Javascript 如何通过按住并拖动在QtQuick/QML画布中绘制矩形
我想在图像的顶部绘制一些矩形,这些矩形由QQuickPaintedItem子类绘制,并在QML中创建。我使用画布绘制矩形,可以使用鼠标对其进行平移和缩放。 以下代码不起作用:Javascript 如何通过按住并拖动在QtQuick/QML画布中绘制矩形,javascript,qt,canvas,qml,qtquick2,Javascript,Qt,Canvas,Qml,Qtquick2,我想在图像的顶部绘制一些矩形,这些矩形由QQuickPaintedItem子类绘制,并在QML中创建。我使用画布绘制矩形,可以使用鼠标对其进行平移和缩放。 以下代码不起作用: Canvas{ id:canvas anchors.fill:parent // zoom in/out managed by mouse wheel property double dx:0.0 property double dy:0.0 property double
Canvas{
id:canvas
anchors.fill:parent
// zoom in/out managed by mouse wheel
property double dx:0.0
property double dy:0.0
property double sx:1.0
property double sy:1.0
// mapped mouse position will be displayed on the left top of the window
property double mx:0
property double my:0
// mapped mouse postion when last left buttion pressed
property double lastx:0.0
property double lasty:0.0
// flag
property bool drawing:false
// map x,y to my coordinate
function mapToPaint(x,y)
{
var mx=(x-dx)/sx;
var my=(y-dy)/sy;
return {"x":mx,"y":my};
}
onPaint:{
var ctx = canvas.getContext("2d");
ctx.lineWidth = 1
ctx.strokeStyle = Qt.lighter(root.color)
ctx.clearRect (0, 0, width, height);
ctx.save();
// transform to my coordinate
ctx.translate(dx,dy);
ctx.scale(sx,sy);
// draw a rect
// !! I hope drawing can be displayed when mouse moving,
// !! but the rect wasn't displayed after the mouse button
// !! was released. Instead many rectangles will be showed when
// !! I rolled the mouse wheel after the press-drag operation.
if(drawing)
ctx.rect(lastx,lasty,mx-lastx,my-lasty);
ctx.stroke();
ctx.restore();
}
MouseArea {
id:area
anchors.fill: parent
hoverEnabled:true
preventStealing:true
property double factor: 1.2
onPressed:
{
if (mouse.button == Qt.LeftButton)
{
var p=canvas.mapToPaint(mouse.x,mouse.y);
canvas.lastx=p.x;
canvas.lasty=p.y;
canvas.drawing=true
}
}
onWheel:
{
if(wheel.angleDelta.y > 0) // zoom in
var zoomFactor = factor
else // zoom out
zoomFactor = 1/factor
canvas.sx*=zoomFactor;
canvas.sy*=zoomFactor;
canvas.dx=wheel.x-(wheel.x-canvas.dx)*zoomFactor;
canvas.dy=wheel.y-(wheel.y-canvas.dy)*zoomFactor;
canvas.requestPaint();
}
onPositionChanged:
{
var p=canvas.mapToPaint(mouse.x,mouse.y);
canvas.mx=p.x;
canvas.my=p.y;
// I hope the rectangle can be showed when draging
// but it didn't work!! why?
// mouse.button == Qt.LeftButton is always false!!!
// so I have to use the canvas.drawing flag
// if (mouse.button == Qt.LeftButton)
if(canvas.drawing)
canvas.requestPaint();
}
当我按下并拖动鼠标时,我看到了以下图片:
更新:
使用ctx.strokeRect而不是ctx.rect,我得到了正确的矩形,但仍然无法接收onPositionChanged中的鼠标对接
一般来说,如果您需要矩形或任何其他对象的实时预览,您需要创建一个临时矩形,以便在单击它时在画布顶部绘制,移动鼠标时,只需将一个矩形的大小调整为鼠标位置增量的大小,松开鼠标后,即可在画布上绘制矩形并删除预览 这就是我要做的,在QML中创建一个临时矩形非常简单,所以我想您应该可以自己实现它
当然,您可以在画布上绘制所有更新,但由于仅删除最后一个更新并不是那么容易,因此我想,使用临时覆盖的方法更容易。您好,请对发布的代码添加一些解释。
//handle Painted
Canvas{
id:canvas
anchors.fill:parent
// zoom in/out managed by mouse wheel
property double dx:0.0
property double dy:0.0
property double sx:1.0
property double sy:1.0
// mapped mouse position will be displayed on the left top of the window
property double mx:0
property double my:0
// mapped mouse postion when last left buttion pressed
property double lastx:0.0
property double lasty:0.0
// flag
property bool drawing:false
// map x,y to my coordinate
function mapToPaint(x,y)
{
var mx=(x-dx)/sx;
var my=(y-dy)/sy;
return {"x":mx,"y":my};
}
function clear(){
var ctx = canvas.getContext("2d");
ctx.reset();
canvas.requestPaint();
}
onPaint:{
var ctx = canvas.getContext("2d");
ctx.lineWidth = 1
ctx.strokeStyle = 'blue'
ctx.save();
// transform to my coordinate
ctx.translate(dx,dy);
ctx.scale(sx,sy);
// draw a rect
// !! I hope drawing can be displayed when mouse moving,
// !! but the rect wasn't displayed after the mouse button
// !! was released. Instead many rectangles will be showed when
// !! I rolled the mouse wheel after the press-drag operation.
if(drawing)
ctx.rect(lastx,lasty,mx-lastx,my-lasty);
ctx.stroke();
ctx.restore();
}
}
MouseArea {
id:area
anchors.fill: parent
hoverEnabled:true
preventStealing:true
property double factor: 1.2
onPressed:
{
var p=canvas.mapToPaint(mouse.x,mouse.y);
canvas.lastx=p.x;
canvas.lasty=p.y;
canvas.drawing=true
}
onPositionChanged:
{
canvas.clear();
var p=canvas.mapToPaint(mouse.x,mouse.y);
canvas.mx=p.x;
canvas.my=p.y;
// I hope the rectangle can be showed when draging
// but it didn't work!! why?
// mouse.button == Qt.LeftButton is always false!!!
// so I have to use the canvas.drawing flag
// if (mouse.button == Qt.LeftButton)
if(canvas.drawing)
canvas.requestPaint();
}
onReleased: {
canvas.clear();
console.log(canvas.lastx,canvas.lasty,canvas.mx,canvas.my);
canvas.drawing=false
}
}