我将图片加载到画布中。旋转后,我无法(拖动)正确移动图像。实际上,它会移动,但会根据图像的坐标平面移动。因此,向右移动90度旋转图像,向下移动,而不是按预期向右移动。什么是解决这个问题的好方法?
这是我的绘图功能:
function draw(){
var im_width = parseInt( imageObj.width + resizeAmount );
var im_height = parseInt( imageObj.height + resizeAmount );
var rotationAmount = rotationVal - prevRotation;
prevRotation = rotationVal;
context.clearRect( 0, 0, canvas.width, canvas.height );
context.translate( canvas.width/2, canvas.height/2 );
context.rotate( rotationAmount * Math.PI / 180 );
context.translate( -canvas.width/2, -canvas.height/2 );
context.drawImage( imageObj, moveXAmount, moveYAmount, im_width, im_height );
}
以下是jsdiddle,您可以在其中模拟并查看我的意思。
PS:您可以使用左侧的滑块旋转图像。底部滑块用于缩放。如果图像没有出现在第一次加载中,请重新运行小提琴。
答案 0 :(得分:6)
绘图后重置转换。当应用于画布上下文时,鼠标事件也会被转换,因此仅在绘图可以解决此问题时才使用变换。但是,这也要求代码使用绝对值,例如:
function draw(){
var im_width = parseInt( imageObj.width + resizeAmount, 10 );
var im_height = parseInt( imageObj.height + resizeAmount, 10 );
var rotationAmount = rotationVal; // disabled: - prevRotation;
context.clearRect( 0, 0, canvas.width, canvas.height );
// move to origin first
context.translate( moveXAmount, moveYAmount );
// rotate
context.rotate( rotationAmount * Math.PI / 180 );
// change to translate back based on image size
// (remember to compensate for scale, not shown here)
context.translate( -imageObj.width/2, -imageObj.height/2 );
context.drawImage( imageObj, 0, 0, im_width, im_height );
// reset transforms (identity matrix)
context.setTransform(1,0,0,1,0,0);
}
<强> Modified fiddle 强>
您可以选择使用逆矩阵。当我们可以根据当前的转换矩阵取出SVGMatrix时,这将会变得可用,但目前还没有广泛使用。否则,逆矩阵将应用于鼠标x / y位置,如名称所示,与主变换的效果相反。
可选择使用自定义转换矩阵解决方案来跟踪转换(我邀请您查看我自己的here方法,它是免费的)。
PS:还修复了图像加载问题(见小提琴)。
答案 1 :(得分:1)
const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
canvas.width = 500;
canvas.height = 500;
var x = 250;
var y = 500;
var width = 100;
var height = 100
var cx = x + 0.5 * width; // x of shape center
var cy = y + 0.5 * height; // y of shape center
class Meteor {
constuctor(degrees){
this.degrees = degrees;
//this.y = 0;
}
draw(d){
//this.y = y++
ctx.save();
ctx.translate(x,d)
ctx.rotate( (Math.PI / 180) * d); //rotate 25 degrees.
ctx.translate(-cx, -cy); //translate center
ctx.fillStyle = "#0000ff";
ctx.fillRect(x, y, width, height);
ctx.restore();
//ctx.setTransform(1, 0, 0, 1, 0, 0);
}
}
let m = new Meteor(90)
d = 0;
function animate(){
ctx.clearRect(0,0,canvas.width,canvas.height)
// Save the default state
d++;
m.draw(d)
// Restore the default state
ctx.fillRect(250, 40, 10, 10); //spaceship
ctx.fillRect(150, d, 100, 100);
window.requestAnimationFrame(animate)
}
animate()
function draw(){
var im_width = parseInt( imageObj.width + resizeAmount, 10 );
var im_height = parseInt( imageObj.height + resizeAmount, 10 );
var rotationAmount = rotationVal; // disabled: - prevRotation;
context.clearRect( 0, 0, canvas.width, canvas.height );
// move to origin first
context.translate( moveXAmount, moveYAmount );
// rotate
context.rotate( rotationAmount * Math.PI / 180 );
// change to translate back based on image size
// (remember to compensate for scale, not shown here)
context.translate( -imageObj.width/2, -imageObj.height/2 );
context.drawImage( imageObj, 0, 0, im_width, im_height );
// reset transforms (identity matrix)
context.setTransform(1,0,0,1,0,0);
}