the listmodel (that is called in onclicked of a button) and it doesn't draw anything.it should draw my rectangles and my text.so there is something wrong with the canvas.
it is a program that I have modified to put a canvas,because I wasn't able to delete my window (and the objects )each time I click on the button to create my objects

Astrinus

You are drawing with fully transparent color (alpha = 0). Furthermore, according to https://doc.qt.io/qt-5/qml-qtqml-qt.html#rgba-method , the values should be 0-1, so you should set context.fillStyle to Qt.rgba(0, 1, 0, 1).

stephane78 0

@Astrinus thank you, I corrected that and the point ptrec but it doesn't still draw anything

stephane78 0

ok it is ```
context.strokeStyle=
....
context.rect(...
context.text(

context.stroke()

so my problem is solved,I should have used strokeStyle and stroke()

Best regards