In qml, canvas width can not be longer than 8520, why?

mileszhang

hi,
I recently develop on QT 5.1,and I have found in my personal computer (cpu : i7), canvas width can not be longer than 8520 in my qml file. why?
can any one tell me?
I need such length of longer than 8520 for my development.
how I fix it?
thx.

the following is the source code for debug.

@Rectangle{
width: 800; height: 480
color:"transparent"

Canvas{
    id:canvas
    width:8520
    height:480;

    onPaint: {
        var ctx = canvas.getContext("2d");//Context2D

        ctx.globalCompositeOperation = "source-over";
        ctx.clearRect(0,0,width,height);//Clears all pixels on the canvas in the given rectangle to transparent black.
        ctx.lineWidth = 1;
        ctx.save();
        ctx.fillStyle = ctx.createPattern("#6699CC",Qt.SolidPattern);
        ctx.beginPath();
        ctx.rect(0,0,canvas.width,canvas.height);
        ctx.closePath();
        ctx.fill();
        ctx.restore();
    }
}

}@

mileszhang

besides,I find Rectangle maximum width is not longer than 8520.
how is that limits determined? Is there something to do with platform frame buffer of display?
for example: it will be failed!

@Rectangle{
width: 8520; height: 480
//color:"transparent"
color:"#6699CC"
} @

jeremy_k

Based on the documentation for Canvas, I suspect you want to set canvasSize and canvasWindow, unless the display being targeted really is greater than 8520 pixels wide.

For me with Qt 5.3.0 and XCB, a canvas with width or height greater than 8192 fails to render. I'm not sure where the limitation comes from, but the fact that it occurs above 8k seems noncoincidental. Does a width of 8519 work for you?

mileszhang

[quote author="jeremy_k" date="1401233474"]Based on the documentation for Canvas, I suspect you want to set canvasSize and canvasWindow, unless the display being targeted really is greater than 8520 pixels wide.

For me with Qt 5.3.0 and XCB, a canvas with width or height greater than 8192 fails to render. I'm not sure where the limitation comes from, but the fact that it occurs above 8k seems noncoincidental. Does a width of 8519 work for you?[/quote]

hi,

thanks for your tips.

I do not test such width 8519.
but I guess the limitation is something to do with hardware platform, may be about the graphics chip.
I port my qml code to arm platform(TI am335x, contex-A8).sadly,beyond my mind, the width can not more than 2400.