[英]How to draw a rectangle in QtQuick/QML canvas by press and draging
我想在圖像的頂部繪制一些矩形,該矩形由QQuickPaintedItem子類繪制並在QML中創建。 我使用畫布繪制矩形,可以使用鼠標將其平移並隨圖像縮放。 以下代碼不起作用:
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 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();
}
當我按下並拖動鼠標時,得到以下圖片:
更新:
使用ctx.strokeRect而不是ctx.rect,我得到了右邊的矩形,但是仍然無法在onPositionChanged中接收鼠標按鈕。
通常,如果需要實時預覽矩形(或任何其他對象)時要執行的操作,則需要創建一個臨時矩形以在單擊畫布時在其上方繪制,而僅移動鼠標即可。將該矩形調整為鼠標位置增量的大小,然后放開鼠標,即可在畫布上實際繪制該矩形並刪除預覽。
那就是我要做的,並且在QML中創建一個臨時矩形非常簡單,因此我想您自己實現就可以了嗎?
您當然可以在畫布上繪制所有更新,但是我想,由於刪除最后一個更新並不容易,因此使用此方法進行臨時覆蓋會更容易。
//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
}
}
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